RT9501A/B
V
IN
R
CS
R4
Q1
Preliminary
Battery
R
FB1
Selecting Input/Output Capacitor
In analog circuit applications, to place a high-frequency
decoupling capacitor nearby the controller IC between
input power source and ground is very important. A 0.1uF
ceramic is recommended. If a high ripple and noise input
power is chosen, it should have enough capacitance to
reduce the disturbance.
A 0.1uF to 1uF output capacitor is recommended to control
the output voltage and keep the output voltage ripple small
when the battery is disconnected.
FB
CS
VDD
STAT
CC
BATT
TS
GND
R
FB2
Figure 8. For FB pin Function
V
O(REG)
= 2.1
×
(1+
R
FB1
R
FB2
) V
Charge status indication
The RT9501 indicates the status of the charger on the 3-
state STAT pin. The following table shows the statuses of
this pin.
Condition
In battery charging cycle
Charge cycle completed
Temperature fault or charge
function disable or sleep mode
STAT Pin
High
Low
High Impedance
Selecting an External PNP Pass-Transistor or
P-Channel MOSFET:
The RT9501 drives an external PNP transistor or
P-
Channel MOSFET to control the charging current. The
specifications
must be concerned are the voltage
and
current rating and package power dissipation. The external
switch is performed as a linear regulator. The maximum
power loss occurs when the constant current regulation
starts at the beginning, and it can be calculated
approximately from following equation:
P
D(MAX)
= I
(SNS)
×
(V
DD
- 0.1V - 2.8V)
I
(SNS)
is the constant regulation current.
The minimum voltage drop between the sense-resistor
is 100mV, and the minimum precharge threshold voltage
is 2.8V.
The external pass device with PCB heatsinking must be
rated for the maximum power dissipation.
www.richtek.com
8
DS9501A/B-07 March 2007
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
