RT9502 RICHTEK [Richtek Technology Corporation], RT9502 Datasheet - Page 10

• Manufacturer Part Number: RT9502
• Description: Linear Single Cell Li-Ion Battery Charger IC with Dual Input Supply
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9502
ACIN Over Voltage Protection
The ACIN input voltage is monitored by an internal OVP
comparator. The comparator has an accurate reference of
2.5V from the band-gap reference. The OVP threshold is
set by the internal resistive. The protection threshold is
set to 6.5V. When the input voltage exceeds the threshold,
the comparator outputs a logic signal to turn off the power
P-MOSFET to prevent the high input voltage from damaging
the electronics in the handheld system. When the input
over oltage condition is removed (ACIN < 6V), the
comparator re-enables the output by running through the
soft-start.
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10
Application Information
Automatically Power Source Selection
The RT9502 is a battery charger IC which is designed for
Li-ion Battery with 4.2V rated voltage.
The RT9502 can be adopted for two input power source,
ACIN or USB Input. It will automatically select the input
source and operate in different mode as below.
ACIN Mode : When the ACIN input voltage (ACIN) is higher
than the UVP voltage level (4.4V), the RT9502 will enter
ACIN Mode. In the ACIN Mode, ACIN P-MOSFET is turned
on and USB P-MOSFET is turned off.
USB Mode : When ACIN input voltage is lower than UVP
voltage level and USB input voltage is higher than UVP
voltage level (4.4V), the RT9502 will operate in the USB
Mode. In the USB Mode, ACIN P-MOSFET is turned off
and USB P-MOSFET is turned on.
Sleep Mode : The RT9502 will enter Sleep Mode when
both ACIN and USB input voltage are removed. This feature
provides low leakage current from the battery during the
absence of input supply.
V
ACIN
Figure 1. Input Power Source Operation Mode.
> UVP
ACIN Mode
Sleep Mode
V
V
ACIN
USB
< UVP
< UVP
USB Mode
V
V
ACIN
USB
> UVP
< UVP
Battery Temperature Monitoring
The RT9502 continuously monitors battery temperature
by measuring the voltage between the TS and GND pins.
The RT9502 has an internal current source to provide the
bias for the most common 10kΩ negative-temperature
coefficient thermal resistor (NTC) (see Figure 2). The
RT9502 compares the voltage on the TS pin against the
internal VTS_HIGH and VTS_LOW thresholds to determine
if charging is allowed.
When the temperature outside the VTS_HIGH and
VTS_LOW thresholds is detected, the device will
immediately stop the charge. The RT9502 stops charge
and keep monitoring the battery temperature when the
temperature sense input voltage is back to the threshold
between VTS_HIGH and VTS_LOW, the charger will be
resumed. Charge is resumed when the temperature returns
to the normal range. However the user may modify
thresholds by the negative-temperature coefficient thermal
resistor or adding two external resistors. (see Figure 3.)
The capacitor should be placed close to TS(Pin 9) and
connected to the ground plane. The capacitance value
(0.1uF to 10uF) should be selected according to the quality
of PCB layout. It is recommended to use 10uF if the layout
is poor if prevent noise.
Turn off when V
V
TS
Temperature
Figure 2. Temperature Sensing Configuration
= I
Sense
TS
×
R
NTC
A
TS
I
TS
≥
TS
2.5V or V
0.1uF to 10uF
TS
DS9502-02 April 2011
≤
Battery
0.5V
NTC
V
BATT