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LTC4078X Dual Input Li-Ion Battery Charger with Overvoltage Protection FEATURES

DESCRIPTION
The LTC(R)4078X is a standalone linear charger that is capable of charging a single-cell Li-Ion/Polymer battery from both wall adapter and USB inputs. The charger can detect power at the inputs and automatically select the appropriate power source for charging. No external sense resistor or blocking diode is required for charging due to the internal MOSFET architecture. The LTC4078X features a maximum 22V rating for both wall adapter and USB inputs, although charging stops if the selected power source exceeds the overvoltage limit. Internal thermal feedback regulates the battery charge current to maintain a constant die temperature during high power operation or high ambient temperature conditions. The float voltage is fixed at 4.2V and the charge current is programmed with an external resistor. The LTC4078X terminates the charge cycle when the charge current drops below the programmed termination threshold after the final float voltage is reached. Other features include battery present detection, automatic recharge, undervoltage lockout, charge status outputs, and "power present" status outputs to indicate the presence of wall adapter or USB power. The device is offered in a low profile (0.75mm) 3mm x 3mm 10-lead DFN package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. *Protected by U.S. Patents including 6522118, 6700364.

22V Maximum Voltage for Wall Adapter and USB Inputs Charge Single-Cell Li-Ion Batteries from Wall Adapter and USB Inputs Automatic Input Power Detection and Selection Charge Current Programmable Up to 950mA from Wall Adapter Input Overvoltage Lockout for Wall Adapter and USB Inputs Battery Detection Input Disables Charger When No Battery is Present No External MOSFET, Sense Resistor or Blocking Diode Needed Thermal Regulation Maximizes Charge Rate Without Risk of Overheating* Preset Charge Voltage with 0.6% Accuracy Programmable Charge Current Termination 40A USB Suspend Current in Shutdown Charge Status Output Automatic Recharge No Trickle Charge Available in a Thermally Enhanced, Low Profile (0.75mm) 10-Lead (3mm x 3mm) DFN Package
APPLICATIONS

Cellular Telephones Handheld Computers Portable MP3 Players Digital Cameras
TYPICAL APPLICATION
High Voltage Dual Input Battery Charger for Li-Ion Battery Pack
WALL ADAPTER USB PORT 1F 1F LTC4078X DCIN USBIN IUSB ITERM GND 2k 1%
4078X TA01
Charger Current vs Supply Voltage
900 800 700 600 IBAT (mA) 500 400 300 200 100 0 2 3 4 5 6 7 8 SUPPLY VOLTAGE (V) 19 20 CHARGE FROM USBIN RIDC = 1.24k RIUSB = 2k VBAT = 3.5V VBATDET = 0V CHARGE FROM DCIN
800mA (WALL) 500mA (USB)
BAT BATDET 3.9k
+
2k IDC 1% 1.24k 1%
4.2V Li-Ion BATTERY PACK
4078x TA01b
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LTC4078X ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW USBIN IUSB ITERM PWR CHRG 1 2 3 4 5 11 10 DCIN 9 BAT 8 IDC 7 BATDET 6 ENABLE
Input Supply Voltage (DCIN, USBIN) ............-0.3 to 22V ENABLE, CHRG, PWR, BATDET, BAT...............-0.3 to 6V IDC, IUSB, ITERM Pin Current .................................1mA DCIN, USBIN, BAT Pin Current ....................................1A BAT Short-Circuit Duration............................Continuous Maximum Junction Temperature .......................... 125C Operating Temperature Range (Note 2) ... -40C to 85C Storage Temperature Range................... -65C to 125C
DD PACKAGE 10-LEAD (3mm x 3mm) PLASTIC DFN TJMAX = 125C, JA = 40C/W (Note 3) EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LTC4078XEDD#PBF TAPE AND REEL LTC4078XEDD#TRPBF PART MARKING LCYP PACKAGE DESCRIPTION 10-Lead (3mm x 3mm) Plastic DFN TEMPERATURE RANGE -40C to 85C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
SYMBOL VDCIN VUSBIN IDCIN PARAMETER Operating Supply Voltage Operating Supply Voltage DCIN Supply Current
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VDCIN = 5V, VUSBIN = 5V unless otherwise noted.
CONDITIONS

MIN 4.3 4.3
TYP
MAX 5.5 5.5
UNITS V V A A A A A A A A A V V mA mA mA A A A
Charge Mode (Note 4), RIDC = 10k Standby Mode; Charge Terminated Shutdown Mode (ENABLE = 5V) Overvoltage Mode (VDCIN = 10V) Charge Mode (Note 5), RIUSB = 10k, VDCIN = 0V Standby Mode; Charge Terminated, VDCIN = 0V Shutdown (VDCIN = 0V, ENABLE = 0V) Overvoltage Mode (VUSBIN = 10V) VDCIN > VUSBIN IBAT = 1mA IBAT = 1mA, 0C < TA < 85C RIDC = 1.25k, Constant-Current Mode RIUSB = 2.1k, Constant-Current Mode RIDC = 10k or RIUSB = 10k Standby Mode, Charge Terminated Shutdown Mode (Charger Disabled) Sleep Mode (VDCIN = 0V, VUSBIN = 0V)

350 70 40 70 350 70 40 70 23 4.185 4.165 4.2 4.2 800 476 100 -7.5 -7.5 -7.5
800 120 80 140 800 120 80 140 40 4.215 4.235 830 495 107 -12 -12 -12
IUSBIN
USBIN Supply Current

VFLOAT IBAT
Regulated Output (Float) Voltage BAT Pin Current

770 455 93
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LTC4078X ELECTRICAL CHARACTERISTICS
SYMBOL VIDC VIUSB ITERMINATE PARAMETER IDC Pin Regulated Voltage IUSB Pin Regulated Voltage Charge Current Termination Threshold
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VDCIN = 5V, VUSBIN = 5V unless otherwise noted.
CONDITIONS Constant-Current Mode Constant-Current Mode RITERM = 1k RITERM = 2k RITERM = 10k RITERM = 20k From Low to High Hysteresis From Low to High Hysteresis From Low to High Hysteresis From Low to High Hysteresis VDCIN from Low to High, VBAT = 4.2V VDCIN from High to Low, VBAT = 4.2V VUSBIN from Low to High VUSBIN from High to Low

MIN
TYP 1 1
MAX
UNITS V V
90 42 8 3.5 4 3.8 5.8 5.8 70 10 70 10 0.6 1 1.65 2 4
100 50 10 5 4.15 190 3.95 170 6 185 6 185 120 40 120 40 0.9 2 1.75 4 4.2 0.12
110 58 12 6.5 4.3 4.1 6.2 6.2 170 70 170 70 1.2 3.5 1.85 6 4.4 0.35 160 6.75 2.4
mA mA mA mA V mV V mV V mV V mV mV mV mV mV V M V A V V mV ms ms m m C
VUVDC VUVUSB VOVDC VOVUSB VASD-DC VASD-USB VENABLE RENABLE VBDET IBATDET VBOC VOL VRECHRG tRECHRG tTERMINATE RON-DC RON-USB TLIM
DCIN Undervoltage Lockout Voltage USBIN Undervoltage Lockout Voltage DCIN Overvoltage Lockout Voltage USBIN Overvoltage Lockout Voltage VDCIN - VBAT Lockout Threshold VUSBIN - VBAT Lockout Threshold ENABLE Input Threshold Voltage ENABLE Pulldown Resistance BATDET Input Threshold Voltage BATDET Pull-Up Current BATDET Open Circuit Voltage Output Low Voltage (CHRG, PWR) Recharge Battery Threshold Voltage Recharge Comparator Filter Time Termination Comparator Filter Time Power FET "ON" Resistance (Between DCIN and BAT) Power FET "ON" Resistance (Between USBIN and BAT) Junction Temperature in ConstantTemperature Mode
From Low to High VBATDET = 0V VDCIN = 5V, VUSBIN = 5V ISINK = 5mA VFLOAT - VRECHRG, 0C < TA < 85C VBAT from High to Low IBAT Drops Below Termination Threshold
90 2.25 1
125 4.1 1.6 600 700 120
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC4078X is guaranteed to meet the performance specifications from 0C to 85C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls.
Note 3: Failure to correctly solder the exposed backside of the package to the PC board will result in a thermal resistance much higher than 40C/W. See Thermal Considerations. Note 4: Supply current includes IDC and ITERM pin current (approximately 100A each) but does not include any current delivered to the battery through the BAT pin. Note 5: Supply current includes IUSB and ITERM pin current (approximately 100A each) but does not include any current delivered to the battery through the BAT pin.
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LTC4078X TYPICAL PERFORMANCE CHARACTERISTICS
Regulated Output (Float) Voltage vs Charge Current
4.26 4.24 4.22 VFLOAT (V) VFLOAT (V) 4.20 4.18 4.16 4.14 4.12 4.10 0 100 200 300 400 500 600 700 800 900 IBAT (mA)
4078x G01
TA = 25C, unless otherwise specified. IDC Pin Voltage vs Temperature (Constant-Current Mode)
1.008 1.006 1.004 1.002 VIDC (V) 1.000 0.998 0.996 0.994 VDCIN = 5V
Regulated Output (Float) Voltage vs Temperature
4.220 4.215 4.210 VDCIN = VUSBIN = 5V
VDCIN = VUSBIN = 5V
RIDC = 1.24k
4.205 4.200 4.195 4.190 4.185 4.180 -10 10 30 50 TEMPERATURE (C) 70 90
4078x G02
RIDC = RIUSB = 2k
0.992 -10
10
30 50 TEMPERATURE (C)
70
90
4078x G03
IUSB Pin Voltage vs Temperature (Constant-Current Mode)
1.008 1.006 1.004 IBAT (mA) VIUSB (V) 1.002 1.000 0.998 0.996 0.994 0.992 -10 10 30 50 TEMPERATURE (C) 70 90
4078x G04
Charge Current vs IDC Pin Voltage
900 800 700 600 500 400 300 200 100 0 0 0.2 0.4 0.6 0.8 VIDC (V) 1.0 1.2 RIDC = 10k RIDC = 2k IBAT (mA) RIDC = 1.24k VDCIN = 5V 900 800
Charge Current vs IUSB Pin Voltage
VUSBIN = 5V RIUSB = 1.24k 700 600 500 400 300 200 100 0 0 0.2 0.4 0.6 0.8 VIUSB (V) 1.0 1.2 RIUSB = 10k RIUSB = 2k
VUSBIN = 5V
4078x G05
4078x G06
PWR Pin I-V Curve
60 50 40 30 20 10 0 0 1 2 3 VPWR (V)
4078x G07
CHRG Pin I-V Curve
60 50 40 ICHRG (mA) 4 5 6 30 20 10 0 0 1 2 3 4 VCHRG (V) 5 6
4078x G08
VDCIN = VUSBIN = 5V
VDCIN = VUSBIN = 5V
IPWR (mA)
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LTC4078X TYPICAL PERFORMANCE CHARACTERISTICS
Charge Current vs Ambient Temperature
1000 900 800 700 IBAT (mA) IBAT (mA) 600 500 400 300 200 V DCIN = VUSBIN = 5V 100 VBAT = 4V JA = 30C/W 0 70 50 30 90 -10 10 TEMPERATURE (C) RIDC = RIUSB = 2k RIDC = 1.24k 900 800 700 600 500 400 300 200 100 110 130
4078x G10
TA = 25C, unless otherwise specified.
Charge Current vs Supply Voltage
1000
Charge Current vs Battery Voltage
800
IBAT (mA) RIDC = 1.24k VBAT = 4V JA = 30C/W 4.5 5.0 5.5 6.0 6.5 VDCIN (V) 7.0 7.5 8.0
600
400
200
0 4.0
0 2.4
VDCIN = VUSBIN = 5V RIDC = 1.24k JA = 30C/W 2.7 3.0 3.3 3.6 VBAT (V) 3.9 4.2 4.5
4078x G11
4078x G12
DCIN Power FET On-Resistance vs Temperature
800 750 700 650 600 550 500 -10 VBAT = 4V IBAT = 200mA 900 850 800 750 700 650
USBIN Power FET On-Resistance vs Temperature
VBAT = 4V IBAT = 200mA 1000 980 960 RDS(ON) (m) VENABLE (V) 940 920 900 880
ENABLE Pin Threshold Voltage (On-to-Off) vs Temperature
VDCIN = VUSBIN = 5V
RDS(ON) (m)
10
30 50 TEMPERATURE (C)
70
90
4078x G13
600 -10
10
30 50 TEMPERATURE (C)
70
90
4078x G14
860 -10
10
30 50 TEMPERATURE (C)
70
90
4078x G15
USBIN Shutdown Current vs Temperature
60 55 50 IUSBIN (A) 45 40 35 30 25 20 -50 -25 0 25 50 TEMPERATURE (C) 75 100 VUSBIN = 4.3V VUSBIN = 5V IDCIN (A) VENABLE = 0V 60 55 50 45 40 35 30 25
DCIN Shutdown Current vs Temperature
VENABLE = 5V 2.4 2.3 VDCIN = 5V RENABLE (M) VDCIN = 4.3V -25 0 25 50 TEMPERATURE (C) 75 100 2.2 2.1 2.0 1.9 1.8 1.7
ENABLE Pin Pulldown Resistance vs Temperature
20 -50
1.6 -50
-25
0 25 50 TEMPERATURE (C)
75
100
4078x G16
4078x G17
4078x G18
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LTC4078X TYPICAL PERFORMANCE CHARACTERISTICS
Undervoltage Lockout Threshold vs Temperature
4.25 4.20 4.15 4.10 VUV (V) 4.05 4.00 3.95 3.90 3.85 -10 10 30 50 TEMPERATURE (C) 70 90
4078x G19
TA = 25C, unless otherwise specified. Overvoltage Lockout Threshold vs Temperature
6.10 6.05 6.00 VOV (V) USBIN OVLO 5.95 5.90 5.85 5.80 -10 DCIN OVLO
DCIN UVLO
USBIN UVLO
10
30 50 TEMPERATURE (C)
70
90
4078x G20
Recharge Threshold Voltage vs Temperature
4.11 VDCIN = VUSBIN = 5V 9.0 8.5 4.09 VRECHRG (V) 8.0 4.07 IBAT (A) 7.5 7.0 4.05 6.5 4.03 -10
Battery Drain Current vs Temperature
VDCIN = VUSBIN = NOT CONNECTED VBAT = 4.2V
10
30 50 TEMPERATURE (C)
70
90
4078x G21
6.0 -50
-25
0 25 50 TEMPERATURE (C)
75
100
4078x G22
BATDET Pin Threshold Voltage (On-to-Off) vs Temperature
2.0 VDCIN = VUSBIN = 5V 1.9 4.3 1.8 VBDET (V) VBOC (V) 1.7 1.6 4.1 1.5 1.4 -10 4.2 4.4
BATDET Voltage/Current vs Temperature
VDCIN = VUSBIN = 5V VBOC 6.00
5.25 IBATDET (A)
4.50 IBATDET 3.75
10
30 50 TEMPERATURE (C)
70
90
4078x G23
4.0 -10
3.00 10 30 50 TEMPERATURE (C) 70 90
4078x G24
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LTC4078X PIN FUNCTIONS
USBIN (Pin 1): USB Input Supply Pin. This input provides power to the battery charger assuming a voltage greater than VUVUSB and less than VOVUSB is present (typically 3.95V to 6V respectively). However, the DCIN input will take priority if a voltage greater than VUVDC is present at DCIN (typically 4.15V). The USBIN input allows charge currents up to 850mA. This pin should be bypassed with a 1F capacitor. IUSB (Pin 2): Charge Current Program for USB Power. The charge current is set by connecting a resistor, RIUSB, to ground. When charging in constant-current mode, this pin servos to 1V. The voltage on this pin can be used to measure the battery current delivered from the USB input using the following formula: IBAT = VIUSB * 1000 RIUSB an internal N-channel MOSFET. When the charge cycle is completed, CHRG becomes high impedance. This output is capable of driving an LED. ENABLE (Pin 6): Enable Input. When the LTC4078X is charging from the DCIN source, a logic low on this pin enables the charger. When the LTC4078X is charging from the USBIN source, a logic high on this pin enables the charger. If this input is left floating, an internal 2M pulldown resistor defaults the LTC4078X to charge when a wall adapter is applied and to shut down if only the USB source is applied. BATDET (Pin 7): Battery Detection Input. When the voltage on this pin falls below VBDET (typically 1.75V), the charger is on and ready for charging a battery. If this input is left floating, an internal pull-up resistor will disable charging. IDC (Pin 8): Charge Current Program for Wall Adapter Power. The charge current is set by connecting a resistor, RIDC, to ground. When charging in constant-current mode, this pin servos to 1V. The voltage on this pin can be used to measure the battery current delivered from the DC input using the following formula: IBAT = VIDC * 1000 RIDC
ITERM (Pin 3): Termination Current Threshold Program. The termination current threshold, ITERMINATE, is set by connecting a resistor, RITERM, to ground. ITERMINATE is set by the following formula: ITERMINATE = 100 V RITERM
When the battery current, IBAT, falls below the termination threshold, charging stops and the CHRG output becomes high impedance. This pin is internally clamped to approximately 1.5V. Driving this pin to voltages beyond the clamp voltage should be avoided. PWR (Pin 4): Open-Drain Power Supply Status Output. When the DCIN or USBIN pin voltage is valid to begin charging (i.e. when the supply is greater than the undervoltage lockout threshold, less than the overvoltage lockout threshold and at least 120mV above the battery terminal), the PWR pin is pulled low by an internal N-channel MOSFET. Otherwise PWR is high impedance. This output is capable of driving an LED. CHRG (Pin 5): Open-Drain Charge Status Output. When the LTC4078X is charging, the CHRG pin is pulled low by
BAT (Pin 9): Battery Charger Output. This pin provides charge current to the battery and regulates the final float voltage to 4.2V. DCIN (Pin 10): Wall Adapter Input Supply Pin. This input provides power to the battery charger assuming a voltage greater than VUVDC and less than VOVDC is present (typically 4.15V to 6V respectively). A valid voltage on the DCIN input will always take priority over the USBIN input. The DCIN input allows charge currents up to 950mA. This pin should be bypassed with a 1F capacitor. Exposed Pad (Pin 11): GND. The exposed backside of the package is ground and must be soldered to PC board ground for electrical connection and maximum heat transfer.
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LTC4078X BLOCK DIAGRAM
DCIN 10 BAT 9 USBIN 1
CC/CV REGULATOR
CC/CV REGULATOR VBOC DC_ENABLE USB_ENABLE
CHARGER CONTROL DISABLE PWR 4
+ -
1.75V
7 BATDET
+
4.15V
+
DCIN UVLO USBIN UVLO
-
-
3.95V
+
BAT
+ -
BAT
-
+
6V
+
DCIN OVLO USBIN OVLO
-
-
6V
ENABLE
6 2M 0.9V
+ -
+ -
TDIE
120C
THERMAL REGULATION
4.075V
+ -
RECHARGE
BAT
CHRG
5
-
TERMINATION
0.1V IBAT/1000 IBAT/1000 IBAT/1000
+
GND 11 3 RITERM ITERM 8 RIDC IDC 2 RIUSB IUSB
4078X BD
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LTC4078X OPERATION
The LTC4078X is designed to efficiently manage charging of a single-cell lithium-ion battery from two separate power sources: a wall adapter and USB power bus. Using the constant-current/constant-voltage algorithm, the charger can deliver up to 950mA of charge current from the wall adapter supply or up to 850mA of charge current from the USB supply with a final float voltage accuracy of 0.6%. The LTC4078X has two internal P-channel power MOSFETs and thermal regulation circuitry. No blocking diodes or external sense resistors are required. Power Source Selection The LTC4078X can charge a battery from either the wall adapter input or the USB port input. The LTC4078X automatically senses the presence of voltage at each input. If both power sources are present, the LTC4078X defaults to the wall adapter source provided a valid voltage is present at the DCIN input. "Valid voltage" is defined as: * Supply voltage is greater than the UVLO threshold and less than the OVLO threshold. * Supply voltage is greater than the battery voltage by 40mV. The open-drain power status output (PWR) indicates which power source has been selected. Table 1 describes the behavior of this status output. Programming and Monitoring Charge Current The charge current delivered to the battery from the wall adapter or USB supply is programmed using a single resistor from the IDC or IUSB pin to ground. Both program resistors and charge currents (ICHRG) are calculated using the following equations: RIDC = 1000 V ICHRG-DC , ICHRG-DC = 1000 V RIDC 1000 V RIUSB Charge current out of the BAT pin can be determined at any time by monitoring the IDC or IUSB pin voltage and applying the following equations: IBAT = IBAT = VIDC * 1000, (ch arg ing from wall adapter ) RIDC VIUSB * 1000, (ch arg ing from USB sup ply) RIUSB
Battery Detection By default, the BATDET pin is pulled high with an internal resistor, disabling the charger. To enable the charger, the BATDET pin must be pulled below the VBDET threshold (typically 1.75V). An external resistor to ground less than 100k (typically 3.9k) located in the battery pack is used to detect battery presence. Programming Charge Termination The charge cycle terminates when the charge current falls below the programmed termination threshold level during constant-voltage mode. This threshold is set by connecting an external resistor, RITERM, from the ITERM pin to ground. The charge termination current threshold (ITERMINATE) is set by the following equation: RITERM = 100 V ITERMINATE , ITERMINATE = 100 V RITERM
The termination condition is detected by using an internal filtered comparator to monitor the ITERM pin. When the ITERM pin voltage drops below 100mV* for longer than tTERMINATE (typically 1.6ms), charging is terminated. The charge current is latched off and the LTC4078X enters standby mode. When charging, transient loads on the BAT pin can cause the ITERM pin to fall below 100mV for short periods of time before the DC charge current has dropped below the
RIUSB =
1000 V ICHRG-USB
, ICHRG-USB =
*Any external sources that hold the ITERM pin above 100mV will prevent the LTC4078X from terminating a charge cycle.
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LTC4078X OPERATION
programmed termination current. The 1.6ms filter time (tTERMINATE) on the termination comparator ensures that transient loads of this nature do not result in premature charge cycle termination. Once the average charge current drops below the programmed termination threshold, the LTC4078X terminates the charge cycle and stops providing current out of the BAT pin. In this state, any load on the BAT pin must be supplied by the battery. Automatic Recharge In standby mode, the charger sits idle and monitors the battery voltage using a comparator with a 4.1ms filter time (tRECHRG). A charge cycle automatically restarts when the battery voltage falls below 4.075V (which corresponds to approximately 80% to 90% battery capacity). This ensures that the battery is kept at, or near, a fully charged condition and eliminates the need for periodic charge cycle initiations. Manual Shutdown The ENABLE pin has a 2M pulldown resistor to GND. The definition of this pin depends on which source is supplying power. When the wall adapter input is supplying power,
Table 1. Power Source Selection (VBATDET < 1.75V)
VUSBIN < 3.95V or VUSBIN < BAT + 50mV ENABLE HIGH LOW or No Connect No Charging. PWR: Hi-Z CHRG: Hi-Z VDCIN < 4.15V or No Charging. VDCIN < BAT + 50mV PWR: Hi-Z CHRG: Hi-Z 6V > VDCIN > 4.15V and VDCIN > BAT + 50mV 22V > VDCIN > 6V No Charging. PWR: LOW CHRG: Hi-Z No Charging. PWR: Hi-Z CHRG: Hi-Z 6V > VUSBIN > 3.95V and VUSBIN > BAT + 50mV HIGH Charging from USBIN source. PWR: LOW CHRG: LOW LOW or No Connect No Charging. PWR: LOW CHRG: Hi-Z 22V > VUSBIN > 6V HIGH No Charging. PWR: Hi-Z CHRG: Hi-Z LOW or No Connect No Charging. PWR: Hi-Z CHRG: Hi-Z Charging from DCIN source. PWR: LOW CHRG: LOW No Charging. PWR: Hi-Z CHRG: Hi-Z
logic low enables the charger and logic high disables it (the pulldown defaults the charger to the charging state). The opposite is true when the USB input is supplying power; logic low disables the charger and logic high enables it (the default is the shutdown state). The DCIN input draws 40A when the charger is in shutdown mode. The USBIN input draws 40A during shutdown if no voltage is applied to DCIN, but draws only 23A when VDCIN provides valid voltage (see Table 1). Status Indicators The charge status open-drain output (CHRG) has two states: pulldown and high impedance. The pulldown state indicates that the LTC4078X is in a charge cycle. Once the charge cycle has terminated or the LTC4078X is disabled, the pin state becomes high impedance. The power supply status open-drain output (PWR) has two states: pulldown and high impedance. The pulldown state indicates that power is present at either DCIN or USBIN. This output is strong enough to drive an LED. If no valid voltage is applied at either pin, the PWR pin is high impedance, indicating that the LTC4078X lacks valid input voltage (see Table 1) to charge the battery.
Charging from DCIN No Charging. PWR: LOW source. PWR: LOW CHRG: Hi-Z CHRG: LOW No Charging. PWR: Hi-Z CHRG: Hi-Z No Charging. PWR: LOW CHRG: Hi-Z
Charging from DCIN No Charging. PWR: LOW source. PWR: LOW CHRG: Hi-Z CHRG: LOW No Charging. PWR: LOW CHRG: Hi-Z No Charging. PWR: Hi-Z CHRG: Hi-Z
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LTC4078X OPERATION
Thermal Limiting An internal thermal feedback loop reduces the programmed charge current if the die temperature attempts to rise above a preset value of approximately 120C. This feature protects the LTC4078X from excessive temperature and allows the user to push the limits of the power handling capability of a given circuit board without risk of damaging the device. The charge current can be set according to typical (not worst-case) ambient temperature with the assurance that the charger will automatically reduce the current in worst case conditions. DFN package power considerations are discussed further in the Applications Information section.
DCIN POWER REMOVED
NO POWER
USB POWER REMOVED
POWER APPLIED ENABLE = LOW ENABLE = HIGH
YES
DCIN > 4.15V AND DCIN > BAT NO
6V > DCIN > 4.15V AND DCIN > BAT YES
NO
NO
6V > USBIN > 3.95V AND USBIN > BAT YES
NO BATDET < 1.75V YES CHARGE MODE (DCIN) FULL CURRENT CHRG STATE: PULLDOWN IBAT < ITERMINATE IN VOLTAGE MODE STANDBY MODE (DCIN) BAT < 4.075V NO CHARGE CURRENT CHRG STATE: Hi-Z
NO BATDET < 1.75V YES CHARGE MODE (USBIN) FULL CURRENT CHRG STATE: PULLDOWN IBAT < ITERMINATE IN VOLTAGE MODE STANDBY MODE (USBIN) BAT < 4.075V NO CHARGE CURRENT CHRG STATE: Hi-Z
SHUTDOWN MODE (DCIN) CHRG STATE: Hi-Z
SHUTDOWN MODE (USBIN) CHRG STATE: Hi-Z
4078X F01
Figure 1. LTC4078X State Diagram of a Charge Cycle
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LTC4078X APPLICATIONS INFORMATION
Using a Single Charge Current Program Resistor The LTC4078X can program the wall adapter charge current and USB charge current independently using two program resistors, RIDC and RIUSB. Figure 2 shows a charger circuit that sets the wall adapter charge current to 800mA and the USB charge current to 500mA. In applications where the programmed wall adapter charge current and USB charge current are the same, a single program resistor can be used to set both charge currents. Figure 3 shows a charger circuit that uses one charge current program resistor.
WALL ADAPTER USB PORT C1 1F C2, 1F R1 2k 1% LTC4078X DCIN BAT R4 3.9k ITERM GND R3 2k 1% 800mA (WALL) 500mA (USB)
Stability Considerations The constant-voltage mode feedback loop is stable without any compensation provided a battery is connected to the charger output. However, a 1F capacitor with a 1 series resistor is recommended at the BAT pin to keep the ripple voltage low when the battery is disconnected. When the charger is in constant-current mode, the charge current program pin (IDC or IUSB) is in the feedback loop, not the battery. The constant-current mode stability is affected by the impedance at the charge current program pin. With no additional capacitance on this pin, the charger is stable with program resistor values as high as 20k (ICHRG = 50mA); however, additional capacitance on these nodes reduces the maximum allowed program resistor. Power Dissipation When designing the battery charger circuit, it is not necessary to design for worst-case power dissipation scenarios because the LTC4078X automatically reduces the charge current during high power conditions. The conditions that cause the LTC4078X to reduce charge current through thermal feedback can be approximated by considering the power dissipated in the IC. Most of the power dissipation is generated from the internal charger MOSFET. Thus, the power dissipation is calculated to be: PD = (VIN - VBAT) * IBAT PD is the dissipated power, VIN is the input supply voltage (either DCIN or USBIN), VBAT is the battery voltage and IBAT is the charge current. The approximate ambient temperature at which the thermal feedback begins to protect the IC is: TA = 120C - PD * JA TA = 120C - (VIN - VBAT) * IBAT * JA Example: An LTC4078X operating from a 5V wall adapter (on the DCIN input) is programmed to supply 800mA full-scale current to a discharged Li-Ion battery with a voltage of 3.3V.
USBIN BATDET IUSB IDC R2 1.24k 1%
+
4.2V Li-Ion BATTERY PACK
4078X F02
Figure 2. Dual Input Charger with Independent Charge Currents
WALL ADAPTER USB PORT C1 1F C2, 1F
LTC4078X DCIN BAT
500mA
USBIN BATDET IUSB IDC R1 2k 1% ITERM GND R3 2k 1%
R4 3.9k
+
4.2V Li-Ion BATTERY PACK
4078X F03
Figure 3. Dual Input Charger Circuit. The Wall Adapter Charge Current and USB Charge Current Are Both Programmed to Be 500mA
In this circuit, the programmed charge current from both the wall adapter supply is the same value as the programmed charge current from the USB supply: ICHRG-DC = ICHRG-USB = 1000 V RISET
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12
LTC4078X APPLICATIONS INFORMATION
Assuming JA is 40C/W (see Thermal Considerations), the ambient temperature at which the LTC4078X will begin to reduce the charge current is approximately: TA = 120C - (5V - 3.3V) * (800mA) * 40C/W TA = 120C - 1.36W * 40C/W = 120C - 54.4C TA = 65.6C The LTC4078X can be used above 65.6C ambient, but the charge current will be reduced from 800mA. The approximate current at a given ambient temperature can be approximated by: IBAT = 120 C - TA ( VIN - VBAT ) * JA 800mA to a battery from a 5V supply at room temperature. Without a good backside thermal connection, this number would drop to much less than 500mA. Input Capacitor Selection When an input supply is connected to a portable product, the inductance of the cable and the high-Q ceramic input capacitor form an L-C resonant circuit. While the LTC4078X is capable of withstanding input voltages as high as 22V, if the input cable does not have adequate mutual coupling or if there is not much impedance in the cable, it is possible for the voltage at the input of the product to reach as high as 2x the input voltage before it settles out. To prevent excessive voltage from damaging the LTC4078X during a hot insertion, it is best to have a low voltage coefficient capacitor at the input pins to the LTC4078X. This is achievable by selecting an X5R or X7R ceramic capacitor that has a higher voltage rating than that required for the application. For example, if the maximum expected input voltage is 15V, a 25V X5R 1F capacitor would be a better choice than the smaller 16V X5R capacitor. Note that no charging will occur with 15V in. Using a tantalum capacitor or an aluminum electrolytic capacitor for input bypassing, or paralleling with a ceramic capacitor will also reduce voltage overshoot during a hot insertion. Ceramic capacitors with Y5V or Z5U dielectrics are not recommeded. Alternatively, the following soft connect circuit can be employed (as shown in Figure 4).
DCIN/USBIN +15V INPUT INPUT CABLE C2 100nF R1 40k C1 1F MN1 GND
4078X F04
Using the previous example with an ambient temperature of 75C, the charge current will be reduced to approximately: IBAT = IBAT 120 C - 75 C 45 C = (5V - 3 . 3V) * 40 C / W 68 C / A = 662mA
It is important to remember that LTC4078X applications do not need to be designed for worst-case thermal conditions, since the IC will automatically reduce power dissipation when the junction temperature reaches approximately 120C. Thermal Considerations In order to deliver maximum charge current under all conditions, it is critical that the exposed metal pad on the backside of the LTC4078X DFN package is properly soldered to the PC board ground. When correctly soldered to a 2500mm2 double sided 1oz copper board, the LTC4078X has a thermal resistance of approximately 40C/W. Failure to make thermal contact between the exposed pad on the backside of the package and the copper board will result in thermal resistances far greater than 40C/W. As an example, a correctly soldered LTC4078X can deliver over
LTC4078X
Figure 4. Input Soft Connect Circuit
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13
LTC4078X APPLICATIONS INFORMATION
In this circuit, capacitor C2 holds MN1 off when the cable is first connected. Eventually C2 begins to charge up to the USB input voltage applying increasing gate drive to MN1. The long time constant of R1 and C1 prevent the current from rapidly building up in the cable, thus dampening out any resonant overshoot. Reverse Polarity Input Voltage Protection In some applications, protection from reverse polarity voltage on the input supply pins is desired. With sufficient supply voltage, a series blocking diode can be used. In other cases where the voltage drop must be kept low, a P-channel MOSFET can be used (as shown in Figure 5).
DRAIN-BULK DIODE OF FET LTC4078X WALL ADAPTER DCIN
4078X F05
Figure 5. Low Loss Reverse Polarity Protection
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14
LTC4078X PACKAGE DESCRIPTION
DD Package 10-Lead Plastic DFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115 TYP 6 0.675 0.05 0.38 0.10 10
3.50 0.05 1.65 0.05 2.15 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.38 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS PIN 1 TOP MARK (SEE NOTE 6)
3.00 0.10 (4 SIDES)
1.65 0.10 (2 SIDES)
(DD10) DFN 1103
5 0.200 REF 0.75 0.05 2.38 0.10 (2 SIDES)
1
0.25 0.05 0.50 BSC
0.00 - 0.05
BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
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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.
15
LTC4078X TYPICAL APPLICATION
Full Featured Li-Ion Charger
WALL ADAPTER USB POWER LTC4078X DCIN USBIN 1F 1F PWR CHRG BATDET ITERM GND 3.9k 1k 1% BAT 1k 1k 800mA (WALL) 475mA (USB)
IUSB IDC 2.1k 1% 1.24k 1%
+
4.2V Li-Ion BATTERY PACK
4078X TA02
RELATED PARTS
PART NUMBER LTC3455 LTC4053 DESCRIPTION Dual DC/DC Converter with USB Power Management and Li-Ion Battery Charger USB Compatible Monolithic Li-Ion Battery Charger COMMENTS Efficiency >96%, Accurate USB Current Limiting (500mA/100mA), 4mm x 4mm QFN-24 Package Standalone Charger with Programmable Timer, Up to 1.25A Charge Current Thermal Regulation Prevents Overheating, C/10 Termination, C/10 Indicator, Up to 800mA Charge Current Charges Single-Cell Li-Ion Batteries Directly from USB Port, Thermal Regulation, 4mm x 4mm QFN-16 Package C/10 Charge Termination, Battery Kelvin Sensing, 7% Charge Accuracy 4.2V, 0.35% Float Voltage, Up to 1A Charge Current Seamless Transition Between Input Power Sources: Li-Ion Battery, USB and Wall Adapter, Low Loss (50m) Ideal Diode, 4mm x 4mm QFN-24 Package Charge Current Up to 950mA, Thermal Regulation, 3mm x 3mm DFN-8 Package 950mA Charger Current, Thermal Regulation, C/X Charge Termination, USB Charge Current Set Via Resistor, 3mm x 3mm DFN Package; LTC4075HVX Has 22V Input Protection. 950mA Charger Current, Thermal Regulation, C/X Charge Termination, Fixed C or C/5 USB Charge Current for Low Power USB Operation, 3mm x 3mm DFN Package 950mA Charger Current, Thermal Regulation, C/X Charge Termination, Programmable C or C/x USB Charge Current for Low Power USB Operation, Fixed C/10 Wall Adapter and C/10 or C/2 Charge Current Termination, 3mm x 3mm DFN Package Charges Single-Cell Li-Ion Batteries Directly from USB Port, Thermal Regulation, 200m Ideal Diode with <50m Option, 4mm x 3mm DFN-14 Package High Efficiency 1.2A Charger from 6V to 36V (40V Max) Input Charges Single-Cell Li-Ion Batteries Directly from USB Port, Thermal Regulation, 200m Ideal Diode with <50m Option, Bat-Track Adaptive Output Control (LTC4089), Fixed 5V Output (LTC4089-5), 4mm x 3mm DFN-14 Package Automatic Switching Between DC Sources, Load Sharing, Replaces ORing Diodes
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ThinSOT and PowerPath are trademarks of Linear Technology Corporation.
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16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0907 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

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