DS9535A Datasheet, PDF (15/18 Pages) Richtek Technology Corporation – High Efficiency Switching Mode Battery Charge

chip. Pulling the VC pin low will only stop switching and
5V5LDO stays active. Make sure there is a pull-up
resistor on the EN pin even if the EN pin is not used,
otherwise internal pull-down current will keep the EN
pin low to shut down mode when power turns on.
Charger Protection
Note that the RT9535A will operate even when VBATT is
grounded. If VBATT of typical application circuit charger
gets shorted to ground very quickly from a high battery
voltage, slow loop response may allow charge current
to build up and damage the high-side internal
N-MOSFET. A small diode from the EN pin to VBATT
will shut down switching and protect the charger.
Temperature Qualification
The controller RT9535A continuously monitors battery
temperature by measuring the voltage between the
NTC pin and GND. A negative temperature coefficient
thermistor (NTC) and an external voltage divider
typically generate this voltage. The controller compares
this voltage against its internal thresholds to determine
if charging is allowed. To initiate a charge cycle, the
battery temperature must be within the VCOLD. If
battery temperature is outside of this range, the
controller suspends charge and the safety timer and
waits until the battery temperature is within the VCOLD
to VHOT range. During the charge cycle, the battery
temperature must be within the VCOLD and VDISNTC
thresholds. If the battery temperature is outside of this
range, the controller suspends charge and waits until
the battery temperature is within the VCOLD to VHOT
range. The controller suspends charge by turning off
the PWM charge MOSFETs.
Copyright © 2016 Richtek Technology Corporation. All rights reserved.
DS9535A-04 February 2016
RT9535A
Assuming a 103AT NTC thermistor on the battery pack
as shown in the below, the values of RT1 and RT2 can
be determined by using the following equations :
RT2 =
V_V5V
 RTH_COLD
 RTH_HOT



1
V_COLD
-
1
V_HOT


RTH_HOT



V_V5V
V_HOT
-1^{} -RTH_HOT



V_V5V
V_COLD
-1^{}
V_{V5V -1}
RT1 =
V_COLD
1+ 1
RT2 RTH_COLD
V5V
RT9535A
NTC
RT1
RT2
RTH
103AT
TS Resistor Network
Where RTHCOLD and RTHHOT which have defined in the
spec of the 103AT NTC thermistor.
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature.
The maximum power dissipation can be calculated by
the following formula :
PD(MAX) = (TJ(MAX)  TA) / JA
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