RT9245PC datasheet(13/22 Pages) RICHTEK

13 / 22 page

RT9245

DS9245-06

March 2007

www.richtek.com

Figure 7. Over Current Protection at steady state

Current Ratio Setting

Figure 8. Application circuit for current ratio setting

For some case with preferable current ratio instead of

current balance, the corresponding technique is provided.

Due to different physical environment of each channel, it

is necessary to slightly adjust current loading between

channels. Figure 8 shows the application circuit of GM for

current ratio requirement. Applying KVL along L+DCR

branch and R1+C//R2 branch :

DCR

For

)

(

DCR

Look for its corresponding conditions :

(R1//R2)

DCR

Let

DCR

(R1//R2)

DCR

With internal current balance function, this phase would

share (R1+R2)/R2 times current than other phases.

Figure 9 &10 show different settings for the power stages.

Figure 11 shows the performance of current ratio compared

with conventional current balance function in Figure 12.

Figure 9. GM4 Setting for current ratio function

Figure 10. GM1~3 Setting for current ratio function

Figure 11

CH1:(5V/Div)

CH2:(5V/Div)

Over Current Protection

Time (25ms/Div)

PWM

VSS

Current Ratio Function

304560

7590

IOUT (A)

IL3

IL4

IL2

IL1

Thus if

(R1//R2)

DCR

Then

DCR

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