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Easily Configure Power Management without Software Controls Up to Four Supplies per Device Cascades for Additional Supplies Staged Supply Sequencing with Adjustable Time Positions Fault Event Reporting with Diagnostics Selectable System Shutdown on Fault 1.5% Undervoltage Monitor Accuracy Overvoltage and/or Fault Indication Configurable Undervoltage and Overvoltage Thresholds Charge Pumped Enable Pins Drive N-Channel MOSFETs Operates from 2.9V to 16.5V 5mm x 7mm 38-lead QFN and 36-lead SSOP Packages Network/Telecom Infrastructure Sequencing for Multiple I/O and Core Voltages Power Management
The LTC(R)2928 is a four channel cascadable power supply sequencer and high accuracy supervisor. Sequencing thresholds, order and timing are configured with just a few external components, negating the need for PC board layout or software changes during system development. Multiple LTC2928s may be easily connected to sequence an unlimited number of power supplies. Sequence outputs control supply enable pins or N-channel pass gates. Precision input comparators with individual outputs monitor power supply voltages to 1.5% accuracy. Supervisory functions include undervoltage and overvoltage monitoring and reporting as well as P reset generation. RST may be forced high to complement margin testing. Application faults, whether internally or externally generated, can shutdown all controlled supplies. The type and source of faults are reported for diagnosis. Individual channel controls are available to independently exercise enable outputs and supervisory functions. A high voltage input allows the LTC2928 to be powered from voltages as high as 16.5V. A buffered reference output permits single negative power supply sequencing and monitoring operations.
APPLICATIO S

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 4843302, 6949965.
12V
VIN
LTM4600 VOUT RUN
10k
LTC1628 VIN VOUT RUN
AUSTIN LYNX VIN VOUT AXA010AY93
Si7894ADP
0.1 F
ON
HVCC
EN2
EN1 EN4
95.3k 24.3k 9.53k 1.5k 3.4k
1F
ON RT1 RT2 RT3 RT4 DONE VCC GND MS1 VSEL
V1 V2 V3 LTC2928 V4 RST OV FLT RTMR PTMR STMR
0.047 F
ALL RESISTORS 1%
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TYPICAL APPLICATIO
3.3V
VIN LTC3414 VOUT
1.2V
RUN
2.5V
3.3V 2.5V 1.8V 1.2V
1.8V 12.1k 23.2k 36.5k 51.1k
1V/DIV ON
100
EN3
DONE
SYSTEM RESET FAULT 10k 10k 10k 10k
3300pF
START SEQUENCE SEQUENCE UP START UP COMPLETE SEQUENCE DOWN
2928 TA06
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FEATURES
LTC2928 Multichannel Power Supply Sequencer and Supervisor DESCRIPTIO
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Sequencing Up and Down
SEQUENCE DOWN COMPLETE
2928 TA07
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LTC2928
Supply Voltages HVCC ...................................................... -0.3V to 18V VCC........................................................ -0.3V to 6.5V Input Voltages V1, V2, V3, V4 ....................................... -0.3V to 12V MS1, MS2, RDIS .................................. -0.3V to 6.5V SQT1, SQT2, VSEL ............................... -0.3V to 6.5V RT1, RT2, RT3, RT4 .............................. -0.3V to 6.5V ON, OVA .........................................-0.3 to VCC + 0.3V STMR, PTMR, RTMR .....................-0.3 to VCC + 0.3V Output Voltages EN1, EN2, EN3, EN4 (Note 3)................. -0.3V to 12V CMP1, CMP2, CMP3, CMP4 ................. -0.3V to 6.5V
TOP VIEW CMP2 CMP1 CMP4 CMP3 CMP1 CMP2 EN2 V2 OVA EN1 V1 REF RT1 1 2 3 4 5 6 7 8 9 36 CMP4 EN2 V2 35 CMP3 34 V3 33 EN3 32 V4 31 EN4 30 RTMR 29 PTMR 28 STMR 27 VSEL 26 GND 25 HVCC 24 VCC 23 RST 22 OV 21 FLT 20 DONE 19 ON OVA 1 EN1 2 V1 3 N/C 4 REF 5 RT1 6 RT2 7 RT3 8 RT4 9 SQT1 10 SQT2 11 MS1 12 13 14 15 16 17 18 19 ON DONE RDIS CAS MS2 N/C FLT 39 TOP VIEW V3 31 EN3 30 V4 29 EN4 28 RTMR 27 PTMR 26 STMR 25 VSEL 24 GND 23 HVCC 22 VCC 21 RST 20 OV
RT2 10 RT3 11 RT4 12 SQT1 13 SQT2 14 MS1 15 MS2 16 RDIS 17 CAS 18
G PACKAGE 36-LEAD PLASTIC SSOP TJMAX = 125C, JA = 95C/W
ORDER PART NUMBER LTC2928CG LTC2928IG
G PART MARKING LTC2928CG LTC2928IG
Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges.
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PACKAGE/ORDER I FOR ATIO W U
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WW
W
ABSOLUTE
AXI U RATI GS (Note 1, 2)
FLT, RST, OV, CAS................................. -0.3V to 6.5V DONE, REF ...................................-0.3V to VCC + 0.3V RMS Currents IVCC .................................................................10mA IHVCC ...............................................................20mA IREF ..................................................................10mA Operating Ambient Temperature Range LTC2928C ................................................ 0C to 70C LTC2928I ............................................. -40C to 85C Storage Temperature Range SSOP Package ................................... -65C to 150C QFN Package...................................... -65C to 150C Lead Temperature (Soldering, 10 sec) SSOP Package .................................................. 300C
38 37 36 35 34 33 32
UHF PACKAGE 38-LEAD (5mm x 7mm) PLASTIC QFN TJMAX = 125C, JA = 34C/W EXPOSED PAD (PIN 39) PCB GND CONNECTION OPTIONAL
ORDER PART NUMBER LTC2928CUHF LTC2928IUHF
UHF PART MARKING LTC2928CUHF LTC2928IUHF
LTC2928
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C, VCC = 3.3V unless otherwise noted.
SYMBOL VVCC IVCC VUVL VUVL(HYST) VHVCC VCC(REG) IREG IHVCC VON VON(HYST) ION(LKG) VMON(TH) VSEQ(TH) PARAMETER VCC Input Supply Range VCC Input Supply Current VCC Input Supply Undervoltage Lockout Undervoltage Lockout Hysteresis High Voltage Input Supply Range Regulated VCC from HVCC Regulated VCC Output Current to External Load (Note 2) HVCC Input Supply Current ON Threshold Voltage ON Hysteresis ON Leakage Current Reset Threshold Voltage V1 Negative Threshold Voltage Sequencing Thresholds 0.67 VMON(TH) 0.33 VMON(TH) 0.10 VMON(TH) Monitor Pin Leakage Current Undervoltage Pulse Width Required to Trip Comparators Overvoltage Pulse Width Required to Trip OV Enable Pin Voltage Output in On State Enable Pin Pull-Up Current Enable Pin Voltage Output Low Comparator Voltage Output Low Comparator Voltage Output High (Note 4) Voltage Input Low Threshold Voltage Input High Threshold High Z Pin Current VHZ = 0.7V VHZ = 1.1V VON = 1V IREG = 0mA, VHVCC = 12V VON Rising VHVCC = 12V HVCC = GND VCC Rising CONDITIONS

ELECTRICAL CHARACTERISTICS
Supply Pins: VCC, HVCC
MIN 2.9
TYP
MAX 6
UNITS V mA V mV V V mA mA V mV nA V mV V V V nA s s
1 2.75 50 7.2 3.2 2.8 100 12 3.3
2.5 2.85 150 16.5 3.4 -10
1 0.985 20 1.00 30
2 1.015 40 50
Sequence Up/Down Pin: ON

Voltage Monitor Pins: V1, V2, V3, V4 VSEL = VCC See Table 4

0.4925
0.500
0.5075 18 0.351 0.185 0.068 15
0.315 0.149 0.032
0.333 0.167 0.05 225 225
IMON(LKG) tMON(UV) tMON(OV)
VMON = 0.55V VMON below VMON(TH) by 1% VMON above Overvoltage Threshold by 1% IEN = -1A Enable Pin On, VEN (VCC + 4V) IEN = 2.5mA ICMP = 2.5mA ICMP = -1A
Supply Enable Pins: EN1, EN2, EN3, EN4 VEN IEN(UP) VEN(OL) VCMP(OL) VCMP(OH)
VCC + 4.5
VCC + 5.5 -10 0.25 0.15
VCC + 6 -12.5 0.4 0.3
V A V V V
-7.5
Comparator Outputs: CMP1, CMP2, CMP3, CMP4
VCC - 1
Three-State Selection Inputs: SQT1, SQT2, MS1, MS2, RDIS VIL VIH IHZ

0.4 1.4 -10 10 0.4 1.4
V V A A V V
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Positive/Negative Selection Input: VSEL VIL VIH Voltage Input Low Threshold Voltage Input High Threshold

3
LTC2928
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C, VCC = 3.3V unless otherwise noted.
SYMBOL VRT(LO) VRT(HI) RRT Cascade Pin: CAS VCAS(OL) ICAS(UP) tCAS(HI) tCAS(MIN) Fault Status Pin: FLT VFLT(OL) IFLT(UP) VFLT(TH) VFLT(HYST) tFLT IFLT(LKG) VDONE(OL) IDONE(DN) RDONE VDONE(LAST) Reset Pin: RST VRST(OL) RST Voltage Output Low VCC = 0.2V, IRST = 0.1A VCC = 0.5V, IRST = 5A VCC = 1V, IRST = 200A VCC = 3V, IRST = 2500A IRST = -1A (Note 7) VTMR = GND VTMR = 1.3V CRTMR = 1500pF CPTMR = 1500pF CSTMR = 1500pF

ELECTRICAL CHARACTERISTICS
PARAMETER Voltage Required to Force Enable Pin Low While Sequencing Voltage Required to Force Enable Pin High Outside of Sequencing RT Pin Input Resistance CAS Voltage Output Low CAS Pull-Up Current Fixed Time Delay between Sequence Time Positions (Note 5) Minimum CAS Low Time During Sequencing FLT Voltage Output Low FLT Pull-Up Current External Fault Input Threshold External Fault Input Hysteresis Minimum Detectable External Fault Pulse Width Fault Pin Leakage Current DONE Voltage Output Low DONE Pull-Down Current Required Pull-Up Resistance on "Last" LTC2928 Voltage Output High when Configured as "Last"
CONDITIONS
MIN
TYP
MAX 0.045 * VCC
UNITS V V
Sequence Time Position Control Inputs: RT1, RT2, RT3, RT4 (see resistor selection Table 3)
0.955 * VCC
11.2
12 0.15
12.8 0.3 -75 15 30
k V A ms s
ICAS = 2.5mA Master Pulling CAS High, VCAS = GND CAS High, CSTMR = 1500pF

-45 11 15
-60 13 22.5
IFLT = 2.5mA VFLT = VCC -1V VFLT Falling

0.15 -12 1.0 25 -17 1.1 100
0.3 -22 1.2 150 2
V A V mV s A V A k V
VFLT = VCC IDONE = 2.5mA VDONE = 3.3V (Note 6) 5% Tolerance or Better
1 0.15 20 2.4 0.8 * VCC 0.3 40 5.1
Done Status Pin: DONE

5 10 25 150 VCC - 1 -1.7 15 5 5 11 -2 20 6 6 13
60 150 300 300
mV mV mV mV V
VRST(OH) ITMR(UP) ITMR(DN) tRTMR tPTMR tSTMR
RST Voltage Output High Timer Pull-Up Current Timer Pull-Down Current Timer Period, RTMR (Note 8) Timer Period, PTMR Timer Period, STMR
Timer Pins: RTMR, PTMR, STMR

-2.3 25 7 7 15
A A ms ms ms
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LTC2928
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C, VCC = 3.3V unless otherwise noted.
SYMBOL VREF PARAMETER CONDITIONS IREF = 0.2mA, -1mA, CREF = 1000pF VSEL = VCC VSEL = VCC VSEL = VCC VSEL = VCC IOV = 2.5mA IOV = -1A OV Low Time Upon Cleared OV Event, CRTMR = 1500pF VOVA = GND VOVA Floating VOVA = VCC = 3.3V

ELECTRICAL CHARACTERISTICS
MIN 1.172 1.172 0.780 0.386 0.109
TYP 1.189 1.189 0.793 0.396 0.119 0.15
MAX 1.205 1.205 0.806 0.406 0.129 0.3 7
UNITS V V V V V V V ms
External Voltage Reference Pin: REF Reference Voltage Output 100% Sequence Threshold 67% Sequence Threshold 33% Sequence Threshold 10% Sequence Threshold Over Voltage Indication Pin: OV VOV(OL) VOV(OH) tOV OV Voltage Output Low OV Voltage Output High (Note 7) OV Indication Time (Note 8)
VCC - 1
5
6
Over Voltage Adjust Pin: OVA VOVA(TH) Over Voltage Threshold at Comparator Inputs (Note 9)

0.546 0.650 1.042
0.556 0.660 1.072
0.566 0.670 1.102
V V V
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: All currents into pins are positive, all voltages are referenced to GND unless otherwise noted. Note 3: Internal circuits regulate the EN output voltage to VEN. Driving this pin to voltages beyond VEN may damage the part. Note 4: The comparator outputs have internal pull-ups to VCC of typically -10A. However, external pull-up resistors may be used when faster rise times are required or for VOH voltages greater than VCC.
Note 5: The CAS high time after an ON edge is stretched by the ON pin propagation delay (20s typical). Note 6: The DONE pull-down current is present when DONE is high to facilitate cascading multiple LTC2928s. Note 7: The RST and OV outputs have an internal pullup to VCC of typically -10A. However, external pull-up resistors may be used when faster rise times are required or for VOH voltages greater than VCC. Note 8: If the termination of under and overvoltage events occur within one nominal tRTMR period, the variation in tRTMR and/or tOV may be 15%. Note 9: Use a resistor from OVA to ground or VCC to configure overvoltage thresholds within the max/min ranges shown. See Applications Information for details.
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LTC2928 TYPICAL PERFORMANCE CHARACTERISTICS
IVCC vs VCC
5 HVCC = GND 85C
25C
IHVCC vs HVCC
1 IREG = 0 3.4
Regulated VCC vs Temperature
IREG = 0
4
0.95
REGULATED VCC (V)
85C
3.35 HVCC = 7.2V 3.3
IHVCC (mA)
IVCC (mA)
3
-40C
0.9
25C
2
0.85
-40C
1
0.8
3.25
HVCC = 16.5V HVCC = 12V
0
2.5
3
3.5
4 4.5 VCC (V)
5
5.5
6
0.75
7
9
2928 G08
11 13 HVCC (V)
15
17
2928 G09
3.2 -50
-25
0 25 50 TEMPERATURE (C)
75
100
2928 G10
Regulated VCC vs HVCC
3.4 IREG = 0
Regulated VCC vs IREG
3.4 HVCC = 12V 12 10 REGULATED VCC (V)
Enable Output Voltage in On State vs VCC
3.35
3.35 8 3.3 85C 3.25 2 25C -40C VEN (V) -10
2928 G12
VCC (V)
3.3
6 4
3.25
3.2
7
9
11 13 HVCC (V)
15
17
2928 G11
3.2
0
-2
-4 -6 IREG (mA)
-8
0
0
1
2
3 VCC (V)
4
5
6
2928 G13
Enable Output Voltage vs Enable Output Current and VCC
12 10 8 VEN (V) 6 4 2 0 VCC = 3V 0.508 VCC = 6V 0.506 0.504 VMON(TH) (mV) 0.502 0.5 0.498 0.496 0.494 0 -2 -4 -6 -8 IEN ( A) -10 -12
2928 G14
Under Voltage Monitor Threshold (100%) vs Temperature
18 12 6 0 -6 -12
V1 Negative Threshold vs Temperature
VSEL = VCC
0.492 -50
VMON(TH) (mV) 75 100
2928 G07
-25
0 25 50 TEMPERATURE (C)
-18 -50
-25
0 25 50 TEMPERATURE (C)
75
100
2928 G06
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LTC2928 TYPICAL PERFORMANCE CHARACTERISTICS
Reference Output Voltage vs Temperature
1.200 1k
Comparator Under-Voltage Glitch Immunity
1k
Comparator Over-Voltage Glitch Immunity
GLITCH DURATION ( s)
RESET OCCURS ABOVE CURVE 100 COMPARATOR IGNORES GLITCH
GLITCH DURATION ( s)
1.196
VREF (V)
1.192
100
OV OCCURS ABOVE CURVE
1.188
COMPARATOR IGNORES GLITCH
1.184 1.180 -50 10 10
-25
0 25 50 TEMPERATURE (C)
75
100
2928 G05
0.1
1 10 COMPARATOR OVERDRIVE (% OF RESET THRESHOLD)
100
0.1
1 10 COMPARATOR OVERDRIVE (% OF OV THRESHOLD)
100
2928 G15
2928 G16
ON Threshold Voltage (Rising) vs Temperature
1.015 1.010 VRST (% OF VCC) 1.005 VON (V) 1.000 0.995 0.990 0.985 -50 50
Relative Reset Output Voltage vs VCC (with Reset Pull-Up Resistor to VCC)
1k 40
RST Pull-Up Current vs External Voltage on RST
-70 -60 -50 IRST (A) VCC = 5V
30 5k 20 10k
-40 -30 -20 -10 0 0 1 2 3 VRST (V) 4 5
2928 G17
VCC = 3.3V
10
100k 0.3 0.5 0.7 0.9 VCC (V) 1.1 1.3 1.5
-25
0 25 50 TEMPERATURE (C)
75
100
2928 G01
0 0.1
2928 G17
Sequence, Reset and PowerGood Timing vs Capacitance
10 THREE STATE PIN CURRENT (A) 20 15 10
Three State Selection Pin Current vs Pin Voltage (SQT1, SQT2, MS1, MS2, RDIS)
-22
IFLT(UP) vs Temperature
VFLT = 2.3V
1 SEQUENCER TIMER TIME (SEC) 100m 10m RESET AND POWER-GOOD TIMER
-20 IFLT(UP) (A)
5 0 -5 -10 -15 -20 0.3 0.6 0.9 1.2 THREE STATE PIN VOLTAGE (V) 1.5
2928 G20
-18
-16
1m 100
-14
10p
100p
1n 10n CAPACITANCE (F)
100n
1
2928 G19
-12 -50
-25
0 25 50 TEMPERATURE (C)
75
100
2928 G21
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LTC2928 TYPICAL PERFOR A CE CHARACTERISTICS
ICAS(UP) vs Temperature (device configured as MASTER)
-75 -69 ICAS(UP) (A) VCAS = GND 3 2.5 2 VEN(OL) (V) VEN(OL) (V) -63 1.5 1 0.5 0 -45
-57 -51
-45 -50
-25
0 25 50 TEMPERATURE (C)
Voltage Output Low vs IOL (CMP, CAS, FLT, DONE, RST, OV)
2 1.75 VOLTAGE OUTPUT LOW (V) 1.5 1.25 1 0.75 0.25 0 0 5 15 10 IOL (mA) 20 25
2928 G25
VCC = 3.3V 85 25 -45 VOLTAGE OUTPUT LOW (V)
1 0.75 0.5 0.25 0 0 5 15 10 IOL (mA) 20
IEN (mA)
Comparator Output Current Sink Capability vs VCC and VOL
12 VOL = 0.4V 10 8 ICMP (mA) 6 4 2 0 IRST (mA) VOL = 0.2V 10 8 6 4 2 0 12
0
1
2
8
UW
75 3 VCC (V)
VEN(OL) vs IEN
VCC = 3.3V 3.5 85 25 3 2.5 2 1.5
VEN(OL) vs IEN
VCC = 5V 85
25 -45
1 0.5 0 5 10 15 IEN (mA) 20 25
2928 G23
100
2928 G22
0
0
5
15 10 IEN (mA)
20
25
2928 G24
Voltage Output Low vs IOL (CMP, CAS, FLT, DONE, RST, OV)
2 1.75 1.5 1.25 4 85 25 -45 3 2 1 0 VCC = 5V 6 5
Enable Current Sink Capability vs VCC and VOL
VOL = 0.4V
VOL = 0.2V
25
2928 G26
0
1
2
3 VCC (V)
4
5
6
2928 G27
Reset Current Sink Capability vs VCC and VOL
VOL = 0.4V
VOL = 0.2V
4
5
6
2928 G28
0
1
2
3 VCC (V)
4
5
6
2928 G29
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LTC2928 PI FU CTIO S
CAS: Cascade Input/Output. Connect the cascade pin between a master and one or more slave devices to increase the number of supplies that can be sequenced per time position. See Applications Information for details. Do not add capacitance to the cascade pin. Leave open if unused. CMP1-CMP4: Comparator and/or Fault Status Outputs. The CMP outputs have a weak internal pull-up to VCC and may be pulled above VCC using an external pull-up. During sequence-up or sequence-down operation, all comparator outputs are low. After sequencing-up, during supply monitoring, comparator outputs pull low if their monitor input drops below its undervoltage threshold. In the event of a system fault, the CMP outputs latch and may be read to diagnose the type and source of fault. See Applications Information for the fault reporting details. Leave the CMP outputs open if unused. DONE: Sequence Done Output. The last (or only) LTC2928 must have DONE pulled high with an external resistor to VCC (3.3k 5% recommended). The LTC2928 floats DONE until the completion of a sequence-up operation when it is pulled down. At the end of a sequence-down operation, the LTC2928 returns DONE to a high-impedance state. If subsequent time positions are required for additional supplies, use the DONE--ON handshake connection. See Applications Information regarding the DONE--ON protocol. EN1-EN4: Enable Outputs. Connect these outputs to a power supply shutdown input or an external N-channel MOSFET gate for the supply to be sequenced. When enabled, each output is connected to an internal charge pumped supply (nominally VCC + 5.5V) via an internal 10A current source. When disabled, each output is pulled to ground. EN outputs operate with their respective RT inputs. Leave enable outputs open when unused. Exposed Pad: Exposed pad may be left floating or connected to device ground. FLT: Fault Input/Output. Pull FLT high with an external resistor (10k recommended). The LTC2928 will pull FLT low if an internal fault condition is detected (see Applications Information for details). An external signal such as OV may also pull down the FLT pin to cause an external fault. Any internal or external fault condition forces all
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enable outputs low. In order to clear a fault condition, a "return-to-zero" state must be reached with all monitored supplies falling below their configured sequence-down thresholds, while the ON input is below 0.97V. Debugging modes are available (use the MS1, MS2 inputs) to leave supplies enabled upon system faults. See Applications Information for configuration tables. GND: Device ground. HVCC: High Voltage (7.2V to 16.5V) Power Supply Input. Bypass HVCC with at least 0.1F to ground in close proximity to this pin. The internal HVCC regulator provides a regulated 3.3V to VCC. VCC may be used to power external circuits (limited to 10 mA external load). Tie HVCC to ground when unused. MS1, MS2: Master/Slave Three State Configuration Inputs. Depending on the application, select each LTC2928 as a master or slave part and whether or not the part is designated as the first part in a cascade application. The RST--FLT relationship (after RST pulls high for the first time) is also configured with these inputs. Select whether or not RST pulling low should cause FLT to pull low and shutdown the system. Select debugging modes to leave supplies enabled upon system faults. See Applications Information for configuration table. N/C: No Connect. Unconnected pins. ON: Sequence Up/Down Input. A voltage transition above 1V starts the sequence-up phase. A voltage transition below 0.97V starts the sequence-down phase. An ON transition applied during a sequence-up (or down) phase is treated as a command fault. See Applications Information for using the DONE--ON handshake protocol when cascading multiple LTC2928s to append additional time positions. OV: Overvoltage Output. Pulls low when any positive supply exceeds its configured overvoltage threshold. OV remains low until all positive supplies have remained below the overvoltage threshold for a time equal to the configured RST delay time. To generate an overvoltage fault, connect OV to FLT. The OV output has a weak pull-up to VCC and may be pulled above VCC using an external pull-up. OV may be left unconnected if unused. See Applications Information for details.
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LTC2928 PI FU CTIO S
OVA: Over Voltage Adjust Input. After configuring the undervoltage thresholds, bias this input to set the overvoltage threshold for all positive supplies. Leave the pin floating to set an overvoltage threshold approximately 32% above the undervoltage threshold. Tie OVA to VCC to move the overvoltage threshold above 1V. Consult the Applications Information for details on OVA biasing. PTMR: Power Good Timer. Attach an external capacitor to ground to set the maximum time allowed for all supplies to reach their configured undervoltage threshold during sequence-up phase (or all supplies below their sequencedown threshold during sequence-down phase). The timer is started when the first enable (EN) is raised (or lowered). The power good timing scale factor is 4000ms/F. A 0.1F capacitor generates a 400ms delay time. If any supply is late, a sequence fault is generated. FLT pulls low and all supply enable outputs are pulled low. Disable the power good timer by grounding PTMR. Consult Applications Information for more details. RDIS: Reset Disable Three State Input. Typically used for supply margining applications. Pull RDIS high or low to force RST high. Leave the RDIS input open to allow RST to operate normally. REF: Reference Output. REF is used to offset negative supplies connected through resistance to V1. The reference will move during sequence-up and sequence-down operation to effect the selected thresholds. The buffered reference sources 1mA and sinks up to 200A of current. The reference drives a bypass capacitor of up to 1000pF without oscillation. RST: Reset Output. If any supply is below its undervoltage threshold, RST pulls low. RST pulls high after all supplies are above their undervoltage threshold for the configured delay time (configure delay time using the RTMR pin). The RST output has a weak pull-up to VCC and may be pulled above VCC using an external pull-up. RST is guaranteed low with VCC down to 0.5V. Configure the RST to FLT relationship using the MS1, MS2 inputs. See Applications Information for details. Leave the RST output open if unused. RTMR: Reset Timer. Attach an external capacitor to ground to set a reset delay time of 4000ms/F. Floating RTMR generates a minimum delay of approximately 50s. A
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0.047F capacitor will generate a 190ms delay time. RT1-RT4: Resistive Time Position Configuration Inputs. Place a single resistor from VCC to each input to select one of eight time positions in which to turn-on or turn-off each enable output (see Application Information for RT table). Each RT input numerically corresponds to a respective EN output and monitor input. During sequencing-up, an enable output (EN) pulls high at the start of its chosen time position. During sequencing-down, an enable output (EN) pulls low at the start of its chosen time position (sequence-down position is the reverse of sequence-up). To remove a monitor channel from participation, command any enable off by pulling its corresponding RT input to ground. Prior to sequencing, any enable may be commanded on by pulling its corresponding RT input to VCC. Maximum capacitive load is 150pF. SQT1, SQT2: Sequencing Threshold Three State Configuration Inputs. Select sequencing thresholds as a percentage of the 0.5V supply monitor threshold for positive supplies and as a percentage of REF for negative supplies. For sequencing-up choose from 33%, 67% or 100%. For sequencing-down choose from 100%, 67%, 33% or 10%. See Applications Information for configuration table. STMR: Sequence Timer. Attach an external capacitor to ground to set the adjacent time-position delay between sequenced supplies. For supplies in adjacent time positions, this delay resides between the previous supply crossing its sequence-up (down) threshold and the next enable (EN) pulling high (low). For a supply in time position 1, the sequence delay is the time from ON going high to its enable pulling high. The sequence timing scale factor is 8670ms/F. Floating STMR generates a minimum sequencing time delay of approximately 100s. A 3300pF capacitor will generate a 29ms delay time. Referring to the timing diagrams, the sequence delay time is equivalent to the cascade (CAS) pin high time. Consult Applications Information for details. VCC: Power Supply Input/Output. All internal circuits are powered from VCC. Bypass VCC with at least 0.1F to ground in close proximity to this pin (1F minimum when using HVCC). VSEL: Voltage Monitor Select Input. Tie to ground to select four positive inputs. Tie to VCC for three positive
2928f
LTC2928 PI FU CTIO S
and one negative adjustable input. Negative supplies are monitored on the V1 input. See Applications Information for configuration table. V1-V4: Voltage Monitor Inputs. Connect these high impedance inputs to external resistive dividers between each
HVCC
VCC
REGULATOR
OVA
UV/OV COMPARATORS
V1 V2
V3
V4
VSEL
SQT1
SQT2
MS1
MS2
RDIS
RT1
12k
RT2
12k
RT3
12k
RT4
12k
ON
1V
W
FU CTIO AL DIAGRA U U
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monitored power supply and ground (or REF for negative supplies monitored on V1). See Applications Information for selecting resistors to configure the monitor thresholds. Voltage monitor inputs operate with their respective RT inputs and EN outputs.
CHARGE PUMP
UVLO
VCP
GND
REFERENCE
GAIN ADJUST
10A VCP
REF
VOVA(TH)
THRESHOLD CONTROL 4
ENABLE CONTROL
4
EN1
EN2
8
2A
EN3
EN4
V1 POLARITY CONTROL
VCC
TIMER CONTROL 3
2uA
2uA
RTMR
PTMR
22A
22uA
STATE DECODERS
5
STMR
SEQUENCING LOGIC
22uA
10A
VCC
TIME POSITION DECODERS
4
OUTPUT CONTROL 6
10uA
10uA
10uA
CMP1
10uA
CMP2
10uA
CMP3
CMP4
VCC
100A 50A
RST
VCC
OV
CAS
+
VCC
20A
-
100A
VCC
FAULT MANAGER
FLT
DONE
20A
2928 BD
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LTC2928 TI I G DIAGRA S
CAS and STMR Relationship
ON tCAS(MINIMUM)
CAS tSTMR STMR 15 CYCLES tSTMR
Undervoltage Timing
Vx tMON(UV) RST VMON(TH) tRTMR
RTMR 7 CYCLES
Overvoltage Timing
Vx tMON(OV) OV VOV(TH) tRTMR
RTMR 7 CYCLES
The LTC2928 is a four channel, cascadable power supply sequencer and supervisor for use with external N-channel MOSFETs or power supplies with shutdown/enable inputs. An unlimited number of power supplies may be fully sequenced at configurable points in time using multiple LTC2928s. A single LTC2928 controls up to four supplies (four positives or three positives and one negative) and one external resistor per supply configures each supply enable (disable) time position. Device power is applied through either VCC (2.9V to 6V) or HVCC (7.2V to 16.5V). When applying power through HVCC, a regulated 3.3V is output on VCC. An internal charge pump provides (VCC + 5.5V) gate drive voltages at the enable outputs EN1 to EN4 for driving external pass FETs.
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OPERATIO
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The LTC2928 monitors four supply thresholds per supply (sequence-up, sequence-down, undervoltage, overvoltage) during a full system cycle. A full cycle comprises a sequence-up phase, monitor phase and sequence-down phase. A sequence timer sets the time delay between supply enables during both the sequence-up and sequencedown phases. The power-good timer is a watchdog for stalled supplies during the sequence-up and sequencedown phases. A microprocessor reset signal is issued once all supplies are above their undervoltage threshold for the chosen reset time. During the monitor phase, all enabled supply voltages are continuously compared with their undervoltage threshold. If any supply falls below its undervoltage threshold, the reset output pulls low. The reset output pulls high once all enabled supplies have been in compliance for the chosen reset time. During any phase, all positive supplies are continuously monitored for overvoltage conditions. Implementing complex power-on and power-off schemes is simple using the LTC2928. System errors are easily diagnosed with the LTC2928 fault event reporting feature. Basic LTC2928 operation is discussed below. Configuration tables are given in the Applications Information section. The Applications Information also includes many of the unique and advantageous extensions to the basic operation, such as Master/Slave configurations.
2928 F13
Sequence-Up Phase While VCC is ramping up, the LTC2928 enters a power-on mode and pulls down its CAS pin. When VCC is stabilized, the LTC2928 is configured for operation and releases its CAS pin. Multiple LTC2928s with common CAS connections will therefore synchronize with each other. The ON input is used to start the sequence-up and sequencedown process. The state of ON is ignored until CAS is released. When the voltage at the ON input exceeds 1V, the sequence-up phase is enabled after a small propagation delay (20s typical). If the ON signal prematurely pulls below 0.97V during the sequence-up phase, a command fault is generated, causing enable (EN) outputs to pull low. For more details refer to the discussion on system faults later in this document.
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At the beginning of the sequence-up phase, a current source begins to charge the STMR capacitance. When the sequence timer has expired the CAS pin pulls low. At this time, any enable (EN) scheduled (using the RT inputs) for "time position 1" pulls high, allowing a supply (or supplies) to be turned on. The CAS pin is held low until all monitored inputs in the current time position exceed their selected sequencing-up threshold (25s minimum). Once all supply monitor inputs cross their sequencing-up threshold, or if no enable was selected for the current time position, the CAS pin is allowed to pull high. The STMR capacitor begins to charge again, moving the system to "time position 2". This process repeats until the system is clocked through "time position 8". During the sequence-up phase, supply monitor inputs are expected to cross their sequence-up threshold (which may be different from their undervoltage threshold). Any supply monitor input failing to cross its sequence-up threshold will stall the process and a sequence-up fault is generated (if the power-good timer is active). The power-good timer starts with the first enable output to go high and is cleared when the last supply monitor input reaches its undervoltage threshold. Any supply monitor input failing to cross its sequence-up threshold before the powergood timer expires also generates a sequence-up fault. A sequence-up fault pulls FLT and all supply enable outputs (EN) low. Use a single capacitor from PTMR to ground to select the power good time. To disable the power good timer, simply tie PTMR to ground. Each comparator switches to its undervoltage threshold when the respective supply monitor input crosses its sequence-up threshold. The comparator outputs are allowed to pull high after the LTC2928 clocks through time position 8. After a system fault, fault information is latched to the CMP outputs. Read the CMP outputs to obtain the fault type (internally generated sequence-fault, reset-fault, command-fault or an externally generated fault) and the fault channel (if any). For more details refer to the discussion on system faults later in this document. After the system has clocked through "time position 8", the last LTC2928 (defined by a 2.4k to 5.1k pull-up resistor on DONE) pulls down on DONE.
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Supply Monitor Phase Once all supply monitor inputs have crossed their sequence-up thresholds, the LTC2928 enters its supply monitor phase. As referred to earlier, the comparators switch to their highly accurate undervoltage thresholds after crossing their sequence-up threshold. The monitor thresholds maintain 1.5% accuracy over temperature. RST pulls high after all supply monitor inputs (V1 to V4) have been above their undervoltage threshold for the selected reset delay time. The reset delay is set with a capacitor attached between RTMR and ground. The supply monitor comparators will filter out minor glitches coupled to their inputs. If any supply falls below threshold with sufficient magnitude and duration, the RST line pulls low. The reset timer starts once all inputs return above threshold. The LTC2928 can be configured to issue a fault if RST pulls low due to an undervoltage event (see master/slave configuration table in Applications Information). Upon a RST fault, FLT and the enable outputs pull low. Use the fault report capability to determine which input was below threshold. For more details refer to the discussion on system faults later in this document. The reset disable input (RDIS) may be pulled high or low to force RST high regardless of voltage monitor level. This feature is useful during voltage margining tests. Sequence-Down Phase The sequence-down phase is initiated by pulling the ON input below 0.97V. This action pulls RST low immediately. The comparator thresholds (and REF for negative supplies) are moved to their selected sequence-down thresholds. Beginning with any supplies in "time position 8", the enable outputs are sequenced-down by pulling enable low in the reverse order of sequence-up (last on, first off). During the sequence-down phase, supply monitor inputs are expected to cross their sequence-down thresold (which may be different from their undervoltage threshold) within the selected power good time. Any supply monitor input failing to cross its sequence-down threshold will stall the process and a sequence-down fault is generated (if the power-good timer is active).The power2928f
OPERATIO
13
LTC2928
good timer starts with the first enable output pulling low and is cleared when the last supply monitor input crosses its sequence-down threshold. A sequence-down fault pulls FLT and all enable outputs low. Use a single capacitor from PTMR to ground to select the power good time. To disable the power good timer, tie PTMR to ground. All comparator outputs pull low at the start of the sequence-down phase (ON low). If a sequence-down fault occurs, use the fault report capability to determine which
Table 1. Input Polarity Selection
V1 + ADJ (0.5V) - ADJ (0V) V2 + ADJ (0.5V) + ADJ (0.5V) V3 + ADJ (0.5V) + ADJ (0.5V) V4 + ADJ (0.5V) + ADJ (0.5V) VSEL GND VCC
Table 2. Master/Slave Configuration Pins
Master

Slave
* No shutdown debug mode. In this mode, any internal or external fault will halt the system with full fault reporting but all enabled supplies remain enabled.
Table 3. Sequence Time Position Resistors (1%)
Position Number 1 2 3 4 5 6 7 8 RT (k) 95.3 42.2 24.3 15.0 9.53 6.04 3.40 1.50
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supply failed to meet threshold (or other source of fault). Force all supplies down in an un-sequenced manner by pulling FLT low (external fault). For more details refer to the Applications Information and discussion on system faults later in this document. After the system has clocked through "time position 1", the last LTC2928 (defined by a 2.4k to 5.1k pull-up resistor on DONE) releases the pull down on DONE and DONE pulls high.
First Not First Cascade Position Cascade Position

OPERATIO
RST Pulls FLT
RST Does not Pull FLT
No Shutdown Debug Mode*
MS1 GND GND GND Open Open Open VCC VCC VCC
MS2 GND Open VCC GND Open VCC GND Open VCC
Table 4. Sequencing Threshold Selection (% of 0.5V for ADJ, % of REF for -ADJ)
Sequence-Up (%) 100 100 100 100 67 67 67 67 33 Sequence-Down (%) 100 67 33 10 100 67 33 10 100 SQT1 VCC Open Open Open VCC GND GND GND VCC SQT2 VCC VCC Open GND Open VCC Open GND GND
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Fault Detection The LTC2928 has sophisticated fault detection circuitry which can detect: * Stalled supplies (with power good timer enabled) during sequencing * Under or overvoltage supplies * System controller command errors * Externally commanded faults If any of the above faults are detected, the LTC2928 immediately pulls the EN1 through EN4 outputs low, turning off all enabled supplies. In order to clear the fault condition within the LTC2928, the following conditions must exist: * All sequenced supplies must be below their sequencedown thresholds * The ON input must be below 0.97V * The FLT pin must be externally released Sequencing Faults The LTC2928 keeps track of power supplies that need to exceed their sequencing thresholds within the configured power good time during the sequence-up and sequencedown phases. Should any supply fail this test a sequence fault is generated. All enable outputs and FLT are pulled low. System Controller Command Faults After the sequence-up phase has begun (ON input high), the ON input must remain above 1V until DONE pulls low (sequence-up complete). Pulling ON low before the sequence-up process is complete is considered a command fault. All enable outputs and FLT are pulled low. Similarly, after the sequence-down phase has begun (ON input low), the ON input must remain below 0.97V until DONE pulls high (sequence-down complete). Pulling ON high before the sequence-down process is complete is considered a command fault. All enable outputs and FLT are pulled low.
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Reset Faults Use the MS1 and MS2 configuration pins to select whether or not the system should fault if any monitored input falls below its undervoltage threshold. A reset fault may only occur after the LTC2928 comes out of reset for the first time after sequencing. All enable outputs and FLT are pulled low. External Faults An external fault is generated by pulling the FLT pin low. Tie the OV pin to FLT to generate overvoltage faults. In applications using multiple LTC2928s, tie all the FLT pins together to ensure proper re-sequencing. Upon detecting an external fault, all enable outputs are pulled low. Fault Reporting Map For diagnostic purposes, fault information is latched to the comparator outputs after a fault. The table below provides a map to the available fault information. The fault information remains latched until the LTC2928 completes the next sequence-up operation.
Table 5. Fault Reporting
Fault Codes Fault Type Sequence Fault Reset Fault Command Fault External Fault Fault Channel 1 2 3 4 CMP1 Low Low High High CMP3 Low Low High High CMP2 Low High Low High CMP4 Low High Low High
APPLICATIO S I FOR ATIO W U U
Should multiple faults occur simultaneously, the reported fault is given priority according to the following order: 1) Sequence Fault 2) External Fault 3) Reset Fault 4) Command Fault (channel code is meaningless)
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LTC2928
Should multiple channels fault simultaneously, the reported channel is given priority according to the channel number (1,2,3,4). In the event of an external fault, the LTC2928 fault manager reports overvoltage channels to the fault channel outputs (CMP3, CMP4). If no channel is overvoltage, the default report is channel 4 (High, High). As such, in certain applications, a potential reporting ambiguity exists. Operating without Pass Transistors The LTC2928 enable outputs may directly drive the shutdown/enable, run/soft-start or control inputs on DC/DC converters. However, since the LTC2928 enable outputs may drive to a relatively high voltage with low current (10A), care must be taken not to exceed the maximum voltage rating on the DC/DC converter enable input. The gate voltage available from the LTC2928 enable output ranges between VCC + 4.5V to VCC + 6V. Use a resistor to limit an enable output to an external supply voltage. A resistor between 4.7k and 27k is recommended. Cascading Multiple LTC2928s LTC2928s can be cascaded in two ways, simultaneously. The first method, time extension, allows an unlimited number of supplies to be sequenced in additional time positions. The second method, supply extension, allows additional supplies to be sequenced in the same time position. The examples below demonstrate how to achieve time and supply extension. Central to configuring a cascade application is the assignment of LTC2928 properties such as master/slave and first/not-first/last status. Master/Slave and first/not-first designation is made with the MS1 and MS2 three-state configuration inputs (see Table 2). An LTC2928 is configured as "LAST" by pulling DONE to VCC with a 2.4k to 5.1k resistor. Next, the appropriate connection of one or both bidirectional communication lines must be made. To achieve supply extension, the CAS pins between master and slave devices are tied together (Figure 1). To achieve time extension, the DONE pin of the preceding LTC2928 is connected to the ON pin of the subsequent LTC2928 (Figure 2). Both connections are allowed to exist within one system (Figure 4).
VCC ON RT1 RT2 RT3 RT4 LTC2928
2928 F01
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It is important not to corrupt these communication lines with added passive or active loads. CAS Connection: Supply Extension When more than four supplies need to be synchronized in time, use the CAS connection. Consider the application in Figure 1. This application allows for 8 supplies in 8 distinct time positions, or all at once depending upon the choice of RT resistors. The upper device is designated as master and the lower device is the slave. Both LTC2928s are configured as "FIRST" and "LAST" and the CAS pins are tied together.
(MASTER/FIRST) ON RT1 RT2 RT3 RT4 CAS STMR DONE LTC2928 VCC VCC CAS VCC DONE (SLAVE/FIRST)
APPLICATIO S I FOR ATIO W U U
Figure 1. Using the CAS pin to synchronize additional power supplies (slave STMR is not used).
The master controls the sequencing. The time delay between adjacent positions is configured with a capacitor on the master's STMR pin and the slave STMR is ignored. After application of the ON signal to start the sequence-up phase, the CAS pin pulls low, enabling any supply configured for time position 1. After supplies in time position 1 cross their sequence-up threshold, CAS is released and pulled high. If no supplies are configured for a particular time position, CAS pulls high after 25s. CAS remains high for one STMR period (100s minimum) and then pulls low again to enable supplies in time position 2. The
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LTC2928
process repeats until CAS clocks through time position 8 and DONE pulls low. To sequence down, the ON input is pulled low. Supplies in time position 8 are disabled. After supplies in time position 8 fall below their sequence-down threshold, CAS is released and pulled high. CAS remains high for one STMR period and then pulls low again to disable supplies in time position 7. The process repeats until CAS clocks through time position 1 and DONE pulls high. DONE-ON Connection: Time Extension When additional time positions and/or additional supplies require control, use the DONE--ON connection. Consider the application in Figure 2. This application allows for 8 supplies in 16 distinct time positions (4 supplies within the first 8 time positions, and 4 more within the second 8 time positions). Both LTC2928s are designated as master. Each has its own STMR capacitor allowing for different sequence timing. The leftmost device is designated as "FIRST", and the rightmost device is "NOT FIRST" and "LAST". It is critical to note here that the DONE pin of the first device is connected to the ON pin of the second device, and that this connection forms a bi-directional communication line for the purposes of sequence control. DONE and ON do not function as typical DONE and ON pins. The handshaking that occurs between these pins is described below.
8 SUPPLIES, 16 TIME POSITIONS (MASTER/FIRST) ON LTC2928 (MASTER/NOT FIRST) ON LTC2928 VCC VCC (MASTER/FIRST) ON LTC2928
DONE
DONE
FLT
STMR
FLT
STMR
Figure 2. Using the DONE--ON interface to extend number of supplies and time positions (STMR capacitors may be different).
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To start the sequence-up process, the first ON input is pulled high. The first device sequences the first 4 supplies as usual. The first DONE pin has recognized that the first device is not the last because it has not been pulled up to VCC with a resistor. Knowing this information, the first DONE pin pulls up the second ON input. The second device now sequences its 4 supplies normally. When the second device is finished, the second DONE pin pulls low as expected. To start the sequence-down process, the first ON input is pulled low. The first device has recognized that the first DONE pin was high and already knows that it is not the last device. The first DONE pin therefore pulls the second ON pin low. The second DONE pin was low and is the last device. Therefore, the second device starts its sequencedown procedure. When finished, the second DONE stays low, and the second ON pin, knowing that it is not first, pulls up the first DONE pin. The first DONE pin senses the pulled up condition and triggers the sequence-down process for the first device. When the first device is finished, the DONE pin pulls down, overriding the pull-up from the second ON pin. The second device then releases its DONE pin, which pulls up to VCC, and the process is complete. Time extension can cascade to more than two devices as shown in Figure 3. It is a simple matter of adding more LTC2928s in the middle of the cascade, with a master/notfirst designation.
12 SUPPLIES, 24 TIME POSITIONS (MASTER/NOT FIRST) ON LTC2928 (MASTER/NOT FIRST) ON LTC2928 VCC DONE DONE DONE VCC FLT STMR FLT STMR FLT STMR
2928 F02 2928 F03
APPLICATIO S I FOR ATIO W U U
Figure 3. Additional supply and time extension.
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LTC2928
Another interesting application combines the usage of both the CAS pin connection and the DONE--ON communications link. Figure 4 shows a two dimensional configuration of four LTC2928s that allows for 16 supplies to be sequenced in up to 16 time positions.
16 SUPPLIES, 16 TIME POSITIONS (MASTER/FIRST) ON LTC2928 (MASTER/NOT FIRST) ON LTC2928 VCC V2 CDEL
2928 F05
DONE
DONE
CAS
STMR
CAS
STMR
ON
CAS
VCC
ON
CAS
DONE
DONE
LTC2928 (SLAVE/FIRST)
LTC2928 (SLAVE/FIRST)
2928 F04
Figure 4. Two-dimensional application.
In this application, both slave devices are clocked by the masters through their CAS pins. Again, sequencing-up begins with ON pulling high. Although the ON input is high on the device in the lower right quadrant, sequencing-up will not begin there until the first master (upper left), and its slave are finished sequencing-up. At that time the DONE pin will pull up the ON pin of the second master. The second master and slave will then start sequencing up their supplies.
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Using an Enable Line to Generate a Sequencing-Up Delay
LTC2928 VCC RT2 EN2 IEN (10uA)
APPLICATIO S I FOR ATIO W U U
Figure 5. Adjustable Sequencing Delay
VCC
An arbitrary delay between enables may be added by using an enable pull-up current (10A) to charge a delay capacitor (Figure 5). Position the delay using an RT resistor. Assuming 100% sequencing thresholds (0.5V) and a fully discharged delay capacitor (CDEL), the added time delay (TDEL) is: TDEL (ms) = 50 * CDEL (F ) Be sure to account for the extra delay when using the power-good timer (PTMR). Extending Sequencing Delay to Subsequent Supplies Sequencing delays can be extended after certain events by paralleling capacitance to the STMR pin. Figure 6 shows one way to add capacitance after a particular enable output pulls high.
VCC LTC2928 EN2 RESISTOR LIMITS GATE VOLTAGE
STMR CSTMR CADD
2928 F06
Figure 6. Adding STMR capacitance
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LTC2928
Correcting for IR Drops Sense feedback is common in high current applications. Parasitic resistance coupled with high currents causes voltage drops. The sense pin of a power module is designed to help regulate the voltage at a point in the distribution circuitry beyond the voltage drops. The output of the power module is raised until the desired voltage is achieved at the sense point. During startup with sense feedback, large inrush currents may cause the output of the power module to exceed its maximum output. This may cause the module to shutdown. The LTC2928 is easily configured to enable a sense transistor after a power supply has been sequenced on and inrush currents have diminished (Figure 7). The sense transistor feeds the sequenced supply voltage back to the sense line of the power module. The power module will raise its output to compensate for voltage drops across the sequencing transistor and other parasitics. During the sequence-down phase, the sense transistor will be disconnected before the supply sequencing transistor. If the supply transistor were to be disconnected first, the power module would sense the voltage drop and may attempt to drive higher in order to compensate.
VCC
POWER MODULE OUT +
IOUT
PARASITIC RDS(ON) RESISTANCE
VOUT
SENSE +
100
100
VCC
EN2
V2
EN1
LTC2928
RT1 RT2
V1
2928 F07
Figure 7. Correcting for IR drops (RT1 > RT2)
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Discharging Load Capacitance It is often necessary to discharge load capacitance quickly. Use the pull-down strength of the LTC2928 enable outputs to achieve faster turn-off times. Sequence the enable outputs in the same time position (RT resistors are identical). With the connections shown in Figure 8, EN1 is used to discharge the load capacitance through its 100 on resistance. If shorter discharge time is required, use external inverters as shown in Figure 9.
POWER MODULE
APPLICATIO S I FOR ATIO W U U
VOUT
SD
+
LOAD
VCC
EN2
EN1
RT1
RT2
LTC2928
V1
V2
2928 F08
Figure 8. Load Capacitance Discharge
POWER MODULE
VOUT VCC
SD
+
LOAD
EN2
EN1
IRF530 2N7002
RT1
RT2
LTC2928
V1
V2
2928 F09
Figure 9. Fast Load Capacitance Discharge
Using the Power Module Voltages to Gate the Sequenced Supplies The application shown in Figure 10 demonstrates how the power module outputs can be enabled and monitored for compliance, and then passed to various loads. Sequencing up and down is controlled by the level of the 12V supply. Sequencing up begins at 10.76V. If the application is disconnected from the 12V supply, an orderly shutdown will commence when the 12V supply drops to 10.43V. The blocking diode (D1) allows the 470F capacitor (C1) to retain enough energy to complete the sequence down process.
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3.3V N1 3.3V 100 DC/DC VIN VOUT SHDN 100 36.5k LTC2928 EN1 EN2 EN3 1N4148 D1 C1 470 F VCC 1.5k 1F 3.4k 95.3k 95.3k VCC RT1 RT2 RT3 RT4 SQT2 SQT1 97.6k ON 10k RST OV FLT DONE 3.32k 10k 10k
2928 TA04
APPLICATIO S I FOR ATIO W U U
12V
DC/DC VIN VOUT SHDN
2.5V
N2
2.5V
36.5k 52.3k 52.3k
V1 V2 V3 V4 10k MS1 MS2 VSEL GND RTMR PTMR STMR 10k 10k 10k
EN4 HVCC
0.047 F 0.1 F 3300pF
SYSTEM RESET FAULT
N1, N2: IRL3714S ALL RESISTORS 1%
Figure 10. Supply Sequencing with Stabilized Power Module Outputs
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LTC2928
Forcing Supplies Off or Disabling Unused Channels The most convenient way to mask an unused channel is to tie its respective RT input to ground. After sequencing begins, any enable output (EN) may be pulled low permanently by driving the respective RT input to ground (asynchronous OFF command). An asynchronously OFF channel cannot be re-enabled until a new sequence-up procedure is started. Any channel that is asynchronously OFF is removed from participation in the sequencing and supply monitoring processes, allowing the LTC2928 to operate normally on the remaining operating channels. When experiencing a fault in the "No Shutdown Debug Mode", the asynchronous OFF feature may be used to conveniently pull down the enable outputs. Alternatively, VCC may be turned off and on again. Clearing a fault condition requires the ON input to be low while the supplies are below their sequence-down thresholds.
VCC
SUPPLY BANK
0.1 F
Figure 11. Quad Supervisor (No Sequencing)
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Forcing Supplies On Prior to Sequencing Prior to sequencing, any or all enable pins may be forced high by pulling the respective RT pin to VCC. In this manner, supplies may be tested individually or together in any combination. With any RT pin at VCC, the respective voltage monitor inputs and comparator outputs become active with thresholds parked at the configured sequence-up threshold. Outside of sequencing, RST (with 100% thresholds selected) and OV are always functional, regardless of RT pin state. If all four RT pins are at VCC, the LTC2928 can be used as a stand-alone quad voltage monitor with under- and overvoltage indication as shown in Figure 11 (100% thresholds). With ON low in the RT forcing mode, sequence, command and reset faults do not occur. External faults however, may be detected (overvoltage, for example). Any previously logged faults remain in memory and their reporting will return upon exiting the forcing mode.
2.5V 1.5V 1.8V 3.3V
APPLICATIO S I FOR ATIO W U U
LTC2928 EN1 EN2 EN3 EN4 RT1
RT2 RT3 RT4 CMP1 CMP2 CMP3 CMP4 VCC SQT2 SQT1 V1 V2 V3 V4
52.3k
23.7k
17.8k
36.5k
HVCC
MS1 MS2 VSEL GND RTMR PTMR STMR REF OVA
10k
10k
10k
10k
0.047 F
RST
OV
FLT
DONE
CAS RDIS
ON
SYSTEM LOGIC
3.32k
10k
10k
2928 TA05
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RT1 RT2 RT3 RT4 VCC LTC2928 EN1 EN2 EN3 EN4 V4 V3 V2 V1 DONE 3.3k VCC SUPPLY BANK ON SEQUENCING DOWN SEQUENCING UP
2928 F11
APPLICATIO S I FOR ATIO W U U
VCC
DONE EN1-4 SEQUENCING UP
Figure 12. Cycle Supply Enables Repeatedly (useful for system burn-in)
VCC RT1 RT2 RT3 RT4 VCC 100k ON
LTC2928
V1 V2 V3 V4 VCC 10k FLT
1N4148
ON V1-4 SEQUENCING UP FLT
2928 F12
SHUTDOWN
RESTART
Figure 13. Automatic Restart After Fault
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RT1 RT2 RT3 RT4 VCC LTC2928 EN1 EN2 EN3 EN4 VCC 3.3k CONTROLLER ON 1N4148 FLT SEQUENCING UP SHUTDOWN
2928 F11a
APPLICATIO S I FOR ATIO W U U
VCC
ON FLT EN1-4
Figure 14. Turn-Off Enables Simultaneously (no sequence-down)
5V
LTC3704 RUN 10k
-5.2V (VMON(TH) = -4.67V) 43.2k V1 11k REF EN1 VCC VSEL VMON(TH) = -VREF (43.2k/11k) LTC2928
2928 F12a
Figure 15. Negative Supply Monitoring
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LTC2928
LTC2928 Design Example The following design example describes a power supply sequencing application using many features of the LTC2928. The example discusses a configuration procedure for the LTC2928 in a system containing a dual-supply DSP and FPGA. The design example schematic is shown in Figure 20. The three main operating phases--sequence-up, supply monitor, and sequence-down are discussed. All resistor, capacitor and configuration settings are reviewed. A timing diagram for sequencing-up is shown in Figure 18 and sequencing-down in Figure 19. A main 3.3V supply provides application power, including VCC for the LTC2928, and is sub-regulated to provide the lower voltages (2.5V, 1.8V, 1.5V). The LTC2928 controls external N-channel MOSFETs connected to two of the four supplies, used to pass power to the loads. The DSP core is powered from 1.8V and its I/O uses the 3.3V supply. The FPGA internals are powered from 1.5V and its I/O uses 2.5V. 1) Configure the LTC2928 based on application requirements a. Apply device power. Since the HVCC input is unused, connect it to ground. Connect the main 3.3V supply to the VCC pin. Bypass VCC with 0.1F to ground. b. Monitored Supply Polarity The application monitors four positive voltages. Connect the voltage selection input (VSEL) to ground (Table 1). c. Device designations The application requires only one LTC2928, and it is considered the MASTER device. By definition, it is also the FIRST and LAST device. Configure the MASTER/FIRST designation with the three-state MS1 and MS2 inputs connected to ground (Table 2). With MS1 and MS2 at ground, a reset fault is generated if RST pulls low during the supply monitor phase. Configure LAST device status with a 3.32k resistor from DONE to VCC. d. Sequence threshold selection
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During the sequencing-up or sequencing-down phase, time positions terminate (CAS is released) when a supply (or supplies) reaches it sequence threshold. This design example requires sequence thresholds at 67% of their under-voltage threshold. Therefore, connect SQT1 to GND and SQT2 to VCC (Table 4). e. Choose minimum power supply enable spacing The shortest time between successive power supply enables (tCAS(HI)) is controlled by a capacitor connected to the STMR pin and ground (also referenced as the sequence timer period, tSTMR). The sequence timer period for this application is 29ms. Calculate the sequence timer capacitor from t (s) CSTMR(F ) = STMR 8.67M For this application, CSTMR = 29ms = 3300pF 8.67M f. Supply order (time position) The application requires the 1.8V DSP core supply to start first, about 100ms after the ON signal is received. The 1.8V supply is monitored on the V3 input and implies selection of the RT3 resistor, since monitor inputs correspond numerically with the RT and EN inputs. The 100ms required delay is approximately three sequence timer periods, so configure the first supply for time position 3 (select RT3 = 24.3k). Table 3 shows the recommended RT resistor values as a function of time position. The 3.3V DSP I/O supply (monitored on V4) needs to turn on just after the core supply is alive, in order to minimize electrical stress and the possibility of bus contention. Turn on pass transistor N4 approximately 29ms after the core supply reaches its sequence threshold by selecting time position 4 (RT4 = 15k). The FPGA needs to be powered about 100ms after the DSP, with its core and I/O supplies enabled simultaneously. The 2.5V I/O supply is monitored on V1, and the 1.5V core supply is monitored on V2. Since the required turn on delay is about three sequence timer periods after the DSP, select RT1 = RT2 = 3.4k (time position 7).
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APPLICATIO S I FOR ATIO W U U
LTC2928
g. Undervoltage thresholds The positive supply monitor undervoltage threshold at all of the monitor inputs is 0.5V. Connect a resistive divider from the sensed voltage to ground. Connect the tap point to the respective high impedance monitor input. Specify the required undervoltage threshold (UVTH) and calculate the divider ratio using RnB UVTH( V) = -1 0.5V RnA This application requires -6.5% undervoltage thresholds for all supplies. For the 1.8V supply monitored on V3, the undervoltage threshold is 1.683V (1.8V x 0.935). The necessary divider ratio is R3B 1.683 = - 1 2.37 R3A 0.5V A good choice for R3B is 23.7k and R3A is 10k. All sequence thresholds are a percentage of the configured undervoltage threshold. The remaining ratios are: R1B 2.338 - 1 3.68 = R1A 0.5V R2B 1.403 - 1 1.81 = R2A 0.5V R4B 3.086 = - 1 5.17 R4A 0.5V h. Power-good timing The "power-good" time defines the maximum time allowed for all monitored voltages to reach their undervoltage threshold when sequencing-up, or the sequence-down threshold (when sequencing-down) with respect to the time of the first enabled (disabled) supply. If the "power-good" timer expires, a sequence fault occurs. The "power-good" time (tPTMR) is set with a capacitor from the PTMR pin to ground. Calculate the "power-good" capacitance from CPTMR (F) = tPTMR (s) 4.0M
For this application, the "power-good" time is 400ms, yielding
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CPTMR = 400ms = 0.1F 4.0M i. Reset delay time The reset delay time is the additional time that RST is held low after all monitor inputs are above their undervoltage threshold. It is also the additional time that OV is held low (after an overvoltage event) after all monitor inputs are below their overvoltage threshold. When the reset timer expires, RST and/or OV is allowed to pull high. The reset delay time (tRTMR) is set with a capacitor from the RTMR pin to ground. Calculate the reset capacitance from CRTMR (F) = tRTMR (s) 4.0M For this application, the reset delay time is 190ms, yielding CRTMR (F) = 190ms = 0.047F 4.0M j. Overvoltage thresholds Configure the OVA pin to set the global overvoltage thresholds. The application requires overvoltage thresholds at approximately 25% above the nominal supply voltage. For the 1.8V supply, the overvoltage threshold (OVTH) equals 2.25V (1.8V x 1.25). Compute the required value for VOVA from: VOVA ( V) = RnA * OVTH( V) RnA + RnB 10k * 2.25 = 0.667 V 10k + 23.7k For this application, VOVA ( V) = From the curves in Figures 16 and 17, the approximate value for VOVA is achieved by leaving the OVA pin open. Since the other monitor inputs were configured for the same relative undervoltage level, the relative overvoltage levels for the other supplies are the same (+ 25%). The application requires a fast shutdown upon overvoltage. To generate a fault upon an overvoltage condition, tie OV to FLT. The fault condition shuts down all controlled supplies.
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APPLICATIO S I FOR ATIO W U U
25
LTC2928
2) Sequence-Up Phase Start the sequence-up phase by transitioning the ON input above 1V. At this point, the LTC2928 senses the sequence position resistors on inputs RT1 through RT4. The sequence timer is operating and the CAS pin pulls low at the start of each time position. The CMP outputs are low during sequencing unless a fault has occurred. Protect shutdown inputs on regulators that are sensitive to high voltage. In this application, the FPGA regulators have their shutdown inputs connected to the 3.3V supply through a 10k resistor, thereby limiting the pull-up voltage on the shutdown inputs (the EN outputs alone may attempt to pull-up as high as 9.3V (VCC + 6V). DONE pulls low when all time positions are clocked through (CAS has completed pulling low 8 times). The comparator outputs become active and are allowed to pull high if the supply monitor inputs are above their under-voltage threshold. The RST output pulls high after all the supplies have remained above their undervoltage threshold for approximately 190ms. After RST is allowed to pull high, the LTC2928 enters its supply-monitor phase. The LTC2928 RST pin pulls up to 3.3V. The schottky diode SD1 and resistor RP1 limit the pull-up voltage at the FPGA reset pin. 3) Supply Monitor Phase During the supply-monitor phase, if any of the four supplies drops below its selected threshold, RST pulls low. Since this application considers an under-voltage condition during the supply-monitor phase to be a reset fault, FLT pulls low. All enable outputs pull low and the pass transistors shut off. Because of the fault condition, the LTC2928 is prevented from re-sequencing until all supplies drop below their sequence-down threshold, and the ON input is below 0.97V. 4) Sequence-Down Phase Begin the sequence-down phase by pulling the ON input below 0.97V. RST and all CMP outputs pull low as soon as the sequence-down command is detected. Beginning with supplies in time position 8, the supplies are sequenceddown reverse of the order in which they came up. At the end of the sequence-down phase, DONE pulls high (CAS has completed pulling low 8 times).
VOVA (V)
VOVA (V)
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Overvoltage Indication If any positive supply monitor input exceeds its overvoltage threshold at any time, OV pulls low. OV returns high once all positive supplies are below their overvoltage threshold for a period equal to the RST delay time. To shutdown all supplies upon overvoltage, tie the OV output to FLT. Overvoltage Threshold Adjustment Use the OVA input to set the overvoltage threshold for all positive supplies. Leave the OVA input open to set the OV threshold at the supply monitor inputs to 32% above the undervoltage threshold (VOVA = 0.660V). Ground the OVA input to set the OV threshold to 12% above the undervolatge threshold (VOVA) = 0.556V). Tie the OVA input to VCC = 3.3V to set the OV threshold to 115% above the undervoltage threshold (VOVA = 1.072V). Select accurate OV thresholds between 0.556V and 0.660V by connecting and external resistor between OVA and ground (Figure 16). Configure higher OV thresholds by connecting an external resistor between OVA and VCC (Figure 17). These higher thresholds are potentially less accurate due to variations in VCC.
0.66
APPLICATIO S I FOR ATIO W U U
32
VOVA (% ABOVE UNDERVOLTAGE THRESHOLD)
0.64
28
0.62
0.60
24 20
0.58
0.56 100
16 12 10M
1k
10k 100k ROVA ( )
1M
2928 G03
Figure 16. External Resistor from OVA to Ground
1.56
1.38
1.20
1.02
VCC = 6V VCC = 5.5V VCC = 5V VCC = 4.5V VCC = 4V VCC = 3.5V VCC = 3V
212
VOVA (% ABOVE UNDERVOLTAGE THRESHOLD)
176
140 104
0.84
0.66 100
68 32 10M
1k
10k 100k ROVA ( )
1M
2928 G04
Figure 17. External Resistor from OVA to VCC
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LTC2928 U
4 5 6 7 8 0.67VMON(TH) 0.67VMON(TH) 0.67VMON(TH) 0.67VMON(TH) VMON(TH) tRTMR RST PTMR RTMR
2928 TA02
APPLICATIO S I FOR ATIO
tSTMR
ON DONE
CAS
1
EN3 V3 EN4
V4 EN1, EN2 V1 V2 CMP3, CMP4, CMP1 CMP2
Figure 18. Design Example Timing Diagram, Sequencing-Up
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U
3
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LTC2928 U
5 4 3 2 1 0.67VMON(TH) EN3 V3 0.67VMON(TH) CMP1, CMP2 CMP3, CMP4 RST
2928 TA03
APPLICATIO S I FOR ATIO
tSTMR
ON
DONE CAS 8 EN1, EN2 V1, V2 0.67VMON(TH) EN4 V4 7 6
PTMR
Figure 19. Design Example Timing Diagram, Sequencing-Down
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LTC2928 U
G Package 36-Lead Plastic SSOP (5.3mm) (Reference LTC DWG # 05-08-1640)
12.50 - 13.10* (.492 - .516) 1.25 0.12 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 5.3 - 5.7 7.40 - 8.20 (.291 - .323) 0.65 BSC 5.00 - 5.60** (.197 - .221)
0 - 8
PACKAGE DESCRIPTIO
RECOMMENDED SOLDER PAD LAYOUT
7.8 - 8.2
0.42 0.03
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
2.0 (.079) MAX
0.09 - 0.25 (.0035 - .010)
0.55 - 0.95 (.022 - .037)
0.65 (.0256) BSC
NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 3. DRAWING NOT TO SCALE
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED .152mm (.006") PER SIDE **DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE
0.22 - 0.38 (.009 - .015) TYP
0.05 (.002) MIN
G36 SSOP 0204
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LTC2928
UHF Package 38-Lead Plastic QFN (5mm x 7mm) (Reference LTC DWG # 05-08-1701)
PIN 1 NOTCH R = 0.30 TYP OR 0.35 x 45 CHAMFER 37 38 0.40 0.10 1 2
5.00 0.10 (2 SIDES)
0.75 0.05 0.00 - 0.05
3.15 0.10 (2 SIDES)
PIN 1 TOP MARK (SEE NOTE 6)
7.00 0.10 (2 SIDES)
5.15 0.10 (2 SIDES)
0.40 0.10 0.200 REF 0.200 REF 0.75 0.05 0.00 - 0.05 0.25 0.05 0.50 BSC R = 0.115 TYP
(UH) QFN 0205
BOTTOM VIEW--EXPOSED PAD
0.70 0.05
5.50 0.05 (2 SIDES) 4.10 0.05 (2 SIDES) 3.15 0.05 (2 SIDES) NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE M0-220 VARIATION WHKD 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
PACKAGE OUTLINE 0.25 0.05 0.50 BSC 5.15 0.05 (2 SIDES) 6.10 0.05 (2 SIDES) 7.50 0.05 (2 SIDES) RECOMMENDED SOLDER PAD LAYOUT
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LTC2928 U
RP1 10k DC/DC VIN VOUT SHDN VCC 3.3V N4 3.3V 10k DC/DC VIN VOUT SHDN 3.3V R4B 52.3k LTC2928 EN1 EN2 EN3 RT1 RT2 RT3 RT4 3.4k 3.4k 24.3k 15k 1k 1k 1k 1k EN4 RT1 RT2 RT3 RT4 CMP1 CMP2 CMP3 CMP4 VCC 0.1 F SQT2 SQT1 CAS RDIS SYSTEM CONTROLLER ON V1 V2 V3 V4 HVCC MS1 MS2 VSEL GND RTMR PTMR STMR REF OVA RST OV FLT DONE N3, N4: IRL3714S ALL RESISTORS 1% CRTMR CPTMR CSTMR R4A 10k 0.047 F 0.1 F 3300pF R3A 10k R2A 10k R1A 10k R3B 23.7k R2B 18.2k R1B 36.5k I/O N3 DC/DC VIN VOUT SHDN 1.8V 1.5V 2.5V CORE FPGA I/O RST CORE DSP RST SD1 BAT85 3.32k VCC 10k 10k
2928 TA01
TYPICAL APPLICATIO
Figure 20. LTC2928 Design Example
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Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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LTC2928 RELATED PARTS
PART NUMBER LTC2920-1 LTC2920-2 LTC2921/LTC2922 LTC2923 LTC2924 LTC2925 LTC2926 LTC2927 LTC2970 DESCRIPTION Single/Dual Power Supply Margining Controller Power Supply Tracker with Input Monitor Power Supply Tracking Controller Quad Power Supply Sequencer Multiple Power Supply Tracking Controller with Power Good Timeout Power Supply Tracking Controller Single Power Supply Tracking Controller Digital Power Monitor and Margining Controller COMMENTS Symmetric/Asymmetric High and Low Voltage Margining Monitor up to Five Supplies, Includes Remote Sense Switches Up to 3 Supplies Cascadable Controls Three Supplies Without FETs, Includes Three Shutdown Control Pins Active Tracking Control with Series MOSFETs Controls Single Supply Without FETs, Daisy-Chain for Multiple Supplies Dual Supply Controller with 14-Bit ADC, 8-Bit DACs, Accurate Reference, Temperature Sensor and Automatic Servo Logic
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32 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
LT 0506 * PRINTED IN USA
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2006

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