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RT9237

Multi-Phase DC/DC Controller for CPU Core Power Supply

Richtek Technology 

RT9237

Operation

Preliminary

RT9237 is a multi-phase DC/DC controller that

precisely regulates CPU core voltage and balances

the current of different power channels. The

converter consists of RT9237 and its companion

MOSFET driver provide high quality CPU power and

all protection function to meet the requirement of

modern VRM.

Voltage control

The reference of VCORE is provided by a 5-bit DAC of

VRM9.0 specification. Control loop consists of error

amplifier, multi-phase pulse width modulator, driver

and power components. Like conventional voltage

mode PWM controller, the output voltage is locked at

the VREF of error amplifier and the error signal is

used as the control signal VC of pulse width

modulator. The PWM signals of different channels

are generated by comparison of EA output and spilt-

phase saw-tooth wave. Power stage transforms VIN

to output by PWM signal on-time ratio.

Current balance

RT9237 senses the current of low side MOSFET in

each synchronous rectifier when it is conducting for

channel current balance and droop tuning. The

differential sensing GM amplifier converts the voltage

on the sense component (can be a sense resistor or

the RDS(ON) of the low side MOSFET) to current

signal into internal balance circuit. The current

balance circuit sums and averages the current

signals then produces the balancing signals injected

to pulse width modulator. If the current of some

power channel is greater than average, the balancing

signal reduces the output pulse width to keep the

balance.

Load Droop

The sensed power channel current signals regulate

the reference of DAC to form a output voltage droop

proportional to the load current. The droop or so call

“active voltage positioning” can reduce the output

voltage ripple at load transient and the LC filter size.

Fault detection

The chip detects VCORE for over voltage and power

good detection. The “hiccup mode” operation of over

current protection is adopted to reduce the short

circuit current. The in-rush current at the start up is

suppressed by the soft start circuit through clamping

the pulse width and output voltage.

Application Circuit setting

Phase setting and converter start up

RT9237 interface with companion MOSFET driver

(like RT9600 or HIP660X series) for correct converter

initialization. The tri-phase PWM output (high, low,

high impedance) pins sense the interface voltage at

IC POR acts (both VDD and DVD trip). The channel

is enabled if the pin voltage is 1.2V less than VDD.

Please tie the PWM output to VDD and the current

sense pins to GND or left float if the channel is

unused. For 2-channel application, connect PWM3

and PWM4 high. 3-channel application connect

PWM4 high.

Current sensing setting

RT9237 senses the current of low side MOSFET in

each synchronous rectifier when it is conducting for

channel current balance and droop tuning. The

differential sensing GM amplifier converts the voltage

on the sense component (can be a sense resistor or

the RDS(ON) of the low side MOSFET) to current

signal into internal circuit (see Fig.1).

IX

Sample & Hold

To Current Balance

To Droop Tune 2/3 IX

_

ISPX RSP

GM IBP ISNX

RS

IBN

RSN

IL

2/3 IX

To Over Current Detection

2/3 IX

Fig.1 Current Sense Circuit

www.richtek-ic.com.tw

8

DS9237-00 January 2002

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