RT9901 Datasheet, PDF (18/19 Pages) Richtek Technology Corporation – 4 Channel DC/DC Converters IC with High-Efficiency Step-Up and Step-Down

RT9901
Preliminary
enters low dropout mode. Duty could be as long as 100%
to extend battery life.
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.
Charge Pump DC/DC converter
This is a low quiescent charge pump DC/DC converter,
which is enabled by ENM. Add a capacitor C_X (~1nF)
between charge pump V_OUT and CP_FB to speed up charge
pump response time. Output ripple can be easily
suppressed by increasing the capacitance ratio of C_OUT
and Cpump. This charge pump DC/DC converter can
apply to μC stanby power or the gate driver power of IGBT
for photoflash, etc.
The maximum output current can be determined by Cpump
and C_OUT ration. This equation would describe the
relationship.
I_MAX = 2 x (V_DDC-V_F) x Cpump x Fpump
z V_F : Schottky diode forward voltage
z Fpump : Charge pump maximum frequency is 500kHz
Recommand Cpump ≤ 0.1μF.
VDDC
CX
Cpump
CPFB
GND
V_BAT
R1
C_X
C_OUT
R2
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
DS9901-12 August 2007