CM9112 Datasheet, PDF (9/18 Pages) California Micro Devices Corp – Dual Inputs Dual Outputs High Accurate Fast Charger

PRELIMINARY
CM9112
Application Information (cont’d)
Pre-
Condition
Constant
Current
TerminationCV
Charging4.0V
Voltage
Charging
Current
3.0V
2.0V
Figure 1. Typical Li-ion Battery Charging Process
Once the battery voltage exceeds the 3.3V threshold,
the CM9112 enters the Fast-charge, constant-current
(CC) mode. The status pins will be set to STAT1=0 and
STAT2=V_IN. During the CC mode, the charging current
is limited by the maximum charging current, pro­
grammed with a single resistor between ISET1 for USB
and ISET2 for adaptor:
I_{F A S T C H G} ( m a x )
=
2----.-5----V------×_{- ---1----0---0----0--}
R_{ISET1, 2}
(4.20V – V_OC) and the internal impedance, R_internal, of
the Li-ion battery-pack. When it reaches termination
current limit, stop charging is triggered and the Battery
is fully charged.
Following the Termination mode, the charger will enter
the Standby mode. The status pins will be set to
STAT1=V_IN and STAT2=0.
If the wall adapter or USB input is left plugged-in while
in the Standby mode, the charger will continue to mon­
itor the battery voltage. It automatically re-charges the
battery when the battery voltage drops below the re­
charge threshold. When the adapter is removed, the
CM9112 will drain less than 1µA from the battery.
VIN
VOUT
ISYS
Conventional ^ICH
Floating
Charger
V_BAT
System
Most battery manufactures recommend an optimal
charging current for their battery. This is typically a time
ratio related to the battery capacity, with a value of .7C
to 1C, once the battery is above the Precharge voltage
level. For example, a 750mAh capacity battery with
recommended charge of .7C could have I_CC set for
about 525mA, with R_ISET2 equal to 4.75kΩ, 1%.
The actual Fast-charge current might be further limited
by the maximum chip temperature limit, determined by
the power dissipation on the CM9112 chip, the ambient
temperature (T_A), and the junction-to-ambient thermal
resistance, Rth_(JA). The current requested by System,
ISYS, might have a significant contribution to the power
dissipated on the chip and reduction of the charging
current. So, it is recommended to reduce as much as
possible the ISYS current during charging. However,
there is not timeout for fast charge period. So, there is
no risk to stop the charging, just delay of it.
When the battery voltage reaches 4.200V it goes into
CV mode and CM9112 turn from a constant current
source to a constant voltage source. As a result, the
charging current start dropping. The actual charging
current is now determined by the differential voltage
Figure 2. Conventional Charger
Limitations of Conventional Chargers
In a conventional floating charging architecture, the
system load is always tied directly to the battery, as
shown in Figure 2. If the adapter is charging a deeply
discharged battery in the Precharge mode, the system
input voltage will be held below 3.2V, the same voltage
as the battery voltage. This charger output voltage may
be too low to allow a user to use the system, even for
non-transmitting (low power) tasks, such as composing
emails. Further, in the Precharge mode, the battery
charge current is typically limited to 100mA or less. If
the system is trying to power up, it may draw more cur­
rent than the Precharge current limit allows. In this con­
dition, the system will continue to drain power from the
battery, potentially causing the battery charger to
remain stuck in a Precharge mode indefinitely. After the
Precharge timeout expires, the charger, thinking it has
a defective battery, will shut down, and the battery is
never charged beyond the Precharge mode.
© 2006 California Micro Devices Corp. All rights reserved.
07/06/06 490 N. McCarthy Blvd., Milpitas, CA 95035-5112 lTel: [phone] lFax: [phone] lwww.cmd.com
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