TPS2552: About fault

Masazumi Ishii

Genius 3945 points

Part Number: TPS2552
Other Parts Discussed in Thread: TPS25221, TPS2553

Hello.

I have a question about TPS 2552.

For details, please see the attached document.

If you need a circuit diagram, please tell me the destination.

Thank you.

TPS2552.pdf

over 5 years ago

0 Bob Ma over 5 years ago

TI__Expert 8980 points

Hi, Masazumi Ishii,

Thank you for your detailed attached file. It's clear for my reference.

From the waveform and your set-up, the current limit function works well and current is limited. To double confirm you can monitor if VOUT=0.957*1.8=~1.72V.

So the current limit works but fault not assert. I think might be noise influences the fault logic. To confirm this, I suggest you:
1. Check if Vin ripple is big?
2. Use a clean DC power supply to supply 3.3V instead of DC-DC to see if this issue still exist.

Regards,
Bob

0 Masazumi Ishii over 5 years ago in reply to Bob Ma

Genius 3945 points

Hello.

Thank you for your answer.
Additional measurements were taken. I have a question.
For details, please see the attached document.

Thank you.TPS2552-3.pdf

0 Bob Ma over 5 years ago in reply to Masazumi Ishii

TI__Expert 8980 points

Hi, Masazumi-san,

A ripple of 50KHz-250KHz, >60mV will influence the internal logic and cause fault flag no asserting.

Please decrease the ripple or use our new generation product : TPS25221. It's cost down version of TPS2552/3, and they have same function and performance. And TPS25221 have filter in internal circuit, so it will not have this problem when Vin ripple is high.

Regards,
Bob

0 Masazumi Ishii over 5 years ago in reply to Bob Ma

Genius 3945 points

Hello.

thank you for your answer.

I have an additional question.

Your answer is that it will affect with ripple of 50 KHz - 250 KHz, 60 mV.
To what extent is it necessary to suppress the ripple?

Thank you.

0 Bob Ma over 5 years ago in reply to Masazumi Ishii

TI__Expert 8980 points

Hi,

If the ripple frequency is from 50KHz-270KHz, you need to suppress the ripple to be below 80mV.

Below is guilde to avoid fault no-assert issue:
1.Optimize the former DCDC control loop, avoid low frequency ripple in TPS2553 Vin from 20kHz to 270kHz.

2. Suggest placing 0.1uF and 100uF ceramic cap on TPS2553 Input pin, make sure the input voltage ripple < 80mV.

3. The trace routing the RILIM resistor to the device must be as short as possible to reduce parasitic.

4. Power pad must be directly connect to PCB ground plane.

Regards,
Bob

0 Masazumi Ishii over 5 years ago in reply to Bob Ma

Genius 3945 points

Hello.

Bob-san Thank you for your reply.
Please let me organize the contents.

· A ripple of 50 KHz - 250 KHz,> 60 mV will influence the internal logic and cause fault flag no asserting.
If the ripple frequency is from 50 KHz - 270 KHz, you need to suppress the ripple to be below 80 mV.

In the case of ripple of 50 KHz - 250 KHz, you can understand that it is okay to keep it below 60 mV. (It is safe to make it below 50 mV)
Is it OK with this understanding?

Thank you.