Datasheet

I
CHG
=
K
ISET
R
ISET
120°C - T
A
T
JA
(V
CC
- V
BATT
)
]
or USB_sel or
I
CHG
= min [
K
ISET
R
ISET
LM3658
SNVS328E –MAY 2005–REVISED MARCH 2007 www.ti.com
LM3658 OPERATION DESCRIPTION
POWER-DOWN MODE
The LM3658 will power down automatically when the voltage on the USBpwr or CHG_IN pin drops below the
battery voltage with an amount that is equal to V
OK_CHG
(V
BATT
> V
CC
- V
OK_CHG
). Power-Down mode shuts off the
internal power FETs as well as the open-drain pull-down transistors on the status pins STAT1 and STAT2. The
only current consumed by the LM3658 is an ultra-low quiescent current of 1 µA typical.
POWER-ON RESET
As soon as the voltage of one of the power sources rises above V
BATT
+ V
OK_CHG
, the charger will wake up.
However, charging will not be initiated unless the supply voltage source exceeds the V
POR
.
AUTOMATIC POWER SOURCE DETECTION
When the voltage of one of the power sources exceeds the V
POR
threshold, the LM3658 detects which power
source is a valid charge supply. When both supply voltages are valid and present, CHG_IN will automatically be
selected over USBpwr. The USBpwr will be the designated power source only if no CHG_IN is present or when
the voltage on the CHG_IN pin is less than the battery voltage.
THERMAL POWER FET REGULATION
The internal power FETs are thermally regulated to the junction temperature of 120ºC to specify optimal charging
of the battery. At all times is the charge current limited by the I
SET
resistor setting, the USB 100 mA/500 mA
selection, or the 100ºC junction temperature of the LM3658. The charge current is therefore a function of the
charge current settings, the thermal conductivity of the package and the ambient temperature as described in the
following equation:
Where T
A
is the ambient temperature and θ
JA
is the thermal resistance of the package. Thermal regulation
specifies maximum charge current and superior charge rate without exceeding the power dissipation limits of the
LM3658.
PRE-QUALIFICATION MODE
During pre-qualification, STAT1 is on and STAT2 is off, and the charger supplies a constant current of 50 mA to
the battery. When the battery voltage reaches V
FULL_RATE
, the charger transitions from pre-qualification to full-rate
charging. The pre-qualification mode aborts when the battery doesn’t reach V
FULL_RATE
within the time allowed in
T
PREQUAL
timer. In this event, charging stops and STAT1 and STAT2 will both be on, indicating a bad battery
condition.
CHG_IN FULL-RATE CHARGING MODE
The full-rate charge cycle is initiated following the successful completion of the pre-qualification mode. Timer
T
CHG
starts to count when the charger enters full-rate charging, with STAT1 on and STAT2 off. When charging
with an AC wall adapter, the full-rate charge current is proportional to the value of the resistor that is connected
to the I
SET
pin as described in the following equation:
It is recommended to charge Li-Ion batteries at 1C rate, where “C” is the capacity of the battery. As an example,
it is recommended to charge a 750 mAh battery at 750 mA, or 1C. Charging at a higher rate can cause damage
to the battery.
8 Submit Documentation Feedback Copyright © 2005–2007, Texas Instruments Incorporated
Product Folder Links: LM3658