RT9228
Functional Pin Description
VCC (Pin 1)
Provide a 12V bias supply for the IC to this pin. This pin
also provides the gate bias charge for all the MOSFETs
controlled by the IC.
VID0, VID1, VID2, VID3, VID4 (Pin 6, 5, 4, 3, and 2)
VIDO-4 are the input pins to the 5-bit DAC. The states of
these five pins program the internal voltage reference,
DACOUT. The level of DACOUT sets the core converter
output voltage. It also sets the core PGOOD and OVP
thresholds. Table 1 specifies the DACOUT voltage of 32
combinations of V
ID
levels.
PGOOD (Pin 7)
PGOOD is an open collector output used to indicate the
status of the output voltage. This pin is pulled low when
the core output is not within
±
10% of the DACOUT
reference voltage and the other outputs are below their
under-voltage thresholds.
The PGOOD output is open for
'11111'
V
ID
codes that
inhibit operation. See table 1.
FAULT (Pin 8)
This pin is low during normal operation, but it is pulled to
about 8V (V
CC
= 12V) in the event of an over-voltage or
over-current condition.
SS (Pin 9)
Connect a capacitor from this pin to ground. This capacitor,
along with an internal 11μA (V
SS
>1V) current source, sets
the soft-start interval of the converter.
FB2 (Pin 11)
Connect this pin to V
OUT2
to set the linear regulator output
voltage.
VIN2 (Pin 12)
This pin supplies power to the internal regulator. Connect
this pin to a suitable 3.3V source.
VOUT2 (Pin 13)
Output of the linear regulator. Supplies current up to 230mA.
GND (Pin 14)
Signal ground for the IC. All voltage levels are measured
with respect to this pin.
GATE3 (Pin 15)
Connect this pin to the gate of an external MOSFET or the
base of an NPN. This pin provides the drive for the linear
controller's pass transistor.
FB3 (Pin 16)
Connect this pin to V
OUT3
to set the linear controller output
voltage.
FB1 (Pin 18)
The FB1 pin is the inverting input of the error amplifier.
VSEN1 (Pin 19)
This pin is connected to the PWM converter's output
voltage. The PGOOD and OVP comparator circuits use
this signal to report output voltage status and for over
voltage protection.
OCSET1 (Pin 20)
Connect a resistor (R
OCSET1
) from this pin to the drain of
the upper MOSFET. R
OCSET1
, an internal 200μA current
source (I
OCSET1
), and the upper MOSFET on-resistance
(R
DS(ON)
) set the PWM converter over-current (OC) trip
point according to the following equation :
Additionally, this pin is used to monitor the 3.3V supply.
If, following a startup cycle, the voltage drops below 2.55V
(typically), the chip shuts down. A new soft-start cycle is
initiated upon return of the 3.3V supply above the under-
voltage threshold.
I
PEAK
=
I
OCSET1
×
R
OCSET1
R
DS (ON)
An over-current trip cycles the soft-start function.
Sustaining an over-current for 2 soft-start intervals shuts
down the controller.
DS9228-06 March 2007
www.richtek.com
5
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
