Preliminary
Functional Pin Description
UGATE1 (Pin 1), UGATE2 (Pin 11)
Upper Gate Drive. These pins drive the gates of the highside
MOSFETs.
BOOT1 (Pin 2), BOOT2 (Pin 10)
Bootstrap Power Pin. These pins power the high-side
MOSFET drivers. Connect These pins to the junctions of
the bootstrap capacitors.
AGND (Pin 3)
Chip Analog Ground.
IMAX (Pin 4)
Maximum Current Setting. This pin sets the current limiting
level. Connect this pin with resistor to ground to set the
current limit.
RT (Pin 5)
Timing Resistor. Connect a resistor from RT to AGND to
set the clock frequency.
SS (Pin 6)
Soft-Start Pin. This pin provides soft-start function for
controller. The COMP voltage of the converter follows the
ramping voltage on the SS pin.
COMP (Pin 7)
Compensation Pin. This pin is output node of the error
amplifier.
FB (Pin 8)
Feedback Pin. This pin is negative input pin of the error
amplifier.
PGOOD (Pin 9)
Power Good. PGOOD is an open drain output used to
indicate the status of the voltages on SS pin and FB pin.
PGOOD will go high impedance when SS > 3.7V and FB
> 0.6V.
LGATE1 (Pin 15), LGATE2 (Pin 13)
Lower Gate Drive. These pins drive the gate of the lowside
MOSFETs.
PHASE1 (Pin 16), PHASE2 (Pin 12)
RT8805
These pins are return nodes of the high-side driver.
Connect These pins to high-side MOSFET sources
together with the low-side MOSFET drains and the
inductors.
VCC (Pin 14)
The VCC pin is the external 12V power. Internal 5V power
(V
DD
) is regulated from this pin. This pin also powers the
low side MOSFETS drivers.
GND (Exposed Pad)
Exposed pad should be soldered to PCB board and
connected to GND.
DS8805-01
November 2005
www.richtek.com
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