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LTC1998 2.5A, 1% Accurate SOT-23 Comparator and Voltage Reference for Battery Monitoring
FEATURES
s s s s s s s
DESCRIPTIO
High Accuracy Trip Voltage: 1% Max Error Using External 1% Resistors Adjustable Threshold Voltage and Hysteresis Quiescent Current: 2.5A Typ Output Swings Rail-to-Rail Thresholds Programmable from 2.5V to 3.25V Output State Guaranteed for VBATT 1.5V Low Profile (1mm) ThinSOTTM Package
The LTC(R)1998 is a micropower comparator and a precision adjustable reference in a 6-pin SOT-23 package that is optimized for lithium-ion low battery detection circuits. The LTC1998 features a voltage detection circuit with an adjustable threshold voltage and hysteresis. The threshold voltage can be programmed from 2.5V to 3.25V with two external resistors. A 10mV to 750mV hysteresis can be added with a third external resistor. A proprietary internal architecture maintains 1% threshold voltage accuracy over temperature with low cost 1% external resistors. A separate power supply pin, VLOGIC, allows the batterylow logic output to operate below the battery voltage, allowing compatibility with low voltage microprocessors without a pull-up resistor. Power supply glitches are eliminated by preventing the cross-conducting current which occurs when the output changes state. The LTC1998 operates with battery or supply voltages up to 5.5V and its battery-low output is valid for battery voltages above 1.5V.
APPLICATIO S
s
Lithium-Ion Battery-Powered Equipment PDAs Cell Phones Handheld Instruments Battery Packs Pagers Palm Top Computers POS Terminals
, LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation.
BLOCK DIAGRA
Threshold Voltage Error vs Temperature
1.0 BATT VLOGIC 1.1R VHYST.A VTH.A 1.2V % ERROR THRESHOLD ADJUST 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1
1998 BD
R
BATTLO
0 -45 -25
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VTH.A SET BY 1% EXTERNAL R, THRESHOLD = 3V VTH.A = 1V THRESHOLD = 3V VTH.A SHORTED TO GROUND, THRESHOLD = 2.5V 35 15 55 -5 TEMPERATURE (C) 75 95
1998 G05
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1998f
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LTC1998
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW BATT 1 GND 2 VTH.A 3 6 BATTLO 5 VLOGIC 4 VH.A
Total Supply Voltage (BATT or V LOGIC to GND) ......... 6V Voltage VTH.A, VH.A ........................... BATT + 0.3V to GND - 0.3V BATTLO ........................ VLOGIC + 0.3V to GND - 0.3V Operating Temperature Range (Note 3) ...-40C to 85C Specified Temperature Range (Note 4) LTC1998C ...........................................-40C to 85C LTC1998I .............................................-40C to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LTC1998CS6 LTC1998IS6 S6 PART MARKING* LTTY
S6 PACKAGE 6-LEAD PLASTIC SOT-23
TJMAX = 150C, JA = 250C/W
*The temperature grades are indentified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges.
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. V GND = 0V, unless otherwise noted.
PARAMETER Power Supply Supply Voltage Range-BATT Supply Voltage Range-VLOGIC Supply Current, VBATT = 3V, VTH.A = 1.5V Supply Current, VBATT = 5.5V, VTH.A = 1.5V Monitor Threshold Accuracy VBATT.Th = 2.5V, Pin 3 Shorted to Ground
q q q
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN 1.5 1
TYP
MAX 5.5 VBATT
UNITS V V A A A A A A % % % % % % % % % % mV mV mV s s
TA = 25C LTC1998CS6 LTC1998IS6 TA = 25C LTC1998CS6 LTC1998IS6
2.5
q q
3.5 4.2 4.5 4.3 5.2 5.5 0.85 1 0.61 0.71 1 1.1 0.65 0.85 1.1 1.3 5 750
3
q q
0.6 0.8 0.5 0.6 0.8 0.9 0.6 0.7 0.9 1 -5 10 350 150 5
VBATT.Th = 3V, Pin 3 Driven by Precision Voltage Source to 1V VBATT.Th = 3V, VTH.A = 1V (Note 5) Programmed with 1% Max External Resistors VBATT.Th = 3.25V, Pin 3 Diven by Precision Voltage Source to 1.5V VBATT.Th = 3.25V, VTH.A = 1.5V (Note 5) Programmed with1% Max External Resistors Hysteresis Accuracy Allowable Hysteresis Range (Note 2) Propagation Delay Threshold Adjust Pin Leakage, ITH.A Hysteresis Adjust Pin Leakage, IH.A Output BATTLO High Voltage BATTLO Low Voltage BATTLO Low Voltage IOUT = -1mA IOUT = 1mA, VBATT 2V IOUT = 0.25mA, VBATT = 1V COUT = 100pF, Overdrive = 10mV Overdrive = 100mV VTH.A 1.5V VH.A 1.5V VHYST 250mV 250mV VHYST 750mV
LTC1998C LTC1998I LTC1998C LTC1998I LTC1998C LTC1998I LTC1998C LTC1998I
q q q q q q q q q q q
q q
0.01 0.01 VLOGIC - 0.3
1 1
q q q
0.2 0.3
2
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nA nA V V V
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LTC1998
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Maximum allowable hysteresis depends on desired trip voltages. See application notes for details. Note 3: LTC1998C and LTC1998I are guaranteed functional over the operating temperature range of - 40C to 85C. Note 4: The LTC1998C is guaranteed to meet specified performance from 0C to 70C. The LTC1998C is designed, characterized and expected to meet specified performance from -40C to 85C but is not tested or QA sampled at these temperatures. The LTC1998I is guaranteed to meet specified performance from -40C to 85C. Note 5: This parameter is not 100% tested.
TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Supply Current vs Supply Voltage
3.5 3.0 TA = 25C VLOGIC = VBATT 3.5 3.0 2.5 VTH.A = 1.5V 2.0 1.5 1.0 0.5 0 -50
2.5 2.0 1.5 1.0 0.5
VTH.A = 0V
THRESHOLD VOLTAGE (V)
SUPPLY CURRENT (A)
SUPPLY CURRENT (A)
VTH.A = 1.5V
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 SUPPLY VOLTAGE (V)
1998 G01
Available Hysteresis vs Threshold Voltage
750
1.0 0.9
AVAILABLE HYSTERESIS (mV)
0.8
500
% ERROR
0.7 0.6 0.5 0.4 0.3 0.2 0.1 VTH.A = 1V THRESHOLD = 3V
VTH.A SET BY 1% EXTERNAL R, THRESHOLD = 3V
INPUT CURRENT VTH.A, VH.A (pA)
250
0 2.5
3.25 2.75 3.0 LOW BATTERY THRESHOLD VOLTAGE (V)
1998 G04
UW
Quiescent Supply Current vs Temperature
VBATT = VLOGIC = 3V
Threshold Voltage vs Threshold Adjust Voltage
3.5
3.0
2.5
-30 -10 10 30 50 TEMPERATURE (C) 70 90
0
0.5 1.0 THRESHOLD ADJUST VOLTAGE (V)
1.5
1998 G02
1998 G03
Threshold Voltage Error vs Temperature
10000
Input Current vs Temperature
VIN = 1.5V 1000
100
VIN = 1V VIN = 0.5V
VTH.A SHORTED TO GROUND, THRESHOLD = 2.5V
10
1
0 -45 -25
35 15 55 -5 TEMPERATURE (C)
75
95
0.1 35 45 55 65 75 85 95 105 115 125 TEMPERATURE (C)
1998 G06
1998 G05
1998f
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LTC1998 TYPICAL PERFOR A CE CHARACTERISTICS
Output Low Voltage vs Load Current
OUTPUT VOLTAGE RELATIVE TO VBATT (mV)
0.6 TA = 25C VLOGIC = VBATT = 3V 0 TA = 85C TA = 25C TA = -40C
OUTPUT VOLTAGE (V)
TA = 85C 0.4
CURRENT (mA)
TA = 25C 0.2 TA = -40C
0 1 2 3 4 OUTPUT SINK CURRENT (mA) 5
1998 G07
PI FU CTIO S
BATT (Pin 1): Battery Voltage to be monitored. Supply current is also drawn from this pin. Board layout should connect this pin to the battery(+) terminal, through a trace that does not conduct load current. GND (Pin 2): Ground should be connected to the battery (-) terminal through a trace that does not conduct load return current. VTH.A (Pin 3): Threshold Adjust Pin. Adjusts the low battery threshold voltage, VBATT.Th = 2.5V + (VTH.A/2). VTH.A can be supplied by a voltage source or a resistor divider. VH.A (Pin 4): Hysteresis Adjust. Hysteresis threshold voltage VTH2 = 2.5V + (VH.A/2). VH.A can be supplied by a voltage source or resistor divider. VH.A must always be programmed to a higher potential than VTH.A. Hysteresis voltage, VHYST = VTH2 - VBATT.Th. VLOGIC (Pin 5): Positive Supply Voltage for Output Driver. This voltage can be driven from an external logic supply or tied to BATT. BATTLO (Pin 6): Output of Comparator. Low for BATT < VBATT.Th (low battery threshold voltage). Output state guaranteed for VBATT 1.5V.
QUICK DESIG GUIDE
How to Calculate the External Resistor Values The LTC1998 is a low battery warning indicator and is especially designed for monitoring the voltage of singlecell Lithium-Ion batteries. The LTC1998 compares its supply pin (BATT) to an accurate internal reference; if the battery voltage falls below the programmed low battery threshold voltage of the LTC1998, the battery low pin (BATTLO) will change state, from high to low, to indicate a low battery condition. The low battery threshold voltage is programmed via the voltage threshold adjust pin (VTH.A). A hysteresis adjust pin (VH.A) will add hysteresis to the programmed value of the low battery threshold voltage.
4
UW
Output High Voltage vs Load Current
120 100 80 60 40 20
BATT = 3V BATT = 5V 5
1998 G08
Output Short-Circuit Current vs Supply Voltage
TA = 25C VBATT = VLOGIC
-50
-100
TA = -40C TA = 25C TA = 85C
SOURCE CURRENT, BATTLO SHORTED TO GND
-150
-200 TA = 25C VLOGIC = VBATT 1
-250
SINK CURRENT, BATTLO SHORTED TO VLOGIC
2 3 4 OUTPUT SOURCE CURRENT (mA)
0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 SUPPLY VOLTAGE (V)
1998 G09
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1998f
LTC1998
QUICK DESIG GUIDE
Typical Application
Table 1: Design Equations for R1, R2, R3, Figure 1
Choose desired values for: * VBATT.Th: Low Battery Threshold Voltage * VHYST: Hysteresis Voltage * IR: Max Allowable Resistor Current Solve:
RTOTAL = R1 + R2 + R3 =
5V R1 = RTOTAL * - 1 VBATT .Th + VHYST 5V R2 = RTOTAL * - 1 - R1 VBATT .Th R3 = RTOTAL - R1 - R2
Li-Ion
APPLICATIO S I FOR ATIO
LOW BATTERY THRESHOLD VOLTAGE AND HYSTERESIS ADJUST
Low Battery Threshold Voltage Adjustment, Pin 3 The low battery threshold voltage is the battery voltage which will trip the (BATTLO) pin high to low. It should be adjusted via the threshold adjust pin (VTH.A). This is a high input impedance pin that senses an externally applied voltage and programs the low battery threshold voltage (VBATT.Th). The VTH.A pin is designed to accommodate voltages from 0V to 1.5V with respect to ground. This allows the low battery threshold voltage to be set to any voltage between 2.5V and 3.25V, that is: (V ) VBATT .Th = 2.5V + TH.A 2
Li-Ion
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Example 1: A system using a 4.2V (fully charged) LithiumIon battery requires a low battery threshold of 2.7V, 100mV hysteresis and can allow up to 4.2A maximum resistor current. RTOTAL = 1M, R1 = 786k, R2 = 66k and R3 = 148k Choose standard 1% values. R1 = 787k, R2 = 66.5k, R3 = 147k
1.5V TO 4.2V REGULATOR 0.1F 4 1 BATT 5 VH.A VLOGIC LTC1998 3 R3 1% 6 VTH.A BATTLO GND 2
1998 F01
VLOGIC
4.2V IR
+
R1 1% R2 1%
P
Figure 1. Low Battery Threshold Detector with Hysteresis
For instance, if the applied voltage at pin 3, VTH.A, is 1V the LTC1998 will indicate a low battery condition when the battery voltage pin (BATT) falls below 3V. The voltage at the threshold adjust pin (VTH.A) can be set with any voltage source. This pin allows a continuous time adjustment, that is, the low battery threshold voltage may be changed at any time. The high input impedance of the VTH.A pin allows the use of a high valued resistive divider (to minimize current drain) from the battery to set the battery low threshold voltage, Figure 2.
+
R1 3 R2 1 BATT VTH.A LTC1998 2
1998 F02
Figure 2. Resistor Divider Sets Threshold
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LTC1998
APPLICATIO S I FOR ATIO
The simple calculations of resistor values R1 and R2 are illustrated below. Set a value for R1 + R2. This value will affect the max amount of current drawn from the battery when fully charged. For instance if R1 + R2 = 1M the resistive divider will draw 4.1A when the battery voltage is 4.1V. Set the desired value of VBATT.Th (this value should be between 2.5V and 3.25V) that is the value of the battery voltage that will trip the internal circuitry of the LTC1998 and change the state of the battery low pin (BATTLO).
5V Solve for R1 = (R1 + R2) - 1 VBATT .Th
Example: A Lithium-Ion battery is monitored and a battery low signal should be issued when it discharges to 2.85V, that is, VBATT.Th = 2.85V; if (R1 + R2) = 1M, then R1 = 754.38k and R2 = 245.62k. Choose the closest 1% value of R1 = 750k and R2 = 243k. Calculate the practical value for VBATT.Th as it will be slightly different from 2.85V, due to the use of standard 1% resistor values.
VBATT .Th = 5V
R1 + R2 = 2.849V R1 + (R1 + R2)
The above low battery threshold of 2.849V is guaranteed to within 1% even though 1% resistors are used to program the VTH.A voltage applied to Pin 3. For sake of completeness, the voltage at Pin 3 (VTH.A) can be easily calculated by VTH.A = VBATT.Th (R2/(R1 + R2) = 0.6972V (when VBATTERY = VBATT.Th). Hysteresis Adjustment, Pin 4. The LTC1998 has an adjustable hysteresis ranging from 10mV to 0.75V. A large hysteresis is useful in the event that a low battery signal at the LTC1998's BATTLO pin causes the system to shed some battery load, thus inducing system confusion as the partially loaded battery recovers and changes the status of Pin 6 (BATTLO). The 2.5V to 3.25V programming window of low battery threshold voltage includes the hysteresis. If, for instance, the low battery threshold voltage is set to 2.5V, 750mV hysteresis can be added on top of the 2.5V. If the low battery threshold voltage is set to 3.15V, only 100mV hysteresis can be applied.
Li-Ion
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The programming of the hysteresis threshold adjust pin (VH.A) is similar to the programming of the voltage threshold adjust pin (VTH.A) already described in the previous paragraph. Pin 4 effectively adjusts the threshold voltage at which the low battery pin (BATTLO) changes state from low to high. This threshold (VTH2) is defined as: VTH2 = 2.5V + (VH.A ) 2 The actual hysteresis voltage is: VHYST = VTH2 - VBATT.Th It is imperative that the hysteresis threshold adjust voltage at Pin 4 be set to a higher voltage than the low battery threshold adjust voltage at Pin 3, at all times, to avoid oscillation at the BATTLO output pin. The hysteresis threshold adjust pin may be set with a voltage source or with a resistor divider, just as with the low battery threshold adjust pin. Combined Control of Threshold and Hysteresis If a resistor divider is desired, then both threshold adjust dividers can be combined in order to save current. This simple technique also guarantees that the hysteresis threshold adjust voltage at Pin 4 is higher than the voltage at the VTH.A pin, Figure 3.
+
R1 4 R2 3 R3
1998 F03
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1 BATT VH.A LTC1998 VTH.A
Figure 3. Combined Resistor Divider
The calculation of the resistor values R1, R2 and R3 is quite straightforward and similar to the procedure outlined in the previous paragraph. Choose a value for the sum of R1 + R2 + R3 as well as the values for low battery threshold and hysteresis. Solve for resistor R1:
1998f
LTC1998
APPLICATIO S I FOR ATIO
5V R1 = (R1 + R2 + R3) - 1 VTH2
Solve for the sum of
5V (R1 + R2) = (R1 + R2 + R3) - 1 VBATT .Th
then solve for R2 and R3. Example: A system needs to detect a low battery voltage of 3V (VBATT.Th = 3V) with 250mV hysteresis (VTH2 = 3.25V). Set the value of the resistor divider (R1 + R2 + R3) = 1M. R1 = 539k, R1 + R2 = 667k, R2 = 128k, R3 = 333k. Choose the closest 1% values, that is 536k, 332k, 127k. Figure 4 graphically shows the function of the LTC1998 as described above. VERSATILE OUTPUT DRIVER VLOGIC, BATTLO (Pins 5,6) The LTC1998 uses a CMOS push-pull output stage to drive the low battery output signal. This output pin (BATTLO)
PACKAGE DESCRIPTIO
(Reference LTC DWG # 05-08-1636)
0.62 MAX 0.95 REF 2.90 BSC (NOTE 4)
3.85 MAX 2.62 REF
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 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
0.20 BSC 1.00 MAX DATUM `A' 0.80 - 0.90 0.09 - 0.20 (NOTE 3) 1.90 BSC
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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has a separate supply pin, (VLOGIC) that can be used to provide an output voltage rail matching the VDD logic of microprocessors. The VLOGIC pin may be tied to a voltage lower than the voltage at the BATT pin. The VLOGIC pin may also be tied to a voltage higher than VBATT via a series resistor greater than 10k. The output will then act as an open-drain device. In a given application, if it is possible for BATTLO to be shorted to GND or a supply, a series resistor should be added to limit the short-circuit current to 5mA.
3.25V PROGRAMMED HYSTERESIS THRESHOLD PROGRAMMED LOW BATT THRESHOLD 2.50V HYSTERESIS PROGRAMMABLE THRESHOLD RANGE BATTERY VOLTAGE RECOVERS UNDER REDUCED LOAD BATTERY VOLTAGE VLOGIC BATTLO
1998 F04
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Figure 4. LTC1998 Function Plot
S6 Package 6-Lead Plastic TSOT-23
1.22 REF
1.4 MIN
2.80 BSC
1.50 - 1.75 (NOTE 4) PIN ONE ID
0.95 BSC
0.30 - 0.45 6 PLCS (NOTE 3)
0.01 - 0.10
0.30 - 0.50 REF
S6 TSOT-23 0302
1998f
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LTC1998
TYPICAL APPLICATIO S
Single Li-Ion Cell Low Battery Detector
VBATT = 1.5V TO 4.2V REGULATOR VLOGIC = 1V TO 5V 1 BATT 5 4 VH.A VLOGIC LTC1998 3 R3 1% 6 VTH.A BATTLO GND 2
1998 TA01
+
Li-Ion
R1 1% R2 1%
0.1F
Li-Ion
Micropower 2.9V VCC Threshold Detector with 15mV Hysteresis
3.3V R1 715k 1% 4 R2 9.09k 1% 3 R3 274k 1%
1 BATT 5 VH.A VLOGIC LTC1998 VTH.A BATTLO GND 2 6 OUT
LOW THRESHOLD = 2.9V HYSTERESIS = 15mV
Low Battery Load Reduction Circuit
REGULATOR R1 787k 1% 4 R2 68.1k 1% 3 R3 147k 1%
+
Li-Ion
1 BATT 5 VH.A VLOGIC LTC1998 6 VTH.A BATTLO GND 2
LOW THRESHOLD = 2.7V HYSTERESIS = 100mV
RELATED PARTS
PART NUMBER LTC1440/LTC1540 LTC1441/LTC1442 LTC1443/LTC1444/LTC1445 DESCRIPTION Micropower Comparator with 1% Reference Micropower Dual Comparator with 1% Reference Micropower Quad Comparator with 1% Reference COMMENTS 1.182V 1% Reference, 10mV (Max) Input Offset 1.182V 1% Reference (LTC1442) LTC1443 has 1.182V Reference, LTC1444/LTC1445 have 1.221V Reference and Adjustable Hysteresis
1998f LT/TP 0802 2K * PRINTED IN USA
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
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Backup Battery Switchover Circuit
2.5V TO 4.2V R1 787k 1% 4 R2 68.1k 1% 3 R3 147k 1% 1 BATT 5 VH.A VLOGIC LTC1998 VTH.A BATTLO GND 2 6 BAT54C BAT54C R4 1M MBRM120 VOUT Si2301
+
P
Si2301
+
3V BACKUP BATTERY
SWITCHES TO BACKUP BATTERY WHEN PRIMARY FALLS BELOW 2.7V. SWITCHES BACK TO PRIMARY WHEN VOLTAGE RECOVERS TO 2.8V
1998 TA04
High Accuracy Window Comparator with Dual Hysteresis
VIN R1 619k 1% 4 R2 6.04k 1% 3
1998 TA03
V+
1 BATT 5 VH.A VLOGIC LTC1998 VTH.A BATTLO GND 2 6 2N7002
R7 1M VOUT VOUT = V + WHEN 2.6V VIN 3.1V
R3 383k 1%
R4 909k 1% 4
CRITICAL CIRCUITRY
1 BATT 5 NC VH.A VLOGIC LTC1998 VTH.A BATTLO GND 2 6 WINDOW LOW THRESHOLD = 2.6V HYSTERESIS = 10mV WINDOW HIGH THRESHOLD = 3.1V HYSTERESIS = 10mV
1998 TA06
Si2301
R5 6.98k 1% 3 R6 76.8k 1%
NONCRITICAL CIRCUITRY
1998 TA05
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(c) LINEAR TECHNOLOGY CORPORATION 2001

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