RT9730 Datasheet, PDF (7/9 Pages) Richtek Technology Corporation – Charging System Safety Device

RT9730
Application information
Operation State
The operation state is shown in the following Figure 1. At
power-off state, the RT9730 will check whether V_IN is >
UVLO threshold. If V_IN is higher than the UVLO threshold,
the RT9730 will check whether the junction temperature
is over the OTP threshold. If the junction temperature is
higher than the OTP threshold, the internal P-MOSFET
will be turned off. If the junction temperature is lower than
the OTP threshold, the RT9730 will check whether V_IN is
higher than the OVP threshold or not, if V_IN is higher than
the OVP threshold, the RT9730 will turn off the internal P-
MOSFET immediately within 1μs.
If all of the checks including V_IN > UVLO, T_J < OTP and
V_IN < OVP are ok, the IC will operate normally.
Internal Over Temperature Protection (OTP)
The RT9730 monitors its own internal temperature to
prevent thermal failures. When the internal temperature
reaches 140°C with a built-in hysteresis of 20°C, the IC
turns off the power MOSFET. The IC does not resume
operation until the internal temperature drops below 120°C.
Input Under Voltage Protection (UVLO)
The RT9730 monitors input voltage to prevent abnormally
low input voltage from causing output system failures.
The RT9730 input under voltage protection threshold is
set to 2.7V. When the input voltage is under the threshold,
the RT9730 will turn off the power MOSFET within 1μs.
When the input voltage returns to normal operation voltage
range, the RT9730 re-enables the MOSFET.
Start
V_IN > UVLO ^Y
N
T_J > OTP ^N
Y
V_IN > OVP ^N
Normal Status
P-MOSFET = ON
and Control by
GATDRV
Y
Power-Off
Status
OTP Status
PFET=OFF
OVP Status
P-MOSFET = Off(Fast)
Figure 1. Operation State Diagram for OVP Function
Input Over Voltage Protection (OVP)
The RT9730 monitors the input voltage to prevent
abnormally high input voltage from causing output system
failures. When the input voltage exceeds the threshold,
the RT9730 will turn off the power MOSFET within 1μs to
prevent damage to the electronics in the handheld system.
The hysteresis for the input OVP threshold is 100mV.
When the input voltage returns to normal operation voltage
range, the RT9730 re-enables the MOSFET. The RT9730
can with stand an input voltage up to 30V without suffering
damage.
Battery Voltage Monitor
The RT9730 monitors the battery voltage by the OUT pin.
When the battery voltage exceeds the voltage level of (V_IN
− 0.2V), the RT9730 will turn off the MOSFET and the
battery will not be charged. The RT9730 will recharge the
battery when the battery voltage is lower than the voltage
level of (V_IN − 0.2V).
System Operation Description
Figure 2 shows the connection of RT9730 in a system
diagram. The OUT pin of the SOC will sense the voltage
of the 0.2Ω sense resistor and the voltage of the VBAT
pin. Then, the GATDRV pin of the SOC can control the
MOSFET of the RT9730 accordingly to determine the level
of the charge current. The power of the SOC is provided
by the CHRIN pin of the RT9730. The RT9730 also provides
OVP function to the SOC. Once the input voltage at the
ACIN pin is higher than the OVP level, the RT9730 will
shutdown to prevent the SOC from damage. If the voltage
of the battery connected to the VBAT pin is full, the RT9730
stops charging by turning off the OUT pin. Input and output
capacitors of 1μF are recommended to be placed as close
to the IC as possible.
V_IN
RT9730
CHRIN
ACIN
C_IN
1µF
GATDRV
GND
OUT
C_OUT
1µF
SOC
CHRIN
GATEDRV
OUT
0.2
1µF
VBAT
Battery
Figure 2. Application Diagram of RT9730 with SOC
DS9730-01 April 2011
www.richtek.com
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