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

Over Current Protection

PWM

ICORE

VSS

VCORE

(5V/Div)

(10A/Div)

(2V/Div)

(500mV/Div)

Time (5ms/Div)

Figure 4. The Over Current Protection in the soft start

interval

where N is the phase number of operation.

The averaged current IX is also injected into the resistor

RIOUT connected to IOUT pin for monitoring load current.

Voltage at IOUT pin VIOUT is proportional to load current

and is calculated as:

VIOUT = 8 IX x RIOUT = 8 x ICORE x RADJ x RLX

N x RCOMM

VCORE

RFB1

IVOSS

4

DAC

Error

- Amp.

+

VADJ

8IX

RADJ

Over Current Protection

(5A/Div)

ICORE

(1V/Div)

VSS

Time (2.5ms/Div)

Figure 5. Over Current Protection at steady state

Droop and Load Line Setting

RT9246A injects averaged phase current IX into the

resistor RADJ connected to ADJ pin to generate a load-

current-dependent voltage VADJ for droop setting:

VADJ = 8IX RADJ

VADJ is then subtracted form VID_DAC output as the real

reference voltage at non-inverting input of the error amplifier

as shown if Figure 6. Consequently, load line slope is

calculated as:

Load Line = ΔVCORE = 8 x RADJ x RLX

ΔICORE

N x RCOMM

Figure 6. Load Line and Offset Function

Output Voltage Offset Function

RT9246A provides programmable initial offset function.

External resistor RVOSS and voltage source at VOSS pin

generate offset current IVOSS = VVOSS

RVOSS

, where VVOSS is 1V typical. One quarter of IVOSS flows

through RFB1 as shown in Figure 6. Error amplifier would

hold the inverting pin equal to VDAC − VADJ. A constant

offset voltage is consequently added to VDAC − VADJ as :

VCORE = VDAC − VADJ + RFB1

4 x RVOSS

Current Ratio Setting

Current ratio adjustment is possible as described below.

It is important for achieving thermal balance in practical

application where thermal conditions between phases are

not identical. Figure 7 shows the application circuit of GM

for current ratio requirement. According to Basic Circuit

Theory, if

LX = (RSX // RPX) x CX then

RLX

VX = RPX x ILX x RLX

RSX+RPX

DS9246A-04 March 2007

www.richtek.com

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