Unstable controller out of TPS40210

Johnny Kim

Intellectual 330 points

Other Parts Discussed in Thread: TPS40210

Hi.

I'm using TPS40210 on my customer's board, but facing urgent problem.

Input: dicharging from 18V, Output: 20V, DIS/EN: floating

In below captured figure, C1 : Drain side of FET, C2: Cathod of DIODE, C4: VDD input

Input start discharging from 18V to fully discharged capacitor, but as below figure, input VDD voltage is held aroung 4.5V for long time, because that time is no load state.

Also this time, device is switch off by UVLO threthold, but after short time, switcher is working again for short time in discharging input voltage.

So I wonder why switcher is working again under UVLO threthold level, and there is any solution figure out this problem.

Pls advise me.

over 13 years ago

0 Na Kong over 13 years ago

TI__Genius 17240 points

Hi Johnny,

Due to dielectric absorption on the input capacitor, it is possible that the input voltage gets back and above UVLO to enable the TPS40210 again after discharging.

For polymer films cap, the bouncing back voltage may be less than 1-2% of the original voltage, but it can be as much as 15 - 25% for electrolytic capacitors or supercapacitors.

I would suggest to try different cap to see whether this problem can be solved or add simple logic circuit to actively disable the TPS40210 through DIS/EN pin when the input voltage drops and before it goes lower than UVLO.

Regards,

0 Johnny Kim over 13 years ago in reply to Na Kong

Intellectual 330 points

Hi Na.

Thanks for your reply.

I have some more question.

By your mention, depend on capacitor's characteristic the bouncing back voltage can be differed, then would you describe about this symptom in more detail, if you have document about that pls share to me.

We have to use over 4000uF capacitor with 30V withstanding voltage, because when input power is cut off, input power have to withstand 20V/3A load during over 10ms.

For this concept, would you recommend proper capacitor.

Additionally do you have experience in similar case, if yes, let me know how can be figured it out.

Thanks & Regards.

Johnny

0 Na Kong over 13 years ago in reply to Johnny Kim

TI__Genius 17240 points

Hi Johnny,

I would suggest add additional circuit for the UVLO. Please refer to the reference design of PMP5702 for the aux UVLO circuit with hysteresis.

http://www.ti.com/tool/pmp5702

Regards,

0 Johnny Kim over 13 years ago in reply to Na Kong

Intellectual 330 points

Hi Na.

Would you pls. explain what is bouncing back voltage, and why dielectric absorption is happen on capacitor, also what bouncing back voltage is different in depend of kind of capacitors.

Thanks&Regards.

0 Na Kong over 13 years ago in reply to Johnny Kim

TI__Genius 17240 points

Hi Johnny,

Attached please find a reference of dielectric absorption in capacitors.

6567.Dielectric Absorption in Caps.pdf

Regards,

0 Johnny Kim over 13 years ago in reply to Na Kong

Intellectual 330 points

Thanks, Na.

Power management

Power management forum

Unstable controller out of TPS40210