BL4054/BL4054B
800mA Standalone Linear Li-Ion Battery Charger
with Thermal Regulation in SOT23-5/TSOT23-5
Operation
The BL4054/BL4054B is a single cell
Lithium-Ion battery charger using a constant
current / constant voltage algorithm. It can
deliver up to 800mA of charge current
(using a good thermal PCB layout) with a
final float voltage accuracy of
1%. The
BL4054/BL4054B 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
BL4054/BL4054B is capable of operating
from a USB power source.
Normal Charge Cycle
A charge cycle begins when the voltage at
the V
CC
pin rises above the UVLO threshold
level and a 1% program resistor is
connected from the PROG pin to ground or
when a battery is connected to the charger
output. If the BAT pin is less than 2.9V, the
charger enters trickle charge mode. In this
mode, the BL4054/BL4054B supplies
approximately 1/10 the programmed charge
current to bring the battery voltage up to a
safe level for full current charging.
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. If the battery voltage
is above 2.9V at power-on, BL4054B enters
the constant-current mode immediately,
while BL4054 will perform one more check.
If the battery voltage is below the
auto-recharge threshold, BL4054 enters the
constant current mode, otherwise it goes to
standby mode. This is the only difference
between the BL4054 and BL4054B. Refer
to Figure 1a and 1b for more details.
PPMIC BU
BL4054/BL4054B Rev 1.4
5/2009
When the BAT pin approaches the final float
voltage (4.2V), the BL4054/BL4054B enters
constant-voltage mode and the charge
current begins to decrease. When the
charge current drops to 1/10 of the
programmed value, the charge cycle ends.
Programming Charge Current
The charge current is programmed using a
single resistor from the PROG pin to ground.
The battery charge current is 1000 times
the current out of the PROG pin. The
program resistor and the charge current are
calculated using the following equations:
R
PROG
=
1000V
I
CHG
I
CHG
=
1000V
R
PROG
The charge current out of the BAT pin can
be determined at any time by monitoring the
PROG pin voltage using the following
equation:
I
BAT
=
V
PROG
•
1000
R
PROG
Charge Termination
A charge cycle is terminated when the
charge current falls to 1/10 the programmed
value after the final float voltage is reached.
This condition is detected by using an
internal, filtered comparator to monitor the
PROG pin. When the PROG pin voltage
falls below 100mV for longer than T
TERM
(typically 1ms), charging is terminated. The
charge current is latched off and the
BL4054/BL4054B enters standby mode,
where the input supply current drops to
100
µ
A. (Note: C/10 termination is disabled
in trickle charging mode).
When charging, transient loads on the BAT
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