LTC4056-4.2
Linear Li-Ion Charger
with Termination in ThinSOT
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FEATURES
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DESCRIPTIO
Standalone Li-Ion Charger with Termination
Programmable Termination Timer
No Sense Resistor or Blocking Diode Required
Suitable for USB-Powered Charging
Undervoltage Charge Current Limiting
Preset Charge Voltage with ±0.6% Accuracy
Programmable Charge Current: 200mA to 700mA
Automatic Recharge with Shortened Charge Cycle
Self-Protection for Overcurrent/Overtemperature
40µA Supply Current in Shutdown Mode
Negligible Battery Drain Current in Shutdown
Low Battery Charge Conditioning (Trickle Charging)
CHRG Status Output including AC Present
PCB Total Solution Area only 75mm2 (700mA)
Low Profile (1mm) SOT-23 Package
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APPLICATIO S
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Cellular Telephones
Handheld Computers
Digital Cameras
Charging Docks and Cradles
Low Cost and Small Size Chargers
The LTC®4056 is a low cost, single-cell, constant-current/
constant-voltage Li-Ion battery charger controller with a
programmable termination timer. When combined with a
few external components, the LTC4056 forms a very small
standalone charger for single cell lithium-ion batteries.
Charge current and charge time are set externally with a
single resistor and capacitor, respectively. The LTC4056
charges to a final float voltage accurate to ±0.6%. Manual
shutdown is accomplished by grounding the TIMER/
SHDN pin, while removing input power automatically puts
the LTC4056 into a sleep mode. Both the shutdown and
sleep modes drain near zero current from the battery; the
shutdown mode reduces supply current to 40µA.
The output driver is both current limited and thermally
protected to prevent operating outside of safe limits. No
external blocking diode or sense resistor is required. The
LTC4056 also includes low battery charge conditioning
(trickle charging), undervoltage charge current limiting,
automatic recharge and a charge status output.
The LTC4056 is available in a low profile (1mm) 8-lead
SOT-23 (ThinSOTTM) package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
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TYPICAL APPLICATIO
VIN Undervoltage Charge
Current Limiting
800
VCC
CHARGE
STATUS
700mA
DRIVE
ZXT1M322
CHRG
TIMER/SHDN
1µF
1µF
LTC4056
ISENSE
+
PROG
1.3k
BAT
GND
1-CELL
4.2V Li-Ion
IBAT (mA)
VIN
4.5V TO 6.5V
VBAT = 4V
700 RPROG = 1.3k
ICHG = 700mA
INPUT Z = 100mΩ
600
500
UNDERVOLTAGE CHARGE
CURRENT LIMITING
400
300
200
100
4056-4.2 TA01
CONSTANT
CURRENT
UNDERVOLTAGE
LOCKOUT
AT 4.35V
0
4.40 4.45
4.50 4.55 4.60 4.65 4.70 4.75
VIN (V)
4056 TA02
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LTC4056-4.2
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
Input Supply Voltage (VCC) ........................– 0.3V to 10V
BAT, CHRG ................................................– 0.3V to 10V
DRIVE, PROG, TIMER/SHDN ....... – 0.3V to (VCC + 0.3V)
Output Current (ISENSE) ...................................... 900mA
Short-Circuit Duration (BAT, ISENSE) ............Continuous
Junction Temperature ........................................... 125°C
Operating Ambient Temperature Range
(Note 2) .............................................. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
TOP VIEW
VCC 1
ISENSE 2
DRIVE 3
GND 4
8 CHRG
TIMER/
7
SHDN
6 BAT
LTC4056ETS8-4.2
5 PROG
TS8 PART
MARKING
TS8 PACKAGE
8-LEAD PLASTIC SOT-23
TJMAX = 125°C, θJA = 120°C/W TO 200°C/W
DEPENDING ON PC BOARD LAYOUT
LTG5
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
6.5
V
400
600
µA
VCC Supply
VCC
Input Supply Voltage (Note 3)
ICC
Quiescent VCC Supply Current
●
VBAT = 4.5V (Forces IDRIVE = 0)
IPROG = 200µA (RPROG = 5k)
4.5
●
ISHDN
VCC Supply Current in Manual Shutdown
VTIMER/SHDN = 0V
40
60
µA
IBMS
Battery Drain Current in
Manual Shutdown (Note 4)
VTIMER/SHDN = 0V
●
–1
0
1
µA
IBSL
Battery Drain Current in
Sleep Mode (Note 5)
VCC = 0V
●
–1
0
1
µA
VUVLOI
Undervoltage Rising Threshold
VCC Increasing
●
4.325
4.40
4.475
V
VUVLOD
Undervoltage Falling Threshold
VCC Decreasing
●
4.275
4.35
4.425
VUVHYS
Undervoltage Hysteresis
VUVLOI-VUVLOD
VUVCL
Undervoltage Charge Current Limit Threshold
50
4.575
VUVCL-VUVLOI UV Charge Current to UVLO Threshold Margin
V
mV
V
●
90
170
250
●
4.175
4.158
4.200
4.200
4.225
4.242
mV
Charging Performance
VFLOAT
IBAT
Output Float Voltage in
Constant Voltage Mode
IBAT = 10mA
IBAT = 10mA, 4.75V ≤ VCC ≤ 6.5V
Output Full-Scale Current in
Constant Current Mode
RPROG = 5k, 4.75V ≤ VCC ≤ 6.5V,
PNP Beta > 50, 0°C ≤ TA ≤ 85°C
137
183
228
mA
RPROG = 1.43k, 4.75V ≤ VCC ≤ 6.5V,
PNP Beta > 50, 0°C ≤ TA ≤ 85°C
590
640
690
mA
IDSINK
Drive Output Current
VDRIVE = 3V
ITRIKL
Trickle Charge Current
VBAT = 2V, RPROG = 5k
VBAT = 2V, RPROG = 1.43k
VTRIKL
Trickle Charge Threshold Voltage
VBAT Falling
∆VTRIKL
Trickle Charge Hysteresis Voltage
VPROG1
PROG Pin Voltage
RPROG = 5k (IPROG = 200µA)
VPROG2
PROG Pin Voltage
RPROG = 1.43k (IPROG = 700µA)
●
30
V
V
mA
5
12
7
20
10
28
2.73
2.80
2.87
45
70
95
●
0.98
1
1.02
V
●
0.98
1
1.02
V
●
mA
mA
V
mV
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LTC4056-4.2
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
∆VRECHRG
Recharge Threshold Voltage
VFLOAT – VRECHRG, VBAT > VTRIKL,
Charge Termination Timer Expired
100
150
200
mV
TTIMER
TIMER/SHDN Accuracy
CTIMER = 1µF RPROG = 1.43k
●
10
12
%
●
0.6
0.82
1
V
Charger Manual Control
VMSDT
Manual Shutdown Threshold Voltage
VTIMER/SHDN Increasing
VMSHYS
Manual Shutdown Hysteresis Voltage
VTIMER/SHDN Decreasing
50
75
125
mV
ISHDN
TIMER/SHDN Pin Pull-up Current
VTIMER/SHDN = 0V
– 10
–7
–4
µA
IDSHRT
Drive Output Short-Circuit Current Limit
VDRIVE = VCC
30
65
130
mA
IPSHRT
PROG Pin Short-Circuit Current Limit
VPROG = 0V
ICHRG
CHRG Pin Weak Pull-Down Current
VCHRG = 1V, VTIMER/SHDN = 0V
VCHRG
CHRG Output Low Voltage
ICHRG = 10mA
Protection
●
1.4
mA
Status Output
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC4056E is guaranteed to meet performance specifications
from 0°C to 70°C ambient temperature range. Specifications over the
– 40°C to 85°C operating ambient temperature range are assured by
design, characterization and correlation with statistical process controls.
Note 3: Although the LTC4056 will operate with input voltages as low as
4.5V, charging will not begin until VCC exceeds VUVCL.
6
●
12
18
µA
0.2
0.4
V
Note 4: Assumes that the external PNP pass transistor has negligible B-C
reverse-leakage current when the collector is biased at 4.2V (VBAT) and the
base is biased at 5V (VCC).
Note 5: Assumes that the external PNP pass transistor has negligible B-E
reverse-leakage current when the emitter is biased at 0V (VCC) and the
base is biased at 4.2V (VBAT).
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TYPICAL PERFOR A CE CHARACTERISTICS
Float Voltage vs Temperature and
Supply Voltage
4.202
IBAT = 10mA
PNP = FZT749
FLOAT VOLTAGE (V)
4.210
VFLOAT (V)
4.205
4.200
4.195
VCC = 4.75V
220
VCC = 5V
TA = 25°C
PNP = FZT749
4.201 RPROG = 1.30k
VCC = 6.5V
RPROG = 4.53k
215 PNP = FZT749
210
IBAT (mA)
4.215
IBAT vs Temperature and
Supply Voltage
Float Voltage vs IBAT
4.200
VCC = 6.5V
200
VCC = 4.75V
195
4.199
190
4.190
4.185
–50 –25
205
185
4.198
50
25
75
0
TEMPERATURE (°C)
100
125
4056-4.2 G01
0
100
200
300 400
IBAT (mA)
500
600
700
4056-4.2 G02
180
– 50 – 25
75
50
25
TEMPERATURE (°C)
0
100
125
4056-4.2 G03
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LTC4056-4.2
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TYPICAL PERFOR A CE CHARACTERISTICS
IBAT vs Temperature and
Supply Voltage
RPROG = 1.30k
PNP = FZT749
VCC = 6.5V
IBAT (mA)
VCC = 4.75V
700
BAT PIN MUST BE
DISCONNECTED
AND SET BETWEEN
2.9V AND 4.2V TO
FORCE CC MODE
IN THIS AREA
400
200
VCC = 5V
RPROG = 1.43k
3
500
300
690
4
RPROG
1.30k
600
710
IBAT (mA)
5
VCC = 5V
700 TA = 25°C
PNP = FZT749
720
RPROG
4.53k
2
1
0
–1
–2
–3
680
670
–50
Timer Error vs Temperature
IBAT vs VBAT
800
TIMER ERROR (%)
730
100
–25
0
25
50
TEMPERATURE (°C)
75
100
0
–4
1
0
2
4
3
VBAT (V)
4056-4.2 G04
50
25
0
75
TEMPERATURE (°C)
4056-4.2 G05
TIMER/SHDN Pin Pull-Up Current
vs Temperature and Supply Voltage
12
–5
–50 –25
5
100
125
4056-4.2 G06
CHRG Pin Weak Pull-Down Current
vs Temperature and VCHRG
20
VTIMER/SHDN = 0V
VTIMER/SHDN = 0V
VCC = 5V
10
15
ICHRG (µA)
ISHDN (µA)
8
VCC = 6.5V
6
VCC = 4.75V
VCHRG = 6.5V
VCHRG = 1V
10
4
2
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
5
–50
125
–25
0
25
50
75
TEMPERATURE (°C)
125
4056-4.2 G08
4056-4.2 G07
CHRG Pin Output Low Voltage
vs Temperature
0.40
100
PROG Pin Voltage
vs Temperature and RPROG
1.0050
VBAT = 0V
ICHRG = 10mA
VCC = 5V
0.35
VCC = 5V
1.0025
VPROG (V)
VCHRG (V)
RPROG = 4.53k
0.30
1.0000
0.25
0.20
–50
RPROG = 1.30k
0.9975
–25
0
25
50
TEMPERATURE (°C)
75
100
4056-4.2 G09
0.9950
–50
–25
75
0
25
50
TEMPERATURE (°C)
100
125
4056-4.2 G10
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LTC4056-4.2
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PI FU CTIO S
VCC (Pin 1): Positive Input Supply Voltage. This pin
supplies power to the internal control circuitry and external PNP transistor through the internal current sense
resistor. This pin should be bypassed to ground with a
capacitor in the range of 1µF to 10µF.
ISENSE (Pin 2): Sense Node for Charge Current. Current
from VCC passes through the internal current sense resistor and out of the ISENSE pin to supply current to the emitter
of the external PNP transistor. The collector of the PNP
provides charge current to the battery.
DRIVE (Pin 3): Base Drive Output for the External PNP
Pass Transistor. Provides a controlled sink current to
drive the base of the PNP. This pin has current limiting
protection.
GND (Pin 4): Ground. Provides a reference for the internal
voltage regulator and a return for all internal circuits.
When in the constant voltage mode, the LTC4056 will
precisely regulate the voltage between the BAT and GND
pins. The battery ground should connect close to the GND
pin to avoid voltage drop errors.
PROG (Pin 5): Charge Current Programming Pin. Provides a virtual reference voltage of 1V for an external
resistor (RPROG) connected between this pin and ground
to program the battery charge current. In constant current
mode the typical charge current is 915 times the current
through this resistor (ICHG = 915V/RPROG). Current is
limited to approximately 1.4mA (ICHG of approximately
1.4A).
BAT (Pin 6): Battery Voltage Sense Input. A precision
internal resistor divider sets the final float voltage on this
pin. This divider is disconnected in the manual shutdown
or sleep mode. No bypass capacitance is needed on this
pin for stable operation when a battery is present. However, any low ESR capacitor exceeding 22µF on this pin
should be decoupled with 0.2Ω to 1Ω resistor. Without a
battery, a minimum bypass capacitance of 4.7µF with
0.5Ω series resistance is required.
TIMER/SHDN (Pin 7): Programmable Charge Termination
Timer and Shutdown Input. Pulling this pin below the
shutdown threshold voltage will shut down the charger
reducing the supply current to approximately 40µA and
the battery drain current to near 0µA. A capacitor on this
pin programs the charge termination timer.
CHRG (Pin 8): Open-Drain Charge Status Output. When
the battery is being charged, the CHRG pin is pulled low by
an internal N-channel MOSFET. When the timer has timed
out (terminating the charge cycle) or when the LTC4056 is
in shutdown, but power is applied to the IC (i.e., VCC >
VUVLOI), a 12µA current source is connected from the
CHRG pin to ground. The CHRG pin is forced to a high
impedance state when input power is not present (i.e., VCC
< VUVLOD).
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LTC4056-4.2
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BLOCK DIAGRA
VCC
1
LTC4056-4.2
CHRG
8
100Ω
110mΩ
UVLO
2
–
12µA
+
CA
CHRG
UV
LOGIC
SHDN
ISENSE
TEMPERATURE
AND
CURRENT LIMIT
SHDN
20µA
SHDN
DRIVE
OUTPUT
DRIVER
3
ITRIKL
20 • IPROG
COUNTER
7µA
TIMER/SHDN
BAT
OSCILLATOR
7
1.2V VOLTAGE
REFERENCE
6
C1
REF
1V
+
–
+
+
IA
+
–
1.2V
VA
–
IPROG
SHDN
5
4
4056-4.2 BD
PROG
RPROG
GND
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LTC4056-4.2
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OPERATIO
The LTC4056 is a linear battery charger controller with a
programmable charge termination timer. Operation can
be understood by referring to the Block Diagram. A charge
cycle begins when VCC rises above the UVLO (undervoltage
lockout) threshold VUVLOI (nominally 4.4V), an external
current programming resistor is connected between the
PROG pin and ground and the TIMER/SHDN pin is allowed
to rise above the shutdown threshold VMSDT (nominally
0.82V).
If the battery voltage is below VTRIKL (2.8V) at the beginning of the charge cycle, the charger goes into trickle
charge mode to bring the cell voltage up to a safe level for
charging at full current. In this mode, an internal current
source provides approximately 2% of the programmed
charge current to the BAT pin. The charger goes into the
full charge constant current mode once the voltage on the
BAT pin rises above VTRIKL + ∆VTRIKL (2.9V).
During full current charging, the collector of the external
PNP provides the charge current. The PNP emitter current
flows through the ISENSE pin and through the internal
110mΩ current sense resistor. This current is close in
magnitude, but slightly more than the collector current
since it includes base current. Amplifier A1 forces 1V on
the PROG pin. Therefore, a current equal to 1V/RPROG will
flow through the internal 100Ω resistor. Amplifier CA will
force the same voltage that appears across the 100Ω
resistor to appear across the internal 110mΩ resistor.
This amplifier ensures that the current flowing out of the
ISENSE pin is equal to 915 times the current flowing out of
the PROG pin. Therefore, neglecting base current, the
charge current will be 915V/RPROG. This region of operation is referred to as constant current mode.
As the battery accepts charge, its voltage rises. When it
reaches the preset float voltage of 4.2V, a precisely divided
down version of this voltage (1.2V) is compared to the
1.2V internal reference voltage by amplifier VA. If the
battery voltage attempts to exceed 4.2V (1.2V at the input
of amplifier VA), the amplifier will divert current away from
the output driver thus limiting charge current to maintain
4.2V on the battery. This is the constant voltage mode.
An external capacitor on the TIMER/SHDN pin and the
resistance between the PROG pin and ground set the total
charge time. When this time elapses, the charge cycle
terminates and the CHRG pin transitions from a strong
pull-down to a weak 12µA pull-down. To restart the charge
cycle, simply remove the input voltage and reapply it or
momentarily force the TIMER/SHDN pin to ground. The
charge cycle will also restart if the BAT pin voltage falls
below the recharge threshold (VRECHRG is nominally 4.05V).
When VCC is applied, pulling the TIMER/SHDN pin to
ground will manually shut down the charger and reset the
timer. When this pin is released an internal 7µA current
source pulls the TIMER/SHDN pin above the 0.82V shutdown threshold to resume charging.
Fault conditions such as overheating of the die or excessive DRIVE pin or PROG pin current are monitored and
limited.
When input power is removed or manual shutdown is
entered, the charger will drain only tiny leakage currents
(<1µA) from the battery, thus maximizing battery standby
time. With VCC removed the external PNP base is connected to the battery by the charger. In manual shutdown
the base is connected to VCC by the charger.
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LTC4056-4.2
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APPLICATIO S I FOR ATIO
Undervoltage Lockout
An internal undervoltage lockout (UVLO) circuit monitors
the input voltage and keeps the charger in shutdown mode
until VCC rises above the UVLO threshold (VUVLOI is
typically 4.4V). Approximately 50mV of hysteresis is built
in to prevent oscillation around the threshold level. In
undervoltage lockout, battery drain current is very low
(<1µA) and supply current is approximately 40µA.
Undervoltage Charge Current Limiting
The LTC4056 includes undervoltage charge current limiting that prevents full charge current until the input supply
voltage reaches a threshold value (VUVCL). This feature is
particularly useful if the LTC4056 is powered from a
supply with long leads (or any relatively high output
impedance).
For example, USB powered systems tend to have highly
variable source impedances (due primarily to cable quality
and length). A transient load combined with such an
impedance can easily trip the UVLO threshold and turn the
charger off unless undervoltage charge current limiting is
implemented.
Consider a situation where the LTC4056 is operating
under normal conditions and the input supply voltage
begins to sag (e.g. an external load drags the input supply
down). If the input voltage reaches VUVCL (approximately
170mV above the rising undervoltage lockout threshold,
VUVLOI), undervoltage charge current limiting will begin to
reduce the charge current in an attempt to maintain VUVCL
at the VCC input of the IC. The LTC4056 will continue to
operate at the reduced charge current until the input
supply voltage is increased or voltage mode reduces the
charge current further.
Trickle Charge and Defective Battery Detection
At the beginning of a charge cycle, if the battery voltage is
low (below VTRIKL of about 2.8V) the charger goes into
trickle charge mode reducing the charge current to approximately 2% of the full-scale current. If the low battery
voltage persists for one quarter of the total charge time,
the battery is assumed to be defective, the charge cycle is
terminated and the CHRG pin output transitions from a
strong pull-down to a 12µA pull-down. To restart the
charge cycle, remove the input voltage and reapply it or
momentarily force the TIMER/SHDN pin to ground.
Programming Charge Current
When in constant current mode, the full-scale charge
current is programmed using a single external resistor
between the PROG pin and ground, RPROG. The current
delivered to the ISENSE pin (flowing from VCC through the
internal 110mΩ sense resistor) will be 915 times the
current in RPROG. Because the LTC4056 provides a virtual
1V source at the PROG pin, the charge current is given by:
 1V 
ICHG = (IPROG ) • 915 = 
 • 915 or
 RPROG 
 1V 
RPROG = 
 • 915
 ICHG 
Under trickle charge conditions, this current is reduced to
approximately 2% of the full-scale value. The actual battery charge current (IBAT) is slightly lower than the expected charge current because the charger forces the
emitter current and the battery charge current will be
reduced by the base current. In terms of β (IC/IB), IBAT can
be calculated as follows:
 β  915V  β 
IBAT A = 915 • IPROG
•
=

 β + 1 RPROG  β + 1
()
If β = 50, then IBAT is 2% low. If desired, reducing RPROG
by 2% can compensate for the 2% drop.
For example, if 700mA charge current is required, calculate:
 1V 
RPROG = 
 • 915 = 1.3k
 700mA 
If a low β needs to be compensated for, say β = 50,
calculate:
RPROG =
915V  50 
•
 = 1.27k
700mA  50 + 1
For best stability over temperature and time, 1% metalfilm resistors are recommended.
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LTC4056-4.2
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APPLICATIO S I FOR ATIO
Termination Timer
The programmable timer is used to terminate the charge
cycle. The timer duration is programmed by an external
capacitor at the TIMER/SHDN pin and the external PROG
resistor. The total charge time is:
the TIMER/SHDN pin is released. Given the low magnitude
of this current, it is a simple matter for an external opendrain (or open-collector) output to pull the TIMER/SHDN
pin to ground for shutdown and release the pin for normal
operation.
Time(Hours) = 1.935 • RPROG(k) • CTIMER(µF) or
Sleep Mode
CTIMER(µF) = Time(Hours)/1.935 • RPROG(k)
When the input supply is disconnected, the IC enters the
sleep mode. In this mode, the battery drain current (IBSL)
is a negligible leakage current, allowing the battery to
remain connected to the charger for an extended period of
time without discharging the battery. The leakage current
is due to the reverse-biased B-E junction of the external
PNP transistor. Furthermore, the CHRG pin assumes a
high impedance state.
For example, to program a three hour timer with a 600mA
charge current (i.e., RPROG = 1.54k), calculate:
CTIMER =
3
= 1µF
1.935 • 1.54
The timer starts when an input voltage greater than the
undervoltage lockout threshold level is applied, a program
resistor is connected to ground and the TIMER/SHDN pin
is allowed to rise above the shutdown threshold. After a
time-out occurs, the charge current stops and the CHRG
output transitions from a strong pull-down to a 12µA pulldown to indicate charging has stopped. As long as the
input supply remains above VUVLOD and the battery voltage remains above VRECHRG the charger will remain in this
standby mode.
If the battery voltage remains below VTRIKL for 25% of the
programmed time, the charger will enter standby mode.
Furthermore, if the battery voltage is above the recharge
threshold (VRECHRG is typically 4.05V) at the beginning of
a charge cycle or if a falling battery voltage triggers a
recharge cycle (following a previous time-out), the charge
cycle will be shortened to 50% of the programmed time.
This feature reduces the charge time for batteries that are
near full capacity. Connecting the TIMER/SHDN pin to VCC
disables the timer function.
Manual Shutdown
Pulling the TIMER/SHDN pin below VMSDT – VMSHYS
(typically 0.745V) will put the charger into shutdown
mode and reset the timer. In this mode, the LTC4056
consumes 40µA of supply current and drains a negligible
leakage current from the battery (IBMS).
A 7µA current source pulls up on the TIMER/SHDN pin
while in shutdown to ensure that the IC will start up once
CHRG Status Output Pin
When the charge cycle starts, the CHRG pin is pulled to
ground by an internal N-channel MOSFET capable of
driving an LED. When the charge cycle ends, the strong
pull-down transitions to a 12µA pull-down on the CHRG
pin as long as the input supply remains above the UVLO
threshold (VUVLOD) and the battery voltage remains above
VRECHRG. If the input supply falls below VUVLOD, the CHRG
pin assumes a high impedance state. Figure 1 shows a
flow diagram for a typical charge cycle. This diagram
indicates the status of the CHRG pin in each charger state.
A microprocessor can be used to distinguish the three
states of the CHRG pin (see Figure 2). To detect whether
the LTC4056 is in trickle charge, charge, or short charge
mode (i.e., strong pull-down), force the digital output pin
(OUT) high and measure the voltage at the CHRG pin. The
internal N-channel MOSFET will pull the pin voltage low
even with the 2k pull-up resistor. Once the charge cycle
terminates, the strong pull-down transitions to a 12µA
pull-down. The IN pin will then be pulled high by the 2k
pull-up resistor. To determine whether sufficient input
voltage is present for charging (i.e., high impedance), the
OUT pin should be forced to a high impedance state. If
VCC␣ >␣ VUVLOI then the 12µA CHRG pull-down will pull the
IN pin low through the 800k resistor; otherwise, the 800k
resistor will pull the IN pin high, indicating that
VCC␣ <␣ VUVLOD.
405642f
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POWER ON
BAT < 2.8V
TIMER/SHDN RELEASED
OR
VCC > VUVLOI
TRICKLE CHARGE MODE
2% FULL CURRENT
CHRG: STRONG PULLDOWN
25% PROGRAMMED
TIME ELAPSES
BAT > 4.05V
BAT > 2.9V
SHUTDOWN MODE
ICC DROPS TO < 40µA
CHRG: Hi-Z if VCC < VUVLOD
WEAK PULLDOWN
OTHERWISE
CHARGE MODE
FULL CURRENT
CHRG: STRONG PULLDOWN
TIMER/SHDN GROUNDED
OR
VCC < VUVLOD
2.8V < BAT < 4.05V
PROGRAMMED
TIME ELAPSES
STANDBY MODE
NO CHARGE CURRENT
CHRG: WEAK PULLDOWN
2.8V < BAT < 4.05V
50%
PROGRAMMED
TIME ELAPSES
RECHARGE/SHORT
CHARGE MODE
CHRG: STRONG PULLDOWN
4056-4.2 F01
Figure 1. State Diagram for a Typical Charge Cycle
V+
V DD
External PNP Transistor
1
VCC
800k
µPROCESSOR
LTC4056
CHRG
8
2k
OUT
IN
4056-4.2 F02
Figure 2. Using a Microprocessor to Determine CHRG State
Recharge
If the battery voltage drops below VRECHRG (typically
4.05V) after a charge cycle has terminated, a new charge
cycle will begin. The recharge circuit integrates the BAT
pin voltage for approximately a millisecond to prevent a
transient from restarting the charge cycle. During a recharge cycle the timer will terminate the charge cycle after
one-half of the programmed time has elapsed.
If the battery voltage remains below VTRIKL (typically 2.8V)
during trickle charge for one-fourth of the programmed
time, the battery may be defective and the charge cycle will
end. In addition, the recharge comparator is disabled and
a new charge cycle will not begin unless the input voltage
is toggled off then on, or the TIMER/SHDN pin is momentarily pulled to ground.
The external PNP pass transistor must have adequate
beta, low saturation voltage and sufficient power dissipation capability (including any heat sinking, if required).
To provide 700mA of charge current with the minimum
available base drive of approximately 30mA requires a
PNP beta greater than 23. If lower beta PNP transistors are
used, more base current is required from the LTC4056.
This can result in the output drive current limit being
reached, or thermal shutdown due to excessive power
dissipation.
With low supply voltages, the PNP saturation voltage
(VCESAT) becomes important. The VCESAT must be less
than the minimum supply voltage minus the maximum
voltage drop across the internal sense resistor and bond
wires (0.20Ω) and battery float voltage. If the PNP transistor cannot achieve the low saturation voltage required,
base current will dramatically increase. This is to be
avoided for a number of reasons: output drive may reach
current limit resulting in the charger characteristics to go
out of specifications, excessive power dissipation may
force the IC into thermal shutdown, or the battery could
become discharged because some of the current from the
405642f
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LTC4056-4.2
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APPLICATIO S I FOR ATIO
DRIVE pin could be pulled from the battery through the
forward biased collector base junction.
For example, to program a charge current of 500mA with
a minimum supply voltage of 4.75V, the minimum operating VCE is:
VCE(MIN)(V) = 4.75 – (0.5) • (0.2) – 4.2 = 0.45V
Another important factor to consider when choosing the
PNP pass transistor is the power handling capability. The
transistor data sheet will usually give the maximum rated
power dissipation at a given ambient temperature with a
power derating for elevated temperature operation. The
maximum power dissipation of the PNP when charging is:
PD(MAX)(W) = IBAT • (VCC(MAX) – VBAT(MIN))
VCC(MAX) is the maximum supply voltage and VBAT(MIN) is
the minimum battery voltage when discharged.
Once the maximum power dissipation and VCE(MIN) are
known, Table 1 can be used as a guide in selecting some
PNPs to consider. In the table, very low VCESAT is less than
0.25V, low VCESAT is 0.25V to 0.5V and the others are 0.5V
to 0.8V all depending on the current. See the manufacturer data sheet for details. All of the transistors are rated
to carry at least 1A continuously as long as the power
dissipation is within limits. In addition, the maximum
supply voltage, minimum battery voltage and chosen
charge current should be checked against the
manufacturer’s data sheet to ensure that the PNP transistor is operating within its safe operating area. The Stability section addresses caution in the use of very high beta
PNP transistors.
Should overheating of the PNP transistor be a concern,
protection can be achieved with a positive temperature
coefficient (PTC) thermistor wired in series with the
current programming resistor and thermally coupled to
the transistor. The PTH9C chip series from Murata has a
steep resistance increase at temperature thresholds from
85°C to 145°C making it behave somewhat like a thermostat switch. For example, the model PTH9C16TBA471Q
thermistor is 470Ω at 25°C but abruptly increases its
resistance to 4.7k at 125°C. Below 125°C, the device
exhibits a small negative TC. The 470Ω thermistor can be
added in series with a 976Ω resistor to form the current
programming resistor for a 640mA charger. Should the
thermistor reach 125°C, the charge current will drop to
160mA and inhibit any further increase in temperature.
Stability
The LTC4056 contains two control loops: constant voltage and constant current. The constant voltage loop is
stable without any compensation when a battery is connected with low impedance leads. Excessive lead length,
Table 1. PNP Pass Transistor Selection Guide
MAXIMUM PD(W)
MOUNTED ON BOARD
PACKAGE STYLE ZETEX PART NUMBER
AT TA = 25°C
3
ROHM PART NUMBER COMMENTS
2 x 2MLP
ZXT1M322
Very Low VCESAT
0.5
SOT-23
FMMT549
Low VCESAT
0.625
SOT-23
FMMT720
Very Low VCESAT, High Beta
1
1.1
1 to 2
SOT-89
FCX589 or BCX69
SOT-23-6
ZXT13P12DE6
SOT-89
FCX717
Very Low VCESAT, High Beta
Low VCESAT
2
SOT-223
FZT589
2
SOT-223
BCP69 or FZT549
0.75
Very Low VCESAT, High Beta, Small
FTR
2SB822
Low VCESAT
1
ATV
2SB1443
Low VCESAT
2
SOT-89
2SA1797
Low VCESAT
10 (TC = 25°C)
TO-252
2SB1182
Low VCESAT, High Beta
405642f
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however, may add enough series inductance to require a
bypass capacitor of at least 1µF from BAT to ground.
Furthermore, a 4.7µF capacitor with a 0.2Ω to 1Ω series
resistor from BAT to ground is required to keep ripple
voltage low when the battery is disconnected.
High value capacitors with very low ESRs (especially
ceramic) reduce the constant voltage loop phase margin,
possibly resulting in instability. Ceramic capacitors up to
22µF may be used in parallel with a battery, but larger
ceramics should be decoupled with 0.2Ω to 1Ω of series
resistance.
In the constant current mode, the PROG pin is in the
feedback loop, not the battery. Because of the additional
pole created by PROG pin capacitance, any additional
capacitance on this pin must be limited. Although higher
charge current applications (i.e., lower program resistance) can tolerate more PROG capacitance, a good rule of
thumb is to keep the capacitive loading on the PROG pin
to less than 660pF.
If additional capacitance on this pin is required (e.g., to
provide an accurate, filtered low current 1V reference to
external circuitry) a 1k to 10k decoupling resistor may be
needed (see Figure 3).
LTC4056
PROG
GND
ACCURATE,
FILTERED 1V
REFERENCE
10k
6
RPROG
CFILTER
4
4056-4.2 F03
Figure 3. Isolating Capacitive Load on PROG Pin and Filtering
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).
*
LTC4056
VIN
VCC
4056-4.2 F04
*DRAIN-BULK DIODE OF FET
Figure 4. Low Loss Input Reverse Polarity Protection
VCC Bypass Capacitor
Many types of capacitors with values ranging from 1µF to
10µF located close to the LTC4056 will provide adequate
input bypassing. However, caution must be exercised
when using multilayer 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 hot power source. For more information refer to Application Note 88.
Internal Protection
Internal protection is provided to prevent excessive PROG
pin currents (IPSHRT), excessive DRIVE pin currents
(IDSHRT) and excessive self-heating of the LTC4056 during
a fault condition. The faults can be generated from a
shorted PROG pin, a shorted DRIVE pin or from excessive
DRIVE pin current to the base of the external PNP transistor when it is in deep saturation from a very low VCE. This
protection is not designed to prevent overheating of the
external pass transistor. However, thermal coupling between the external PNP and the LTC4056 will allow the
internal thermal limit to deprive the PNP of base current
when the junction temperature of the IC rises above about
135°C. The temperature of the PNP at that point, however,
will be well in excess of 135°C. The exact temperature of
the PNP depends on the thermal coupling between the
LTC4056 and the PNP and on the θJA of the transistor. See
the section titled “External PNP Transistor” for information on protecting the transistor from overheating.
405642f
12
LTC4056-4.2
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TYPICAL APPLICATIO S
USB Charging
the input voltage does not drop below the undervoltage
lockout threshold.
The applications shown in Figures 5 and 6 are USB Li-Ion
chargers with automatic PowerPathTM control. In order to
comply with USB power specifications a Li-Ion battery
charger must be able to limit the current draw from the
USB power port to 500mA, operate at input voltages as low
as 4.75V (ignoring resistive drops in the cable and connectors which further reduce this value to 4.4V), and have a
low current standby mode.
The TIMER/SHDN pin can be used to put the LTC4056 into
a low current standby mode. By pulling TIMER/SHDN to
GND, the LTC4056 and LTC4412 will draw about 50µA to
60µA combined from the USB power port.
The LTC4056 actually regulates the current delivered to
the ISENSE pin (rather than the BAT pin current). This fact
allows the 500mA maximum USB power port consumption to be easily enforced by tying all system loads to the
ISENSE pin and programming the charger to supply just
under 500mA (Figures 5 and 6 are programmed for
490mA). The total impedance between the VCC pin and
ISENSE pin is typically 0.2Ω, so the maximum drop is just
100mV (at 500mA).
As described in Undervoltage Charge Current Limiting, the
LTC4056 will automatically reduce charge current if the
input supply voltage reaches VUVCL (typically 4.575V).
This feature ideally solves the additional 350mV of resistive drop that the USB power specification requires. If an
LTC4056 is connected to a particularly resistive USB
cable, then charge current will be reduced to ensure that
PowerPath is a trademark of Linear Technology Corporation.
USB
POWER
R1
750Ω
RED
LTC4056
1
CHRG
VCC
7
2
TIMER/SHDN ISENSE
6
3
BAT
DRIVE
5
4
PROG
GND
8
ON 0FF
M1
2N7002
R2
1.87k
M2B
1/2 IRF7329
Q1
ZXT1M322
SYSTEM
LOAD
C3
1µF
C4
4.7µF
R5
0.5Ω
C1
1µF
M2A
1/2 IRF7329
BAT
+
VIN SENSE
LTC4412
GND
GATE
C2
0.1µF
CTL
Li-Ion
R3
470k
STAT
4056-4.2 F05
Figure 5. USB Charging and Automatic PowerPath Control with Auxiliary P-Channel MOSFET for Lowest Loss
USB
POWER
R1
750Ω
RED
LTC4056
1
CHRG
VCC
7
2
TIMER/SHDN ISENSE
6
3
BAT
DRIVE
5
4
PROG
GND
8
ON 0FF
M1
2N7002
R2
1.87k
C1
1µF
C4
4.7µF
R5
0.5Ω
MBRS130LT3
Q1
ZXT1M322
M2
Si2315BDS
BAT
C3
1µF
+
C2
0.1µF
Li-Ion
VIN SENSE
LTC4412
GND
GATE
CTL
SYSTEM
LOAD
R4
750Ω
R3
470k
GREEN
STAT
M3
Si1301DL
4056-4.2 F06
Figure 6. USB Charging and Automatic PowerPath Control with LTC4412 in Comparator Mode
405642f
13
LTC4056-4.2
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TYPICAL APPLICATIO S
It is important to keep in mind that the LTC4056 can only
control charge current. If the system load is less than
500mA, then the LTC4056 can simply reduce the charge
current by an amount equal to the system load current and
the USB specification can be met. For instance, if the system load is 150mA, then the charge current will be reduced
from 490mA to 340mA and the total USB input current will
remain at 490mA, thereby meeting the specification.
However, if the system load is increased beyond 500mA
the LTC4056 will reduce the charge current to zero, and all
of the system load will be provided by the USB input. This
scenario will violate the USB power specification. In order
to avoid this situation, it is important to ensure that the
system load never exceeds 500mA.
The LTC4412 provides automatic switchover of the system load between a battery and the USB input supply. This
feature reduces the current drain on the battery to just a
few microamps when a USB input is present. Figure 5
shows a dual FET solution to minimize voltage drop
between the USB input voltage and the system load and
Figure 6 uses a Schottky diode to simplify the design.
Please refer to the LTC4412 data sheet for more information on the operation of the Ideal Diode Controller.
In both designs all USB input current passes through the
sense resistor of the LTC4056 to ensure that the maximum
current drawn from the USB input supply is limited to less
than 500mA (assuming the system load is less than
500mA).
In Figure 6, P-channel MOSFET, M3, provides drive for the
green LED that illuminates when the USB input supply is
present. In both designs, the CHRG pin of the LTC4056
drives the red LED to indicate charging. Keep in mind that
the Li-Ion battery will charge at a reduced rate if a significant system load is present. This is due to the fact that the
490mA charge current is split between the battery and the
system load.
Optional N-channel MOSFET, M1, can be used to shut
down the LTC4056 thereby reducing its input supply
current to about 40µA. This will automatically turn off the
red LED. However, since voltage will still be present on the
USB input (and therefore the ISENSE pin), Figure 6 will
continue to draw power through the green LED. The green
LED should not be used without additional control logic if
a low current standby mode is required.
NiCd or NiMH Charging
The application circuit in Figure 7 shows how to use an
LTC4056 to charge Nickel chemistry batteries with user
termination. NiCd or NiMH batteries require constant
current charging regardless of the battery voltage. To
disable the voltage mode of the LTC4056 it is necessary to
connect the BAT pin to a voltage between the trickle charge
threshold and the final float voltage.
Assuming a reasonably well controlled input voltage, this
can be accomplished with a simple resistor divider connected between the input supply and the BAT pin. In
Figure␣ 7, resistors R3 and R4 keep the BAT pin voltage
between the required voltage levels provided the input
voltage is between 4.5V and 6.1V (encompassing nearly
the entire specified operating input supply range of 4.5V to
6.5V). The LTC4056 has an internal impedance of approximately 2MΩ to GND on the BAT pin, so it is important to
keep the impedance of the resistor divider considerably
below that value. Furthermore, a 0.1µF bypass capacitor
may be required between the BAT pin and GND. If the input
voltage rises above 6.1V then it is possible that the battery
charge current will decrease due to the voltage mode
amplifier of the LTC4056.
The TIMER/SHDN manual shutdown threshold of the
LTC4056 is typically 0.82V, allowing the I/O port of a
microcontroller to drive this pin with standard logic levels
to manually control termination. Holding the TIMER/SHDN
pin high simultaneously enables the charger and disables
the internal timer function. A programmed constant current will be provided to the battery until the I/O port pulls
the TIMER/SHDN pin to GND.
VIN
4.5V TO 6.1V
R1
750Ω
RED
R3
31.6k 8
7
I/O
µCONTROL
TERM CHRG
6
5
R4
68.1k
R2
1.3k
LTC4056
CHRG
VCC
TIMER/SHDN ISENSE
BAT
PROG
DRIVE
GND
1
2
3
Q1
ZXT1M322
4
C3
1µF
NiCd
4056-4.2 F07
Figure 7. Nickel Chemistry Battery Charging
405642f
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LTC4056-4.2
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PACKAGE DESCRIPTIO
TS8 Package
8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
0.52
MAX
2.90 BSC
(NOTE 4)
0.65
REF
1.22 REF
1.4 MIN
3.85 MAX 2.62 REF
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.22 – 0.36
8 PLCS (NOTE 3)
0.65 BSC
0.80 – 0.90
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
0.09 – 0.20
(NOTE 3)
1.95 BSC
TS8 TSOT-23 0802
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
405642f
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
LTC4056-4.2
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1732
Lithium-Ion Linear Battery Charger Controller
Simple Charger uses External FET, Features Preset Voltages, C/10
Charger Detection and Programmable Timer, Input Power Good Indication
LTC1733
Monolithic Lithium-Ion Linear Battery Charger
Standalone charger with Programmable Timer, Up to 1.5A Charge Current,
Thermal Regulation Prevents Overheating
LTC1734
Lithium-Ion Linear Battery Charger in ThinSOT
200mA to 700mA, Simple ThinSOT Charger, No Blocking Diode,
No Sense Resistor Needed
LTC1734L
Lithium-Ion Linear Battery Charger Controller
50mA to 180mA, No Blocking Diode, No Sense Resistor Needed
LTC4002
Switch Mode Li-Ion Charger
4.7V ≤ VIN ≤ 24V, Up to 3A, 3Hr Timer, SO-8, DFN
LTC4050
Lithium-Ion Linear Battery Charger Controller
Simple Charger uses External FET, Thermistor Input for
Battery Temperature Sensing
LTC4052
Lithium-Ion Linear Battery Pulse Charger
Fully Integrated, Standalone Pulse Charger, Minimal Heat Dissipation,
Over Current Protection
LTC4053
USB Compatible Lithium-Ion Battery
Linear Monolithic Charger
Fully Integrated, Standalone Charger, 10-Lead MSOP, Thermal Regulation
Prevents Overheating when Powered from Wall Adapter and
≥1A Charge Current
LTC4054
Standalone Lithium-Ion Linear Battery Charger
in ThinSOT
Programmable Charge Current Up to 800mA; C/10 Charge Termination,
Complete Charger; No External MOSFET, Diode or Sense Resistor
LTC4057
800mA Linear Li-Ion Charger
Thermal Regulation, Charge Current Monitor Pin, SOT-23
LTC4058
950mA Linear Li-Ion Charger
3mm × 3mm DFN Package, C/10 Charge Termination, Standalone
LTC4064
Back-Up Li-Ion Battery Charger
Preset 4V Charge Voltage, Prolongs Battery Life Time, Standalone
LTC4410
USB Power Manager
Manages Total Power Between a USB Peripheral and Battery Charger;
Ensures Simultaneous Charging and use of Peripheral, ThinSOT Package
405642f
16
Linear Technology Corporation
LT/TP 1103 1K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
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