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FEATURES

LTC2953 Push Button On/Off Controller with Voltage Monitoring DESCRIPTION
The LTC(R)2953 is a push button On/Off controller that manages system power via a push button interface. An enable output toggles system power while an interrupt output provides debounced push button status. The interrupt output can be used in menu driven applications to request a system power down. The LTC2953 also features input and output power supply monitors. An uncommitted power fail comparator provides real time input monitor information, while a de-glitched under voltage lockout comparator gracefully initiates a system power down. The under voltage lockout comparator prevents the system from powering from a low power supply. The adjustable supply monitor input is compared against an accurate internal 0.5V reference. The reset output remains low until the supply monitor input has been in compliance for 200ms. The LTC2953 operates over a wide 2.7V to 27V input voltage range and draws only 14A of current. Two versions of the part accommodate either positive or negative enable polarities.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
Wide Operating Voltage Range: 2.7V to 27V Push Button Control of System Power Low Supply Current: 14A Power Fail Comparator Generates Warning UVLO Comparator Gracefully Latches Power Off Adjustable Supply Monitor with 200ms Reset Adjustable Power Down Timer Low Leakage EN Output (LTC2953-1) Allows DC/DC Converter Control High Voltage EN Output (LTC2953-2) Allows Circuit Breaker Control Simple Interface Allows Orderly System Power Up and Power Down 1.5% Threshold Tolerances 10kV ESD HBM on PB Input 12-Pin 3mm x 3mm DFN
APPLICATIONS

Push Button Power Path Control Battery Power Supervisor Portable Instrumentation, PDA Blade Servers Desktop and Notebook Computers
TYPICAL APPLICATION
VIN VOUT DC/DC SHDN 100k 100k 100k 100k RST PFO INT KILL PDT 1F tPDT = 6.4 SECONDS
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2953 TA01
Push Button On/Off Control with Interrupt
3.3V
TURN ON PULSE PB SHORT INTERRUPT PULSE LONG TURN OFF PULSE
+
8.4V 2150k UVLO VIN EN
100k
23.2k PFI 196k
LTC2953-1 VM
499k
EN
TURNS ON
STAYS ON
TURNS OFF
PB ON/OFF GND
RST GPIO INT SYSTEM LOGIC KILL
INT INTERRUPT INTERRUPT
2954 TD01b
1
LTC2953 ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW GND VM KILL PDT PB VIN 1 2 3 4 5 6 13 12 INT 11 EN/EN 10 RST 9 PFO 8 PFI 7 UVLO
Supply Voltage (VIN) .................................. -0.3V to 33V Input Voltages PB, PFI, UVLO........................................... -6V to 33V VM ......................................................... -0.3V to 20V KILL ....................................................... -0.3V to 10V PDT....................................................... -0.3V to 2.7V Output Voltages EN/EN, PFO ............................................ -0.3V to 50V RST, INT ................................................ -0.3V to 10V Operating Temperature Range LTC2953C ................................................ 0C to 70C LTC2953I ............................................. -40C to 85C Storage Temperature Range................... -65C to 125C
DD PACKAGE 12-LEAD (3mm 3mm) PLASTIC DFN TJMAX = 125C, JA = 43C/W EXPOSED PAD (PIN 13) PCB GROUND CONNECTION OPTIONAL
ORDER INFORMATION
LEAD FREE FINISH LTC2953CDD-1#PBF LTC2953CDD-2#PBF LTC2953IDD-1#PBF LTC2953IDD-2#PBF TAPE AND REEL LTC2953CDD-1#TRPBF LTC2953CDD-2#TRPBF LTC2953IDD-1#TRPBF LTC2953IDD-2#TRPBF PART MARKING* LCWT LCQT LCWT LCQT PACKAGE DESCRIPTION 12-Lead (3mm x 3mm) Plastic DFN 12-Lead (3mm x 3mm) Plastic DFN 12-Lead (3mm x 3mm) Plastic DFN 12-Lead (3mm x 3mm) Plastic DFN TEMPERATURE RANGE 0C to 70C 0C to 70C -40C to 85C -40C to 85C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
SYMBOL Supply Pin (VIN) VIN IIN VUVL VPB(MIN, MAX) IPB Supply Voltage Range VIN Supply Current VIN Undervoltage Lockout PB Operating Voltage Range PB Input Current PARAMETER
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 2.7V to 27V, unless otherwise noted (Note 2).
CONDITIONS Steady State Operation VIN = 2.7V to 27V VIN Falling Single-Ended 2.5V < VPB < 27V VPB = 1V VPB = 0.6V PB Falling IPB = -1A

MIN 2.7
TYP
MAX 27
UNITS V A V V A A A V V
14 2.2 -1 -1 -3 0.6 1 -6 -9 0.8 1.6 2.3
26 2.5 27 1 -12 -15 1 2
Push Button, Enable (PB, EN/EN)
VPB(VTH) VPB(VOC)
PB Input Threshold PB Open Circuit Voltage
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LTC2953 ELECTRICAL CHARACTERISTICS
SYMBOL IEN(LKG) VEN(VOL) tEN, Lock Out tDB, ON IPDT(PU) IPDT(PD) tDB, OFF tPD, Min tPDT tINT, Min tINT, Max VKILL(TH) VKILL(HYST) t KILL(PW) tKILL(PD) tKILL, ON BLANK IKILL(LKG) IINT(LKG) VINT(VOL) VPFI(TH) VUVLO(TH) VM(TH) VTH VPFI(HYST) VUVLO(HYST) VPFO(VOL) VRST(VOL) PARAMETER EN/EN Leakage Current EN/EN Voltage Output Low EN/EN Lock Out Time (Note 3) Turn On Debounce Time PDT Pull Up Current PDT Pull Down Current Turn Off Interrupt Debounce Time Internal PB Power Down Delay Time (Note 4) Additional Adjustable PB Power Down Delay Time Minimum INT Pulse Width Maximum INT Pulse Width KILL Input Threshold Voltage KILL Input Threshold Hysteresis KILL Minimum Pulse Width KILL Propagation Delay KILL Turn On Blanking (Note 5) KILL Leakage Current INT Leakage Current INT Output Voltage Low PFI Input Threshold Voltage UVLO Input Threshold Voltage Adjustable Reset Threshold PFI-UVLO Threshold Mismatch PFI Input Hysteresis UVLO Input Hysteresis PFO Output Voltage Low RST Output Voltage Low IPFO = 500A I = 3mA KILL Falling Enable Released KILL = Low, Enable Asserted Enable Released VKILL = 0.6V VINT = 3V IINT = 3mA Falling Falling Falling/Rising
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 2.7V to 27V, unless otherwise noted (Note 2).
CONDITIONS VEN/ EN = 1V, Sink Current Off VEN/ EN = 40V, Sink Current Off IEN/ EN = 500A Enable Released Enable Asserted PB Falling Enable Asserted VPDT = 0V VPDT = 1.3V PB, UVLO Falling INT Falling PB, UVLO Falling Enable Released PDT Open CPDT = 1500pF INT Asserted INT Released CPDT = 1500pF, INT Asserted INT Released KILL Falling

MIN
TYP
MAX 0.1 1
UNITS A A V ms ms A A ms ms ms ms ms V mV s s ms A A V mV mV mV mV mV mV V V
0.11 52 26 -2.4 2.4 26 52 9 26 35 0.57 10 30 64 32 -3 3 32 64 11.5 32 43.5 0.6 30
0.4 82 41 -3.6 3.6 41 82 13.5 41 54.5 0.63 50 30
On/Off Timing Pins (PB, UVLO, PDT, INT)
P Handshake Pins (KILL, INT)
400
512
650 0.1 0.1
0.11 492 492 492 -5 2 30 500 500 500 0 4 50 0.11 0.11
0.4 508 508 508 5 10 70 0.4 0.4
Power Fail and Voltage Monitor Pins (PFI, PFO, UVLO, VM, RST)
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LTC2953 ELECTRICAL CHARACTERISTICS
SYMBOL IPFI(LKG) IPFO(LKG) IUVLO(LKG) IVM(LKG) IRST(LKG) tPFI tRST tuv PARAMETER PFI Leakage Current PFO Leakage Current UVLO Leakage Current VM Input Leakage Current RST Output Leakage Current PFI Delay to PFO Reset Timeout Period VM Under Voltage Detect to RST VM Less Than VM(TH) By More Than 1%
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 2.7V to 27V, unless otherwise noted (Note 2).
CONDITIONS VPFI = 0.5V VPFI = 27V VPFO = 1V VPFO = 40V VUVLO = 0.5V VUVLO = 27V VM = 0.5V VRST = 3V

MIN
TYP 2 2 2 2
MAX 10 1 10 1 10 1 10 0.1 200 260
UNITS nA A nA A nA A nA A s ms s
40 140
100 200 250
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: The Enable Lock Out time is designed to allow an application to properly power down such that the next power up sequence starts from a consistent powered down configuration. PB is ignored during this lock out time. This time delay does not include tDB, ON.
Note 4: To manually force a release of the EN/EN pin, either PB or UVLO must be held low for at least tPD, Min (internal default power down timer) + tPDT (adjustable by placing external capacitor at PDT pin). Note 5: The KILL turn on blanking timer period (tKILL, ON BLANK) is the waiting period immediately after enable output is asserted. This blanking time allows sufficient time for the DC/DC converter and the P to perform power up tasks. The KILL, PB and UVLO inputs are ignored during this period. If KILL remains low at the end of this blanking period, the enable output is released, thus turning off system power.
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LTC2953 TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Temperature
20 VIN = 27V 18 15 IVIN (A) VIN = 3.3V IVIN (A) 16 tDB, ON (ms) 30 40 20 TA = 25C
Supply Current vs Supply Voltage
50
Turn On Debounce Time (tDB, ON) vs VIN
TA = 25C
VIN = 2.7V 10
14
20
12
10
5 -50
-25
0 25 50 TEMPERATURE (C)
75
100
2953 G01
10 0 5 10 20 15 VIN (V) 25 30 35
0
0
5
10
15 VIN (V)
20
25
30
2953 G03
2953 G02
Turn Off Interrupt Debounce Time (tDB, OFF) vs VIN
50 TA = 25C 40 tPD,MIN + tPDT (ms) 1000 tDB, OFF (ms) 10000
Forced Power Down Delay Time (tPD, MIN + tPDT) vs PDT External Capacitance
TA = 25C VIN = 3.3V PDT PULL-DOWN CURRENT (A) -3.4
PDT Pull-Down Current vs Temperature
VIN = 3.3V
-3.2
30
-3.0
20
100
-2.8
10 10 0 5 10 15 VIN (V) 20 25 30
2953 G04
0
1
10 100 PDT EXTERNAL CAPACITANCE (nF)
1000
'#! /#
-2.6 -50
-25
0 25 50 TEMPERATURE (C)
75
100
2953 G06
PDT Pull-Up Current vs Temperature
3.4 -300 VIN = 3.3V -250 3.2 -200 -150 -100 -50 2.6 -50
PB Current vs PB Voltage
TA = 25C VIN = 3.3V 300 250
PB Voltage vs External PB Resistance to Ground
VIN = 3.3V
PDT PULL-UP CURRENT (A)
TA = 100C PB VOLTAGE (mV) PB CURRENT (A) 200 150 100 50 0 0 10 20 PB VOLTAGE (V) 30
'#! /&
3.0
TA = -45C TA = 25C
2.8
-25
0 25 50 TEMPERATURE (C)
75
100
2953 G07
0 -10
0 5 10 15 20 EXTERNAL PB RESISTANCE TO GROUND (k)
'#! /'
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LTC2953 TYPICAL PERFORMANCE CHARACTERISTICS
EN (LTC2953-1) Voltage vs VIN
1.0 4 TA = 25C 100k PULL-UP FROM EN TO VIN 3
EN (LTC2953-2) Voltage vs VIN
TA = 25C 100k PULL-UP FROM EN TO VIN 4
PFO Voltage vs VIN
TA = 25C PFI = 1V 100k PULL-UP FROM PFO TO VIN
0.8
3
EN (V)
EN (V)
2
PFO (V) 0 1 2 VIN (V) 3 4
2953 G11
0.6
2
0.4 1 0.2
1
0
0 0 1 2 VIN (V)
'#! /
3
4
0 0 0.5 1.0 1.5 2.0 2.5 VIN (V) 3.0 3.5 4.0
2953 G12
RST Voltage vs VIN
4 600 TA = 25C VM = 1V 100k PULL-UP FROM RST TO VIN RST, INT VOL (mV) 500 400 300 200 100 0 0 0.5 1.0 1.5 2.0 2.5 VIN (V) 3.0 3.5 4.0 0
RST, INT VOL vs Current Load
TA = 25C VIN = 3.3V
3
RST (V)
2
1
0
2 4 6 8 RST, INT CURRENT LOAD (mA)
10
2953 G14
2953 G13
Threshold Voltage (VM, PFI, UVLO) vs Temperature
504 VIN = 3.3V 800
EN/EN, PFO VOL vs Current Load
TA = 25C VIN = 3.3V EN/EN, PFO VOL (mV) 600
502 THRESHOLD (mV)
500
400
498
200
496 -50
0 -25 0 25 50 TEMPERATURE (C) 75 100
2953 G15
0
0.5 2 2.5 1 1.5 EN/EN, PFO CURRENT LOAD (mA)
3
2953 G16
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LTC2953 PIN FUNCTIONS
GND (Pin 1): Ground. VM (Pin 2): Voltage Monitor Input. Input to an accurate comparator with a 0.5V threshold. VM controls the state of the RST output pin and is independent of PB, PFI and UVLO status. A voltage below 0.5V on this pin asserts RST low. Connect to GND if unused. KILL (Pin 3): KILL Input. Forcing KILL low releases the enable output. During system turn on, this pin is blanked by a 512ms internal timer (tKILL, ON BLANK) to allow the system to pull KILL high. This pin has an accurate 0.6V threshold and can be used as a power kill voltage monitor. Set the pin voltage above its threshold if unused. PDT (Pin 4): Power Down Time Input. A capacitor to ground determines the additional time (6.4 seconds/F) that PB or UVLO must be held low before releasing the EN/EN and INT outputs. If this pin is left open, the power down delay time defaults to 64ms. PB (Pin 5): Push Button Input. Connecting PB to ground through a momentary switch provides On/Off control via the EN/EN and INT outputs. An internal 100k pull-up resistor connects to an internal 1.9V bias voltage. The rugged PB input withstands 10kV ESD HBM and can be pulled up to 27V externally without consuming extra current. Voltages below ground will not damage the pin. VIN (Pin 6): Power Supply Input: 2.7V to 27V. UVLO (Pin 7): UVLO Comparator Input. When UVLO drops below its falling threshold (0.5V) for more than 32ms, the LTC2953 asserts INT low, thereby requesting a system power down. If UVLO remains below its falling threshold (0.5V) for longer than the adjustable power down delay, the enable output is released. Additionally, UVLO provides a PB lock out feature that prevents the user from asserting the enable output when UVLO falls below its threshold. Connect to VIN if unused. PFI (Pin 8): Power Fail Comparator Input. Input to an accurate comparator with a 0.5V falling threshold and 4mV of hysteresis. PFI controls the state of the PFO output pin and is independent of PB, VM and UVLO status. Connect to GND if unused. PFO (Pin 9): Power Fail Output. This pin is a high voltage open drain pull-down. PFO pulls low when PFI is below 0.5V. Open circuit when unused. RST (Pin 10): Reset Output. This pin is an open drain pull-down. Pulls low when VM input is below 0.5V and is held low for 200ms after VM input is above 0.5V. Open circuit when unused. EN (LTC2953-1, Pin 11): Open Drain Enable Output. This output is intended to enable system power. EN is asserted high after a valid PB turn on event (tDB, ON). EN is released low if: a) KILL is not driven high (by P) within 512ms of the initial valid PB power turn on event, b) KILL is driven low during normal operation, c) PB or UVLO is asserted and held low (t > tPD, Min + tPDT) during normal operation. EN (LTC2953-2, Pin 11): Open Drain Enable Output. This output is intended to enable system power. EN is asserted low after a valid PB turn on event (tDB, ON). EN is released high if: a) KILL is not driven high (by P) within 512ms of the initial valid PB power turn-on event, b) KILL is driven low during normal operation, c) PB or UVLO is asserted and held low (t > tPD, Min + tPDT) during normal operation. INT (Pin 12): Open Drain Interrupt Output. After a turn off event is detected (tDB, OFF) from PB or UVLO, the LTC2953 interrupts the system (P) by asserting INT low. The P would perform power down and housekeeping tasks and then assert the KILL pin low, thus releasing the enable output. The INT pulse width is a minimum of 32ms and stays low as long as PB is asserted. If PB is asserted for longer than tPD, Min + tPDT, however, the INT and EN/EN outputs are immediately released. Open circuit when unused. Exposed Pad (Pin 13): Exposed Pad may be left open or connected to ground.
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LTC2953 BLOCK DIAGRAM
VIN 2.7V TO 27V REGULATOR 1.5k 34V ZENER 2.4V HV PFI
0.5V VM
+ -
HV 200 ms RST DELAY
RST
2.4V
HV
PB
100k HV DEBOUNCE AND 10s FILTER 0.8V LOGIC 0.6V INT KILL
UVLO
0.5V
8
+
-
HV
DEBOUNCE AND 10s FILTER
OSCILLATOR GND HV INDICATES A HIGH VOLTAGE PIN
2953 BD
PDT
- +
0.5V
PFO
EN (-1) EN (-2)
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LTC2953 TIMING DIAGRAMS
PB tDB, ON PB, UVLO AND KILL IGNORED tKILL, ON BLANK
EN (LTC2953-1)
KILL
DO NOT CARE
SYSTEM SETS KILL HIGH
2953 TD01
Figure 1. Power On Timing (UVLO > 0.55V)
PB tDB, OFF
PB AND UVLO IGNORED t < tPDT
PDT tPD, Min INT tINT, Min UVLO
UVLO IGNORED
EN (LTC2953-1)
ENABLE DOES NOT SWITCH LOW
2953 TD02
Figure 2. PB Interrupt Pulse: PB Low for tDB,OFF < t < (tPD, Min + tPDT) (Enable Remains Active)
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LTC2953 TIMING DIAGRAMS
UVLO tDB, OFF PB AND UVLO IGNORED t < tPDT
PDT tPD, Min INT tINT, Min
PB
PB IGNORED
EN (LTC2953-1)
ENABLE DOES NOT SWITCH LOW
2953 TD03
Figure 3. UVLO Interrupt Pulse: UVLO Low for tDB,OFF < t < (tPD, Min + tPDT) (Enable Remains Active)
PB tDB, OFF
PB IGNORED
16 CYCLES PDT tPD, Min INT tINT, Max EN (LTC2953-1) tPDT
UVLO
UVLO IGNORED
2953 TD04
Figure 4. Push Button Power Down Timing: PB Pressed and Held Low for t > (tPD, Min + tPDT)
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LTC2953 TIMING DIAGRAMS
UVLO UVLO IGNORED tDB, OFF 16 CYCLES PDT tPD, Min INT tINT, Max EN (LTC2953-1) tPDT
PB
PB IGNORED
2953 TD05
Figure 5. UVLO Power Down Timing: UVLO Low for t > (tPD, Min + tPDT)
0.5V VM
0.5V PFI
0.5V
0.504V
tUV RST
tRST PFO
2953 TD06
tPFI
tPFI
2953 TD07
Figure 6. Voltage Monitor Reset Timing
Figure 7. Power Fail Comparator Timing
0.6V KILL
tKILL(PW)
0.63V
EN (LTC2953-1)
tKILL(PD)
2953 TD08
Figure 8. KILL Minimum Pulse Width and Propagation Delay
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LTC2953 OPERATION
The LTC2953 is a push button On/Off controller with dual function input and output supply monitors. The part contains all the circuitry needed to debounce a push button input and provides a simple P handshake protocol for reliable toggling of system power. The LTC2953 operates over a wide 2.7V to 27V input voltage range and draws only 14A of current. The LTC2953 features dual function supply monitoring: a power fail comparator generates an early warning and an under voltage lock-out comparator initiates a controlled system power down. Push Button Controller The push button input controls the enable and interrupt outputs. The enable output toggles system power while the interrupt output provides debounced push button status. The interrupt output can be used in menu driven applications to request a system power down. A power kill input allows a microprocessor or other logic to release the enable output, thus immediately powering down the system. To assert the enable output (turn on system power), press the push button (PB) input and hold for at least 32ms. See Figure 1. Once system power has been enabled, a user can request a system power down by again pressing the push button for at least 32ms and releasing it before the PDT timer counts 16 cycles. The LTC2953 then asserts the interrupt output and the P subsequently sets the KILL input low to turn off system power. Note that the UVLO input can also assert the interrupt output. See Figure 2 and Figure 3 and Dual Function Supply Monitors section. In the event that the P does not respond to the interrupt request, the user can force release of the enable output by pressing and holding down the push button (or UVLO) until the PDT timer times out. See Figure 4 and Figure 5. Dual Function Supply Monitors An uncommitted power fail comparator provides real time supply threshold information. The power fail input (PFI) is compared against an accurate internal 0.5V reference and the comparison result is passed directly to the power fail output (PFO) pin. The operation of the power fail comparator is de-coupled from all other functionality and is always active. See Figure 7. The under voltage lockout comparator provides the user with another method to initiate a controlled system power down. If the UVLO pin voltage falls below its falling threshold (0.5V) for longer than 32ms, the interrupt output is asserted for a minimum of 32ms. If the UVLO pin voltage remains below its threshold (0.5V) for an additional time given by the PDT external capacitor, then the enable pin is automatically released (thus powering down the system). See Figure 3 and Figure 5. This comparator also serves as an under voltage lockout. If system power is off (enable released) and UVLO < 0.5V, the UVLO comparator prevents the push button from turning on system power (asserting enable output). Voltage Supervisor with 200ms P Reset The LTC2953 provides a single adjustable supply monitor with a nominal 200ms reset delay. When the VM input voltage drops below 0.5V, the RST output is pulled low. RST remains low for 200ms after the VM input has risen above 0.5V. The input 0.5V threshold has a guaranteed accuracy of 1.5% over temperature and process. The operation of the supply monitor is de-coupled from all other functionality and is always active. See Figure 6.
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LTC2953 APPLICATIONS INFORMATION
PUSH BUTTON CONTROL Power On Sequence To enable system power, the push button input (PB) must be held low continuously for 32ms (tDB, ON). Once the enable output (EN/EN) is asserted, the LTC2953 starts a 512ms internal timer (tKILL, ON BLANK). The KILL input must be driven high within this 512ms window. This blanking time represents the maximum time allowed for the system to power up and initialize the circuits driving the KILL input. If KILL remains low at the end of the blanking period, the enable output is released (see "Aborted Power On Sequence" section). Figure 9 shows a normal power on sequence.
PB tDB, ON PB, UVLO AND KILL IGNORED tKILL, ON BLANK
Short Pulse Interrupt To interrupt the P, either PB or UVLO must be low for at least 32ms (tDB, OFF). This signals the P either that a user has pressed the push button or that the supply is running low. The P would then perform power down and housekeeping tasks and assert KILL low when done. This in turn releases the enable output, thus shutting off system power. See Figure 10. Note that either PB or UVLO can control the power down sequence, but not both at the same time. For example, if both PB and UVLO are high and the user presses the push button, PB will be active and UVLO will be ignored until PB is released or the power down sequence is complete. Forced Power Off Sequence The LTC2953 provides a failsafe feature that allows a user to manually force a system power down. For cases when the P fails to respond to the interrupt signal, the user can force a power down by pressing and holding either the push button or the UVLO inputs low. The length of time required to release the enable output is given by a fixed internal 64ms delay (tPD, Min) plus an adjustable power down timer delay (tPDT). The adjustable delay is set by placing an external capacitor on the PDT pin. Use the following equation to calculate the capacitance for the desired extra delay. CPDT is the PDT pin external capacitor: CPDT = 1.56E-4 [F/ms] * (tPDT - 1ms) See Figure 11.
EN (LTC2953-1)
KILL
DO NOT CARE
SYSTEM SETS KILL HIGH
2953 F09
Figure 9. Power On Timing (UVLO > 0.55V)
Note that only the push button input can enable system power. The LTC2953 provides two enable output polarities to allow DC/DC converter control (LTC2953-1) and external power PFET control (LTC2953-2).
PB OR UVLO SHORT PULSE tDB, OFF
PB OR UVLO
LONG PULSE
INT PDT tPD, Min EN (LTC2953-1)
16 CYCLES tINT, Min
KILL
DO NOT CARE
SYSTEM SETS KILL LOW
tPDT
EN (LTC2953-1)
SYSTEM POWER OFF
2953 F10
2953 F11
Figure 10. Power Off Interrupt Timing
Figure 11. Forced Power Off Timing with Adjustable Delay (See Figure 5 for More Details)
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LTC2953 APPLICATIONS INFORMATION
PB tDB, ON PB, UVLO AND KILL IGNORED tKILL, ON BLANK KILL SYSTEM SETS KILL LOW
EN (LTC2953-1)
TURN ON ABORTED EN (LTC2953-1) SYSTEM FAILS TO SET KILL HIGH
2953 F12
SYSTEM POWER OFF
2953 F13
KILL
tKILL(PD)
Figure 12. Aborted Power On Sequence, KILL Remaining Low Aborts Power On Sequence
Figure 13. P Turns Off System Power
Aborted Power On Sequence The LTC2953 provides an internal 512ms timer to detect when a system fails to power on properly. A power on sequence begins by debouncing the PB input. After the enable pin is subsequently asserted, the LTC2953 starts the 512ms blanking timer (tKILL, ON BLANK). If the KILL input is not driven high within this 512ms time window, the enable pin is immediately released, thus turning off system power. This failsafe feature prevents a user from turning on the device when the circuits driving the KILL input do not respond within 512ms after enable has been asserted. See Figure 12. P Turns Off System Power During Normal Operation Once the system has powered on and is operating normally, the P can turn off power by asserting the KILL input low. See Figure 13. DUAL FUNCTION BATTERY SUPERVISOR The LTC2953 provides two comparators for battery monitoring: an uncommitted power fail comparator and a latched low battery comparator with P interrupt. The application shown in Figure 14 monitors a 2 cell Li-Ion battery stack.
Power Fail Comparator This comparator provides real time threshold information and can serve as the first warning of a decaying battery or supply. The PFO output is driven low when the PFI input voltage drops below its falling threshold (0.5V) and is high impedance when PFI rises above its rising threshold (0.504V). The low leakage, high voltage PFI input (10nA, maximum) allows the use of large valued external resistors, which lowers system current consumption. UVLO Comparator The under voltage lockout comparator performs three functions: a) interrupts the P when a supply glitch drives the UVLO voltage below its falling threshold (0.5V) for longer than 32ms, followed by b) forces system power off when the UVLO voltage falls below its falling threshold (0.5V) for tPD, Min + tPDT, c) locks out the enable (prevents system power on) output if UVLO voltage is below its falling threshold (0.5V) during system power on. See Figures 15A and 15B. The low leakage (10nA, maximum), high voltage UVLO input allows the use of large valued external resistors. See Figure 14.
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LTC2953 APPLICATIONS INFORMATION
+
8.4V LTC2953-1 VIN INT
DEBOUNCE R14 2150k UVLO VTH = 5.4V UVLO COMPARATOR EN
to the low offset architecture of the comparators, the UVLO and PFI thresholds can be set to as close as 5mV apart. The trip thresholds of the circuit of Figure 14 are 6.04V and 5.40V for the power fail and low battery (UVLO) comparators, respectively. Push Button Lockout The LTC2953 provides a push button lock out feature that prevents a user from turning on a system with a dead battery. The push button input is ignored when the UVLO input voltage is less than the falling threshold (0.5V). See Figure 15B.
UVLO 0.5V SUPPLY GLITCH 0.55V
-
50mV 0.5V PFI
R13 23.2k
+
DEBOUNCE AND DELAY
PFO
VTH = 6.04V R12 196k
-
4mV 0.5V
+
POWER FAIL COMPARATOR
2953 F14
tDB, OFF
2953 F15a
INT
tINT, Min
Figure 14. Dual Function Battery Comparators
Which Input Initiated Power Down: PB or UVLO? The circuit in Figure 14 determines whether a power down was initiated by a user pressing the push button or by a battery drooping too low. If both INT and PFO outputs are low, then a low battery condition initiated a power down. PFI and UVLO Thresholds The circuit depicted in Figure 14 uses one resistive divider network for both power fail and low battery comparators. The power fail comparator trips at a higher battery voltage than the low battery comparator, thus providing a battery warning before a power down sequence is initiated. Due
EN UVLO
Figure 15A. Supply Glitch Generates P Interrupt
0.5V tDB, OFF LOW SUPPLY CONDITION
INT
tPD, Min + tPDT LOW SUPPLY LOCKS OUT ENABLE
2953 F15b
Figure 15B. Low Supply Initiates System Power Down and Locks Out Enable
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15
LTC2953 TYPICAL APPLICATIONS
Push Button Buffer The circuit of Figure 16 shows the power fail comparator sensing the push button input. The PFO output toggles each time the push button crosses 0.5V. This application provides an early warning of push button activity. Disconnect Input Resistive Divider To Save Power In order to prolong battery life when system power has been turned off, the LTC2953-2 power fail comparator can be used to disconnect the external battery monitor resistive divider. The circuit in Figure 18 connects PFI to EN and PFO to the bottom end of the resistive divider.
8.4V R14 1070k UVLO PB ON/OFF
2953 F16
PFO 0.5V PFI + -
R5 100k VIN EN
R9 100k
R12 110k
PFO -
PFI 0.5V
Figure 16. Push Button Buffer
Power Path Switching The high voltage EN output of the LTC2953-2 is designed to switch On/Off an external power PFET. This allows a user to connect/disconnect a power supply (or battery) to its load by toggling the PB pin. Figure 17 shows the LTC2953-2 in a 12V wall adapter application.
12V R5 100k PB ON/OFF VIN LTC2953-2 EN R9 100k TO LOAD
LTC2953-2
2953 F18
Figure 18. Disconnect Input Resistive Divider to Save Power
When the user presses the push button to turn on system power (EN low), the output of the power fail comparator asserts PFO low. The low battery external resistive divider is thus enabled to monitor the input supply. If the voltage on the UVLO input falls to less than 0.5V, a system power down sequence is initiated. Note that the IR drop across the internal NFET is typically less than 0.2mV when the UVLO pin voltage is 0.5V. Once system power has been turned off (EN high), the external resistive divider is disconnected and thus consumes zero DC current.
2953 F17
Figure 17. Power Path Switching
16
+
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LTC2953 TYPICAL APPLICATIONS
Push Button Controlled P Reset The circuit of Figure 19 can be used to keep a P in reset for 200ms after the push button has enabled system power. After system power has stabilized, the voltage monitor input continues to monitor the supply at the load end.
TO LOAD 3.3V R5 100k VIN PB LTC2953-2 ON/OFF RST
2953 F19
Push Button Controlled Supply Sequencing The circuit in Figure 20 uses the LTC2953-2 to sequence 3 supply rails. Power on sequencing begins by pressing the push button for 32ms. This asserts the EN output low, which turns on the V1 supply. 200ms after V1 reaches 80% of its final value (2.66V), the V2 supply is enabled. When the V2 DC voltage reaches 80% of its final value (2V), the V3 supply is enabled. Note that there is no internal delay from the PFI input to the PFO output and so V3 is enabled at the same time V2 rises above 2V. A power down supply sequence begins when any of these inputs is asserted: PB , UVLO or KILL . When EN pulls up to VIN, V1 disconnects first. When V1 decays to 2.66V, V2 is immediately disabled (there is no 200ms delay from VM to RST during power down). When V2 decays to 2V, V3 is immediately disabled. See Figure 21 timing diagram.
PB 200ms 32ms POWER ON POWER OFF
R9 100k R3 499k R2 100k R11 510k
EN VM
PB
VM
0.5V
RST
Figure 19. Push Button Controlled P Reset
3.3V R5 100k VIN PB LTC2953-2 ON/OFF EN VM VTH = 2.66V R9 100k R3 866k R2 200k V1 3.3V
EN
80% V1 200ms V2 80%
80%
80%
V3
2953 F21
VIN DC/DC #1 RST VTH = 2.01V PFI R16 200k SHDN VOUT R15 604k V2 2.5V
Figure 21. Push Button Controlled Supply Sequence Timing
VIN DC/DC #2 PFO
2953 F20
SHDN VOUT
V3 1.8V
Figure 20. Push Button Controlled Supply Sequencing
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17
LTC2953 TYPICAL APPLICATIONS
Dual Supply Monitor with P Reset The circuit of Figure 22 monitors two supplies and provides a P reset. When either the PFI or the VM input voltage falls below its threshold (0.5V), the RST output is asserted low. RST remains low for 200ms after both inputs rise above 0.5V. The low leakage PFO output allows for large valued external resistors.
V2 LTC2953 PFI
Operation with Supply Transients over 40V The application circuit of Figure 24 operates from a 24V nominal supply, but can withstand supply transients as high as 40V. The high voltage EN output of the LTC2953-2 has an absolute maximum rating of 50V, which makes it suitable for driving the gate of the external power PFET. The external 30V Zener diode (Z1) and the 10k current limiting resistor (RZ) protect the VIN supply pin of the LTC2953-2. Note that under normal 24V operation, the external Zener diode does not conduct any current. The voltage drop across RZ should be kept below 1V. Z2 should have a breakdown voltage smaller than the PFET's gate-to-source breakdown voltage.
24V NOMINAL, 40V TRANSIENTS FDS4685 Si2319DS NDS9407 R9 100k EN LTC2953-2 ON/OFF 50V ABS MAX
PFO
-
V1
+
VM
0.5V RST
-
0.5V
RST P
RZ 10k 1F 50V VIN PB
+
2953 F22
30V Z1 BZX84C30
10V Z2 BZX84C10 R5 100k
Figure 22. Dual Supply Monitor with P Reset
Reverse Battery Protection To protect the LTC2953 from a reverse battery connection, place a 1k resistor (R8) in series with the VIN pin. See Figure 23.
VIN
2953 F24
Figure 24. Operation with 40V Supply Transients
Power Path Controller with Low Battery Detect
+
8.4V R8 1k PB ON/OFF LTC2953-1 VIN EN R5 910k SHDN
2953 F23
VOUT LT1761
The application in Figure 25 uses the push button to completely disconnect the load from the battery. If the battery voltage falls below the user specified threshold, the push button is prevented from turning on system power (asserting the enable output).
Figure 23. Reverse Battery Protection Using R8
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18
LTC2953 PACKAGE DESCRIPTION
DD Package 12-Lead Plastic DFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1725 Rev A)
0.70 0.05
3.50 0.05 2.10 0.05
2.38 0.05 1.65 0.05 PACKAGE OUTLINE
0.25 0.05 0.45 BSC 2.25 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
R = 0.115 TYP 7
0.40 0.10 12
3.00 0.10 (4 SIDES) PIN 1 TOP MARK (SEE NOTE 6)
2.38 0.10 1.65 0.10 PIN 1 NOTCH R = 0.20 OR 0.25 x 45 CHAMFER
6 0.200 REF 0.75 0.05 2.25 REF 0.00 - 0.05
0.23 0.05 0.45 BSC
(DD12) DFN 0106 REV A
1
BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 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 0.15mm ON ANY SIDE 5. EXPOSED PAD AND TIE BARS SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
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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.
19
LTC2953 TYPICAL APPLICATION
FDN360P VIN VOUT
+
8.4V
R14 2150k UVLO R13 23.2k PFI R12 196k VIN
R5 100k EN
R9 100k
DC/DC SHDN
3.3V
LTC2953-2 VM
R3 499k R2 100k RST PFO INT KILL PDT
R11 100k R10 100k R1 100k RST PFO INT SYSTEM LOGIC KILL
2953 F25
PB ON/OFF GND
1F tPDT = 6.4 SECONDS
Figure 25. PowerPath Controller with Low Battery Detect
RELATED PARTS
PART NUMBER LTC2900 LTC2904/LTC2905 LTC2909 LTC2912 LTC2950/LTC2951 LTC2952 LTC2954 LTC4055 LTC4411 LTC4412HV DESCRIPTION Programmable Quad Supply Monitor Pin-Programmable Dual Supply Monitors COMMENTS Adjustable Reset, 10-Lead MSOP and 3mm x 3mm DFN Packages Adjustable Reset and Tolerance, 8-Lead SOT-23 and 3mm x 2mm DFN Packages
Precision Tripple/Dual Input UV, OV and Negative 6.5V Shunt Regulator for High Voltage Operation Voltage Monitor Single UV/OV Monitor Push Button On/Off Controllers Push Button Power Path Controller with Supervisor Push Button On/Off Controller with P Interrupt USB Power Controller and Li-Ion Charger 2.6A Low Loss Ideal Diode in ThinSOT PowerPath Controller in ThinSOT 3mm x 2mm DFN, 8-Pin ThinSOT Packages High Voltage, Low Power Push Button Controller Automatic Low Loss Switchover Between DC Sources Allow Controlled Software System Shutdown Automatic Switchover, Charges 1-Cell Li-Ion Batteries No External MOSFET, Automatic Switching Between DC Sources Efficient Diode-ORing, Automatic Switching Between DC Sources, 3V to 36V
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20 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0607 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

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