TPS61194: about SYNC and PWM

Hey E2E,
Please help me!!!!

Hi ACGUY,
I'm sorry for the late response. What you 'SYNC" frequency and waht's your PWM frequency? And in which situation you find this situation? And how you control the phase bethween "SYNC" and "PWM". I have talked with our designer, it seems those are two different parts. We don't have strict requiremnet about the phase. You can also observe the inductor current. Is there any difference on the inductor current? Thanks.
Sean

Hello Sean,

What you 'SYNC" frequency and waht's your PWM frequency?
-> This is for automotive application. SYNC is provided from MCU. Frequency synchronize is for EMC.

And in which situation you find this situation?
-> The designer intends to make EN high at an arbitrary timing. However, Negative Spike occurs in the SW - pin, which exceeds the absolute maximum rating. Negative Spike has correlation with SYNC and EN.

Is there any difference on the inductor current?
-> I will check with the designer and reply at a later date.

Thanks,
ACGUY

Hi ACGUY,
What's the frequency to "SYNC" pin and what's the frequency to "PWM" pin?
Regards
Sean

Hi sean,

PWM is about 200-Hz. SYNC is 2-MHz. I got inductor current waveform.

Please let me know your opinion.

Regards,

ACGUY

Neg-spike_2.pdf

Hi ACGUY,
The inductor current waveform seems stable, I have aligned with our designer, he thought that those two frequency will flow to different parts and boost swithing frequency is very high, the pwm dimming is very low, it should has litle effects on the boost performance. To be honest, I don't have much ideal on this phenomenon. Do you find same phenomenon on different parts? Have you tried any other frequency? And dose those spike has any infulence on your performance? or EMC performance?
Regards
Sean

Hi Sean,

> And dose those spike has any infulence on your performance? or EMC performance?
No. This negative spike is over the absolute max ratings for this device.
But, If you say "no problem", we will relieved.

> Have you tried any other frequency?
Not yet. I will suggest it to our designer.

Regards,
ACGUY

Hello Sean,

Do you have any update information about this topic?

Regards,
ACGUY

Hi ACGUY,
I'm sorry that I don't have much update information about this topic. As I have said before:"Do you find same phenomenon on different parts? Have you tried any other frequency?"
Regards
Sean

Hi Sean,

> Do you find same phenomenon on different parts?
Yes. this phenomenon is reproduce at other same device.

> Have you tried any other frequency?
Yes. However, negative spike was not disappear.
(The phase difference at which a negative spike occurs is different.)

Why does a negative spike occur due to the phase difference between PWM and SYNC?

Regards,
ACGUY