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LTC2908 Precision Six Input Supply Monitor FEATURES
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DESCRIPTION
The LTC(R)2908 is a six input supply monitor for systems requiring a precise and compact monitoring solution for multiple supply voltages. The inputs can be shorted together for monitoring systems with fewer than six supply voltages, and the open drain RST output of two or more LTC2908 can be wired-OR together for monitoring systems with more than six supply voltages. The common reset output remains low until all six inputs have been in compliance for 200ms. The LTC2908 features a tight 1.5% threshold accuracy over the entire operating temperature range and glitch immunity to ensure reliable reset operation without false triggering. The open-drain RST output state is guaranteed to be in the correct state as long as V1 and/or V2 is 0.5V or greater. The LTC2908 also features adjustable inputs with a nominal threshold level at 0.5V. This product provides a precise, space-conscious, micropower and general purpose solution for any kind of system requiring supply monitors.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. *Patent pending.
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Ultralow Voltage Reset: VCC = 0.5V Guaranteed* Monitors Six Inputs Simultaneously: 5V, 3.3V, 2.5V, 1.8V, ADJ1, ADJ2 (LTC2908-A1) 3.3V, 2.5V, 1.8V, 1.5V, ADJ1, ADJ2 (LTC2908-B1) 2.5V, ADJ1, ADJ2, ADJ3, ADJ4, ADJ5 (LTC2908-C1) Guaranteed Threshold Accuracy: 1.5% of Monitored Voltage Over Temperature Internal VCC Auto Select Power Supply Glitch Immunity 200ms Reset Time Delay Active Low Open-Drain RST Output Low Profile (1mm) 8-Lead SOT-23 (ThinSOTTM) and Plastic (3mm x 2mm) DFN Packages
APPLICATIONS
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Network Servers Wireless Base Stations Optical Networking Systems Multivoltage Systems Desktop and Notebook Computers
TYPICAL APPLICATION
Six Supply Monitor with 5% Tolerance (12V, 3.3V, 2.5V, 1.8V, 1.5V, 1.2V)
12V DC/DC DC/DC DC/DC DC/DC DC/DC 3.3V 2.5V
RST Output Voltage vs V1 with 10k Pull-Up Resistor to V1
0.4 V3 = V4 = VADJ1 = VADJ2 = VADJ3 = VADJ4 = VADJ5 = GND
RST OUTPUT VOLTAGE (V)
1.8V 1.5V 1.2V 0.1F 0.1F 2.15M 100k 124k 100k
SYSTEM
0.3 V1 INPUT 0.2 V2 = GND 0.1
V2 = V1 (A1/B1)
V1 V2 V3 V4 VADJ1 LTC2908-B1 GND VADJ2 RST
2908 TA01a
0
0
0.2
0.4 V1 (V)
0.6
0.8
2908 TA01b
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LTC2908 ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
Terminal Voltages V1, V2, V3, V4 .........................................- 0.3V to 7V VADJ1, VADJ2, VADJ3, ..................-0.3V to (VCC + 0.6V) VADJ4, VADJ5 .............................-0.3V to (VCC + 0.6V) RST.......................................................... -0.3V to 7V Operating Temperature Range LTC2908C ................................................ 0C to 70C LTC2908I..............................................-40C to 85C
Storage Temperature Range DFN Package......................................-65C to 125C TSOT-23 Package...............................-65C to 150C Lead Temperature (Soldering, 10 sec) .................. 300C
PIN CONFIGURATION
LTC2908CDDB-A1 LTC2908IDDB-A1 LTC2908CDDB-B1 LTC2908IDDB-B1
TOP VIEW GND 1 RST 2 V4 3 V2 4 9 8 VADJ2 7 V3 6 VADJ1 5 V1 GND 1 RST 2 VADJ5 3 V1 4 9
LTC2908CDDB-C1 LTC2908IDDB-C1
LTC2908CTS8-A1 LTC2908ITS8-A1 LTC2908CTS8-B1 LTC2908ITS8-B1
LTC2908CTS8-C1 LTC2908ITS8-C1
TOP VIEW 8 VADJ4 7 VADJ3 6 VADJ2 5 VADJ1 V2 1 V4 2 RST 3 GND 4
TOP VIEW 8 V1 7 VADJ1 6 V3 5 VADJ2 V1 1 VADJ5 2 RST 3 GND 4
TOP VIEW 8 VADJ1 7 VADJ2 6 VADJ3 5 VADJ4
DDB8 PACKAGE 8-LEAD (3mm x 2mm) PLASTIC DFN TJMAX = 125C, JA = 76C/W EXPOSED PAD (PIN 9) (PCB CONNECTION OPTIONAL)
DDB8 PACKAGE 8-LEAD (3mm x 2mm) PLASTIC DFN TJMAX = 125C, JA = 76C/W EXPOSED PAD (PIN 9) (PCB CONNECTION OPTIONAL)
TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 TJMAX = 125C, JA = 250C/W
TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 TJMAX = 125C, JA = 250C/W
ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI) TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION LTC2908CDDB-A1#TRMPBF LTC2908CDDB-A1#TRMPBF LBFD 8-LEAD (3mm x 2mm) PLASTIC DFN LTC2908IDDB-A1#TRMPBF LTC2908IDDB-A1#TRMPBF LBFF 8-LEAD (3mm x 2mm) PLASTIC DFN LTC2908CDDB-B1#TRMPBF LTC2908CDDB-B1#TRMPBF LBFG 8-LEAD (3mm x 2mm) PLASTIC DFN LTC2908IDDB-B1#TRMPBF LTC2908IDDB-B1#TRMPBF LBFH 8-LEAD (3mm x 2mm) PLASTIC DFN LTC2908CDDB-C1#TRMPBF LTC2908CDDB-C1#TRMPBF LCFV 8-LEAD (3mm x 2mm) PLASTIC DFN LTC2908IDDB-C1#TRMPBF LTC2908IDDB-C1#TRMPBF LCFV 8-LEAD (3mm x 2mm) PLASTIC DFN LTC2908CTS8-A1#TRMPBF LTC2908CTS8-A1#TRMPBF LTBFJ 8-LEAD PLASTIC TSOT-23 LTC2908ITS8-A1#TRMPBF LTC2908ITS8-A1#TRMPBF LTBFK 8-LEAD PLASTIC TSOT-23 LTC2908CTS8-B1#TRMPBF LTC2908CTS8-B1#TRMPBF LTBFM 8-LEAD PLASTIC TSOT-23 LTC2908ITS8-B1#TRMPBF LTC2908ITS8-B1#TRMPBF LTBFN 8-LEAD PLASTIC TSOT-23 LTC2908CTS8-C1#TRMPBF LTC2908CTS8-C1#TRMPBF LTCFT 8-LEAD PLASTIC TSOT-23 LTC2908ITS8-C1#TRMPBF LTC2908ITS8-C1#TRMPBF LTCFT 8-LEAD PLASTIC TSOT-23 TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on 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/ TEMPERATURE RANGE 0C to 70C -40C to 85C 0C to 70C -40C to 85C 0C to 70C -40C to 85C 0C to 70C -40C to 85C 0C to 70C -40C to 85C 0C to 70C -40C to 85C
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LTC2908 ELECTRICAL CHARACTERISTICS
SYMBOL VRT50 VRT33 VRT25 VRT18 VRTADJ PARAMETER 5V, 5% Reset Threshold 3.3V, 5% Reset Threshold 2.5V, 5% Reset Threshold 1.8V, 5% Reset Threshold ADJ, 5% Reset Threshold
(LTC2908-A1) The denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25C, VCC = 5V unless otherwise noted. (Note 2)
CONDITIONS V1 Input Threshold V2 Input Threshold V3 Input Threshold V4 Input Threshold VADJ1, VADJ2 Input Threshold
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MIN 4.600 3.036 2.300 1.656 0.492
TYP 4.675 3.086 2.338 1.683 0.500
MAX 4.750 3.135 2.375 1.710 0.508
UNITS V V V V V
(LTC2908-B1) The denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25C, VCC = 3.3V unless otherwise noted. (Note 2)
SYMBOL VRT33 VRT25 VRT18 VRT15 VRTADJ PARAMETER 3.3V, 5% Reset Threshold 2.5V, 5% Reset Threshold 1.8V, 5% Reset Threshold 1.5V, 5% Reset Threshold ADJ, 5% Reset Threshold CONDITIONS V1 Input Threshold V2 Input Threshold V3 Input Threshold V4 Input Threshold VADJ1, VADJ2 Input Threshold
l l l l l
MIN 3.036 2.300 1.656 1.380 0.492
TYP 3.086 2.338 1.683 1.403 0.500
MAX 3.135 2.375 1.720 1.425 0.508
UNITS V V V V V
(LTC2908-C1) The denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25C, VCC = 2.5V unless otherwise noted. (Note 2)
SYMBOL VRT25 VRTADJ PARAMETER 2.5V, 5% Reset Threshold ADJ, 5% Reset Threshold CONDITIONS V1 Input Threshold VADJ1, VADJ2, VADJ3, VADJ4, VADJ5, Input Threshold
l l
MIN 2.300 0.492
TYP 2.338 0.500
MAX 2.375 0.508
UNITS V V
The denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25C. VCC = 5V for the LT2908-A1, VCC = 3.3V for the LTC2908-B1or VCC = 2.5V for the LTC2908-C1, unless otherwise noted. (Notes 2, 3)
SYMBOL VCC IV1 PARAMETER Internal Supply Voltage V1 Input Current (Note 4) CONDITIONS RST in Correct Logic State V1 = 5.0V (LTC2908-A1) V1 = 3.3V (LTC2908-B1) V1 = 2.5V (LTC2908-C1) V2 = 3.3V (LTC2908-A1) V2 = 2.5V (LTC2908-B1) V3 = 2.5V (LTC2908-A1) V3 = 1.8V (LTC2908-B1) V4 = 1.8V (LTC2908-A1) V4 = 1.5V (LTC2908-B1) VADJ1 = VADJ2 = VADJ3 = VADJ4 = VADJ5 = 0.55V
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MIN 0.5
TYP 26 24 22 10 8 2 2 2 2
MAX 6 70 70 70 30 30 5 5 5 5 15
UNITS V A A A A A A A A A nA
IV2 IV3 IV4 IVADJ
V2 Input Current (Note 4) V3 Input Current V4 Input Current VADJ1, VADJ2, VADJ3, VADJ4, VADJ5 Input Current
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LTC2908 ELECTRICAL CHARACTERISTICS
The denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25C. VCC = 5V for the LT2908-A1, VCC = 3.3V for the LTC2908-B1 or VCC = 2.5V for the LTC2908-C1, unless otherwise noted. (Notes 2, 3)
SYMBOL tRST tUV VOH PARAMETER Reset Time-Out Period VX Undervoltage Detect to RST Output Voltage High RST (Note 5) VX Less Than Reset Threshold VRTX by More Than 1% IRST = -1A, VCC = 5V (LTC2908-A1) IRST = -1A, VCC = 3.3V (LTC2908-B1) IRST = -1A, VCC = 2.5V (LTC2908-C1) VCC = 0.5V, IRST = 5A VCC = 1.0V, IRST = 100A VCC = 3.0V, IRST = 2500A
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CONDITIONS
l
MIN 160
TYP 200 250
MAX 260
UNITS ms s V V V
VCC - 1.5 VCC - 1.0 VCC - 1.0 0.01 0.01 0.10 0.15 0.15 0.30
VOL
Output Voltage Low RST
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 reliabilty and lifetime. Note 2: The greater of V1, V2 is the internal supply voltage (VCC) for the LTC2908-A1 and the LTC2908-B1. V1 is the internal supply voltage (VCC) for the LTC2908-C1.
Note 3: All currents into pins are positive; all voltages are referenced to GND unless otherwise noted. Note 4: Under typical operating conditions, most of the quiescent current is drawn from the V1 input. When V2 exceeds V1, V2 supplies most of the quiescent current. Note 5: The output pin RST has an internal pull-up to VCC of typically 6A. However, an external pull-up resistor may be used when a faster rise time is required or for VOH voltages greater than VCC.
TYPICAL PERFORMANCE CHARACTERISTICS
Specifications are at TA = 25C unless otherwise noted. 5V Threshold Voltage vs Temperature
4.750
THRESHOLD VOLTAGE, VRT50 (V)
3.3V Threshold Voltage vs Temperature
3.135
THRESHOLD VOLTAGE, VRT33 (V)
2.5V Threshold Voltage vs Temperature
2.375
THRESHOLD VOLTAGE, VRT25 (V)
4.725 4.700 4.675 4.650 4.625 4.600 -50
3.115
2.360
3.095
2.345
3.075
2.330
3.055
2.315
-25
50 25 0 TEMPERATURE (C)
75
100
2908 G01
3.035 -50
-25
50 25 0 TEMPERATURE (C)
75
100
2908 G02
2.300 -50
-25
50 25 0 TEMPERATURE (C)
75
100
2908 G03
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LTC2908 TYPICAL PERFORMANCE CHARACTERISTICS
Specifications are at TA = 25C unless otherwise noted. 1.8V Threshold Voltage vs Temperature
1.710 THRESHOLD VOLTAGE, VRT18 (V) THRESHOLD VOLTAGE, VRT15 (V) 1.425 THRESHOLD VOLTAGE, VRTADJ (V) 1.420 1.415 1.410 1.405 1.400 1.395 1.390 1.385 1.660 -50 -25 50 25 0 TEMPERATURE (C) 75 100
2908 G04
1.5V Threshold Voltage vs Temperature
0.5080 0.5060 0.5040 0.5020 0.5000 0.4980 0.4960 0.4940
ADJ Threshold Voltage vs Temperature
1.700
1.690
1.680
1.670
1.380 -50 -25 0 25 50 TEMPERATURE (C) 75 100
2908 G05
0.4920 -50
-25
0 50 25 TEMPERATURE (C)
75
100
2908 G06
IV1 vs Temperature
33 V1 = 5.0V (A1)/V1 = 3.3V (B1)/V1 = 2.5V (C1) 31 V2 = 3.3V (A1)/V2 = 2.5V (B1) V3 = 2.5V (A1)/V3 = 1.8V (B1) 29 V4 = 1.8V (A1)/V1 = 1.5V (B1) VADJ1 = VADJ2 = VADJ3 = 27 VADJ4 =VADJ5 = 0.55V IV1 (A) IV2 (A) A1 25 23 C1 21 19 17 -50 -25 0 25 50 TEMPERATURE (C) 75 100
2908 G07
IV2 vs Temperature
V1 = 5.0V (A1)/V1 = 3.3V (B1) 13 V2 = 3.3V (A1)/V2 = 2.5V (B1) V3 = 2.5V (A1)/V3 = 1.8V (B1) 12 V4 = 1.8V (A1)/V4 = 1.5V (B1) 11 VADJ1 = VADJ2 = 0.55V A1 B1 IV3 (A) 10 9 8 7 6 5 4 -50 -25 50 25 TEMPERATURE (C) 0 75 100
2908 G08
IV3 vs Temperature
V1 = 5.0V (A1)/V1 = 3.3V (B1) 2.1 V2 = 3.3V (A1)/V2 = 2.5V (B1) V3 = 2.5V (A1)/V3 = 1.8V (B1) 2.0 V4 = 1.8V (A1)/V4 = 1.5V (B1) VADJ1 = VADJ2 = 0.55V 1.9 1.8 1.7 1.6 1.5 1.4 -50 -25 0 50 25 TEMPERATURE (C) 75 100
2908 G09
14
2.2
B1
IV4 vs Temperature
TYPICAL TRANSIENT DURATION (s) V1 = 5.0V (A1)/V1 = 3.3V (B1) 2.1 V2 = 3.3V (A1)/V2 = 2.5V (B1) V3 = 2.5V (A1)/V3 = 1.8V (B1) 2.0 V4 = 1.8V (A1)/V4 = 1.5V (B1) VADJ1 = VADJ2 = 0.55V 1.9 IV4 (A) 1.8 1.7 1.6 1.5 1.4 -50 -25 50 25 TEMPERATURE (C) 0 75 100
2908 G10
Typical Transient Duration vs Comparator Overdrive
700 600 500 400 300 200 100 0 0.1 1 10 100 COMPARATOR OVERDRIVE VOLTAGE (% OF VRTX)
2908 G11
Reset Time-Out Period (tRST) vs Temperature
TA = 25C RESET TIME-OUT PERIOD, tRST (ms) 250 240 230 220 210 200 190 180 170 160 150 -50 -25 0 50 25 TEMPERATURE (C) 75 100
2908 G12
2.2
RESET OCCURS ABOVE CURVE
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LTC2908 TYPICAL PERFORMANCE CHARACTERISTICS
Specifications are at TA = 25C unless otherwise noted. RST Output Voltage vs V1 with 10k Pull-Up Resistor to V1
5.0 V1 = V2 (A1/B1) V3 = 2.5V (A1)/V3 = 1.8V (B1) V4 = 1.8V (A1)/V4 = 1.5V (B1) 4.0 V ADJ1 = VADJ2 = VADJ3 = VADJ4 = VADJ5 = 0.55V 3.0 VRT33 LTC2908-B1 2.0 0.4
RST Output Voltage vs V1 with 10k Pull-Up Resistor to V1
RST PULL-DOWN CURRENT, IRST (mA) V3 = V4 = VADJ1 = VADJ2 = GND (A1/B1) VADJ1 = VADJ2 = VADJ3 = VADJ4 = VADJ5 = GND (C1) V1 = INPUT 0.2 V2 = GND 0.1 V2 = V1 0 6
RST Pull-Down Current vs Supply Voltage LTC2908-A1/LTC2908-B1
VCC = V1 = V2 V3 = 2.5V (A1)/V3 = 1.8V (B1) 5 V4 = 1.8V (A1)/V4 = 1.5V (B1) VADJ1 = VADJ2 = 0.55V 4 3 2 1 0 0 1 VRT33 LTC2908-B1 RST AT 50mV VRT50 LTC2908-A1 5
2908 G15
RST OUTPUT VOLTAGE (V)
RST OUTPUT VOLTAGE (V)
0.3
RST AT 150mV
1.0 VRT25 LTC2908-C1 0 0 1 2 V1 (V)
2908 G13
VRT50 LTC2908-A1 3 4 5 0 0.2
0.4 V1 (V)
0.6
0.8
2908 G14
2 3 4 SUPPLY VOLTAGE, VCC (V)
RST Pull-Down Current vs Supply Voltage LTC2908-C1
4.0 RST PULL-DOWN CURRENT, IRST (mA) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 0 0.5 1.0 VRT25 LTC2908-C1 2.0 1.5 SUPPLY VOLTAGE VCC (V) 2.5
2928 G25
RST Pull-Down Current vs Supply Voltage with 2 Inputs LTC2908-A1/LTC29089-B1
10 RST PULL-DOWN CURRENT, IRST (mA) RST PULL-DOWN CURRENT, IRST (mA) VCC = V1 = V2 V3 = V4 = VADJ1 = VADJ2 = GND RST AT 150mV 10
RST Pull-Down Current vs Supply Voltage with 1 Input
VCC = V1 V2 = V3 = V4 = VADJ1 = VADJ2 = VADJ3 = VADJ4 = VADJ5 = GND
VCC = V1 VADJ1 = VADJ2 = VADJ3 = VADJ4 = VADJ5 = 0.55V
RST AT 150mV
1
1
0.1 RST AT 50mV
0.1
RST AT 150mV
RST AT 50mV
RST AT 50mV
0.01
0.01
0.001 0 0.2 0.4 0.6 0.8 SUPPLY VOLTAGE, VCC (V) 1
2908 G16
0.001 0 0.2 0.4 0.6 0.8 SUPPLY VOLTAGE, VCC (V) 1
2908 G17
RST Output Voltage Low vs RST Pull-Down Current LTC2908-A1
0.8 RST OUTPUT VOLTAGE LOW, VOL (V) RST OUTPUT VOLTAGE LOW, VOL (V) V1 = 5.0V 0.7 V2 = 3.3V V3 = 2.5V 0.6 V4 = 1.8V VADJ1 = VADJ2 = 0.4V 0.5 85C 0.4 25C 0.3 0.2 0.1 0 0 25 30 35 20 15 RST PULL-DOWN CURRENT, IRST (mA) 5 10
2908 G18
RST Output Voltage Low vs RST Pull-Down Current LTC2908-B1
0.8 RST OUTPUT VOLTAGE LOW, VOL (V) V1 = 3.3V 0.7 V2 = 2.5V V3 = 1.8V 0.6 V4 = 1.5V VADJ1 = VADJ2 = 0.4V 0.5 85C 0.4 25C 0.3 0.2 0.1 0 0 20 15 RST PULL-DOWN CURRENT, IRST (mA) 5 10 25 -40C 1.20 1.0
RST Output Voltage Low vs RST Pull-Down Current LTC2908-C1
V1 = 2.5V VADJ1 = VADJ2 = VADJ3 = VADJ4 = VADJ5 = 0.4V 85C 25C
0.80 -40C 0.60 0.40 0.20
-40C
0.00 0.0 25.0 5.0 10.0 15.0 20.0 RST PULL-DOWN CURRENT, IRST (mA)
2908 G23
2908 G19
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LTC2908 TYPICAL PERFORMANCE CHARACTERISTICS
Specifications are at TA = 25C unless otherwise noted. RST Pull-Up Current vs Supply Voltage
-30
RST PULL-UP CURRENT, IRST (A)
RST Output Voltage High vs RST Output Source Current LTC2908-A1
5
-25 -20 -15 -10 -5
RST OUTPUT VOLTAGE HIGH, VOH (V)
VCC = V1 = V2 (A1/B1), VCC = V1(C1) V3 = 2.5V (A1)/V3 = 1.8V (B1) V4 = 1.8V (A1)/V4 = 1.5V (B1) VADJ1 = VADJ2 = 0.55V (A1/B1) VADJ1 = VADJ2 = VADJ3 = VADJ4 = VADJ5 = 0.55V(C1) RST HELD AT 0V VRT25 LTC2908-C1 VRT33 LTC2908-B1 VRT50 LTC2908-A1 2 3.5 4.5 3 4 2.5 SUPPLY VOLTAGE, VCC (V) 5
4
3 25C 2 V1 = 5.0V V2 = 3.3V V3 = 2.5V V4 = 1.8V VADJ1 = VADJ2 = 0.55V 0 -40C 85C
0 1.5
1
2908 G20
-4 -12 -16 -20 -8 OUTPUT SOURCE CURRENT, IRST (A)
2908 G21
RST Output Voltage High vs RST Output Source Current LTC2908-B1
3.0
RST Output Voltage High vs RST Output Source Current LTC2908-C1
2.0
RST OUTPUT VOLTAGE HIGH VOH (V)
RST OUTPUT VOLTAGE HIGH, VOH (V)
2.5
1.5 85C
2.0 25C 85C -40C V1 = 3.3V V2 = 2.5V 1.0 V3 = 1.8V V4 = 1.5V VADJ1 = VADJ2 = 0.55V 0.5 -4 -6 -8 -10 -12 0 -2 OUTPUT SOURCE CURRENT, IRST (A)
2908 G22
1.5
1.0 -40C V1 = 2.5V VADJ1 = VADJ2 = VADJ3 = VADJ4 = VADJ5 = 0.55V 0
25C -8
0.5
-1 -2 -3 -4 -5 -6 -7 OUTPUT SOURCE CURRENT, IRST (A)
2908 G24
PIN FUNCTIONS
(TS8 Package/DDB8 Package) LTC2908-A1/LTC2908-B1
V2 (Pin 1/Pin 4): Voltage Input 2. The greater of V1, V2 is also the internal VCC. The operating voltage on this pin shall not exceed 6V. When in normal operation (V1 > V2), this pin draws approximately 8A. When this pin is acting as the VCC (V2 > V1), this pin draws an additional 16A. Bypass this pin to ground with a 0.1F (or greater) capacitor. V4 (Pin 2/Pin 3): Voltage Input 4. RST (Pin 3/Pin 2): Reset Logic Output. Pulls low when any voltage input is below the reset threshold and is held low for 200ms after all voltage inputs are above threshold. This pin has a weak pull-up to VCC and may be pulled above VCC using an external pull-up. GND (Pin 4/Pin 1): Device Ground.
VADJ2 (Pin 5/Pin 8): Adjustable Voltage Input 2. See Table 1 for recommended ADJ resistors values. V3 (Pin 6/Pin 7): Voltage Input 3. VADJ1 (Pin 7/Pin 6): Adjustable Voltage Input 1. See Table 1 for recommended ADJ resistors values. V1 (Pin 8/Pin 5): Voltage Input 1. The greater of V1, V2 is also the internal VCC. The operating voltage on this pin shall not exceed 6V. When in normal operation (V1 > V2), this pin draws approximately 26 A. When this pin is not acting as the VCC (V2 > V1), this pin draws approximately 8A. Bypass this pin to ground with a 0.1F (or greater) capacitor. Exposed Pad (Pin 9, DDB8 Only): Exposed Pad may be left open or connected to device ground.
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LTC2908 PIN FUNCTIONS
(TS8 Package/DDB8 Package) LTC2908-C1
V1 (Pin 1/Pin 4): Voltage Input 1. V1 is the internal VCC. The operating voltage on this pin shall not exceed 6V. When in normal operation, this pin draws approximately 22A. Bypass this pin to ground with a 0.1F (or greater) capacitor. VADJ5 (Pin 2/Pin 3): Adjustable Voltage Input 5. See Table 1 for recommended ADJ resistors values. RST (Pin 3/Pin 4): Reset Logic Output. Pulls low when any voltage input is below the reset threshold and is held low for 200ms after all voltage inputs are above threshold. This pin has a weak pull-up to Vcc and may be pulled above Vcc using an external pull-up.
GND (Pin 4/Pin 1): Device Ground. VADJ4 (Pin 5/Pin 8): Adjustable Voltage Input 4. See Table 1 for recommended ADJ resistors values. VADJ3 (Pin 6/Pin 7): Adjustable Voltage Input 3. See Table 1 for recommended ADJ resistors values. VADJ2 (Pin 7/Pin 6): Adjustable Voltage Input 2. See Table 1 for recommended ADJ resistors values. VADJ1 (Pin 8/Pin 5): Adjustable Voltage Input 1. See Table 1 for recommended ADJ resistors values. Exposed Pad (Pin 9, DDB8 Only): Exposed Pad may be left open or connected to device ground.
BLOCK DIAGRAMS
LTC2908-A1/LTC2908-B1
POWER DETECT V2
VCC
GND
8
+
-
VADJ2
+
-
VADJ1
+
-
V4
+
-
V3
+ + -
C2 VCC 6A C3 RST 200ms RESET PULSE GENERATOR C4 C5 C6 BANDGAP REFERENCE
2908 BD
-
C1
V1
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LTC2908 BLOCK DIAGRAMS
LTC2908-C1
GND
TIMING DIAGRAM
VX Monitor Timing
VRTX tUV RST tRST 1V
2908 TD
VX
+
-
VADJ5
+
-
VADJ4
+
-
VADJ3
+
-
VADJ2
+
-
VADJ1
+
C2 V1 6A C3 RST 200ms RESET PULSE GENERATOR C4 C5 C6 BANDGAP REFERENCE
2908 BDa
-
C1
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V1
9
LTC2908 APPLICATIONS INFORMATION
Supply Monitoring The LTC2908 is a low power, high accuracy, six input supply monitoring circuit with two adjustable inputs. The reset delay is set to a nominal of 200ms with an internal capacitor, eliminating the need for an external timing capacitor. All input voltages must be above predetermined thresholds for the reset not to be invoked. The LTC2908 asserts the reset output during power-up, power-down and brownout conditions on any one of the voltage inputs. Ultralow Voltage Pull-Down on RST The LTC2908 issues a logic low on the RST output when any one of the inputs falls below its threshold. Ideally, the RST logic output would remain low with the input supply voltage down to zero volts. Most supervisors lack pulldown capability below 1V. The LTC2908 power supply supervisor incorporates a novel low voltage pull-down circuit that can hold the RST line low with as little as 200mV of input supply voltage on V1 and/or V2 (see Figures 1 and 2). The pull-down circuit helps maintain a low impedance path to ground, reducing the risk of the RST node from floating to an indeterminate voltage.
10
Such an indeterminate voltage may trigger external logic causing erroneous reset operation(s). Furthermore, a mid-scale voltage level could cause external circuits to operate in the middle of their voltage transfer characteristic, consuming more quiescent current than normal. These conditions could cause serious system reliability problems. Power-Up During power-up, RST starts asserting low as soon as there is at least 200mV on V1 and/or V2. The RST pulldown capability is a function of V1 and V2 as shown in the Typical Performance Characteristics. The greater of V1, V2 is the internal supply voltage (VCC) that powers the other internal circuitry. Once all the V X inputs rise above their thresholds, an internal timer is started. After the internal timer counts a 200ms delay time, RST weakly pulls high to VCC. Power-Down On power-down, once any of the V X inputs drop below their threshold, RST asserts logic low. VCC of at least 0.5V guarantees a logic low of 0.15V at RST.
RST PULL-DOWN CURRENT, IRST (mA)
1
RST PULL-DOWN CURRENT, IRST (mA)
VCC = V1 = V2 V3 = V4 = VADJ1 = VADJ2 = GND RST AT 150mV
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VCC = V1 V2 = V3 = V4 = VADJ1 = VADJ2 = VADJ3 = VADJ4 = VADJ5 = GND
1
0.1 RST AT 50mV
0.1
RST AT 150mV
RST AT 50mV
0.01
0.01
0.001 0 0.2 0.4 0.6 0.8 SUPPLY VOLTAGE, VCC (V) 1
2908 G16
0.001 0 0.2 0.4 0.6 0.8 SUPPLY VOLTAGE, VCC (V) 1
2908 G17
Figure 1. RST Pull-Down Current vs Supply Voltage with 2 Inputs LTC2908-A1/ LTC2908-B1
Figure 2. RST Pull-Down Current vs Supply Voltage with 1 Input
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10
LTC2908 APPLICATIONS INFORMATION
Adjustable Input The noninverting input on the VADJ comparator is set to 0.5V. And the high impedance inverting input directly ties to the VADJ pin. In a typical application, this pin connects to a tap point on an external resistive divider between the positive voltage being monitored and ground (see Figure 3). The following formula derives the value of the R1 resistor in the divider from a particular value of R2 and the desired trip voltage: R1= VTRIP - 1 R2 0.5V In an application with less than six supply voltages, the unused supervisor inputs should be tied to the closest higher supply voltage available. Threshold Accuracy Specifying system voltage margin for worst-case operation requires the consideration of three factors: power supply tolerance, IC supply voltage tolerance and supervisor reset threshold accuracy. Highly accurate supervisors ease the design challenge by decreasing the overall voltage margin required for reliable system operation. Consider a 5V system with a 5% power supply tolerance band. System ICs powered by this supply must operate reliably within this band (and a little more, as explained below). The bottom of the supply tolerance band, at 4.75V (5% below 5V), is the exact voltage at which a perfectly accurate supervisor generates a reset (see Figure 4). Such a perfectly accurate supervisor does not exist--the actual reset threshold may vary over a specified band (1.5% for the LTC2908 supervisors). Figure 5 shows the typical relative threshold accuracy for all six inputs over temperature.
5.000V NOMINAL SUPPLY VOLTAGE
R2 = 100k is recommended. Table 1 shows suggested 1% resistor values for various adjustable applications and their corresponding trip thresholds.
Table 1. Suggested 1% Resistor Values for the VADJ Inputs
VSUPPLY (V) 12 10 8 7.5 6 5 3.3 3 2.5 1.8 1.5 1.2 1.0 0.9 0.8 0.7 0.6
VTRIP R1 1% VADJ R2 1% LTC2908-A1/LTC2908-B1/LTC2908-C1
VTRIP (V) 11.25 9.4 7.5 7 5.6 4.725 3.055 2.82 2.325 1.685 1.410 1.120 0.933 0.840 0.750 0.655 0.561
R1 (k) 2150 1780 1400 1300 1020 845 511 464 365 237 182 124 86.6 68.1 49.9 30.9 12.1
R2 (k) 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
MINIMUM SUPPLY IDEAL RELIABLE TOLERANCE SUPERVISOR SYSTEM THRESHOLD VOLTAGE
4.750V 1.5% THRESHOLD 4.675V BAND 4.600V 4.500V
-5.0% -6.5% REGION OF POTENTIAL MALFUNCTION WITH 2.5% MONITOR
2908 F04
-8.0% -10%
2.5% THRESHOLD BAND
Figure 4. Threshold Band Diagram
1.5
TYPICAL THRESHOLD ACCURACY (%)
1.0 0.5 0 -0.5 -1.0 -1.5 -50
- + + -
0.5V
-25
0 25 50 TEMPERATURE (C)
75
100
2908 F05
2908 F03
Figure 3. Setting the Adjustable Trip Point
Figure 5. Typical Threshold Accuracy vs Temperature
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11
LTC2908 APPLICATIONS INFORMATION
With this variation of reset threshold in mind, the nominal reset threshold of the supervisor resides below the minimum supply voltage; just enough so that the reset threshold band and the power supply tolerance bands do not overlap. If the two bands overlap, the supervisor could generate a false or nuisance reset when the power supply remains within its specified tolerance band (for example at 4.8V). Adding half of the reset threshold accuracy spread (1.5%) to the ideal 5% thresholds puts the LTC2908 thresholds at 6.5% (typ) below the nominal input voltage. For example, the 5V typical threshold is 4.675V, or 75mV below the ideal threshold of 4.750V. The guaranteed threshold lies in the band between 4.600V (8% below 5V) and 4.750V (5% below 5V) over temperature. The powered system must work reliably down to the lowest voltage in the threshold band or risk malfunction before the reset line falls. In the 5V example, using the 1.5% accurate supervisor, the system ICs must work down to 4.60V (8% below 5V). System ICs working with a 2.5% accurate supervisor must operate down to 4.50V (10% below 5V), increasing the required system voltage margin and the probability of system malfunction. In any supervisory application, supply noise riding on the monitored DC voltage can cause spurious resets, particularly when the monitored voltage is near the reset threshold. A less desirable but common solution to this problem is to introduce hysteresis around the nominal threshold. Notice however, this hysteresis introduces an error term in the threshold accuracy. Therefore, a 2.5% accurate monitor with 1% hysteresis is equivalent to a 3.5% monitor with no hysteresis. Therefore, the LTC2908 takes a different approach to solving this problem of supply noise causing spurious reset. The first line of defense against this spurious reset is a first order lowpass filter at the output of the comparators. Therefore, each comparator output is integrated over time before triggering the output logic. Therefore, any kind of transient at the input of the comparator needs to be of sufficient magnitude and duration before it can trigger a change in the output logic. The second line of defense is the 200ms delay time tRST. This delay eliminates the effect of any supply noise, whose frequency is above 1/200ms = 5Hz, on the RST output. When any one of the supply voltages drops below its threshold, the RST pin asserts low. When the supply recovers above its threshold, the reset-pulse-generator timer starts counting. If all the supplies remain above their corresponding threshold when the timer finishes counting, the RST pin weakly pulls high. However, if any of the supplies falls below its threshold any time during the period when the timer is still counting, the timer resets and it starts fresh when all the supplies rise above their corresponding threshold. Note that this second line of defense is only effective for a rising supply and does not affect the sensitivity of the system to a falling supply. Therefore, the first line of defense that works for both cases of rising and falling is necessary. These two approaches prevent spurious reset caused by supply noise without sacrificing the threshold accuracy. Although all six comparators for the six inputs have builtin glitch filtering, use bypass capacitors on the V1 and V2 inputs because the greater of V1 or V2 supplies the VCC for the part (a 0.1F ceramic capacitor satisfies most applications). Apply filter capacitors on the V3, V4, VADJ1, VADJ2, VADJ3, VADJ4 and VADJ5 inputs in extremely noisy situations.
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12
LTC2908 APPLICATIONS INFORMATION
RST Output Characteristics The DC characteristics of the RST pull-up and pull-down strength are shown in the Typical Performance Characteristics section. The RST output has a weak internal pull-up to VCC = Max(V1, V2) and a strong pull-down to ground. The weak pull-up and strong pull-down arrangement allows this pin to have open-drain behavior while possessing several other beneficial characteristics. The weak pull-up eliminates the need for external pull-up resistors when the rise time on these pins is not critical. On the other hand, the open-drain RST behavior allows for wired-OR connections and can be useful when more than one signal needs to pull down on the RST line. As noted in the discussion of power-up and power-down, the circuits that drive RST are powered by VCC. During fault condition, VCC of at least 0.5V guarantees a maximum VOL = 0.15V at RST. Output Rise and Fall Time Estimation The following formula estimates the output fall time (90% to 10%) for a particular external load capacitance (CLOAD): tFALL 2.2 * RPD * CLOAD where RPD is the on-resistance of the internal pull-down transistor estimated to be typically 40 at room temperature (25C) and CLOAD is the external load capacitance on the pin. Assuming a 150pF load capacitance, the fall time is about 13ns. The rise time on the RST pin is limited by a weak internal pull-up current source to VCC. The following formula estimates the output rise time (10% to 90%) at the RST pin: tRISE 2.2 * RPU * CLOAD where RPU is the on-resistance of the pull-up transistor. Notice that this pull-up transistor is modeled as a 6A current source in the Block Diagram as a typical representation. The on-resistance as a function of the VCC = Max(V1, V2) voltage (for VCC > 1V) at room temperature is estimated as follows: 6 * 105 RPU = MAX ( V1,V2) - 1V At VCC = 3.3V, RPU is about 260k. Using 150pF for load capacitance, the rise time is 86s. A smaller external pull-up resistor may be used if the output needs to pull up faster and/or to a higher voltage. For example, the rise time reduces to 3.3s for a 150pF load capacitance when using a 10k pull-up resistor.
TYPICAL APPLICATIONS
Six Supply Monitor, 5% Tolerance, 12V, 5V, 3.3V, 2.5V, 1.8V, 1V
12V DC/DC DC/DC DC/DC DC/DC DC/DC 5V 3.3V 2.5V 1.8V 1.0V C1 C2 0.1F 0.1F R1 2.15M R3 R2 100k 86.6k R4 100k SYSTEM
V1
V2 V3 V4 VADJ1 LTC2908-A1 GND
VADJ2 RST
2908 TA02
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13
LTC2908 TYPICAL APPLICATIONS
Quad Supply Monitor with One Adjustable Input, 5% Tolerance, 3.3V, 2.5V, 1.8V, 1.2V
3.3V 2.5V 1.8V 1.2V C1 C2 0.1F 0.1F R3 124k R4 100k SYSTEM
DC/DC DC/DC DC/DC
V1
V2
V3 V4 VADJ1 LTC2908-B1 GND
VADJ2 RST
2908 TA03
Pin Programmable Dual Supply Monitor with Possible Future Expansion up to Six Supplies, 5% Tolerance, 3.3V and 2.5V
3.3V DC/DC 2.5V C1 0.1F C2 0.1F SYSTEM
V1
V2 V3 V4 LTC2908-B1 GND
VADJ1 VADJ2 RST
2908 TA05
Six Supply Monitor, 5% Tolerance 12V, 2.5V, 1.8V, 1.5V, 1.2V, 1.0V
12V DC/DC DC/DC DC/DC DC/DC DC/DC 2.5V 1.8V 1.5V 1.2V 1.0V C1 0.1F R1 2.15M R3 R2 100k 237k R4 100k R5 182k R6 100k R7 124k R9 R8 100k 86.6k R10 100k SYSTEM
V1
VADJ1
VADJ2
VADJ3 LTC2908-C1 GND
VADJ4
VADJ5 RST
2908 TA06
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14
LTC2908 PACKAGE DESCRIPTION
DDB Package 8-Lead Plastic DFN (3mm x 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
0.61 0.05 (2 SIDES) 0.70 0.05 2.55 0.05 1.15 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.20 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS PIN 1 BAR TOP MARK (SEE NOTE 6)
3.00 0.10 (2 SIDES)
R = 0.05 TYP
R = 0.115 TYP 5
0.40 0.10 8
2.00 0.10 (2 SIDES) 0.56 0.05 (2 SIDES) 0.75 0.05
0.200 REF
4 0.25 0.05 2.15 0.05 (2 SIDES)
1 0.50 BSC
PIN 1 R = 0.20 OR 0.25 x 45 CHAMFER
(DDB8) DFN 0905 REV B
0 - 0.05
BOTTOM VIEW--EXPOSED PAD
NOTE: 1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229 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 SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
TS8 Package 8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
0.52 MAX 0.65 REF 2.90 BSC (NOTE 4)
1.22 REF
3.85 MAX 2.62 REF
1.4 MIN
2.80 BSC
1.50 - 1.75 (NOTE 4) PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR
0.65 BSC 0.80 - 0.90
0.22 - 0.36 8 PLCS (NOTE 3)
0.20 BSC 1.00 MAX DATUM `A'
0.01 - 0.10
0.30 - 0.50 REF
NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING
0.09 - 0.20 (NOTE 3)
1.95 BSC
TS8 TSOT-23 0802
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193
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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.
15
LTC2908 TYPICAL APPLICATION
Six Supply Monitor with Manual Reset Button, 5% Tolerance, 12V, 5V, 3.3V, 2.5V, 1.8V, 1.5V
12V (VTRIP = 11.25V) DC/DC DC/DC DC/DC DC/DC DC/DC 5V (VTRIP = 4.675V) 3.3V (VTRIP = 3.086V) 2.5V (VTRIP = 2.338V) 1.8V (VTRIP = 1.685V) 1.5V (VTRIP = 1.410V) C1 C2 0.1F 0.1F R1 182k R2 100k R3 MANUAL 2.15M RESET BUTTON R5* (NORMALLY OPEN) 10k R4 100k V1 *OPTIONAL RESISTOR RECOMMENDED TO EXTEND ESD TOLERANCE V2 V3 V4 VADJ1 LTC2908-A1 GND VADJ2 RST
2908 TA04
SYSTEM
RELATED PARTS
PART NUMBER LTC690 LTC694-3.3 LTC699 LTC1232 LTC1326/LTC1326-2.5 LTC1536 LTC1726-2.5/LTC1726-5 LTC1727-2.5/LTC1727-5 LTC1728-2.5/LTC1728-5 LTC1985-1.8 LTC2900 LTC2901 LTC2902 LTC2903 LTC2904 LTC2905 LTC2906 LTC2907 LTC2909 DESCRIPTION 5V Supply Monitor, Watchdog Timer and Battery Backup 3.3V Supply Monitor, Watchdog Timer and Battery Backup 5V Supply Monitor and Watchdog Timer 5V Supply Monitor, Watchdog Timer and Pushbutton Reset Precision Triple Supply Monitor for PCI Applications Micropower Triple Supply Monitor for 2.5V/5V, 3.3V and ADJ Micropower Triple Supply Monitor with Open-Drain Reset Micropower Triple Supply Monitor with Open-Drain Reset Micropower Triple Supply Monitor with Push-Pull Reset Output Programmable Quad Supply Monitor Programmable Quad Supply Monitor Programmable Quad Supply Monitor Precision Quad Supply Monitor Three-State Programmable Precision Dual Supply Monitor Three-State Programmable Precision Dual Supply Monitor Dual Supply Monitor with One Pin Selectable Threshold and One Adjustable Input Dual Supply Monitor with One Pin Selectable Threshold and One Adjustable Input Precision Triple/Dual Input UV, OV and Negative Voltage Monitor COMMENTS 4.65 Threshold 2.9V Threshold 4.65 Threshold 4.37V/4.62V Threshold Meets PCI tFAIL Timing Specifications Adjustable Reset and Watchdog Time-Outs Individual Monitor Outputs in MSOP 5-Lead SOT-23 Package 5-Lead SOT-23 Package 5-Lead SOT-23 Package Adjustable Reset, 10-Lead MSOP and DFN Packages Adjustable Reset and Watchdog Timer, 16-Lead SSOP Package Adjustable Reset and Tolerance, 16-Lead SSOP Package 6-Lead SOT-23 Package Adjustable Tolerance, 8-Lead SOT-23 and DFN Packages Adjustable Reset and Tolerance, 8-Lead SOT-23 and DFN Packages 0.5V Adjustable Threshold and Three Supply Tolerances, 8-Lead SOT-23 and DFN Packages 0.5V Adjustable Threshold, Reset and Three Supply Tolerances, 8-Lead SOT-23 and DFN Packages Shunt Regulated VCC Pin, Adjustable Threshold and Reset, 8-Lead SOT-23 and DFN Packages
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Micropower Precision Triple Supply Monitor for 5V/2.5V, 3.3V and ADJ 4.725V, 3.118V, 1V Threshold (0.75%)and ADJ
LTC1728-1.8/LTC1728-3.3 Micropower Triple Supply Monitor with Open-Drain Reset
16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0708 REV C * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2004

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