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LTC1985-1.8 Micropower Precision Triple Supply Monitor with Push-Pull Reset Output in a 5-Lead SOT-23 Package
FEATURES
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DESCRIPTIO
Monitors Three Inputs Simultaneously: 3V, 1.8V and Adjustable 1.5% Threshold Accuracy Over Temperature Very Low Supply Current: 10A Typ 200ms Reset Time Delay Power Supply Glitch Immunity Guaranteed RESET for VCC3 1V or VCC18 1V 3V Active-Low Push-Pull Reset Output 5-Lead SOT-23 Package
The LTC(R)1985-1.8 is a triple supply monitor intended for systems with multiple supply voltages. The reset output remains low until all three supplies have been in compliance for 200ms. Tight 1.5% accuracy specifications and glitch immunity ensure reliable reset operation without false triggering. The RST output is guaranteed to be in the correct state for VCC18 or VCC3 down to 1V. The LTC1985 may also be configured to monitor any one or two VCC inputs instead of three, depending on system requirements. Very low (10A typical) supply current makes the LTC1985 ideal for power conscious systems. The LTC1985 is available in a 5-lead SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Desktop Computers Notebook Computers Intelligent Instruments Portable Battery-Powered Equipment Network Servers
TYPICAL APPLICATION
DC/DC CONVERTER 3V 1.8V 2.5V SYSTEM LOGIC 1 5 VCC3 RST
LTC1985-1.8 4 0.1F R1 130k 1% 3 0.1F R2 100k 1% VCC18
VCCA GND 2
1985-1.8 TA01
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LTC1985-1.8
ABSOLUTE
(Notes 1, 2)
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RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW RST 1 GND 2 VCCA 3 4 VCC18 5 VCC3
VCC3, VCC18, VCCA ...................................... - 0.3V to 7V RST .......................................... - 0.3V to (VCC3 + 0.3V) Operating Temperature Range (Note 3) ............................................. - 40C to 85C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................ 300C
ORDER PART NUMBER LTC1985ES5-1.8 S5 PART MARKING LTNM
S5 PACKAGE 5-LEAD PLASTIC SOT-23
TJMAX = 125C, JA = 250C/W
Consult factory for Industrial and Military grade parts.
The q denotes specifications which apply over the full operating temperature range, otherwise specificaitons are at TA = 25C. VCC3 = 3V, VCC18 = 1.8V, VCCA = VCC3 unless otherwise noted.
SYMBOL VRT3 VRT18 VRTA VCCOP IVCC3 IVCC18 IVCCA tRST tUV VOL PARAMETER Reset Threshold VCC3 Reset Threshold VCC18 Reset Threshold VCCA VCC3, VCC18 Operating Voltage VCC3 Supply Current VCC18 Supply Current VCCA Input Current Reset Pulse Width VCC Undervoltage Detect to RST Output Voltage Low, RST CONDITIONS VCC3 Input Threshold VCC18 Input Threshold VCCA Input Threshold RST in Correct Logic State VCC18 > VCC3 VCC18 < VCC3, VCC3 = 3V (Note 4) VCC18 < VCC3, VCC18 = 1.8V (Note 4) VCCA = 1V RST Low (Note 5) VCC18, VCC3 or VCCA Less Than Reset (Note 5) Threshold VRT by More Than 1% ISINK = 2.5mA, VCC3 = 3V, VCC18 = 0V ISINK = 100A, VCC3 = 1V, VCC18 = 0V ISINK = 100A, VCC3 = 0V, VCC18 = 1V ISINK = 100A, VCC3 = 1V, VCC18 = 1V ISOURCE = 200A
q q q q q q q q q q q q q q
ELECTRICAL CHARACTERISTICS
MIN 2.760 1.656 0.985 1
TYP 2.805 1.683 1.000 1 10 1
MAX 2.850 1.710 1.015 7 2 20 2 15 280
UNITS V V V V A A A nA ms s
- 15 140
0 200 110 0.15 0.05 0.05 0.05
0.4 0.3 0.3 0.3
VOH
Output Voltage High, RST
0.8VCC3
Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: All voltage values are with respect to GND. Note 3: The LTC1985E is guaranteed to meet specified performance from 0C to 70C and is designed, characterized and assured to meet the
extended temperature limits of - 40C to 85C but are not tested at these temperatures. Note 4: Both VCC3 and VCC18 can act as the supply depending on which pin has the greatest potential. Note 5: Measured from when input passes through the input threshold voltage (VRTX) until RST passes through 1.5V.
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LTC1985-1.8 TYPICAL PERFOR A CE CHARACTERISTICS
IVCC3 vs Temperature
15 14 13 12
IVCC18 (A) IVCC3 (A)
1.2 1.1 1.0 0.9 0.8 0.7 0.6
INPUT CURRENT (nA)
11 10 9 8 7 6 5 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C) 80 100
VCCA Threshold Voltage vs Temperature
1.015 2.845 2.835 2.825 2.815 2.805 2.795 2.785 2.775
VCC18 THRESHOLD VOLTAGE, VRT18 (V)
VCCA THRESHOLD VOLTAGE, VRTA (V)
VCC3 THRESHOLD VOLTAGE, VRT3 (V)
1.010 1.005 1.000 0.995 0.990 0.985 -60 -40 -20 0 20 40 60 TEMPERATURE (C)
Typical Transient Duration vs Comparator Overdrive
450
TYPICAL TRANSIENT DURATION (s)
400 350 300 250 200 150 100 50 0 0.1 1 10 100 RESET COMPARATOR OVERDRIVE VOLTAGE (% OF VCC)
1985-18 G07
RESET OCCURS ABOVE CURVE
RESET PULSE WIDTH, tRST (ms)
220 200 180 160 140 -60 -40 -20
ISINK (mA)
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1985-18 G01
IVCC18 vs Temperature
1.5 1.4 1.3 VCC3 = 3V VCCA = 3V VCC18 = 1.8V 2.0 1.5 1.0 0.5 0 - 0.5 -1.0 -1.5 80 100
VCCA Input Current vs Input Voltage
TA = 25C
0.5 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C)
- 2.0 0.80 0.85 0.90 0.95 1 1.05 1.10 1.15 1.20 INPUT VOLTAGE (V)
1985-18 G03
1985-18 G02
VCC3 Threshold Voltage vs Temperature
1.710 1.700 1.690 1.680 1.670 1.660
VCC18 Threshold Voltage vs Temperature
80
100
2.765 - 60 -40 - 20 0 20 40 60 TEMPERATURE (C)
80
100
1.650 -60 -40 -20 0 20 40 60 TEMPERATURE (C)
80
100
1985-18 G04
1985-18 G05
1985-18 G06
Reset Pulse Width vs Temperature
TA = 25C
280 260 240
ISINK vs Supply Voltage
8 7 6 VOL = 0.4V 5 4 VOL = 0.2V 3 2 1 0 TA = 25C
0
20
40
60
80
100
0
0.5
TEMPERATURE (C)
1985-18 G08
1.0 1.5 2.0 VCC3 OR VCC18 (V)
2.5
3.0
1985-18 * G09
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LTC1985-1.8 TYPICAL PERFOR A CE CHARACTERISTICS
RST High Level Output Voltage vs Output Source Current
3.5 3.0 2.5 VOH (V) VCC3 = VCC18 = VCCA = 3.0V
VOL (V)
1.0 0.8 0.6 0.4
VOL (V)
2.0 - 40C 1.5 1.0 85C 0.5 0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 ISOURCE (mA)
1985-81 G10
25C
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RST (Pin 1): Reset Logic Output. Active low, 3V pushpull output. Asserted when one or all of the supplies are below trip thresholds and held for 200ms after all supplies become valid. GND (Pin 2): Ground. VCCA (Pin 3): 1V Sense, High Impedance Input. If unused it can be tied to either VCC3 or VCC18. VCC18 (Pin 4): 1.8V Sense Input and Power Supply Pin. This pin is used on the LTC1985 to provide power to the part when the voltage on VCC18 is greater than the voltage on VCC3. Bypass to ground with a 0.1F ceramic capacitor. VCC3 (Pin 5): 3V Sense Input and Power Supply Pin. This pin provides power to the part when the voltage on VCC3 is greater than the voltage on VCC18. Bypass to ground with a 0.1F ceramic capacitor.
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RST Voltage Output Low vs Output Sink Current
1.8 1.6 1.4 85C 1.2 - 40C
2.0 1.5 1.0 0.5 3.0
RST Voltage Output Low vs Output Sink Current
VCC3 = VCC18 = 3V VCCA = 0V 85C - 40C 25C
VCC3 = VCC18 = 1.8V VCCA = 0V
25C
2.5
0.2 0 0 2 4 8 ISINK (mA) 6 10 12 14
0 0 5 10 15 20 25 30 ISINK (mA) 35 40 45
1985-81 G11
1985-81 G12
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LTC1985-1.8
BLOCK DIAGRA
VCC3 5
POWER DETECT VCC18 4
VCC INTERNAL VCC3
VCCA 3
GND 2
TI I G DIAGRA
VCCX
VRTX t UV tRST 1.5V
1985-18 TD
RST
+
+
+
-
-
-
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LTC1985-1.8 200ms PULSE GENERATOR 200ms DELAY 1 RST BANDGAP REFERENCE
1985-18 BD
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VCC Monitor Timing
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LTC1985-1.8
APPLICATIO S I FOR ATIO
Supply Monitoring
The LTC1985 is a low power, high accuracy triple supply monitoring circuit with a single 200ms microprocessor reset output. All three VCC inputs must be above predetermined thresholds for reset not to be invoked. The LTC1985 will assert reset during power-up, power-down and brownout conditions on any one or all of the VCC inputs. 3V or 1.8V Power Detect The LTC1985 is powered from the 3V input pin (VCC3) or the 1.8V input pin (VCC18), whichever pin has the highest potential. This ensures the part pulls the RST pin low as soon as either input pin is 1V. Power-Up Upon power-up, either the VCC18 or VCC3 pin, can power the part. This ensures that RST will be low when either VCC18 or VCC3 reaches 1V. As long as any one of the VCC inputs is below its predetermined threshold, RST will stay a logic low. Once all of the VCC inputs rise above their thresholds, an internal timer is started and RST is driven high after 200ms. RST is reasserted whenever any one of the VCC inputs drops below its predetermined threshold and remains asserted until 200ms after all of the VCC inputs are above their thresholds. Power-Down
RST VOLTAGE (V)
On power-down, once any of the VCC inputs drop below its threshold, RST is held at a logic low. A logic low of 0.3V is guaranteed until both VCC3 and VCC18 drop below 1V.
LTC1985-1.8 3V ADJUSTABLE SUPPLY R1 1.8V 5 4 3 R2 2 VCC3 VCC18 VCCA GND
1985-18 TA06
RST
1 R3 100k
Resistor on RST Output to Ground Ensures RST Valid to VCC = 0V Figure 1. Typical Application Showing Resistor on RST Output to Ground Figure 2. RST Voltage vs VCC3 with a 100k Resistor on RST to Ground
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Override Functions The VCCA pin, if unused, can be tied to either VCC3 or VCC18. This is an obvious solution since the trip points for VCC3 and VCC18 will always be greater than the trip point for VCCA. Likewise, the VCC18, if unused, can be tied to VCC3. VCC3 must always be used. Tying VCC3 to VCC18 and operating off of a 1.8V supply will result in the continuous assertion of RST. Ensuring RST Valid for Supply Voltages Under 1V When the supplies drops below 1V the RST output current sink capability is drastically reduced. The combination of stray currents and stray capacitance to signals other than ground can cause the RST output pin to float around. In a lot of applications this is not a problem since most microprocessors and other circuits do not operate with the supply voltage less than 1V. In applications where the RST output must be valid down to 0V the addition of a pulldown resistor from RST to ground will ensure RST is held low. The circuit in Figure 1 shows an application employing this technique. The value chosen for the pull-down resistor (R3) is a trade-off between pull-down strength and loading of the RST pin. If the value of the resistor is too large the pin may still float and if the resistor value is too low it may load down the RST as well as burn excess supply current, a value of 100k is a good compromise.
4 VCC3 = VCC18 = VCCA 3 2 1 0 0 1 2 VCC3 (V)
1985-18 TA06b
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LTC1985-1.8
TYPICAL APPLICATIO S
Triple Supply Monitor (3V, 1.8V and Adjustable)
LTC1985-1.8 3V ADJUSTABLE SUPPLY OR DC/DC FEEDBACK DIVIDER R1* 1.8V 5 4 3 R2* 2 VCC3 VCC18 VCCA GND
1985-18 TA02
*TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL COMBINATION OF R1 AND R2 66.5k
Dual Supply Monitor (3V Plus Adjustable)
LTC1985-1.8 3V ADJUSTABLE SUPPLY R1* R2* 5 4 3 2 VCC3 VCC18 VCCA GND
1985-18 TA04
*TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL COMBINATION OF R1 AND R2 66.5k
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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Dual Supply Monitor (3V and 1.8V, Defeat VCCA Input)
LTC1985-1.8 3V 1.8V 5 4 3 2 VCC3 VCC18 VCCA GND
1985-18 TA03
RST
1
SYSTEM RESET
RST
1
SYSTEM RESET
Using VCCA Tied to DC/DC Feedback Divider
2.5V
RST
1
SYSTEM RESET
LTC1435 VOSENSE 6
27.4k 1% 3V 2.26k 1.8V 1% 22.6k 1%
LTC1985-1.8 5 4 3 2 VCC3 VCC18 VCCA GND
1985-18 TA05
RST
1
SYSTEM RESET
ADJUSTABLE RESET TRIP THRESHOLD 2.31V
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LTC1985-1.8
TYPICAL APPLICATIO
MANUAL RESET BUTTON (NORMALLY OPEN) *OPTIONAL RESISTOR RECOMMENDED TO EXTEND ESD TOLERANCE
PACKAGE DESCRIPTIO
2.60 - 3.00 (0.102 - 0.118) 1.50 - 1.75 (0.059 - 0.069) 0.00 - 0.15 (0.00 - 0.006) 0.90 - 1.45 (0.035 - 0.057) 2.80 - 3.00 (0.110 - 0.118) (NOTE 3)
0.35 - 0.55 (0.014 - 0.022)
NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DIMENSIONS ARE INCLUSIVE OF PLATING 3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 4. MOLD FLASH SHALL NOT EXCEED 0.254mm 5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ)
RELATED PARTS
PART NUMBER LTC690 LTC694-3.3 LTC699 LTC1232 LTC1326 LTC1326-2.5 LTC1536 LTC1726-2.5 LTC1726-5 LTC1727-2.5/1727-5 LTC1728-1.8 LTC1728-2.5/1728-5 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 Push-Button Reset Micropower Precision Triple Supply Monitor for 5V, 3.3V and ADJ Micropower Precision Triple Supply Monitor for 2.5V, 3.3V and ADJ Precision Triple Supply Monitor for PCI Applications Micropower Triple Supply Monitor for 2.5V, 3.3V and ADJ Micropower Triple Supply Monitor for 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 Open-Drain Reset COMMENTS 4.65V Threshold 2.9V Threshold 4.65V Threshold 4.37V/4.62V Threshold 4.725V, 3.118V, 1V Thresholds (0.75%) 2.363V, 3.118V, 1V Thresholds (0.75%) Meets PCI tFAIL Timing Specifications Adjustable RESET and Watchdog Time Outs Adjustable RESET and Watchdog Time Outs Individual Monitor Outputs in MSOP 5-Lead SOT-23 Package 5-Lead SOT-23 Package
1985f LT/TP 0900 4K * PRINTED IN THE USA
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
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Triple Supply Monitor with Manual Reset Button
2.5V VTRIP = 2.3V 1.8V 3V SYSTEM RESET 1 5 100nF R3* 10k 5% R1 130k 0.1% R2 100k 0.1% 4 100nF 3 VCCA GND 2 V VTRIP = CCA (R1 + R2) R2 V R1 = R2 TRIP - 1 VCCA
1985-18 TA07
RST VCC3 LTC1985-1.8 VCC18
(
)
Dimensions in inches (millimeters) unless otherwise noted. S5 Package 5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
0.09 - 0.20 (0.004 - 0.008) (NOTE 2)
0.35 - 0.50 0.90 - 1.30 (0.014 - 0.020) (0.035 - 0.051) FIVE PLACES (NOTE 2)
1.90 (0.074) REF
0.95 (0.037) REF
S5 SOT-23 0599
(c) LINEAR TECHNOLOGY CORPORATION 2000

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