1730-4/4.2 layout

FEATURES
DESCRIPTIO
The LTC®1730 is a complete pulse charger for 1-cell Complete Pulse Charger for 1-Cell Lithium-Ion
lithium-ion batteries. When charging a depleted cell, the Batteries
internal MOSFET is fully on allowing the current limited Sense Resistor Limits Maximum Current for Safety
input power source to provide charge current to the 1% Float Voltage Accuracy
battery, virtually eliminating heat generation in the charger.
End-of-Charge (C/10) Detection Output
■ Programmable Charge Termination Timer
As the battery accepts charge and approaches the pro- ■ Internal 0.35Ω NMOS Switch
grammed voltage, the internal MOSFET begins switching ■ No Blocking Diode Required
off and on with the duty cycle gradually decreasing as the ■ SEL Pin to Set Either 4.1V or 4.2V/Cell (LTC1730-4) battery approaches a fully charged condition. A program- ■ Low-Battery Drain (1µA Max) when Input Supply Is mable timer ends the charge cycle. The end-of-charge condition is indicated at the CHRG pin when the average ■ Battery Temperature Sensing and Charge charge current falls to C/10. Removing the input voltage
puts the LTC1730 into a sleep mode, dropping the battery ■ Automatic Trickle Charge for Low-Battery current drain to less than 1µA (maximum).
An external sense resistor limits the maximum charge current as a safety precaution against a user connecting a APPLICATIO S
wall adapter with the incorrect or no current limit. Theinternal MOSFET prevents reverse battery current from ■ Standalone Lithium-Ion Battery Charger flowing if the input voltage is shorted to ground, eliminat- The LTC1730-4 is available in the 16-pin SSOP packageand the LTC1730-4.2 is available in the 8-pin SO package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
1A, Single Cell 4.2V Li-Ion Battery Charger (8-Pin Package)
ABSOLUTE AXI U
RATI GS (Note 1)
Temperature Range (Note 2) . – 40°C to 85°C Storage Temperature Range . – 65°C to 150°C Lead Temperature (Soldering, 10 sec). 300°C INTERNAL DIE ATTACH PADDLE FORHEAT SINKING. CONNECT THESE FOURPINS TO EXPANDED PC LANDS FORPROPER HEAT SINKING.
Consult LTC Marketing for parts specified with wider operating temperature ranges.
DC ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 6V unless otherwise noted.
PARAMETER
CONDITIONS
LTC1730EGN-4 (5V ≤ VCC ≤ 12V), SEL = GND LTC1730EGN-4 (5V ≤ VCC ≤ 12V), SEL = VCC DC ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 6V unless otherwise noted.
PARAMETER
CONDITIONS
∆VRECHRG Recharge Battery Voltage Offset from VNTC_COLD NTC/SHDN Pin Threshold Voltage (Cold) Note 1: Absolute Maximum Ratings are those values beyond which the life
operating temperature range are assured by design, characterization and correlation with statistical process controls.
Note 2: The LTC1730-4/LTC1730-4.2 are guaranteed to meet performance
Note 3: For the LTC1730-4 version, the full charged VBAT value is
specifications from 0°C to 70°C. Specifications over the – 40°C to 85°C TYPICAL PERFOR A CE CHARACTERISTICS
Trickle Charge Current vs Input
Trickle Charge Threshold Voltage
Trickle Charge Current vs
Supply Voltage
vs Temperature
Temperature
Internal Switch On-Resistance vs
Temperature
Timer Accuracy vs Temperature
Overcurrent vs Temperature
Battery Recharge Threshold Offset
CHRG Pin Output Low Voltage vs
from VBAT vs Temperature
Temperature
PI FU CTIO S
LTC1730ES8-4.2
above 0.875 • VCC, or 3.5V at cold (with VCC = 4V), thecharge cycle is suspended and the internal timer is frozen.
SENSE (Pin 1): Maximum Overcurrent Sense Input. A
The CHRG pin output status is not affected in this hold sense resistor (RSENSE) should be connected from VCC to the SENSE pin. When the voltage drop across RSENSEexceeds 100mV, the pass transistor immediately turns off When this pin is pulled below 50mV, the IC goes into the and turns back on after a 400ms time-out period (CTIMER shutdown mode. The charging stops (the GATE pin is = 0.1µF). The on-off cycle will continue, as long as the pulled to ground) the timer is reset and the CHRG pin goes overcurrent condition persists or until the timer runs out.
If overcurrent protection is not needed, short SENSE to GATE (Pin 7): Gate Drive Output Pin for Internal and
External Pass Transistors. An external N-MOSFET transis- VCC (Pin 2): Positive Input Supply Voltage (4.5V ≤ VCC ≤
tor can be connected in parallel with the internal transistor 13.2V). Bypass this pin with a 1µF capacitor in series with to reduce the on-resistance for higher charge current. In a 4.7Ω resistor. An RC network from the VCC pin to the this case, an external blocking diode is required to prevent GATE pin is also required. The capacitor controls the slew damage to the battery if VCC is shorted to ground. A 10µA rate at the VCC pin, while the resistor limits the inrush current source pulls this pin up to the charge pump current when the input voltage is first applied. When the potential when turned on and a 40µA current source pulls pass transistor turns on, VCC ramps down in a controlled it down to ground to turn it off. If an overcurrent condition manner, with a slope equal to 10µA/C. When the pass is detected, the GATE pin is immediately pulled to ground.
transistor turns off, VCC ramps up with a slope of 40µA/C.
A series RC network from the GATE to the VCC pin is CHRG (Pin 3): Open-Drain Charge Status Output. When a
required to control the slew rate at the VCC pin when the depleted battery is being charged, the CHRG pin is pulled switch is turned on or off. The slew rate control prevents to ground by an N-MOSFET capable of driving an LED.
excessive current from the capacitor located in the wall Once the duty cycle at the GATE pin drops below 10%, the adapter from flowing into the battery when the pass N-MOSFET turns off and a weak 40µA current source to transistor is turned on. The voltage at this pin is internally ground turns on to indicate a near end-of-charge (C/10)
condition. When a time-out occurs or the input supply is BAT (Pin 8): Battery Sense Input Pin. This pin is clamped
removed, the CHRG pin goes high impedance.
to 4.7V if the battery is disconnected while charging. An GND (Pin 4): Electrical Ground Connection and provides
internal resistor divider presets the final float voltage to a thermal path from the IC to the PC board copper. Use large copper pads and traces for maximum heat transfer.
If the voltage at the BAT pin drops 150mV below final float TIMER (Pin 5): Timer Set Pin. The timer period is set by a
voltage after the charge cycle has ended, the timer resets capacitor (CTIMER) to ground. The timer period is: tTIMER = (CTIMER • 3Hr)/(0.1µF). The minimum ON time,OFF time and the overcurrent time-out period are all set by LTC1730EGN-4
GND (Pins 1, 8, 9, 16): Refer to LTC1730ES8-4.2
NTC/SHDN (Pin 6): Input to the NTC (Negative Tempera-
ture Coefficient) Thermistor Monitoring and Shutdown
SENSE (Pin 2): Refer to LTC1730ES8-4.2
Circuitry. With an external 10kΩ NTC thermistor to ground VCC (Pin 3): Refer to LTC1730ES8-4.2
and a 1% resistor to VCC, this pin can sense the tempera- ACPR (Pin 4): Wall Adapter Present Open-Drain Output.
ture of the battery pack and stop charging when the When the input voltage (wall adapter) is applied to the temperature is out of range. When the voltage at this pin LTC1730, this pin is pulled to ground by an internal drops below 0.5 • VCC, or 2V at hot temperature or rises PI FU CTIO S
N-channel MOSFET. This output can sink up to 5mA condition is detected, the FAULT pin is pulled low and FAULT (Pin 5): Fault Condition Detection Open-Drain
CHRG (Pin 6): Refer to LTC1730ES8-4.2
Output. This output can sink up to 3mA suitable for driving NC (Pins 7, 14): No Internal Connection. Connecting these
an external LED. The internal N-channel MOSFET pulls this pins to ground will help transfer heat from the package.
pin to ground when either one of the following conditionsis detected: TIMER (Pin 10): Refer to LTC1730ES8-4.2
1. The voltage at the NTC pin is out of the normal operation NTC/SHDN (Pin 11): Refer to LTC1730ES8-4.2
range. This usually means the battery pack temperature SEL (Pin 12): 4.1V/4.2V Battery Selection Input. Ground-
is too high or too low. Once the temperature is back to ing this pin will set the output float voltage to 4.1V, while normal, the FAULT pin becomes high impedance.
connecting to VCC will set the voltage to 4.2V.
2. The BAT pin potential stays below 2.45V for more GATE (Pin 13): Refer to LTC1730ES8-4.2
than 1/4 of the programmed charge time. When this BAT (Pin 15): Refer to LTC1730ES8-4.2
BLOCK DIAGRA
OPERATIO
The LTC1730 is a complete lithium-ion battery pulse When the battery voltage reaches the final float voltage, charger with an internal 0.35Ω N-MOSFET switch driven the pass transistor turns off for 100ms (minimum off- by an internal charge pump. The charge current is set by
time). It remains off as long as the battery voltage stays the current limit of the input supply (wall adapter). An
above the float voltage after the 100ms off-time. After the minimum off-time, if the battery voltage drops below the SENSE sets the maximum allowable charge over float voltage, the pass transistor turns back on for at least MAX = 0.1V/RSENSE) and prevents a wall adapter with the wrong current limit from damaging the battery. If 380ms (minimum on-time). As the battery approaches full the current limit of the input supply is above I charge, the off-time will get longer and the on-time will charging will be immediately terminated and will retry after stay at 380ms. The voltage at the BAT pin will be slightly higher than the final float voltage due to the ESR associ- TIMER = 0.1µF). If the battery is disconnected while in fast charge mode, the N-channel MOSFET turns ated with the battery pack. This voltage level should not off when the voltage at the BAT pin rises above 4.7V, and turn on the overvoltage protection circuitry often located turns back on when the voltage drops below the float in the battery pack. When the duty cycle at the GATE pin drops below 10%, a comparator turns off the N-FET at theCHRG pin and connects a weak current source (40µA) to A charge cycle begins when the voltage at the VCC pin rises ground to indicate a near end-of-charge (C/10) condition.
above the BAT pin by 40mV and the voltage at the NTC/ The pulse charging will continue until the timer stops.
SHDN pin is in between 0.5 • VCC and 0.875 • VCC. Thecharger will go into trickle charge mode if the battery An external capacitor at the TIMER pin sets the total charge voltage is below 2.45V. The trickle charge current is preset time, the minimum on- and off-time and the overcurrent to 35mA and is provided by an internal current source. In retry period. After a time-out has occurred, the charge trickle mode, the charge pump and pass transistor are off.
cycle is terminated and the CHRG pin is forced highimpedance. To restart the charge cycle, momentarily pull When the battery voltage exceeds 2.45V, the charger goes the NTC/SHDN pin below 50mV or remove and reapply the into the fast charge mode. In this mode, the charge pump input voltage. After the charging stops, if the battery turns on and ramps up the gate voltage of the pass voltage drops 150mV below the final float voltage, due to transistor turning it on. The voltage at the VCC pin then external loading or internal leakage, a new charge cycle ramps down to VBAT plus the voltage drop across the pass transistor and RSENSE, thus reducing the power dissipa-
tion in the pass transistor. The charge current is deter-
The charger can be shut down by pulling the NTC/SHDN mined by the current limit of the input supply.
pin to ground. When the input voltage is not present, thecharger goes into a sleep mode, dropping battery draincurrent to less than 1µA.
APPLICATIO S I FOR ATIO
Stop Charging
an external capacitor from the TIMER pin to ground. Thetotal charge time is: The charger is off when any of the following conditionsexist. The voltage at the VCC pin is less than 40mV above VBAT (sleep mode), or the potential at the NTC/SHDN pin The timer starts when the input voltage (at least 40mV is less than 50mV (shutdown mode). The trickle charge greater than VBAT) is applied and the potential at the NTC/ current source and the internal pass transistor are turned SHDN pin is between 0.5 • VCC and 0.875 • VCC. After a off. The internal resistor divider is disconnected to reduce time-out has occurred, the charging stops and the CHRG the current drain on the battery when in sleep mode.
Input Voltage (Wall Adapter)
CHRG Status Output Pin
The input voltage to the LTC1730 must have some
This open-drain output requires a pull-up resistor and can method of current limit capability. The current limit level
be used to indicate three charging conditions. When fast of the input power source must be lower than the charging begins, an N-FET (capable of driving an LED) overcurrent limit (IMAX) set by the sense resistor (IMAX = turns on, pulling this pin to ground. Once the duty cycle at 100mV/RSENSE). If a wall adapter without current limit is the GATE pin drops below 10%, the N-FET turns off and a used, or the current limit level is above IMAX, the charger 40µA current source to ground turns on. When a time-out will turn on briefly and then immediately turn off after the occurs or the input supply is removed, the CHRG pin goes overcurrent condition is detected. This cycle will be re- high impedance indicating that the charge cycle has ended.
sumed every 400ms (CTIMER = 0.1µF) until the total charge By using two different value resistors, a microprocessor time has run out. If overcurrent protection is not needed, can detect three states from this pin: charging, C/10 and
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.
Figure 1. Interfacing with Microprocessor
Battery Charge Current
When the LTC1730 is in charge mode, the CHRG pin is The battery charge current is determined by the current
pulled to ground by an internal N-MOSFET. To detect this limit of the input supply (wall adapter). However, this
mode, force the digital output pin, OUT, high and measure current must not exceed the maximum charge overcurrent, the voltage at the CHRG pin. The N-MOSFET will pull the IMAX. If an overcurrent condition is detected, the charging pin low even with a 2k pull-up resistor. Once the charge is immediately terminated, the GATE pin is pulled to current drops below 10% of the full scale current (C/10),
ground and the charge pump turns off. The charging will the N-MOSFET is turned off and a 40µA current source is resume after a 400ms time off (CTIMER = 0.1µF).
connected to the CHRG pin. By forcing the OUT pin to ahigh impedance state, the current source will pull the pin Programming the Timer
low through the 620k resistor. When the internal timer has The programmable timer is used to terminate the charge expired, the CHRG pin becomes high impedance and the and sets the minimum ON/OFF time and the overcurrent 620k resistor will pull the pin high to indicate that charging time-off period. The length of the timer is programmed by 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 (40µA) current source to Figure 2. Slew Rate at GATE and V
ground. The end-of-charge comparator is disabled in with the RC Network from GATE to VCC
above VBAT, the external N-MOSFET gate to source break- Internal Pass Transistor
down voltage should be rated at 20V or more.
An N-channel MOSFET (0.35Ω) is included in the LTC1730 Battery Temperature Detection
as the pass transistor. The gate of the MOSFET is con-trolled by an internal charge pump. The body is connected A negative temperature coefficient (NTC) thermistor lo- to ground instead of source terminal. There is no body cated close to the battery pack can be used to monitor diode from the BAT pin back to the VCC pin; therefore, no battery temperature and will not allow charging unless the blocking diode is required in series with the battery or the battery temperature is within an acceptable range. Connect input supply. This will not only reduce the cost but also the a 10kΩ thermistor between ground and the NTC/SHDN pin heat generated when in fast charge mode. An internal and a 4.1k resistor from the NTC/SHDN pin to VCC. If the thermal shutdown circuit turns off the pass transistor if temperature rises to 50°C, the resistance of the thermister the die temperature exceeds approximately 140°C with will be approximately 4.1kΩ (Dale NTHS-1206N02) and the LTC1730 will go into a hold mode. For cold tempera-tures, the threshold of the hold mode is at 0°C (RNTC ≈ Gate Drive
28kΩ). The pass transistor turns off and the timer is frozen The pass transistor gate drive consists of a regulated 10µA at hold mode while the output status at the CHRG pin current source charge pump. A series RC network is remains the same. The charge cycle begins or resumes once the temperature is within the acceptable range.
transistor is turned on, the voltage at the VCC pin starts Thermal Considerations
slewing down to a voltage equal to VBAT plus the voltagedrop across the pass transistor and RSENSE. The slew rate The power handling capability is limited by the maximum is equal to 10µA/C. By ramping the VCC pin down slowly, rated junction temperature (125°C) and the amount of PC the inrush current is reduced. The resistor in series with board copper used as a heat sink. The power dissipated by the capacitor is required to limit the transient current when 1. Input supply current multiplied by the input voltage When the charge pump is turned off, a 40µA current 2. The voltage drop across the switch (SENSE pin to BAT source to ground starts pulling the GATE voltage down.
Once the pass transistor is off, the voltage at the VCC pinbegins slewing up with the rate equal to 40µA/C. With this The LTC1730 has internal thermal shutdown designed to protect the IC from overtemperature conditions. For con- tinuous charging in the fast charge mode, the maximumjunction temperature must not be exceeded. It is important For higher current applications an external power N-MOSFET to give careful consideration to all sources of thermal can be connected in parallel with the internal pass transis- resistance from junction to ambient. Additional heat sources tor. Because the charge pump output is clamped to 12V mounted nearby must also be considered.
APPLICATIO S I FOR ATIO
Surface mount packages rely primarily on the copper leads Table 1. SO-8 Package Thermal Resistance
(pins) to conduct the heat from the package to the sur- rounding 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 gener- ous amounts of copper around the ground pin and also consider feedthrough vias (plated through holes) to back- side or inner copper layers to maximize power dissipation.
Output Voltage Selection (LTC1730EGN-4)
Table 1 lists the thermal resistance for the SO-8 package.
The float voltage at the BAT pin can be selected by the SEL Measured values of thermal resistance for several differ- pin. Shorting the SEL pin to ground will set the float ent board sizes and copper areas are listed. All measure- voltage to 4.1V, while connecting it to VCC sets it to 4.2V.
ments were taken in still air on 0.062" FR-4 board with one This feature allows the charger to be used with different Calculating Junction Temperature
ACPR Output Pin (LTC1730EGN-4)
Example: Find the maximum junction temperature for a When the input voltage is 40mV higher than the voltage at battery voltage of 4V (VCC will collapse to approximately the BAT pin, the ACPR pin is pulled low to ground to VBAT in the fast charge mode), charge current of 1A and a indicate that the input supply (wall adapter) is applied.
maximum ambient temperature of 75°C.
After the input supply is removed, this pin becomes high impedance. An internal 80ms delay prevents the LTC1730from turning off if the voltage at the VCC pin rings and gets P = (IBAT • IBAT • RDS(ON)) + (VCC • ICC) too close to VBAT because of the parasitic inductance.
FAULT Output Pin (LTC1730EGN-4)
The FAULT pin is pulled to ground when either one of the The SO-8 package for the LTC1730 features a special lead 1. The voltage at the NTC/SHDN pin is out of the operation frame with a lower thermal resistance and higher allow- range. With a 10k negative temperature coefficient able power dissipation. The junction-to-ambient thermal thermistor placed near the battery pack, this pin indi- resistance of this package when soldered to a PC board is cates that the temperature of the pack is either too cold approximately 80°C/W depending on the copper area. So or too hot and the charger is suspended. Once the the junction temperature rise above ambient will be temperature is back to the operational range, the FAULT pin becomes high impedance and the charging re- The maximum junction temperature is equal to the maxi- 2. The voltage at the BAT pin stays below 2.45V for 1/4 of mum junction temperature rise above ambient plus the the programmed charge time. If VBAT remains low even with 35mA of trickle charge current for 1/4 of the total APPLICATIO S I FOR ATIO
charge time, the battery is considered defective. The shutting down the charger. After reset, the charger is charger turns off and the FAULT pin is pulled low. This back in the charge mode and the FAULT pin becomes 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)
* 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 S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
*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 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 represen-tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
TYPICAL APPLICATIO S
Single Cell 4.2V Li-Ion Battery Charger (16-Pin Package)
Using External N-MOSFET for Higher Charge Current
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
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/BatteryDetection Status Output, Preconditioning, 8-Lead MSOP 1.5A CC/CV, 10-Lead Enhanced MSOP, Thermal Regulation for ConstantTemperature, No Blocking Diode, No Sense Resistor Required Only Two External Components, Up to 700mA ICHARGE, No ReverseCurrent Diode Required, No Sense Resistor Required Li-Ion Linear Charger with Thermistor Interface Stand Alone Charger; 10-Lead MSOP, Up to 1A Charge Current 1630 McCarthy Blvd., Milpitas, CA 95035-7417(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

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