LTC1998 2.5µA, 1% Accurate SOT-23 Comparator and Voltage Reference for Battery Monitoring U FEATURES ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO High Accuracy Trip Voltage: 1% Max Error Using External 1% Resistors Adjustable Threshold Voltage and Hysteresis Quiescent Current: 2.5µA 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 U APPLICATIO 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. The LTC®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. W BLOCK DIAGRA Threshold Voltage Error vs Temperature 1.0 BATT 0.9 0.7 THRESHOLD ADJUST R BATTLO VTH.A % ERROR 1.1R VHYST.A VTH.A SET BY 1% EXTERNAL R, THRESHOLD = 3V 0.8 VLOGIC 0.6 0.5 0.4 VTH.A = 1V THRESHOLD = 3V 0.3 1.2V 0.2 VTH.A SHORTED TO GROUND, THRESHOLD = 2.5V 0.1 1998 BD 0 –45 –25 35 15 55 –5 TEMPERATURE (°C) 75 95 1998 G05 1998f 1 LTC1998 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) 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) ...–40°C to 85°C Specified Temperature Range (Note 4) LTC1998C ...........................................–40°C to 85°C LTC1998I .............................................–40°C to 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C TOP VIEW BATT 1 6 BATTLO GND 2 5 VLOGIC VTH.A 3 4 VH.A ORDER PART NUMBER LTC1998CS6 LTC1998IS6 S6 PART MARKING* LTTY S6 PACKAGE 6-LEAD PLASTIC SOT-23 TJMAX = 150°C, θJA = 250°C/W *The temperature grades are indentified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V GND = 0V, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Power Supply Supply Voltage Range-BATT Supply Voltage Range-VLOGIC ● 1.5 ● 1 5.5 V VBATT V 2.5 3.5 4.2 4.5 µA µA µA 3 4.3 5.2 5.5 µA µA µA ● 0.6 0.8 0.85 1 % % Supply Current, VBATT = 3V, VTH.A = 1.5V TA = 25°C LTC1998CS6 LTC1998IS6 ● ● Supply Current, VBATT = 5.5V, VTH.A = 1.5V TA = 25°C LTC1998CS6 LTC1998IS6 ● ● Monitor Threshold Accuracy Hysteresis Accuracy VBATT.Th = 2.5V, Pin 3 Shorted to Ground VBATT.Th = 3V, Pin 3 Driven by Precision Voltage Source to 1V LTC1998C LTC1998I ● ● 0.5 0.6 0.61 0.71 % % VBATT.Th = 3V, VTH.A = 1V (Note 5) Programmed with 1% Max External Resistors LTC1998C LTC1998I ● ● 0.8 0.9 1 1.1 % % VBATT.Th = 3.25V, Pin 3 Diven by Precision Voltage Source to 1.5V LTC1998C LTC1998I ● ● 0.6 0.7 0.65 0.85 % % VBATT.Th = 3.25V, VTH.A = 1.5V (Note 5) Programmed with1% Max External Resistors LTC1998C LTC1998I ● ● 0.9 1 1.1 1.3 % % 5 mV mV 750 mV VHYST ≤ 250mV 250mV ≤ VHYST ≤ 750mV Allowable Hysteresis Range (Note 2) ● ● –5 ● 10 ±5 µs µs Propagation Delay COUT = 100pF, Overdrive = 10mV Overdrive = 100mV 350 150 Threshold Adjust Pin Leakage, ITH.A VTH.A ≤ 1.5V ● 0.01 1 nA Hysteresis Adjust Pin Leakage, IH.A VH.A ≤ 1.5V ● 0.01 1 nA BATTLO High Voltage IOUT = –1mA ● BATTLO Low Voltage IOUT = 1mA, VBATT ≥ 2V ● BATTLO Low Voltage IOUT = 0.25mA, VBATT = 1V ● Output VLOGIC – 0.3 V 0.2 0.3 V V 1998f 2 LTC1998 ELECTRICAL CHARACTERISTICS Note 4: The LTC1998C is guaranteed to meet specified performance from 0°C to 70°C. The LTC1998C is designed, characterized and expected to meet specified performance from –40°C to 85°C but is not tested or QA sampled at these temperatures. The LTC1998I is guaranteed to meet specified performance from –40°C to 85°C. Note 5: This parameter is not 100% tested. 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 – 40°C to 85°C. U W TYPICAL PERFOR A CE CHARACTERISTICS Quiescent Supply Current vs Supply Voltage 3.0 3.5 TA = 25°C VLOGIC = VBATT 3.0 SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) VTH.A = 1.5V 2.5 3.5 VBATT = VLOGIC = 3V VTH.A = 0V 2.0 1.5 1.0 THRESHOLD VOLTAGE (V) 3.5 Threshold Voltage vs Threshold Adjust Voltage Quiescent Supply Current vs Temperature 2.5 VTH.A = 1.5V 2.0 1.5 1.0 3.0 0.5 0.5 0 –50 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) 2.5 –30 –10 10 30 50 TEMPERATURE (°C) 70 90 0 1998 G03 1998 G02 1998 G01 Available Hysteresis vs Threshold Voltage Threshold Voltage Error vs Temperature Input Current vs Temperature 1.0 750 10000 0.7 250 0.6 0.5 0.4 VTH.A = 1V THRESHOLD = 3V 0.3 0.2 VTH.A SHORTED TO GROUND, THRESHOLD = 2.5V INPUT CURRENT VTH.A, VH.A (pA) VTH.A SET BY 1% EXTERNAL R, THRESHOLD = 3V 0.8 % ERROR AVAILABLE HYSTERESIS (mV) 0.9 500 1.5 0.5 1.0 THRESHOLD ADJUST VOLTAGE (V) VIN = 1.5V 1000 VIN = 1V 100 VIN = 0.5V 10 1 0.1 0 2.5 3.25 2.75 3.0 LOW BATTERY THRESHOLD VOLTAGE (V) 1998 G04 0 –45 –25 35 15 55 –5 TEMPERATURE (°C) 75 95 1998 G05 0.1 35 45 55 65 75 85 95 105 115 125 TEMPERATURE (°C) 1998 G06 1998f 3 LTC1998 U W TYPICAL PERFOR A CE CHARACTERISTICS Output Low Voltage vs Load Current Output High Voltage vs Load Current OUTPUT VOLTAGE (V) TA = 25°C VLOGIC = VBATT = 3V TA = 85°C 0.4 TA = 25°C 0.2 TA = –40°C 120 0 TA = 85°C TA = 25°C TA = –40°C –50 –100 TA = –40°C TA = 25°C –150 TA = 85°C –200 TA = 25°C VLOGIC = VBATT –250 0 1 2 3 4 OUTPUT SINK CURRENT (mA) 5 100 CURRENT (mA) OUTPUT VOLTAGE RELATIVE TO VBATT (mV) 0.6 Output Short-Circuit Current vs Supply Voltage 1 2 3 4 OUTPUT SOURCE CURRENT (mA) 1998 G07 80 60 5 1998 G08 SOURCE CURRENT, BATTLO SHORTED TO GND 40 20 BATT = 3V BATT = 5V TA = 25°C VBATT = VLOGIC SINK CURRENT, BATTLO SHORTED TO VLOGIC 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 U U U 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. U 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. 1998f 4 LTC1998 U 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: 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 4.2µA maximum resistor current. RTOTAL = 1MΩ, R1 = 786k, R2 = 66k and R3 = 148k Choose standard 1% values. R1 = 787k, R2 = 66.5k, R3 = 147k 1.5V TO 4.2V RTOTAL = R1 + R2 + R3 = 4.2V IR + Li-Ion 5V R1 = RTOTAL • – 1 VBATT .Th + VHYST VLOGIC 0.1µF R1 1% 4 R2 1% 1 BATT 5 VH.A VLOGIC µP LTC1998 3 R3 1% 5V R2 = RTOTAL • – 1 – R1 VBATT .Th R3 = RTOTAL – R1 – R2 REGULATOR 6 VTH.A BATTLO GND 2 1998 F01 Figure 1. Low Battery Threshold Detector with Hysteresis U W U U APPLICATIO S I FOR ATIO 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 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. + 1 BATT R1 Li-Ion LOW BATTERY THRESHOLD VOLTAGE AND HYSTERESIS ADJUST 3 R2 VTH.A LTC1998 2 1998 F02 Figure 2. Resistor Divider Sets Threshold 1998f 5 LTC1998 U W U U 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 4.1µA 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. 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 + 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. 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). 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 Hysteresis Adjustment, Pin 4. (VH.A ) 2 R1 4 1 BATT VH.A LTC1998 R2 3 VTH.A R3 1998 F03 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 6 LTC1998 U W U U APPLICATIO S I FOR ATIO 5V R1 = (R1 + R2 + R3) – 1 VTH2 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 10kΩ. The output will then act as an open-drain device. 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. 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 HYSTERESIS PROGRAMMABLE THRESHOLD RANGE PROGRAMMED LOW BATT THRESHOLD 2.50V BATTERY VOLTAGE RECOVERS UNDER REDUCED LOAD BATTERY VOLTAGE VERSATILE OUTPUT DRIVER VLOGIC VLOGIC, BATTLO (Pins 5,6) BATTLO The LTC1998 uses a CMOS push-pull output stage to drive the low battery output signal. This output pin (BATTLO) 1998 F04 Figure 4. LTC1998 Function Plot U PACKAGE DESCRIPTIO S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 0.62 MAX 2.90 BSC (NOTE 4) 0.95 REF 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 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 0.30 – 0.45 6 PLCS (NOTE 3) 0.95 BSC 0.20 BSC 0.01 – 0.10 1.00 MAX DATUM ‘A’ 0.80 – 0.90 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) 1.90 BSC S6 TSOT-23 0302 1998f 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. 7 LTC1998 U TYPICAL APPLICATIO S Backup Battery Switchover Circuit Single Li-Ion Cell Low Battery Detector VLOGIC = 1V TO 5V VBATT = 1.5V TO 4.2V REGULATOR 0.1µF 1 BATT 5 4 VH.A VLOGIC R2 1% LTC1998 3 R3 1% + Li-Ion R1 1% Li-Ion + MBRM120 2.5V TO 4.2V µP 6 VTH.A BATTLO GND 2 R1 787k 1% 4 R2 68.1k 1% 3 R3 147k 1% VOUT BAT54C R4 1M 1 BATT 5 VH.A VLOGIC Si2301 Si2301 LTC1998 VTH.A BATTLO GND 2 BAT54C 6 + 3V BACKUP BATTERY 1998 TA01 SWITCHES TO BACKUP BATTERY WHEN PRIMARY FALLS BELOW 2.7V. SWITCHES BACK TO PRIMARY WHEN VOLTAGE RECOVERS TO ≥ 2.8V 1998 TA04 Micropower 2.9V VCC Threshold Detector with 15mV Hysteresis High Accuracy Window Comparator with Dual Hysteresis 3.3V R1 715k 1% 4 R2 9.09k 1% 3 R3 274k 1% 1 VIN BATT 5 VH.A VLOGIC R1 619k 1% 4 LTC1998 VTH.A BATTLO GND 2 6 OUT R2 6.04k 1% 3 LOW THRESHOLD = 2.9V HYSTERESIS = 15mV R3 383k 1% 1998 TA03 Low Battery Load Reduction Circuit R4 909k 1% 4 REGULATOR Li-Ion + R1 787k 1% 4 R2 68.1k 1% 3 R3 147k 1% Si2301 1 BATT 5 VH.A VLOGIC CRITICAL CIRCUITRY LTC1998 6 VTH.A BATTLO GND 2 NONCRITICAL CIRCUITRY LOW THRESHOLD = 2.7V HYSTERESIS = 100mV R5 6.98k 1% 3 R6 76.8k 1% V+ 1 R7 1M BATT 5 VH.A VLOGIC VOUT LTC1998 VTH.A BATTLO GND 2 6 2N7002 VOUT = V + WHEN 2.6V ≤ VIN ≤ 3.1V 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 1998 TA05 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1440/LTC1540 Micropower Comparator with 1% Reference 1.182V ±1% Reference, ±10mV (Max) Input Offset LTC1441/LTC1442 Micropower Dual Comparator with 1% Reference 1.182V ±1% Reference (LTC1442) LTC1443/LTC1444/LTC1445 Micropower Quad Comparator with 1% Reference LTC1443 has 1.182V Reference, LTC1444/LTC1445 have 1.221V Reference and Adjustable Hysteresis 1998f 8 Linear Technology Corporation LT/TP 0802 2K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2001