RT9501A/B
Application Information
Charge Profile
Precharge
mode
Preliminary
Constant current
regulation mode
Constant voltage regulation
and charge termination mode
Recharge
mode
Regulation voltage
Recharge voltage
Regulation current
Precharge threshold
voltage
Precharge current =
Charge termination current
Figure 3. Typical charge profile
Detection
First, the FB/CE pin must connect to VDD or a voltage
divider to enable the charge function. And then if a battery
is already inserted and the input power source is absent,
the RT9501 will enter sleep mode to prevent draining
power from battery. When input power source and battery
are both existed, another detection is the battery
temperature. The TS pin voltage must be in the allowed
range as shown in Figure 6 and the electrical
characteristics, and then the RT9501 will start the charge
cycle according to the battery voltage conditions.
Precharge Mode
When the battery voltage is lower than the precharge
threshold V
O(MIN)
, the RT9501 begins to charge the battery
in precharge mode. In this condition, the precharge current
is set at approximately 10% of the constant regulation
current. The purposes of small precharge current are to
minimize the power dissipation on the external switch
during the precharge period and to revive deeply
discharged battery cells.
V
IN
Constant Current Regulation Charge Mode
When the battery voltage is between the precharge
threshold V
O(MIN)
and the regulation voltage V
O(REG)
, the
RT9501 starts the constant current regulation charge
mode. RT9501 monitors charge current with voltage drop
between two terminals of a sense-resistor, R
CS
, which
connects to pin VDD and CS. The following equation can
calculate the desired charging current.
I
O(REG)
=
V
I(SNS)
R
CS
R
CS
R4
FB/CE
CS
VDD
GND
CC
BATT
TS
STAT
Q1
Battery
Figure 4
www.richtek.com
6
DS9501A/B-07 March 2007
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
