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LTC1730-4/LTC1730-4.2 Lithium-Ion Battery Pulse Charger with Overcurrent Protection
FEATURES
s s s s s s s s s
DESCRIPTIO
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s s
Complete Pulse Charger for 1-Cell Lithium-Ion Batteries Sense Resistor Limits Maximum Current for Safety 1% Float Voltage Accuracy End-of-Charge (C/10) Detection Output Programmable Charge Termination Timer Internal 0.35 NMOS Switch No Blocking Diode Required SEL Pin to Set Either 4.1V or 4.2V/Cell (LTC1730-4) Low-Battery Drain (1A Max) when Input Supply Is Removed Battery Temperature Sensing and Charge Qualification Automatic Trickle Charge for Low-Battery Automatic Battery Refresh
The LTC(R)1730 is a complete pulse charger for 1-cell lithium-ion batteries. When charging a depleted cell, the internal MOSFET is fully on allowing the current limited input power source to provide charge current to the battery, virtually eliminating heat generation in the charger. As the battery accepts charge and approaches the programmed voltage, the internal MOSFET begins switching off and on with the duty cycle gradually decreasing as the battery approaches a fully charged condition. A programmable timer ends the charge cycle. The end-of-charge condition is indicated at the CHRG pin when the average charge current falls to C/10. Removing the input voltage puts the LTC1730 into a sleep mode, dropping the battery current drain to less than 1A (maximum). An external sense resistor limits the maximum charge current as a safety precaution against a user connecting a wall adapter with the incorrect or no current limit. The internal MOSFET prevents reverse battery current from flowing if the input voltage is shorted to ground, eliminating the need for a blocking diode. The LTC1730-4 is available in the 16-pin SSOP package and the LTC1730-4.2 is available in the 8-pin SO package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Standalone Lithium-Ion Battery Charger Handheld Computers Cellular Telephones
TYPICAL APPLICATIO
1A, Single Cell 4.2V Li-Ion Battery Charger (8-Pin Package)
VIN = 4.5V TO 12V WITH 1A CURRENT LIMIT R1 1k R3 4.1k CHARGE STATUS 3 CHRG SENSE 6 T R4 10k NTC* CTIMER 0.1F *NTC: DALE NTHS-1206N02
1730 TA01
2 VIN LTC1730ES8-4.2 GATE 7
R2 10k C3 0.047F
RSENSE 0.05
D3
0.022F 1 8 1-CELL Li-Ion BATTERY
NTC/SHDN
BAT
TIMER 5
GND 4
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4.7 C1 1F
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LTC1730-4/LTC1730-4.2
ABSOLUTE
AXI U RATI GS
Supply Voltage (VCC) ............................................ 13.2V SENSE, GATE, BAT, TIMER, NTC/SHDN, SEL ............................ - 0.3V to VCC CHRG, ACPR, FAULT ..............................- 0.3V to 13.2V
TOP VIEW GND* SENSE VCC ACPR FAULT CHRG NC** GND* 1 2 3 4 5 6 7 8 16 GND* 15 BAT 14 NC** 13 GATE 12 SEL 11 NTC/SHDN 10 TIMER 9 GND*
ORDER PART NUMBER LTC1730EGN-4
GN PART MARKING 17304
GN PACKAGE 16-LEAD PLASTIC SSOP * FOUR CORNER PINS ARE FUSED TO INTERNAL DIE ATTACH PADDLE FOR HEAT SINKING. CONNECT THESE FOUR PINS TO EXPANDED PC LANDS FOR PROPER HEAT SINKING. ** NO INTERNAL CONNECTION
TJMAX = 125C, JA = 90C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
DC ELECTRICAL CHARACTERISTICS
SYMBOL VCC ICC PARAMETER Supply Voltage Supply Current CONDITIONS
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 6V unless otherwise noted.
MIN
q
Charger On; Fast Charge Mode Shutdown: VNTC/SHDN = 0V Sleep Mode; VBAT = 4V LTC1730ES8-4.2 (5V VCC 12V) LTC1730EGN-4 (5V VCC 12V), SEL = GND LTC1730EGN-4 (5V VCC 12V), SEL = VCC RSENSE = 0.1 VBAT = 2V (VCC - VBAT) Low to High (VCC - VBAT) High to Low VBAT = 4V NTC/SHDN Pin High to Low
VBAT
Regulated Output Voltage
IMAX ITRICKL VTRICKL VASD RDS(ON) VSHDN
Maximum Charge Overcurrent Trickle Charge Current Trickle Charge Trip Threshold Automatic Shutdown Threshold Voltage (Sleep Mode) Internal Switch On-Resistance Shutdown Threshold Voltage
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WW
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(Note 1)
Operating Junction Temperature Range (Note 2) .................. - 40C to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
TOP VIEW SENSE 1 ACPRB 2 VIN 3 GND 4 8 7 6 5 BAT GATE CHRG TIMER
ORDER PART NUMBER LTC1730ES8-4.2
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 125C, JA = 110C/W
S8 PART MARKING 173042
TYP 2 2
MAX 12 5 5 1 4.242 4.141 4.242 1.3 60 2.55 150
UNITS V mA mA A V V V A mA V mV mV mV
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4.5
q q q q q q q
4.158 4.059 4.158 0.7 15
4.2 4.1 4.2 1 35 2.45
0 0.35 50
LTC1730-4/LTC1730-4.2
DC ELECTRICAL CHARACTERISTICS
SYMBOL ICHRG TTIMER VGATE TSHDN TSHDN VRECHRG VNTC_HOT VNTC_COLD VSEL VACPR VFAULT VCHRG PARAMETER CHRG Pin Pull-Down Current TIMER Accuracy GATE Pin Voltage Thermal Shutdown Temperature Thermal Shutdown Hysteresis Recharge Battery Voltage Offset from Full Charged Battery Voltage NTC/SHDN Pin Threshold Voltage (Hot) NTC/SHDN Pin Threshold Voltage (Cold) SEL Pin Threshold ACPR Pin Output Low Voltage FAULT Pin Output Low Voltage CHRG Pin Output Low Voltage VBAT(Full Charged) - VRECHRG (Note 3) High to Low; VCC = 4V Hysteresis Low to High; VCC = 4V Hysteresis LTC173ECGN-4 LTC1730EGN-4, IACPR = 5mA LTC1730EGN-4, IFAULT = 3mA ICHRG = 5mA, Charging Mode
q q
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 6V unless otherwise noted.
CONDITIONS VCHRG = 1V, C/10 Mode CTIMER = 0.1F VBAT = 3V VBAT = 4V 7.5 10 140 5 150 1.95 3.4 2 50 3.5 45 0.7 0.6 1.2 0.9 2.05 3.6 MIN 10 TYP 40 MAX 70 10 UNITS A % V V C C mV V mV V mV V V V V
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC1730-4/LTC1730-4.2 are guaranteed to meet performance specifications from 0C to 70C. Specifications over the - 40C to 85C
operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: For the LTC1730-4 version, the full charged VBAT value is typically 4.1V.
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LTC1730-4/LTC1730-4.2 TYPICAL PERFOR A CE CHARACTERISTICS
Trickle Charge Current vs Input Supply Voltage
50 45 40 TA = 25C 2.50
VTRIKL (V)
I (mA)
I (mA)
35 30 25 20
5
6
7
9 8 VCC (V)
10
Internal Switch On-Resistance vs Temperature
0.50 VBAT = 4V 0.45 0.40
RDS(ON) () tTIMER (%)
100 95 90
IMAX (A)
0.35 0.30
0.25 0.20 -50
-25
50 25 75 0 TEMPERATURE (C)
Battery Recharge Threshold Offset from VBAT vs Temperature
300 VCC = 6V 250 0.9 0.8 1.0
VRECHRG (mV)
200 VCHRG (V) 0.7 0.6 0.5 0.4 0.3 -50 150 100 50 0 -50 -25
0
4
UW
11 12
1730 G01
Trickle Charge Threshold Voltage vs Temperature
50
VCC = 6V
Trickle Charge Current vs Temperature
VCC = 6V 45 40
2.48
2.46
35 30
2.44
2.42
25 20 -50
2.40 -50
-25
50 25 75 0 TEMPERATURE (C)
100
125
-25
50 25 75 0 TEMPERATURE (C)
100
125
1730 G02
1730 G03
Timer Accuracy vs Temperature
115 110 105 VCC = 6V CTIMER = 0.1F 1.3 1.2 1.1 1.0 0.9 0.8 0.7
Overcurrent vs Temperature
VCC = 6V RSEN = 0.1
85 80 -50
100
125
-25
50 25 75 0 TEMPERATURE (C)
100 125
1730 G06
0.6 -50
-25
50 25 75 0 TEMPERATURE (C)
100
125
1730 G05
1730 G07
CHRG Pin Output Low Voltage vs Temperature
25 50 75 100 125 150 TEMPERATURE (C)
1730 G09
-25
50 25 75 0 TEMPERATURE (C)
100
125
1730 G08
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LTC1730-4/LTC1730-4.2
PI FU CTIO S
LTC1730ES8-4.2 SENSE (Pin 1): Maximum Overcurrent Sense Input. A sense resistor (RSENSE) should be connected from VCC to the SENSE pin. When the voltage drop across RSENSE exceeds 100mV, the pass transistor immediately turns off and turns back on after a 400ms time-out period (CTIMER = 0.1F). The on-off cycle will continue, as long as the overcurrent condition persists or until the timer runs out. If overcurrent protection is not needed, short SENSE to VCC. VCC (Pin 2): Positive Input Supply Voltage (4.5V VCC 13.2V). Bypass this pin with a 1F capacitor in series with a 4.7 resistor. An RC network from the VCC pin to the GATE pin is also required. The capacitor controls the slew rate at the VCC pin, while the resistor limits the inrush current when the input voltage is first applied. When the pass transistor turns on, VCC ramps down in a controlled manner, with a slope equal to 10A/C. When the pass transistor turns off, VCC ramps up with a slope of 40A/C. CHRG (Pin 3): Open-Drain Charge Status Output. When a depleted battery is being charged, the CHRG pin is pulled to ground by an N-MOSFET capable of driving an LED. Once the duty cycle at the GATE pin drops below 10%, the N-MOSFET turns off and a weak 40A current source to ground turns on to indicate a near end-of-charge (C/10) condition. When a time-out occurs or the input supply is removed, the CHRG pin goes high impedance. GND (Pin 4): Electrical Ground Connection and provides a thermal path from the IC to the PC board copper. Use large copper pads and traces for maximum heat transfer. TIMER (Pin 5): Timer Set Pin. The timer period is set by a capacitor (CTIMER) to ground. The timer period is: tTIMER = (CTIMER * 3Hr)/(0.1F). The minimum ON time, OFF time and the overcurrent time-out period are all set by the same timer period. NTC/SHDN (Pin 6): Input to the NTC (Negative Temperature Coefficient) Thermistor Monitoring and Shutdown Circuitry. With an external 10k NTC thermistor to ground and a 1% resistor to VCC, this pin can sense the temperature of the battery pack and stop charging when the temperature is out of range. When the voltage at this pin drops below 0.5 * VCC, or 2V at hot temperature or rises above 0.875 * VCC, or 3.5V at cold (with VCC = 4V), the charge cycle is suspended and the internal timer is frozen. The CHRG pin output status is not affected in this hold state. When this pin is pulled below 50mV, the IC goes into the shutdown mode. The charging stops (the GATE pin is pulled to ground) the timer is reset and the CHRG pin goes into a high impedance state. GATE (Pin 7): Gate Drive Output Pin for Internal and External Pass Transistors. An external N-MOSFET transistor can be connected in parallel with the internal transistor to reduce the on-resistance for higher charge current. In this case, an external blocking diode is required to prevent damage to the battery if VCC is shorted to ground. A 10A current source pulls this pin up to the charge pump potential when turned on and a 40A current source pulls it down to ground to turn it off. If an overcurrent condition is detected, the GATE pin is immediately pulled to ground. A series RC network from the GATE to the VCC pin is required to control the slew rate at the VCC pin when the switch is turned on or off. The slew rate control prevents excessive current from the capacitor located in the wall adapter from flowing into the battery when the pass transistor is turned on. The voltage at this pin is internally clamped to 12V above the BAT pin. BAT (Pin 8): Battery Sense Input Pin. This pin is clamped to 4.7V if the battery is disconnected while charging. An internal resistor divider presets the final float voltage to 4.2V. If the voltage at the BAT pin drops 150mV below final float voltage after the charge cycle has ended, the timer resets and a new charge cycle begins. LTC1730EGN-4 GND (Pins 1, 8, 9, 16): Refer to LTC1730ES8-4.2 SENSE (Pin 2): Refer to LTC1730ES8-4.2 VCC (Pin 3): Refer to LTC1730ES8-4.2 ACPR (Pin 4): Wall Adapter Present Open-Drain Output. When the input voltage (wall adapter) is applied to the LTC1730, this pin is pulled to ground by an internal
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LTC1730-4/LTC1730-4.2
PI FU CTIO S
N-channel MOSFET. This output can sink up to 5mA suitable for driving an LED. FAULT (Pin 5): Fault Condition Detection Open-Drain Output. This output can sink up to 3mA suitable for driving an external LED. The internal N-channel MOSFET pulls this pin to ground when either one of the following conditions is detected: 1. The voltage at the NTC pin is out of the normal operation range. This usually means the battery pack temperature is too high or too low. Once the temperature is back to normal, the FAULT pin becomes high impedance. 2. The BAT pin potential stays below 2.45V for more than 1/4 of the programmed charge time. When this condition is detected, the FAULT pin is pulled low and latched. CHRG (Pin 6): Refer to LTC1730ES8-4.2 NC (Pins 7, 14): No Internal Connection. Connecting these pins to ground will help transfer heat from the package. TIMER (Pin 10): Refer to LTC1730ES8-4.2 NTC/SHDN (Pin 11): Refer to LTC1730ES8-4.2 SEL (Pin 12): 4.1V/4.2V Battery Selection Input. Grounding this pin will set the output float voltage to 4.1V, while connecting to VCC will set the voltage to 4.2V. GATE (Pin 13): Refer to LTC1730ES8-4.2 BAT (Pin 15): Refer to LTC1730ES8-4.2
BLOCK DIAGRA
CHRG
N1 40A Q-PUMP (3X) 0.125R 40mV C/10 COLD 0.375R STOP IMAX ACPR
- +
NTC/SHDN
- +
0.5R
+
121mV
-
C1 VMIN FAULT ON RECHRG C9
OSCILLATOR FAULT
ACPR
6
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VCC
100mV C5
+ -
35mA
+ -
SENSE GATE
+ -
NSW
C6
C4
+ -
BAT
C7 LOGIC HOT VMAX
C3
- +
R1
C8 SHDN VBAT
C2
- +
R2
CLK
- +
R3
R5 R4 SEL
+
4.1V/4.2V
-
-+
150mV
1.21V
1703 BD
TIMER
GND
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LTC1730-4/LTC1730-4.2
OPERATIO
The LTC1730 is a complete lithium-ion battery pulse charger with an internal 0.35 N-MOSFET switch driven by an internal charge pump. The charge current is set by the current limit of the input supply (wall adapter). An external RSENSE sets the maximum allowable charge over current (IMAX = 0.1V/RSENSE) and prevents a wall adapter with the wrong current limit from damaging the battery. If the current limit of the input supply is above IMAX, the charging will be immediately terminated and will retry after 400ms (CTIMER = 0.1F). If the battery is disconnected while in fast charge mode, the N-channel MOSFET turns off when the voltage at the BAT pin rises above 4.7V, and turns back on when the voltage drops below the float voltage. A charge cycle begins when the voltage at the VCC pin rises above the BAT pin by 40mV and the voltage at the NTC/ SHDN pin is in between 0.5 * VCC and 0.875 * VCC. The charger will go into trickle charge mode if the battery voltage is below 2.45V. The trickle charge current is preset to 35mA and is provided by an internal current source. In trickle mode, the charge pump and pass transistor are off. When the battery voltage exceeds 2.45V, the charger goes into the fast charge mode. In this mode, the charge pump turns on and ramps up the gate voltage of the pass transistor turning it on. The voltage at the VCC pin then ramps down to VBAT plus the voltage drop across the pass transistor and RSENSE, thus reducing the power dissipation in the pass transistor. The charge current is determined by the current limit of the input supply.
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When the battery voltage reaches the final float voltage, the pass transistor turns off for 100ms (minimum offtime). It remains off as long as the battery voltage stays above the float voltage after the 100ms off-time. After the minimum off-time, if the battery voltage drops below the float voltage, the pass transistor turns back on for at least 380ms (minimum on-time). As the battery approaches full charge, the off-time will get longer and the on-time will stay at 380ms. The voltage at the BAT pin will be slightly higher than the final float voltage due to the ESR associated with the battery pack. This voltage level should not turn on the overvoltage protection circuitry often located in the battery pack. When the duty cycle at the GATE pin drops below 10%, a comparator turns off the N-FET at the CHRG pin and connects a weak current source (40A) to ground to indicate a near end-of-charge (C/10) condition. The pulse charging will continue until the timer stops. An external capacitor at the TIMER pin sets the total charge time, the minimum on- and off-time and the overcurrent retry period. After a time-out has occurred, the charge cycle is terminated and the CHRG pin is forced high impedance. To restart the charge cycle, momentarily pull the NTC/SHDN pin below 50mV or remove and reapply the input voltage. After the charging stops, if the battery voltage drops 150mV below the final float voltage, due to external loading or internal leakage, a new charge cycle will automatically begins. The charger can be shut down by pulling the NTC/SHDN pin to ground. When the input voltage is not present, the charger goes into a sleep mode, dropping battery drain current to less than 1A.
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LTC1730-4/LTC1730-4.2
APPLICATIO S I FOR ATIO
Stop Charging The charger is off when any of the following conditions exist. The voltage at the VCC pin is less than 40mV above VBAT (sleep mode), or the potential at the NTC/SHDN pin is less than 50mV (shutdown mode). The trickle charge current source and the internal pass transistor are turned off. The internal resistor divider is disconnected to reduce the current drain on the battery when in sleep mode. Input Voltage (Wall Adapter) The input voltage to the LTC1730 must have some method of current limit capability. The current limit level of the input power source must be lower than the overcurrent limit (IMAX) set by the sense resistor (IMAX = 100mV/RSENSE). If a wall adapter without current limit is used, or the current limit level is above IMAX, the charger will turn on briefly and then immediately turn off after the overcurrent condition is detected. This cycle will be resumed every 400ms (CTIMER = 0.1F) until the total charge time has run out. If overcurrent protection is not needed, short the SENSE pin to VCC. Trickle Charge and Defective Battery Detection At the begining of the charge cycle, if the cell voltage is low (less than 2.45V) the charger goes into a 35mA trickle charge mode. If the low cell voltage persists for one quarter of the total charge time, the battery is considered defective and the charge cycle is terminated. The CHRG pin output is then forced to a high impedance state. Battery Charge Current The battery charge current is determined by the current limit of the input supply (wall adapter). However, this current must not exceed the maximum charge overcurrent, IMAX. If an overcurrent condition is detected, the charging is immediately terminated, the GATE pin is pulled to ground and the charge pump turns off. The charging will resume after a 400ms time off (CTIMER = 0.1F). Programming the Timer The programmable timer is used to terminate the charge and sets the minimum ON/OFF time and the overcurrent time-off period. The length of the timer is programmed by When the LTC1730 is in charge mode, the CHRG pin is pulled to ground by an internal N-MOSFET. To detect this mode, force the digital output pin, OUT, high and measure the voltage at the CHRG pin. The N-MOSFET will pull the pin low even with a 2k pull-up resistor. Once the charge current drops below 10% of the full scale current (C/10), the N-MOSFET is turned off and a 40A current source is connected to the CHRG pin. By forcing the OUT pin to a high impedance state, the current source will pull the pin low through the 620k resistor. When the internal timer has expired, the CHRG pin becomes high impedance and the 620k resistor will pull the pin high to indicate that charging has stopped.
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an external capacitor from the TIMER pin to ground. The total charge time is: Time (Hours)= (3 Hour)(CTIMER/0.1F) The timer starts when the input voltage (at least 40mV greater than VBAT) is applied and the potential at the NTC/ SHDN pin is between 0.5 * VCC and 0.875 * VCC. After a time-out has occurred, the charging stops and the CHRG pin becomes high impedance. CHRG Status Output Pin This open-drain output requires a pull-up resistor and can be used to indicate three charging conditions. When fast charging begins, an N-FET (capable of driving an LED) turns on, pulling this pin to ground. Once the duty cycle at the GATE pin drops below 10%, the N-FET turns off and a 40A current source to ground turns on. When a time-out occurs or the input supply is removed, the CHRG pin goes high impedance indicating that the charge cycle has ended. By using two different value resistors, a microprocessor can detect three states from this pin: charging, C/10 and stop charging (see Figure 1).
V+ 2 VCC LTC1730 CHRG 3 620k 2k MICROPROCESSOR OUT IN
1730 F01
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VDD
Figure 1. Interfacing with Microprocessor
LTC1730-4/LTC1730-4.2
APPLICATIO S I FOR ATIO
End-of-Charge (C/10) The LTC1730 includes a comparator to monitor the duty cycle at the GATE pin to detect a near end-of-charge condition. When the duty cycle falls below 10%, the comparator trips and turns off the N-MOSFET at the CHRG pin and switches in a weak (40A) current source to ground. The end-of-charge comparator is disabled in trickle charge mode. Internal Pass Transistor An N-channel MOSFET (0.35) is included in the LTC1730 as the pass transistor. The gate of the MOSFET is controlled by an internal charge pump. The body is connected to ground instead of source terminal. There is no body diode from the BAT pin back to the VCC pin; therefore, no blocking diode is required in series with the battery or the input supply. This will not only reduce the cost but also the heat generated when in fast charge mode. An internal thermal shutdown circuit turns off the pass transistor if the die temperature exceeds approximately 140C with 5C of thermal hysteresis. Gate Drive The pass transistor gate drive consists of a regulated 10A current source charge pump. A series RC network is required from the GATE pin to the VCC pin. When the pass transistor is turned on, the voltage at the VCC pin starts slewing down to a voltage equal to VBAT plus the voltage drop across the pass transistor and RSENSE. The slew rate is equal to 10A/C. By ramping the VCC pin down slowly, the inrush current is reduced. The resistor in series with the capacitor is required to limit the transient current when the input supply is first applied. When the charge pump is turned off, a 40A current source to ground starts pulling the GATE voltage down. Once the pass transistor is off, the voltage at the VCC pin begins slewing up with the rate equal to 40A/C. With this external capacitor, the voltage at the VCC pin is ramping at a controlled manner (Figure 2). For higher current applications an external power N-MOSFET can be connected in parallel with the internal pass transistor. Because the charge pump output is clamped to 12V
VCC 40A/C GATE VOLTAGE 10A/C
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10A/C 40A/C 10A/C 40A/C
1730 TA02
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Figure 2. Slew Rate at GATE and VCC Pins with the RC Network from GATE to VCC
above VBAT, the external N-MOSFET gate to source breakdown voltage should be rated at 20V or more. Battery Temperature Detection A negative temperature coefficient (NTC) thermistor located close to the battery pack can be used to monitor battery temperature and will not allow charging unless the battery temperature is within an acceptable range. Connect a 10k thermistor between ground and the NTC/SHDN pin and a 4.1k resistor from the NTC/SHDN pin to VCC. If the temperature rises to 50C, the resistance of the thermister will be approximately 4.1k (Dale NTHS-1206N02) and the LTC1730 will go into a hold mode. For cold temperatures, the threshold of the hold mode is at 0C (RNTC 28k). The pass transistor turns off and the timer is frozen at hold mode while the output status at the CHRG pin remains the same. The charge cycle begins or resumes once the temperature is within the acceptable range. Thermal Considerations The power handling capability is limited by the maximum rated junction temperature (125C) and the amount of PC board copper used as a heat sink. The power dissipated by the device consists of two components: 1. Input supply current multiplied by the input voltage 2. The voltage drop across the switch (SENSE pin to BAT pin) multiplied by the charge current The LTC1730 has internal thermal shutdown designed to protect the IC from overtemperature conditions. For continuous charging in the fast charge mode, the maximum junction temperature must not be exceeded. It is important to give careful consideration to all sources of thermal resistance from junction to ambient. Additional heat sources mounted nearby must also be considered.
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LTC1730-4/LTC1730-4.2
APPLICATIO S I FOR ATIO
Surface mount packages rely primarily on the copper leads (pins) to conduct the heat from the package to the surrounding PC board copper which is acting as a heat sink. The ground pin is especially important for conducting heat as well as providing an electrical connection. Use generous amounts of copper around the ground pin and also consider feedthrough vias (plated through holes) to backside or inner copper layers to maximize power dissipation. Table 1 lists the thermal resistance for the SO-8 package. Measured values of thermal resistance for several different board sizes and copper areas are listed. All measurements were taken in still air on 0.062" FR-4 board with one ounce copper. Calculating Junction Temperature Example: Find the maximum junction temperature for a battery voltage of 4V (VCC will collapse to approximately VBAT in the fast charge mode), charge current of 1A and a maximum ambient temperature of 75C. The power dissipated by the IC is: P = (IBAT * IBAT * RDS(ON)) + (VCC * ICC) = (1A * 1A * 0.35) + (4V * 1mA) = 0.35 + 0.004 = 0.354W The SO-8 package for the LTC1730 features a special lead frame with a lower thermal resistance and higher allowable power dissipation. The junction-to-ambient thermal resistance of this package when soldered to a PC board is approximately 80C/W depending on the copper area. So the junction temperature rise above ambient will be approximately: (0.354W)(80C/W) = 28.3C The maximum junction temperature is equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: TJMAX = 75C + 28.3C = 103.3C FAULT Output Pin (LTC1730EGN-4) The FAULT pin is pulled to ground when either one of the following conditions is detected: 1. The voltage at the NTC/SHDN pin is out of the operation range. With a 10k negative temperature coefficient thermistor placed near the battery pack, this pin indicates that the temperature of the pack is either too cold or too hot and the charger is suspended. Once the temperature is back to the operational range, the FAULT pin becomes high impedance and the charging resumes. 2. The voltage at the BAT pin stays below 2.45V for 1/4 of the programmed charge time. If VBAT remains low even with 35mA of trickle charge current for 1/4 of the total
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Table 1. SO-8 Package Thermal Resistance
COPPER AREA TOPSIDE BACKSIDE 2500mm2 1000mm2 250mm2 2500mm2 2500mm2 2500mm2 TOTAL BOARD AREA 2500mm2 2500mm2 2500mm2 THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 80C/W 80C/W 85C/W
*Device is mounted on topside.
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Output Voltage Selection (LTC1730EGN-4) The float voltage at the BAT pin can be selected by the SEL pin. Shorting the SEL pin to ground will set the float voltage to 4.1V, while connecting it to VCC sets it to 4.2V. This feature allows the charger to be used with different types of Li-Ion cells. ACPR Output Pin (LTC1730EGN-4) When the input voltage is 40mV higher than the voltage at the BAT pin, the ACPR pin is pulled low to ground to indicate that the input supply (wall adapter) is applied. After the input supply is removed, this pin becomes high impedance. An internal 80ms delay prevents the LTC1730 from turning off if the voltage at the VCC pin rings and gets too close to VBAT because of the parasitic inductance.
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LTC1730-4/LTC1730-4.2
APPLICATIO S I FOR ATIO
charge time, the battery is considered defective. The charger turns off and the FAULT pin is pulled low. This pin will stay low until the LTC1730 is reset by either removing the input power supply or momentarily
PACKAGE DESCRIPTIO
GN Package 16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
0.015 0.004 x 45 (0.38 0.10) 0.007 - 0.0098 (0.178 - 0.249) 0.016 - 0.050 (0.406 - 1.270) * DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 0 - 8 TYP
0.053 - 0.068 (1.351 - 1.727)
0.008 - 0.012 (0.203 - 0.305)
S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
0.189 - 0.197* (4.801 - 5.004) 0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP 0.053 - 0.069 (1.346 - 1.752) 8 0.004 - 0.010 (0.101 - 0.254) 0.228 - 0.244 (5.791 - 6.197) 0.150 - 0.157** (3.810 - 3.988) 7 6 5
0.014 - 0.019 (0.355 - 0.483) TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0.016 - 0.050 (0.406 - 1.270)
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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shutting down the charger. After reset, the charger is back in the charge mode and the FAULT pin becomes high impedance again.
0.189 - 0.196* (4.801 - 4.978) 0.004 - 0.0098 (0.102 - 0.249) 16 15 14 13 12 11 10 9 0.009 (0.229) REF 0.0250 (0.635) BSC 0.229 - 0.244 (5.817 - 6.198) 0.150 - 0.157** (3.810 - 3.988)
GN16 (SSOP) 1098
U
W
U
U
1
23
4
56
7
8
0.050 (1.270) BSC
SO8 1298
1
2
3
4
1730f
11
LTC1730-4/LTC1730-4.2
TYPICAL APPLICATIO S
Single Cell 4.2V Li-Ion Battery Charger (16-Pin Package)
VIN = 5V TO 12V WITH 600mA CURRENT LIMIT 3 VCC LTC1730EGN-4 6 4 5 11 VCC 12 10k NTC* SEL GND TIMER 10 0.1F *NTC: DALE NTHS-1206N02
1730 TA04
4.1k
CHARGE STATUS
*NTC: DALE NTHS-1206N02
RELATED PARTS
PART NUMBER LTC1731 LTC1732 LT1510-5 LTC1729 LTC1733 LTC1734 LTC4050 DESCRIPTION Li-Ion Linear Battery Charger Controller Li-Ion Linear Battery Charger Controller 500kHz CC/CV Switching Battery Charger Termination Controller for Li-Ion Li-Ion Battery Charger with Internal FET ThinSOT Li-Ion Battery Charger Li-Ion Linear Charger with Thermistor Interface COMMENTS CC/CV Charges Li-Ion Cells, 8-Lead MSOP Stand Alone Charger, Automatic Battery Detection, 10-Lead MSOP Most Compact, Up to 1.5A, Charges NiCd, NiMH, Li-Ion Cells Time or Charge Current Termination, Automatic Charger/Battery Detection Status Output, Preconditioning, 8-Lead MSOP 1.5A CC/CV, 10-Lead Enhanced MSOP, Thermal Regulation for Constant Temperature, No Blocking Diode, No Sense Resistor Required Only Two External Components, Up to 700mA ICHARGE, No Reverse Current Diode Required, No Sense Resistor Required Stand Alone Charger; 10-Lead MSOP, Up to 1A Charge Current
1730f LT/TP 0902 1K * PRINTED IN USA
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
q
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1k
1k
1k
4.7 10k 1F 0.047F SENSE GATE BAT 2 13 15 0.022F 0.1
CHRG ACPR FAULT NTC/SHDN
1, 8, 9,16
NC 7, 14
Li-Ion BATTERY
Using External N-MOSFET for Higher Charge Current
VIN = 5V TO 12V WITH 2A CURRENT LIMIT D1 MBRS120T3 2 R4 4.1k D3 3 6 R3 10k NTC* TIMER 5 CTIMER 0.1F
1730 TA03
R1 1k
VCC LTC1730ES8-4.2 SENSE CHRG NTC/SHDN GATE BAT 1 7 8
R2 10k C3 0.047F
4.7 RSENSE 25m C1 1F
Q1 Si2302DS
0.022F Li-Ion BATTERY GND 4
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2001

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