RT9246A データシートの表示（PDF） - Richtek Technology

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RT9246A

Multi-Phase PWM Controller for CPU Core Power Supply

Richtek Technology 

RT9246A

LX

RLX

ILX

RX

CX

+ VX -

S/H CKT

T1

+

-

T2

Ix

T3

T1

T4

RCOMM

Figure 2

VCORE

+

The sensed current IX is used for current balance and droop

tuning as described as followed. Since all phases share

one common GM, GM offset and linearity variation effect

is eliminated in practical applications. As sub-milli-ohm-

grade inductors are widely used in modern mother boards,

slight mismatch of GM amplifiers offset and linearity results

in considerable current shift between phases. The time-

sharing DCR current sensing technical is extremely

important to guarantee phase current balance at mass

production.

Phase Current Balance

The sampled and held phase current IX are summed and

averaged to get the averaged current IX . Each phase

current IX then is compared with the averaged current.

The difference between IX and IX is injected to

corresponding PWM comparator. If phase current IX is

smaller than the averaged current , RT9246A increases

the duty cycle of corresponding phase to increase the

phase current accordingly, vice versa.

Over Current Protection

RT9246A uses an external resistor RIMAX connected to

IMAX pin to generate a reference current IIMAX for over

current protection:

IIMAX= VIMAX

RIMAX

where VIMAX is 1.0V typical. OCP comparator compares

each sensed phase current IX with this reference current

as shown in Figure 3. Equivalently, the maximum phase

current is calculated as:

3

ILX(MAX)=

VIMAX

RCOMM

2 RIMAX RLX

OCP Comparator

+

1/3 IX

-

1/2 IIMAX

Figure 3. Over Current Comparator

RT9246A uses hiccup mode to eliminate nuisance

detection of OCP or reduce output current when output is

shorted to ground as shown in Figure 4 and 5.

www.richtek.com

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DS9246A-04 March 2007

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