RT9241CS datasheet(9/13 Pages) ETC

9 / 13 page

Preliminary

RT9241

DS9241-00 November 2001

www.richtek-ic.com.tw

Operation

RT9241 is a two-phase DC/DC controller that

precisely regulates CPU core voltage and balances

the current of different power channels. The

converter consists of RT9241 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, two-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

RT9241 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

MOSFET driver detection and converter start up

RT9241 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 both PWM output to driver input for

correct converter start-up.

Current sensing setting

RT9241 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).

Fig.1 Current Sense Circuit

Sample & Hold

To Current Balance

To Droop Tune

To Over Current Detection

2/3 IX

IBP

IBN

RSP

RSN

ISPX

ISNX

Sample & Hold

To Current Balance

To Droop Tune

To Over Current Detection

2/3 IX

IBP

IBN

RSP

RSN

ISPX

ISNX

RT9241CS 数据表(PDF) 9 Page - List of Unclassifed Manufacturers

RT9241CS 数据表(HTML) 9 Page - List of Unclassifed Manufacturers

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13

数据表下载