TPS23521: ICL1

Hi Ishiwata

I should not shutoff at 15mA

Did timer started during that event? Can you share test waveforms

BR,

Rakesh

Hello Rakesh

Thank you for your support.

The waveform will be sent via private message as this is confidential customer information.

I will also briefly explain the circuit considerations along with the past E2E inquiry.

The customer was considering the TPS23521 with a low current limit (about 150mA), but the current is limited at 15mA.

The reason for the 15mA limit was not clear in the previous E2E inquiry.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1328835/tps23521-current-limit/5079349#5079349　

So the customer considered using a two-stage FET configuration using the PG terminal.

When using a two-stage configuration, the current limit of about 150mA was successfully achieved.

After that, as the customer continued with the verification, a startup failure occurred due to a large inrush current. As a countermeasure, the current limit value was increased, but the TPS23521 and FET were damaged.

The E2E inquiry is as follows.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1402417/csd19538q3a-measures-to-prevent-breakage/5371105#5371105　

One of the customer's questions is why the TPS23521 is limited to 15mA in the first place.

And now that xx and the FET are damaged, I would like to know what to do about it.

Best Regards,
Ishiwata

Hi Ishiwata

Can you check whether there is any scaling factor on the current 10:1. ?  or whether the current probe is calibrated ? 

I don't see any reason for it to limit at 15mA

BR,

Rakesh

Hello Rakesh

At the time, we checked various measurement environments and found that the current was limited to around 15mA.
I sent you a waveform in a private message.

Can you check the operation yourself? Is it difficult since I don't have an EVM?

Best Regards,
Ishiwata

Hi Ishiwata

I have seen that test result. 

My question was whether the current probe has attenuation factor of 10  or not ? I think it has and that's the reason to read 150mA  as 150mA/10=15mA.

BR,

Rakesh

Hi Rakesh,

When ICL1 is set to 150mA, ICL2 will be around 15mA.
On the customer's board, current limiting is activated by ICL2.
If ICL1 is set low, the TPS23521 will not start up correctly at startup due to ICL2.

The TPS23521 is not limited by ICL1, but current is limited by ICL2. Can you tell me why?

Best Regards,
Ishiwata

If ICL1 is set to 150mA, does ICL2 become about 15mA? Is this correct operation of the device?

ICL2 depends on the RSNS value. Please refer Equation (5) in Page-13 in https://www.ti.com/lit/ds/symlink/tps23521.pdf 

Hi Rakesh,

Thanks for your reply.

As you say, ICL2 depends on the RSNS value, but it may cause startup failure.

I have an additional question.
The sense resistor detects overcurrent, but could you tell me how long it takes for the GATE terminal to start controlling the FET?
I would like to know at what level of current spike it starts to limit the current.

Best Regards,
Ishiwata

Can you please share test waveform of FET current, TMR voltage and GATE during startup.

Thank you for your support.

I will requet the customer about the start-up waveforms.
However, I think the time the restriction applies (the time until the GATE terminal starts controlling the FET) is determined by the device, so I would appreciate an answer.

I think the time the restriction applies (the time until the GATE terminal starts controlling the FET) is determined by the device, do you have any answers?

GATE response time is in the order of 30us (typical)

Hi Rakesh,

Thank you for your answer.

I have an additional question.
I have a question about the TMR terminal.

When a 0.15uF + 0.047uF capacitor is connected to the TMR terminal, the retry interval is about 6.2sec.

When the TMR terminal capacitor is changed to 0.15uF + 0.22uF, it operates between retries of 65msec.

I checked the datasheet, and it seems that the retry time does not affect the TMR terminal.

Is my understanding correct?

I sent a private message showing the current waveform when the output is shorted.

Best Regards,
Ishiwata

My customer is in desperate need of an answer.

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