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LTC4050EMS-4.2#TRPBF

P1-P3P4-P6P7-P9P10-P12
7
LTC4050
4050f
at the CHRG pin and connect a weak current source to
ground, indicating that the battery is nearly fully charged
(C/10 occurs at approximately 94% charge).
An external capacitor on the TIMER pin sets the total
charge time. After a time-out occurs, the charge cycle is
terminated and the CHRG pin is forced high impedance. To
restart the charge cycle, remove the input voltage and
reapply it, or momentarily float the PROG pin.
Replacing the battery when charging will cause the timer
to be reset if the cell voltage of the new battery is below
3.88V (for 4.1V cells) or 3.98V (for 4.2V cells). If the
voltage is above 3.88V(for 4.1V cells) or 3.98V (for 4.2V
cells) the timer will continue for the remaining charge
time. In the case when a time out has occurred, a new
battery with a cell voltage of less than 3.88V or 3.98V can
be inserted and charged automatically with the full pro-
grammed charge time.
For batteries like lithium-ion that require accurate final
float voltage, the internal 2.47V reference, voltage ampli-
fier and the resistor divider provide regulation with ±1%
(max) accuracy.
The charger can be shut down by floating the PROG pin.
An internal current source will pull it high and clamp at
3.5V.
When the input voltage is not present, the charger goes
into a sleep mode, dropping I
CC
to 5µA. This greatly
reduces the current drain on the battery and increases the
standby time.
OPERATIO
U
The LTC4050 is a linear battery charger controller. The
charge current is programmed by the combination of a
program resistor (R
PROG
) from the PROG pin to ground
and a sense resistor (R
SENSE
) between the V
CC
and SENSE
pins. R
PROG
sets a program current through an internal
trimmed 800Ω resistor setting up a voltage drop from V
CC
to the input of the current amplifier (CA). The current
amplifier servos the gate of the external P-channel MOSFET
to force the same voltage drop across R
SENSE
which sets
the charge current. When the voltage at the BAT pin
approaches the preset float voltage, the voltage amplifier
(VA) will start sinking current which reduces the voltage
drop across R
SENSE
, thus reducing the charge current.
A charge cycle begins when the voltage at V
CC
pin rises
above the UVLO level, a program resistor is connected
from the PROG pin to ground, and the NTC thermistor
temperature is between 0°C and 50°C. At the beginning of
the charge cycle, if the battery voltage is below 2.49V, the
charger goes into trickle charge mode. The trickle charge
current is 10% of the full-scale current. If the cell voltage
stays low for one quarter of the total charge time, the
charge sequence will terminate.
The charger goes into the fast charge constant-current
mode after the voltage on the BAT pin rises above 2.49V.
In constant-current mode, the charge current is set by the
combination of R
SENSE
and R
PROG
.
When the battery approaches the final float voltage, the
charge current will begin to decrease. When the current
drops to 10% of the full-scale charge current, an internal
comparator will turn off the pull-down N-channel MOSFET
8
LTC4050
4050f
APPLICATIONS INFORMATION
WUU
U
Figure 1. Microprocessor Interface
Charger Conditions
The charger is off when any of the following conditions exist:
the voltage at the V
CC
pin is below 4V, the voltage at the V
CC
pin is greater than 4V but is less than 54mV above V
BAT
,
the PROG pin is floating, the timer has timed out or the
thermistor temperature is outside the acceptable range. In
this condition, the DRV pin is pulled to V
CC
and the internal
resistor divider is disconnected to reduce the current drain
on the battery.
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in shutdown mode until V
CC
rises above the undervoltage lockout threshold of 4V. To
prevent oscillation around V
CC
= 4V, the UVLO circuit has
built-in hysteresis.
Trickle Charge and Defective Battery Detection
At the beginning of the charging sequence, if the battery
voltage is low (below 2.49V), the charger goes into trickle
mode. In this mode, the charge current is reduced to 10%
of the full-scale current. If the low cell voltage persists for
one quarter of the total charge time, the battery is consid-
ered defective, the charge cycle is terminated and the
CHRG pin output becomes high impedance.
Shutdown
The LTC4050 can be forced into shutdown by floating the
PROG pin and allowing the internal 2.3µA current source
to pull the pin above the 3.6V shutdown threshold voltage.
In shutdown, the DRV pin is pulled up to V
CC
, turning off
the external P-channel MOSFET and resetting the internal
timer.
Programming Charge Current
The formula for the battery charge current (see Block
Diagram) is:
I
BAT
= (I
PROG
)(800Ω/R
SENSE
)
= (2.47V/R
PROG
)(800Ω/R
SENSE
) or
R
PROG
= (2.47V/I
BAT
)(800Ω/R
SENSE
)
where R
PROG
is the total resistance from the PROG pin to
ground.
For example, if 0.5A charge current is needed, select a
value for R
SENSE
that will drop 100mV at the maximum
charge current. R
SENSE
= 0.1V/0.5A = 0.2Ω, then calculate:
R
PROG
= (2.47V/500mA)(800Ω/0.2Ω) = 19.76k
For best stability over temperature and time, 1% resistors
are recommended. The closest 1% resistor value is 19.6k.
Programming the Timer
The programmable timer terminates the charge cycle.
Typically when charging at a 1C rate, a discharged Li-Ion
battery will become fully charged in 3 hours. For lower
charge current rates, extend the time accordingly. The
length of the timer is programmed by an external capaci-
tor at the TIMER pin. The total charge time is:
Time (Hours) = (3 Hours) • (C
TIMER
/0.1µF) or
C
TIMER
= 0.1µF • Time (Hours)/3 Hours
The timer starts when an input voltage greater than 4V is
applied and the program resistor is connected to ground.
After a time-out occurs, the CHRG output will go high
impedance to indicate that charging has stopped. To dis-
able the timer function, short the TIMER pin to GND.
2k
400k
CHRG
4050 F01
V
CC
LTC4050
V
+
OUT
µPROCESSOR
IN
3
8
V
DD
9
LTC4050
4050f
APPLICATIONS INFORMATION
WUU
U
CHRG Status Output Pin (C/10)
When the charge cycle starts, the CHRG pin is pulled to
ground by an internal N-channel MOSFET that can drive an
LED. When the charge current drops to 10% of the full-
scale current (C/10), the N-channel MOSFET turns off and
a weak 32µA current source to ground is connected to the
CHRG pin. After a time-out occurs, the pin goes high
impedance. By using two different value pull-up resistors,
a microprocessor can detect three states from this pin
(charging, C/10 and stop charging). See Figure 1.
When the LTC4050 is in charge mode, the CHRG pin is
pulled low by an internal N-channel MOSFET. To detect
this mode, force the digital output pin, OUT, high and
measure the voltage at the CHRG pin. The N-channel
MOSFET will pull the pin low even with a 2k pull-up
resistor. Once the charge current drops to 10% of the full-
scale current (C/10), the N-channel MOSFET turns off and
a 32µA current source is connected to the CHRG pin. The
IN pin will then be pulled high by the 2k pull-up. By forcing
the OUT pin into a high impedance state, the current
source will pull the pin low through the 400k resistor.
When the internal timer has expired, the CHRG pin will
change to high impedance state and the 400k resistor will
then pull the pin high to indicate charging has stopped.
The CHRG pin open-drain device will turn on if the BAT pin
falls below the trickle charge threshold and the LTC4050
has neither timed out nor been put into shutdown. For
example, if the battery and NTC thermistor are both
disconnected from the typical application circuit, the BAT
voltage will collapse due to the thermal fault and CHRG will
pull low. Entering shutdown by floating the PROG pin will
prevent the CHRG pulldown from turning␣ on.
ACPR Output Pin
The LTC4050 has an ACPR output pin to indicate that the
input supply (wall adapter) is higher than 4V and 54mV or
more above the voltage at the BAT pin. When both condi-
tions are met, the ACPR pin is pulled to ground by an
N-channel MOSFET that is capable of driving an LED.
Otherwise, this pin is in a high impedance state.
Gate Drive
Typically the LTC4050 controls an external P-channel
MOSFET to supply current to the battery. An external PNP
transistor can also be used as the pass transistor instead
of the P-channel MOSFET. Due to the low current gain of
the current amplifier (CA), a high gain Darlington PNP
transistor is recommended to avoid excessive charge
current error. The gain of the current amplifier is around
0.6µA/mV. For every 1µA of base current, a 1.6mV of gain
error shows up at the inputs of CA. With R
PROG
= 19.6k
(100mV across R
SENSE
), it represents 1.67% of error in
charge current.
Battery Detection
The LTC4050 can detect the insertion of a new battery.
When a battery with a voltage of less than 3.88V (for 4.1V
cells) or 3.98V (for 4.2V cells) is inserted, the LTC4050
resets the timer and starts a new charge cycle. If the cell
voltage of the new battery is above 3.88V (for 4.1V cells)
or 3.98V (for 4.2V cells), a new charge cycle will not begin.
If a new battery (with cell voltage above 3.88V) is inserted
while in the charging process, the timer will not be reset,
but will continue until the timer runs out.
After a time out has occurred and the battery remains
connected, a new charge cycle will begin if the battery
voltage drops below the recharge threshold of 3.88V (for
4.1V cells) or 3.98V (for 4.2V cells) due to self-discharge
or external loading.
Stability
The charger is stable without any compensation when a
P-channel MOSFET is used as the pass transistor.
However, a 10µF capacitor is recommended at the BAT
pin to keep the ripple voltage low when the battery is
disconnected.
P1-P3P4-P6P7-P9P10-P12

LTC4050EMS-4.2#TRPBF

Mfr. #:
Buy LTC4050EMS-4.2#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Battery Management Li-Ion Battery Charger w/ Thermistor Interface
Lifecycle:
New from this manufacturer.
Delivery:
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