RT9907 Datasheet, PDF (18/19 Pages) Richtek Technology Corporation – 3 Channel DC/DC Converters IC with High-Efficiency Step-Up and Step-Down

RT9907
Preliminary
Protection
Current limit (CH2, CH3)
The current of high-side PMOS is sensed cycle by cycle
to prevent over current. If the current is higher than 1.5A
(typical), then the high-side PMOS is off and the low-side
NMOS is on. This state is latched and then reset
automatically at next clock cycle.
Under Voltage (CH2, CH3)
The status of under voltage is decided by comparing FB2
(or FB3) voltage with 0.4V. This function is enabled after
soft start finishes. If the FB2 (or FB3) voltage is less than
0.4V, then the high/low-side Power MOS are turned off
immediately. And this state is latched. After a dummy
count period, the CH2 (or CH3) begins a soft-start
procedure.
However, if the status of under voltage remains after 3
successive times of soft-start, then CH2 (or CH3) is
latched.
UV remain after 3
How to reset?
successive soft-start
CH2 CH2 is latched, and whole Toggle ENM
IC is shut down
CH3 CH3 is latched
Toggle EN3 or ENM
Over Voltage Protection (CH2)
Over voltage protection (OVP) is used to protect the
external parts connected to the output of CH2. If the FB2
voltage is higher than 1V, the high-side PMOS is off and
low-side NMOS is on. This status is latched and could be
reset by toggling ENM.
Reference
The chip has an internal 0.8V reference voltage, which is
the inputs of the error amplifiers of the CH1, CH2, and CH3
to compare the difference of feedback voltage. The
reference voltage can be set up stably when the supplied
power (VDDM) is above 1.5V, and EN1 (or EN2, EN3) goes
high.
Thermal Protection
Thermal protection function is integrated in the chip. When
the chip temperature is higher than 178 degree C, the
controllers of CH1, CH2, and CH3 are shutdown. 10 degree
C is the hysteresis range of temperature to prevent unstable
operation when the thermal protection happens. When the
thermal protection is relieved, the chip operates well again.
www.richtek.com
18
DS9907-07 August 2007