LP8868X-Q1: Please review the schematic, and some questions.

Chase Jeong

Mastermind 7365 points

Part Number: LP8868X-Q1

Tool/software:

Dear TI experts,

My customer made a sample module using LP8868XQDMTR-Q1.

Could you review the schematic below first?

And here is a question ;

If the VIn is normal(usually 13.5V), everything is okay but if VIN is under 10V, they found high frequency noise. So they changed the value of C16 from 1nF to 100nF. And hthe noise disappeared.

- Is it okay to set C16 100nF?

Please check this issue. Thanks.

Best regards,

Chase

7 months ago

0 Zhiqian Wu 7 months ago

TI__Mastermind 31255 points

Hi, Chase

I will check it and give you a feedback late.

0 Chase Jeong 7 months ago in reply to Zhiqian Wu

Mastermind 7365 points

Dear Zhiqian,

Please let me know if there are any updates about the issue above .Thanks.

Best regards,

Chase

+1 Zhiqian Wu 7 months ago in reply to Chase Jeong

TI__Mastermind 31255 points

Hi, Chase

Pls see my feedback in below:

Add 100 Ohm resistor in CSN
Fault pin needs a pull-up resistor
Change the cap between CSP/CSN with 1nF cap
The pull up resistor needs to change to 10k for ADIM/EN.

0 Chase Jeong 7 months ago in reply to Zhiqian Wu

Mastermind 7365 points

Dear Zhiqian,

Thank you for your support.

- What is your opinion of changing the value of C16 from 1nF to 100nF? Is it okay?

Best regards,

Chase

+1 Zhiqian Wu 7 months ago in reply to Chase Jeong

TI__Mastermind 31255 points

Hi, Chase

As this cap is used as a filter, a RC filter influence can also have the similar impact and no need such a large cap.

0 Chase Jeong 7 months ago in reply to Zhiqian Wu

Mastermind 7365 points

Dear Zhiqian,

Thank you for your support.

My customer just changed the value of capacitor from 1nF to 100nF because of high frequency noise.

I understand your saying that it is used as a filter, but I need to confirm that it is "okay" to change the value or I "should not" change the value.

Please check this issue. Thanks.

Best regards,

Chase

+1 Zhiqian Wu 7 months ago in reply to Chase Jeong

TI__Mastermind 31255 points

Hi, Chase

Pls change it, because 100ohm and 100nf means a high delay for sense voltage during the operation. It is not recommended.

0 Chase Jeong 7 months ago in reply to Zhiqian Wu

Mastermind 7365 points

Dear Zhiqian,

Thank you for your support, and sorry for late reply due to national holidays.

You said that the right value of C16 is 1nF, then do you have any idea to reduce high frequency noise?

Please check this issue. Thanks.

Best regards,

Chase

0 Steven Li 7 months ago in reply to Chase Jeong

TI__Mastermind 23150 points

Hi Chase,

Our expert is currently out of office for Chinese New Year Holiday. He will reply to you after Feb.5 when back to office. Thanks for your understanding.

Best Regards,

Steven

+1 Zhiqian Wu 6 months ago in reply to Chase Jeong

TI__Mastermind 31255 points

Hi, Chase

Sorry for the late reply due to the Chinese New Year.

Could you pls kindly share the waveform (SW voltage/SW current/COMP voltage/Output Voltage) to do more analysis? for the noise, it should be lower than 20kHz. Pls remove the R10 and add the C16 to 2nF to have a try.

0 Chase Jeong 6 months ago in reply to Zhiqian Wu

Mastermind 7365 points

Dear Zhiqian,

Thank you for your support.

EMC test of the product is on the way. They did EMC test with R10=1M and C16=2.2nF and everything is fine.

Could you confirm that these values are okay?

Best regards,

Chase

+1 Zhiqian Wu 6 months ago in reply to Chase Jeong

TI__Mastermind 31255 points

Hi, Chase

Sure, it is fine.

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LP8868X-Q1: Please review the schematic, and some questions.