TPS2421-1: About CT pin

Hi Ishiwata-san,

CT pin should go to low logic level after the UVLO. Also CT doesn't go more than 1.4V as there is comparator in device which turns off the main FET and charging current of CT pin when 1.4V threshold is crossed. Let me verify this on bench by Wednesday (23rd oct) and get back to you on this. 

Best Regards,
Arush 

Hi Arush-san,

Thank you for your support.

I received the waveform from the customer, so I will send it to you via private message.
Can I send you a friend request?

We are waiting for the bench test results.

Best Regards,
Ishiwata

Shuji Ishiwata said:

Can I send you a friend request?

Sure

Hi Arush-san,

I sent the waveform at the CT terminal in a private message, but do you have any ideas what the cause might be?

I will also send the circuit diagram in a private message.

Best Regards,
Ishiwata

Hi Ishiwata-san,

It looks like this is happening due to load. If the load is constant power type load, when the Vin is dropping, the current draw will rise and cause overcurrent event which effectively cause the CT pin rising. 

Can they try this test 1) without the load, 2) with some constant resistor load 3) actual load.

Ask them to probe Vin, Iin, Vout, CT pin. Probing all signals will be more helpful. 

Best Regards,
Arush

Also, I apologies but I wasn't able to test this yesterday. I will try if I can get some testing done tomorrow but it will be much better if they can test this. For me failure replication itself will take lot of efforts but for them the system will be ready and will only have to focus on resolving the issue. 

Hi Arush-san,

Thank you for your support.

We have currently requested the customer to obtain the waveform.
Please wait.

And we look forward to your test results.

A customer is using TPS2421-1 and is having trouble start up. We are currently investigating the cause, but have a follow-up question.
After power is input to VIN, the input is stopped. Operation as the TPS2421-1 is turned off.
At that time, a small amount of charge remains in the capacitor at the CT terminal. Is there a possibility that a startup failure will occur if power is input again in that state?
I think that if a charge has accumulated in the capacitor at the CT terminal, and if the device is started again, the fault timer may be triggered even if no large current is generated.

Best Regards,
Ishiwata

Hi Ishiwata-san,

Shuji Ishiwata said:

I think that if a charge has accumulated in the capacitor at the CT terminal, and if the device is started again, the fault timer may be triggered even if no large current is generated.

I don't that will be the case unless they are doing startup with very less time delay. With very quick startup also, they will still need fault event and CT timer will be inaccurate. 

Best Regards,
Arush

Hi Arush-san,

Thank you for your reply.

The customer turns the power on and off about 500 times while the board is in a low temperature state. The startup failure occurs about 2 times out of 500 times.
Is it possible that the startup failure is caused by a charge on the CT terminal? It restarts repeatedly in a very short time.

Best Regards,
Ishiwata

Hi Ishiwata-san,

There were some holidays last week hence the delays.

Is there any update from the customer side? 

Best Regards,
Arush

Hi Arush-san,

Thank you for contacting us.
We haven't heard back from the customer yet.
We'll get in touch when we receive feedback from the customer.

Best Regards,
Ishiwata

Hi Ishiwata-san,

Sure.

Best Regards,
Arush

Hi Arush-san,

We have received a waveform from a customer.
We have sent the waveform via private message. Please check it.

Best Regards,
Ishiwata

Hi Ishiwata-san,

I will get back to you by EOD.

Best Regards,
Arush

Hi Arush-san,

I am waiting for your reply.

Best Regards,
Ishiwata

Hi Arush-san,

I have been waiting for your reply, but have not heard from you.
Could you give us a response?

Best Regards,
Ishiwata

Hi All,

I have been waiting for your reply, but have not heard from you.
Could you give us a response?

Best Regards,
Ishiwata