TPS7A6401-Q1: The abnormal waveform of nRST pin

Shaw Wong

Part Number: TPS7A6401-Q1

Hi,

Our customer used TPS7A6401-Q1 to convert 12V to 5V/300mA, but they encountered problems. When nWD_EN and WD pin keep low level, the waveform of nRST pin should be a low reset level periodically. However, actually, the time of low level is very short, and then ramp up slowly. So, what reason may result in the abnormal waveform of nRST pin? If this waveform apply to the RST pin of MCU, can MCU reset normally? Thanks!

Note: The schematic as same as that of TPS7A6350, because it is pin to pin with TPS7A6401, and FB pin has connect correctly. The waveform of nRST pin as picture 2.

over 6 years ago

0 Jason Song over 6 years ago

TI__Mastermind 23361 points

Hi Shaw,

I am looking into your issue and will get back to you soon.

Regards,
Jason

0 Shaw Wong over 6 years ago in reply to Jason Song

Intellectual 590 points

Hi Jason,

Can you help to analyze this problem? I am waiting for your reply, thank you very much!

0 Jason Song over 6 years ago in reply to Shaw Wong

TI__Mastermind 23361 points

Hi Shaw,

Will you provide more details on the HC08RST load, like input impedance and capacitance? It seems the nRST is having a hard time to charge that particular node.

While waiting, I am still checking and trying if there are other problem. I will try to see if I can find one EVM in the lab, I plan to verify this on the bench as well.

Regards,
Jason Song

0 Jason Song over 6 years ago in reply to Jason Song

TI__Mastermind 23361 points

Hi Shaw,

I have ordered an EVM for me to do bench evaluation. It should arrive in 2-3 business day.

Regards,
Jason

0 Shaw Wong over 6 years ago in reply to Jason Song

Intellectual 590 points

Hi Jason,

Thank you for your reply. I have asked our customer, and they verified that it did not exist capacitance on RST pin, so I am confused about it. Anyway, thank you for your action, and I am waiting your test result.

0 Jason Song over 6 years ago in reply to Shaw Wong

TI__Mastermind 23361 points

Will keep you updated once I get the EVM.

Jason

0 Jason Song over 6 years ago in reply to Jason Song

TI__Mastermind 23361 points

Hi Shaw,

I was able to verify the nRST behaves normally on the EVM, please see the attached screenshot. I highly suspect your customer has some kind of capacitance load on the nRST pin. The waveform you provided clearly shows a capacitance being gradually charged.

I would suggest to ask your customer check that nRST pin and provide details on the circuit that connects to that node.

Regards,
Jason

0 Shaw Wong over 6 years ago in reply to Jason Song

Intellectual 590 points

Hi Jason,

Thank you for your test. I have asked our customer and they verified that it did not exist any capacitance load on the nRST pin. Becauce the customer does not provide the actual circuit, so I can not judge what's problem now. If such as the customer said, what other reason may result in the abnormal waveform?

0 Jason Song over 6 years ago in reply to Shaw Wong

TI__Mastermind 23361 points

Hi Shaw,

As I stated earlier, the waveform your customer provided clearly showed something was getting charged. I would suggest you to ask them to ship you their board. At this step, I am not sure what else I can suggest.

Regards,
Jason

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TPS7A6401-Q1: The abnormal waveform of nRST pin