TPS61170: Abnormal SW Frequency

CHEN YAN

Part Number: TPS61170

Hi,

My customer met an issue about TPS61170 SW frequency, the datasheet says it's 1.2MHz fixed-frequency while the test result is 600KHz tested by customer.

The input voltage is 12V, output voltage is 24V, and load is 0.4A, change another chip wouldn't solve this problem.

The schematic and waveforms are as following, the inductor in their board is 20uH under testing, and C209 is 1nF, R219 is 10KΩ.

Could you please help analysis this issue? Thanks.

Best Regards,

Chen

over 5 years ago

0 Helen chen over 5 years ago

TI__Mastermind 40080 points

Dear Sir,

Please change to R212 to 2k, C209 to 47nF to check whether it could be helpful.

By the way, could you please post the datasheet of the 22uH inductor for a double check?

0 CHEN YAN over 5 years ago in reply to Helen chen

TI__Intellectual 1430 points

Hi, Helen

Thanks for you suggestion, I attached the recommended inductor value. Customer changed R212 to 2K and solved the issue. Customer keep C209 unchanged, so they want to know the reason why change R212 and C209 can solve this problem, and if it is safe to only change the resistor while keep the capacitor unchanged? Thanks.

Best Regards,

Chen

0 Helen chen over 5 years ago in reply to CHEN YAN

TI__Mastermind 40080 points

Hi Yan,

Reduce the Rcomp value can lower the gain and the cross over frequency. Make the phase margin higher.

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TPS61170: Abnormal SW Frequency