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LTC4068-4.2/LTC4068X-4.2 Standalone Linear Li-Ion Battery Charger with Programmable Termination
FEATURES

DESCRIPTIO
Programmable Charge Current Up to 950mA Complete Linear Charger in DFN Package No MOSFET, Sense Resistor or Blocking Diode Required Thermal Regulation Maximizes Charge Rate Without Risk of Overheating* Charges Directly from a USB Port Programmable Charge Current Termination Preset 4.2V Charge Voltage with 1% Accuracy Charge Current Monitor Output for Gas Gauging* Automatic Recharge Charge Status Output "AC Present" Output 2.9V Trickle Charge Threshold (LTC4068) Available Without Trickle Charge (LTC4068X) Soft-Start Limits Inrush Current Low Profile (3mm x 3mm x 0.75mm) DFN Package
The LTC(R)4068 is a complete constant-current/constantvoltage linear charger for single cell lithium-ion batteries. Its DFN package and low external component count make the LTC4068 ideally suited for portable applications. Furthermore, the LTC4068 is designed to work within USB power specifications. No external sense resistor or external blocking diode are required due to the internal MOSFET architecture. Thermal feedback regulates the charge current to limit the die temperature during high power operation or high ambient temperature conditions. The charge voltage is fixed at 4.2V and the charge current is programmed with a resistor. The LTC4068 terminates the charge cycle when the charge current drops below the programmed termination threshold after the final float voltage is reached. When the input supply (wall adapter or USB supply) is removed, the LTC4068 enters a low current state dropping the battery drain current to less than 2A. Other features include charge current monitor, undervoltage lockout, automatic recharge and status pins to indicate charge termination and the presence of adequate input voltage.
, LTC and LT are registered trademarks of Linear Technology Corporation. Protected by U.S. Patents, including 6522118.
APPLICATIO S

Cellular Telephones, PDAs, MP3 Players Bluetooth Applications
TYPICAL APPLICATIO
Complete Charge Cycle (750mAh Battery)
700
Single Cell Li-Ion Battery Charger with C/5 Termination
CHARGE CURRENT (mA)
600 500 400 300 200 100
CONSTANT CURRENT CONSTANT VOLTAGE
600mA VIN 4.5V TO 6.5V VCC BAT
LTC4068-4.2 CHRG ACPR ITERM EN PROG GND
+
825 1.65k
1-CELL Li-Ion BATTERY
1F
406842 TA01
0
3.00 0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25 406842 TA02 TIME (HOURS)
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VCC = 5V JA = 40C/W RPROG = 1.65k RTERM = 825 TA = 25C
U
4.75 4.50
BATTERY VOLTAGE (V)
U
U
4.25 4.00 3.75 3.50 3.25
1
LTC4068-4.2/LTC4068X-4.2
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW ITERM 1 BAT 2 CHRG 3 GND 4 9 8 7 6 5 EN ACPR VCC PROG
Input Supply Voltage (VCC) ....................... -0.3V to 10V PROG, ITERM ................................ - 0.3V to VCC + 0.3V BAT ............................................................. -0.3V to 7V CHRG, ACPR, EN ...................................... -0.3V to 10V BAT Short-Circuit Duration .......................... Continuous BAT Pin Current ........................................................ 1A PROG Pin Current ................................................... 1mA Maximum Junction Temperature .......................... 125C Operating Temperature Range (Note 2) .. - 40C to 85C Storage Temperature Range ................. - 65C to 125C
ORDER PART NUMBER LTC4068EDD-4.2 LTC4068XEDD-4.2 DD PART MARKING LBHZ LBQB
DD PACKAGE 8-LEAD (3mm x 3mm) PLASTIC DFN
TJMAX = 125C, JA = 40C/W (NOTE 3) EXPOSED PAD IS GROUND (PIN 9) MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V, unless otherwise noted.
SYMBOL VCC ICC PARAMETER Input Supply Voltage Input Supply Current Charge Mode (Note 4), RPROG = 10k Standby Mode (Charge Terminated) Shutdown Mode (EN = 5V, VCC < VBAT or VCC < VUV) 0C TA 85C, 4.3V < VCC < 6.5V RPROG = 10k, Current Mode RPROG = 2k, Current Mode Standby Mode, VBAT = 4.2V Shutdown Mode (EN = 5V, VCC < VBAT or VCC < VUV) Sleep Mode, VCC = 0V VBAT < VTRIKL, RPROG = 2k (Note 5) RPROG = 10k, VBAT Rising (Note 5) RPROG = 10k (Note 5) From VCC Low to High

ELECTRICAL CHARACTERISTICS
CONDITIONS

MIN 4.25
TYP 0.4 200 25
MAX 6.5 1 500 50 4.242 105 535 -6 2 2 60 3 3.92 300 1 5 140 50 110 22.5 1.07 0.6 0.6 140
UNITS V mA A A V mA mA A A A mA V mV V mV V V M mV mV mA mA V V V mV
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VFLOAT IBAT
Regulated Output (Float) Voltage BAT Pin Current
4.158 92 465
4.2 100 500 -2.5 1 1
ITRIKL VTRIKL VTRHYS VUV VUVHYS VEN(IL) VEN(IH) REN VASD ITERM VPROG VCHRG VACPR VRECHRG
Trickle Charge Current Trickle Charge Threshold Voltage Trickle Charge Hysteresis Voltage VCC Undervoltage Lockout Voltage VCC Undervoltage Lockout Hysteresis EN Pin Input Low Voltage EN Pin Input High Voltage EN Pin Pull-Down Resistor VCC - VBAT Lockout Threshold Charge Termination Current Threshold PROG Pin Voltage CHRG Pin Output Low Voltage ACPR Pin Output Low Voltage Recharge Battery Threshold Voltage
30 2.8 3.7 150 0.4 1.2 70 5
45 2.9 80 3.8 200 0.7 0.7 2 100 30 100 20 1 0.35 0.35
VCC from Low to High VCC from High to Low RTERM = 1k RTERM = 5k RPROG = 10k, Current Mode ICHRG = 5mA IACPR = 5mA VFLOAT - VRECHRG, 0C TA 85C

90 17.5 0.93
60
100
2
U
W
U
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WW
W
LTC4068-4.2/LTC4068X-4.2
The denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V, unless otherwise noted.
SYMBOL TLIM RON tSS tRECHARGE tTERM PARAMETER Junction Temperature in Constant Temperature Mode Power FET "ON" Resistance (Between VCC and BAT) Soft-Start Time Recharge Comparator Filter Time Termination Comparator Filter Time IBAT = 0 to IBAT =1000V/RPROG VBAT High to Low IBAT Drops Below Charge Termination Threshold 0.75 400 CONDITIONS MIN TYP 120 600 100 2 1000 4.5 2500 MAX UNITS C m s ms s
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: The LTC4068E-4.2/LTC4068XE-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: Failure to solder the exposed backside of the package to the PC board will result in a thermal resistance much higher than 40C/W. Note 4: Supply current includes PROG pin current and ITERM pin current (approximately 100A each) but does not include any current delivered to the battery through the BAT pin (approximately 100mA). Note 5: This parameter is not applicable to the LTC4068X.
TYPICAL PERFOR A CE CHARACTERISTICS
PROG Pin Voltage vs Supply Voltage (Constant Current Mode)
1.015 1.010 1.005 VCC = 5V VBAT = 4V TA = 25C RPROG = 10k
VPROG (V)
VPROG (V)
1.000 0.995
1.0000 0.9975 0.9950
IBAT (mA)
0.990 0.985
4
4.5
5
5.5 VCC (V)
6
UW
6.5 7
405842 G01
PROG Pin Voltage vs Temperature
1.0100 1.0075 1.0050 1.0025
400 300 200 100 0
Charge Current vs PROG Pin Voltage
600 500 VCC = 5V TA = 25C RPROG = 2k RTERM = 2k
VCC = 5V VBAT = 4V RPROG = 10k
0.9925 0.9900 -50 -25 50 25 TEMPERATURE (C) 0 75 100
0
0.2
0.4
0.6 0.8 VPROG (V)
1
1.2
405842 G02
405842 G03
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LTC4068-4.2/LTC4068X-4.2 TYPICAL PERFOR A CE CHARACTERISTICS
Regulated Output (Float) Voltage vs Charge Current
4.26 VCC = 5V 4.24 TA = 25C RPROG = 1.25k 4.22
VFLOAT (V) VFLOAT (V)
4.215 4.210 4.205 4.200 4.195 4.190 4.185 -50
4.18 4.16 4.14 4.12 4.10 0 100 200 300 400 IBAT (mA) 500 600 700
VFLOAT (V)
4.20
CHRG Pin I-V Curve (Pull-Down State)
30 TA = -40C 25 20 TA = 25C 30
ICHRG (mA)
IACPR (mA)
15 10 5 0 0 1 2 4 3 VCHRG (V) 5 VCC = 5V VBAT = 4V 6 7
15 10 5 0 0 1 2 4 3 VACPR (V) 5 6 7
ITRKL (mA)
TA = 90C
Trickle Charge Current vs Supply Voltage
60 50 RPROG = 2k 40 ITRKL (mA) VTRKL (V) 30 20 10 0 RPROG = 10k VBAT = 2.5V TA = 25C LTC4068 ONLY
3.000 2.975 2.950
2.900 2.875 2.850 2.825
IBAT (mA)
4
4.5
5
5.5 VCC (V)
6
4
UW
405842 G04
405842 G07
Regulated Output (Float) Voltage vs Temperature
VCC = 5V RPROG = 10k 4.215 4.210 4.205 4.200 4.195 4.190 4.185
Regulated Output (Float) Voltage vs Supply Voltage
TA = 25C RPROG = 10k
-25
0 25 50 TEMPERATURE (C)
75
100
4
4.5
5
5.5 VCC (V)
6
6.5
7
405842 G05
405842 G06
ACPR Pin I-V Curve (Pull-Down State)
60
TA = -40C 25 20 TA = 25C
Trickle Charge Current vs Temperature
VCC = 5V VBAT = 2.5V LTC4068 ONLY RPROG = 2k
TA = 90C
50 40 30 20 10 0 -50 RPROG = 10k
VCC = 5V VBAT = 4V
-25
0 25 50 TEMPERATURE (C)
75
100
405842 G08
405842 G09
Trickle Charge Threshold Voltage vs Temperature
VCC = 5V RPROG = 10k LTC4068 ONLY 600 500 400 300 200 100
Charge Current vs Battery Voltage
LTC4068 ONLY
2.925
6.5
7
2.800 -50
-25
50 25 TEMPERATURE (C)
0
75
100
0 2.4
VCC = 5V JA = 40C/W RPROG = 2k 2.7 3 3.3 3.6 VBAT (V) 3.9 4.2 4.5
405842 G10
405842 G11
405842 G12
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LTC4068-4.2/LTC4068X-4.2 TYPICAL PERFOR A CE CHARACTERISTICS
Charge Current vs Supply Voltage
600 500 400 RPROG = 2k
500 RPROG = 2k 400
IBAT (mA)
IBAT (mA)
VBAT = 4V 300 TA = 25C JA = 40C/W 200 100 0 RPROG = 10k
4
4.5
Power FET "ON" Resistance vs Temperature
700 650 600 VCC = 4.2V IBAT = 100mA RPROG = 2k
RDS(ON) (m)
550 500 450 400 350 -50
VRECHRG (V)
-25
PI FU CTIO S
ITERM (Pin 1): Charge Termination Program. The charge termination current threshold current is programmed by connecting a 1% resistor, RTERM, to ground. The current threshold ITERM, is set by the following formula: voltage. This divider is disconnected in shutdown mode to minimize current drain from the battery. CHRG (Pin 3): Charge Status Open-Drain Output. When the battery is charging, the CHRG pin is pulled low by an internal N-channel MOSFET. When the charge cycle is completed, CHRG becomes high impedance. GND (Pins 4, 9): Ground/Exposed Pad. The exposed backside package pad (Pin 9) is electrical ground and must be soldered to the PC board for maximum heat transfer.
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ITERM =
100V 100V , RTERM = RTERM ITERM
BAT (Pin 2): Charge Current Output. Provides charge current to the battery from the internal P-channel MOSFET, and regulates the final float voltage to 4.2V. An internal precision resistor divider from this pin sets the float
UW
5
Charge Current vs Ambient Temperature
600 ONSET OF THERMAL REGULATION
300 200 100 0 -50
VCC = 5V VBAT = 4V JA = 40C/W
RPROG = 10k
5.5 VCC (V)
6
6.5
7
-25
50 25 75 0 TEMPERATURE (C)
100
125
405842 G13
405842 G14
Recharge Threshold Voltage vs Temperature
4.16 4.14 4.12 4.10 4.08 4.06 4.04 -50 VCC = 5V RPROG = 10k
0 25 50 75 TEMPERATURE (C)
100
125
-25
0 25 50 TEMPERATURE (C)
75
100
405842 G17
405842 G15
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5
LTC4068-4.2/LTC4068X-4.2
PI FU CTIO S
PROG (Pin 5): Charge Current Program and Charge Current Monitor. Charge current is programmed by connecting a 1% resistor, RPROG, to ground. When charging in constant-current mode, this pin servos to 1V. In all modes, the voltage on this pin can be used to measure the charge current using the following formula: IBAT = (VPROG/RPROG) * 1000 This pin is clamped to approximately 2.4V. Driving this pin to voltages beyond the clamp voltage can draw large currents and should be avoided. VCC (Pin 6): Positive Input Supply Voltage. Provides power to the charger. VCC can range from 4.25V to 6.5V. This pin should be bypassed with at least a 1F capacitor. When VCC is within 100mV of the BAT pin voltage, the LTC4068 enters shutdown mode dropping the battery drain current to less than 2A. ACPR (Pin 7): Power Supply Status Open-Drain Output. When VCC is greater than the undervoltage lockout threshold and at least 100mV above VBAT, the ACPR pin is pulled to ground; otherwise, the pin is high impedance. EN (Pin 8): Enable Input . A logic high on the EN pin will put the LTC4068 into shutdown mode where the battery drain current is reduced to less than 2A and the supply current is reduced to less than 50A. A logic low or floating the EN pin (allowing an internal 2M pull-down resistor to pull this pin low) enables charging.
BLOCK DIAGRA
MA
ACPR 7 VA
CHRG 3
CA
-
* CHARGE ACPR
+
R3 1V R4
LOGIC TERM C1
+ -
0.1V R5
EN EN 8
SHDN
C2*
-
2.9V
+
TO BAT
*TRICKLE CHARGE DISABLED ON THE LTC4068X ITERM 1 RTERM 5 RPROG PROG GND 4, 9
6
+
-
W
U
U
U
6 VCC 120C TA TDIE 1x 1x 1000x
BAT 5A R1
2
+
R2
-
REF 1.211V
406842 BD
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LTC4068-4.2/LTC4068X-4.2
OPERATIO
The LTC4068 is a single cell lithium-ion battery charger using a constant-current/constant-voltage algorithm. It can deliver up to 950mA of charge current (using a good thermal PCB layout) with a final float voltage accuracy of 1%. The LTC4068 includes an internal P-channel power MOSFET and thermal regulation circuitry. No blocking diode or external current sense resistor is required; thus, the basic charger circuit requires only two external components. Furthermore, the LTC4068 is capable of operating from a USB power source. Normal Charge Cycle A charge cycle begins when the voltage at the VCC pin rises above the UVLO threshold level and a 1% program resistor is connected from the PROG pin to ground. If the BAT pin is less than 2.9V, the charger enters trickle charge mode. In this mode, the LTC4068 supplies approximately 1/10th the programmed charge current to bring the battery voltage up to a safe level for full current charging. (Note: The LTC4068X does not include this trickle charge feature.) When the BAT pin voltage rises above 2.9V, the charger enters constant-current mode where the programmed charge current is supplied to the battery. When the BAT pin approaches the final float voltage (4.2V), the LTC4068 enters constant-voltage mode and the charge current begins to decrease. When the charge current drops to the programmed termination threshold (set by the external resistor RTERM), the charge cycle ends. Programming Charge Current The charge current is programmed using a single resistor from the PROG pin to ground. The charge current out of the BAT pin is 1000 times the current out of the PROG pin. The program resistor and the charge current are calculated using the following equations:
RPROG =
1000 V 1000 V , I CHG = ICHG RPROG
Charge current out of the BAT pin can be determined at any time by monitoring the PROG pin voltage and using the following equation:
IBAT =
VPROG * 1000 RPROG
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Programming Charge Termination The charge cycle terminates when the charge current falls below the programmed termination threshold. This threshold is set by connecting an external resistor, RTERM, from the ITERM pin to ground. The charge termination current threshold (ITERM) is set by the following equation:
ITERM = 100V ICHG RPROG 100V = * , RTERM = RTERM 10 RTERM ITERM
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 tTERM (typically 1ms), charging is terminated. The charge current is latched off and the LTC4068 enters standby mode where the input supply current drops to 200A. (Note: Termination is disabled in trickle charging and thermal limiting modes.) ITERM can be set to be 1/10th of ICHG by shorting the ITERM pin to the PROG pin, thus eliminating the need for external resistor RTERM. When configured in this way, ITERM is always set to ICHG/10, and the programmed charge current is set by the equation:
500V 500V ICHG = ,RPROG = RPROG ICHG
**
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 to 10% of the programmed value. The 1ms filter time (tTERM) 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 LTC4068 terminates the charge cycle and ceases to provide any current out of the BAT pin. In this state, any load on the BAT pin must be supplied by the battery. The LTC4068 constantly monitors the BAT pin voltage in standby mode. If this voltage drops below the 4.1V recharge
* Any external sources that hold the ITERM pin above 100mV will prevent the LTC4068 from terminating a charge cycle. ** These equations apply only when the ITERM pin is shorted to the PROG pin.
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LTC4068-4.2/LTC4068X-4.2
OPERATIO
threshold (VRECHRG), another charge cycle begins and charge current is once again supplied to the battery. To manually restart a charge cycle when in standby mode, the input voltage must be removed and reapplied or the charger must be shut down and restarted using the EN pin. Figure 1 shows the state diagram of a typical charge cycle.
POWER ON BAT < 2.9V TRICKLE CHARGE MODE 1/10TH FULL CURRENT CHRG: STRONG PULL-DOWN BAT > 2.9V SHUTDOWN MODE ICC DROPS TO <25A CHRG: Hi-Z CHARGE MODE FULL CURRENT CHRG: STRONG PULL-DOWN ITERM < 100mV STANDBY MODE NO CHARGE CURRENT EN DRIVEN HIGH OR UVLO CONDITION CHRG: Hi-Z
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EN DRIVEN LOW OR UVLO CONDITION STOPS
Figure 1. State Diagram of a Typical Charge Cycle
Charge Status Indicator (CHRG) The charge status output has two states: pull-down and high impedance. The pull-down state indicates that the LTC4068 is in a charge cycle. Once the charge cycle has terminated or the LTC4068 is disabled, the pin state becomes high impedance. Power Supply Status Indicator (ACPR) The power supply status output has two states: pull-down and high impedance. The pull-down state indicates that VCC is above the UVLO threshold (3.8V) and is also 100mV above the battery voltage. If these conditions are not met, the ACPR pin is high impedance indicating that the LTC4068 is unable to charge the battery.
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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 LTC4068 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 LTC4068. 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 power considerations are discussed further in the Applications Information section. Undervoltage Lockout (UVLO)
BAT > 2.9V LTC4068 ONLY 2.9V < BAT < 4.1V
An internal undervoltage lockout circuit monitors the input voltage and keeps the charger in shutdown mode until VCC rises above the undervoltage lockout threshold. The UVLO circuit has a built-in hysteresis of 200mV. Furthermore, to protect against reverse current in the power MOSFET, the UVLO circuit keeps the charger in shutdown mode if VCC falls to within 30mV of the BAT voltage. If the UVLO comparator is tripped, the charger will not come out of shutdown mode until VCC rises 100mV above the BAT voltage. Manual Shutdown At any point in the charge cycle, the LTC4068 can be put into shutdown mode by driving the EN pin high. This reduces the battery drain current to less than 2A and the supply current to less than 50A. When in shutdown mode, the CHRG pin is in the high impedance state. A new charge cycle can be initiated by driving the EN pin low. An internal resistor pull-down on this pin forces the LTC4068 to be enabled if the pin is allowed to float. Automatic Recharge Once the charge cycle is terminated, the LTC4068 continuously monitors the voltage on the BAT pin using a comparator with a 2ms filter time (tRECHARGE). A charge cycle restarts when the battery voltage falls below 4.10V (which corresponds to approximately 80% to 90% battery capacity). This ensures that the battery is kept at, or near, a fully
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LTC4068-4.2/LTC4068X-4.2
APPLICATIO S I FOR ATIO
charged condition and eliminates the need for periodic charge cycle initiations. The CHRG output enters a pulldown state during recharge cycles. If the battery is removed from the charger, a sawtooth waveform of approximately 100mV appears at the charger output. This is caused by the repeated cycling between termination and recharge events. This cycling results in pulsing at the CHRG output; an LED connected to this pin will exhibit a blinking pattern, indicating to the user that a battery is not present. The frequency of the sawtooth is dependent on the amount of output capacitance. Stability Considerations The constant-voltage mode feedback loop is stable without an output capacitor, provided a battery is connected to the charger output. With no battery present, an output capacitor on the BAT pin is recommended to reduce ripple voltage. When using high value, low ESR ceramic capacitors, it is recommended to add a 1 resistor in series with the capacitor. No series resistor is needed if tantalum capacitors are used. In constant-current mode, the PROG pin is in the feedback loop, not the battery. The constant-current mode stability is affected by the impedance at the PROG pin. With no additional capacitance on the PROG pin, the charger is stable with program resistor values as high as 20k; however, additional capacitance on this node reduces the maximum allowed program resistor. The pole frequency at the PROG pin should be kept above 100kHz. Therefore, if the PROG pin is loaded with a capacitance, CPROG, the following equation can be used to calculate the maximum resistance value for RPROG: RPROG 1 2 * 105 * CPROG
Average, rather than instantaneous charge current may be of interest to the user. For example, if a switching power supply operating in low current mode is connected in parallel with the battery, the average current being pulled out of the BAT pin is typically of more interest than the instantaneous current pulses. In such a case, a simple RC
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filter can be used on the PROG pin to measure the average battery current, as shown in Figure 2. A 10k resistor has been added between the PROG pin and the filter capacitor to ensure stability.
LTC4068-4.2 PROG GND RPROG CFILTER
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10k
CHARGE CURRENT MONITOR CIRCUITRY
Figure 2. Isolating Capacitive Load on PROG Pin and Filtering
Power Dissipation It is not necessary to design for worst-case power dissipation scenarios because the LTC4068 automatically reduces the charge current during high power conditions. The conditions that cause the LTC4068 to reduce charge current through thermal feedback can be approximated by considering the power dissipated in the IC. Nearly all of this power dissipation is generated by the internal MOSFET--this is calculated to be approximately: PD = (VCC - VBAT) * IBAT where PD is the power dissipated, VCC is the input supply voltage, 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 - PDJA TA = 120C - (VCC - VBAT) * IBAT * JA Example: An LTC4068 operating from a 5V supply is programmed to supply 800mA full-scale current to a discharged Li-Ion battery with a voltage of 3.3V. Assuming JA is 50C/W (see Thermal Considerations), the ambient temperature at which the LTC4068 will begin to reduce the charge current is approximately: TA = 120C - (5V - 3.3V) * (800mA) * 50C/W TA = 120C - 1.36W * 50C/W = 120C - 68C TA = 52C
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LTC4068-4.2/LTC4068X-4.2
APPLICATIO S I FOR ATIO
The LTC4068 can be used above 52C ambient but the charge current will be reduced from the programmed 800mA. The approximate current at a given ambient temperature can be approximated by:
IBAT =
120C - TA
(VCC - VBAT ) * JA
Using the previous example with an ambient temperature of 60C, the charge current will be reduced to approximately:
IBAT =
120C - 60C
(5V - 3.3V) * 50C/W
=
60C 85C/A
IBAT = 706mA
Moreover, when thermal feedback reduces the charge current the voltage at the PROG pin is also reduced proportionally as discussed in the Operation section. It is important to remember that LTC4068 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 LTC4068 package is soldered to the PC board ground. Correctly soldered to a 2500mm2 doublesided 1oz copper board, the LTC4068 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 LTC4068 can deliver over 800mA to a battery from a 5V supply at room temperature. Without a good backside thermal connection, this number will drop considerably. VCC Bypass Capacitor Many types of capacitors can be used for input bypassing; however, caution must be exercised when using multilayer
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ceramic capacitors. Because of the self-resonant and high Q characteristics of some types of ceramic capacitors, high voltage transients can be generated under some start-up conditions such as connecting the charger input to a live power source. Adding a 1.5 resistor in series with an X5R ceramic capacitor will minimize start-up voltage transients. For more information, see Application Note 88. Charge Current Soft-Start The LTC4068 includes a soft-start circuit to minimize the inrush current at the start of a charge cycle. When a charge cycle is initiated, the charge current ramps from zero to full-scale current over a period of approximately 100s. This has the effect of minimizing the transient current load on the power supply during start-up. USB and Wall Adapter Power The LTC4068 allows charging from both a wall adapter and a USB port. Figure 3 shows how to combine wall adapter and USB power inputs. A P-channel MOSFET, MP1, is used to prevent back conducting into the USB port when a wall adapter is present and a Schottky diode, D1, is used to prevent USB power loss through the 1k pulldown resistor. Typically a wall adapter can supply more current than the 500mA-limited USB port. Therefore, an N-channel MOSFET, MN1, and an extra 3.3k program resistor are used to increase the charge current to 800mA when the wall adapter is present. The charge termination threshold remains fixed at 80mA.
5V WALL ADAPTER 800mA ICHG USB POWER 500mA ICHG D1 MP1 LTC4068-4.2 2 BAT 1 6 VCC ITERM 5 4, 9 GND PROG 3.3k 1k MN1 2k ICHG SYSTEM LOAD 1.25k
W
UU
+
Li-Ion BATTERY
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Figure 3. Combining Wall Adapter and USB Power
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LTC4068-4.2/LTC4068X-4.2
APPLICATIO S I FOR ATIO
Reverse Polarity Input Voltage Protection
In some applications, protection from reverse polarity voltage on VCC is desired. If the supply voltage is high enough, 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 4).
PACKAGE DESCRIPTIO
DD Package 8-Lead Plastic DFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1698)
3.5 0.05 1.65 0.05 2.15 0.05 (2 SIDES) PACKAGE OUTLINE 0.28 0.05 0.50 BSC 2.38 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP 5 0.38 0.10 8
PIN 1 TOP MARK
(DD8) DFN 0203
0.200 REF
NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-1) 2. ALL DIMENSIONS ARE IN MILLIMETERS 3. 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 4. EXPOSED PAD SHALL BE SOLDER PLATED
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.
U
DRAIN-BULK DIODE OF FET VIN LTC4068 VCC
405842 F04
U
W
UU
Figure 4. Low Loss Input Reverse Polarity Protection
0.675 0.05
3.00 0.10 (4 SIDES)
1.65 0.10 (2 SIDES)
0.75 0.05
4 0.28 0.05 2.38 0.10 (2 SIDES)
1 0.50 BSC
0.00 - 0.05
BOTTOM VIEW--EXPOSED PAD
406842fa
11
LTC4068-4.2/LTC4068X-4.2
TYPICAL APPLICATIO S
Full Featured Single Cell Li-Ion Charger
VIN 5V 1k 1k 6 VCC 500mA
1F
1F
2 7 ACPR BAT 1 3 CHRG ITERM LTC4068-4.2 8 5 EN PROG GND 4, 9
5V WALL ADAPTER USB POWER 1k 6 1F
RELATED PARTS
PART NUMBER LTC1732 LTC1733 LTC1734 LTC1734L LTC1998 LTC4007 LTC4050 LTC4052 LTC4053 LTC4054 LTC4057 LTC4058 LTC4058X LTC4410 DESCRIPTION Lithium-Ion Linear Battery Charger Controller Monolithic Lithium-Ion Linear Battery Charger Lithium-Ion Linear Battery Charger in ThinSOT Lithium-Ion Linear Battery Charger in ThinSOT Lithium-Ion Low Battery Detector 4A Multicell Li-Ion Battery Charger Lithium-Ion Linear Battery Charger Controller Monolithic Lithium-Ion Battery Pulse Charger USB Compatible Monolithic Li-Ion Battery Charger Standalone Linear Li-Ion Battery Charger in ThinSOT Li-Ion Linear Battery Charger Standalone Li-Ion Linear Charger in DFN USB Power Manager
TM
LTC4411 LTC4412
Low Loss PowerPathTM Controller in ThinSOT
ThinSOT and PowerPath are trademarks of Linear Technology Corporation.
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12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
U
Li-Ion Battery Charger with Reverse Polarity Input Protection
5V WALL ADAPTER 6 VCC BAT LTC4068-4.2 ITERM 8 EN PROG GND 4, 9
406842 TA04
500mA 2 1 5 1k
1k
1F 1-CELL Li-Ion BATTERY
405642 TA03
+
1-CELL Li-Ion BATTERY
2k
+
USB/Wall Adapter Power Li-Ion Charger
BAT LTC4068-4.2 VCC ITERM PROG GND 4, 9 1 5 1.25k 5k 100mA/ 500mA C
406842 TA05
2
IBAT
+
1-CELL Li-Ion BATTERY
COMMENTS Simple Charger uses External FET, Features Preset Voltages, C/10 Charger Detection and Programmable Timer, Input Power Good Indication Standalone Charger with Programmable Timer, Up to 1.5A Charge Current Simple ThinSOT Charger, No Blocking Diode, No Sense Resistor Needed Low Current Version of LTC1734; 50mA ICHRG 180mA 1% Accurate 2.5A Quiescent Current, SOT-23 Standalone Charger, 6V VIN 28V, Up to 96% Efficiency, 0.8% Charging Voltage Accuracy C/10 Charger Detection and Programmable Timer, Thermistor Interface No Blocking Diode or External Power FET Required, 1.5A Charge Current 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 Up to 800mA Charge Current, Thermal Regulation, ThinSOT Package Up to 950mA Charge Current, Kelvin Sense for High Accuracy, C/10 Charge Termination For Simultaneous Operation of USB Peripheral and Battery Charging from USB Port, Keeps Current Drawn from USB Port Constant, Keeps Battery Fresh, Use with the LTC4053, LTC1733, or LTC4054 Automatic Switching Between DC Sources, Load Sharing, Replaces ORing Diodes
LT/TP 0904 1K REV A * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2004

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