RT9245BGC 查看數據表（PDF） - Richtek Technology

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RT9245BGC

Multi-Pha se PWM Controller forK8 CPU CorePower Supply

Richtek Technology 

Application Information

RT9245B is a multi-phase DC/DC controller that precisely

regulates CPU core voltage and balances the current of

different power channels. The converter consisting of

RT9245B and its companion MOSFET driver RT9619

provides high quality CPUpower and all protection functions

to meet the requirement of modern VRM.

Voltage Control

RT9245B senses the CPU VCORE by SGND pin to sense

the return of CPU to minimize the voltage drop on PCB

trace at heavy load. OVP is sensed at FB pin. The internal

high accuracy VIDDAC provides the reference voltage for

K8 compliance. Control loop consists of error amplifier,

multi-phase pulse width modulator, driver and power

components. As 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 of pulse width modulator. The PWM signals of

different channels are generated by comparison of EA

output and split-phase sawtooth wave. Power stage

transforms VIN to output by PWM signal on-time ratio.

Current Balance

RT9245B senses the inductor current via inductor's DCR

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 DCR of the

inductor) to current signal into internal balance circuit.

The current balance circuit sums and averages the current

signals and then produces the balancing signals injected

to pulse width modulator. If the current of some power

channel is larger than average, the balancing signal

reduces that channels pulse width to keep current balance.

The use of single GM amplifier via time sharing technique

to sense all inductor currents can reduce the offset errors

and linearity variation between GMs. Thus it can greatly

improve signal processing especially when dealing with

such small signal as voltage drop across DCR.

Droop & Load Line Setting

RT9245B injects averaged current IX into the resistor RADJ

connected to ADJ pin to generate a load-current-

dependent voltage RADJ for droop setting:

RT9245B

VADJ = 8 x IX x RADJ

VADJ is then subtracted from VID_DAC output as the real

reference voltage at non-inverting input of the error amplifier

as shown if Figure 1. Consequently, load line slope is

calculated as :

Load

Line

=

ΔVCORE

ΔICORE

=

8

x RADJ x DCR

N x RCSN

where N is the phase number of operation.

IVOSS /4

VCORE

RCSN

-

EA

+

VADJ

DAC

8IX

RADJ

Figure 1. Load Line and Offset Function

Fault Detection

The chip detects FB 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.

Phase Setting and Converter Start Up

RT9245B interfaces with companion MOSFET drivers (like

RT9619, RT9607 series) for correct converter initialization.

The tri-state PWM output (high, low and high impedance)

senses its interface voltage when IC POR acts (both VCC

and DVD trip). The channel is enabled if the pin voltage is

1.2V less than VCC. Tie the PWM to VCC and the

corresponding current sense pins to GND or left float if

the channel is unused. For example, for 3-Channel

application, connect PWM4 high.

Current Sensing Setting

RT9245B senses the current flowing through inductor via

its DCR for channel current balance and droop tuning.

DS9245B-02 March 2007

www.richtek.com

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