
Preliminary
RT9238
DS9238-01 July 2001
www.richtek-ic.com.tw
1
VRM8.5 PWM and Triple Linear Power System Controller
General Description
The RT9238 is a 4-in-one power controller optimized
for high-performance microprocessor and computer
applications. The IC integrates a PWM controller,
triple linear controller as well as monitoring and
protection functions into a 28-pin SOP package. The
PWM controller regulates the microprocessor core
voltage with a synchronous buck converter. The first
linear controller supplies the computer system’s
AGTL+ 1.2V bus power. The second linear controller
provides power for the 1.5V AGP bus and the 3rd
linear controller provides 1.8V power for the chipset
core voltage and/or cache memory circuits.
The RT9238 features an Intel VRM8.5 compatible,
TTL 5-bit programmable DAC that adjusts the core
voltage from 1.090V to 1.865V in 25mV steps. The 5-
bit DAC has a typical
±
1% tolerance. The linear
regulators provide fixed output voltages of 1.2V
(V
OUT2
), 1.5V (V
OUT3
) and 1.8V (V
OUT4
) or user-
adjustable with an internal 1.265V reference. All the
three linear regulators drive external N-MOSFET or
NPNs bipolar for the pass transistor.
The RT9238 monitors all the output voltages. A
power-good signal is issued when the core voltage is
within
±
10% of the DAC setting and the other levels
are above their under-voltage levels. Additional build-
in over-voltage protection for the core output uses the
lower MOSFET to prevent output voltage above
115% of the DAC setting. The PWM over-current
function monitors the output current using the voltage
drop
across
the
MOSFET’s
eliminates the need for a current sensing resistor.
R
DS(ON)
,
which
Applications
z
Motherboard Power Regulation for Computers
Features
z
4-in-one Regulated Voltages for Microprocessor
Core, AGTL+ Bus, AGP Bus Power, and
North/South Bridge Core
z
Compatible with ISL6524
z
Power-good Output Voltage Monitor
Switching section
z
VRM8.5 TTL-Compatible 5-bit DAC
Programmable from 1.090V to 1.865V
z
±
1% DAC Accuracy
z
Fast Transient Response
z
VRM 8.5 Voltage Droop Tuning Uses MOSFET
R
DS(ON)
z
Fixed 200KHz Switching Frequency
z
Adaptive Non-overlapping Gate Driver
z
Over-current Monitor Uses MOSFET R
DS(ON)
z
Over-voltage Protection Uses Lower MOSFET
Linear Section
z
Fixed or User-adjustable Linear Regulator
Output Voltage
z
MOSFET and NPN Driving Capability
z
Ultra Fast Response Speed
z
Under-voltage Protection
z
Internal Thermal Shutdown
Pin Configurations
Part Number
Pin Configurations
RT9238CS
(Plastic SOP-28)
1
2
3
4
5
6
7
8
9
10
11
12
17
18
19
20
21
22
23
24
25
26
27
28
13
14
16
15
FIX
VID3
VID2
VID1
VID0
VID25
PGOOD
VTTPG
FAULT/VID4
VSEN2
DRIVE2
SS24
SS13
VSEN4
LGATE1
PGND
OCSET1
FB1
VDAC
ICOMP
VCC
UGATE1
PHASE1
VSEN3
DRIVE3
GND
VAUX
DRIVE4