CSD95490Q5MC: There is a undershoot on Vsw( with Buck converter), when i used CSD95490Q5MC.

TaoTao

Intellectual 255 points

Part Number: CSD95490Q5MC

There is a undershoot on Vsw( with Buck converter), when i used CSD95490Q5MC.

The Waveform and Schematic are as follows.

over 5 years ago

0 Qian Chen over 5 years ago

TI__Mastermind 24075 points

Hi Tao,

Can you provide PWM waveform?

Thanks

Qian

0 TaoTao over 5 years ago in reply to Qian Chen

Intellectual 255 points

hello Qian，

Thanks for your reply.

This is the PWM waveform, The ‘undershoot of Vsw’ appears at an unspecified period(see first figure), and it's good at some period(see second figure).

Today, I find that ‘undershoot of Vsw’ appears at the period with a short Δt(pointed out in the first picture), and third figure shows a dynamic waveform.

And, Vin=12V, L=2.2uH, Cout = 100uF, Iout = 3A. Vout = 1.5V.

Thanks.

Tao

0 Qingquan Tang over 5 years ago in reply to TaoTao

TI__Expert 3525 points

Hi Tao,

I have below comments for your schematic:

1. We suggest to choose Lout upto 1uH, and then need to select Lset according to the output inductance value. You can find the chart of Lset value in figure 17 from the datasheet. For example, you need Lset=1.75Mohm (close to this value) if Lout=1uH.

2. The 0ohm resistor from REFIN to GND should be removed.

3. We suggest to place 2*22uf/16V/0805 +1*1uf/25V/0402 caps between Vin and PGND close to power stage, 1uf cap should be as close as possible to power stage VIN/PGND pins on the same side of PCB as power stage.

Please try above mentioned modification, then see if the problem goes away. If you still have issue, you may want to measure:

1. PWM1B to see if any noise coupling.

2. High side FET Vds, to check if the FET was turned off due to noise coupling;

3. Improve noise on both PWM1A and PWM1B if due to noise coupling;

4. In the meantime, you may also monitor inductance current and Iout/REFIN with differential probe to see if current signals are normal.

Best,

Qingquan

0 TaoTao over 5 years ago in reply to Qingquan Tang

Intellectual 255 points

Hi, Qingquan,

First, Thanks for your reply.

I find that EPWM1B is not right, it should be HIGH when normal. I put a pull-up resistance on this pin, then it work well without undershoot on Vsw.

By the way, how can I get the full datasheet of CSD95490Q5MC. I requested full datasheet several times, but didn't got it.

Thanks again!

Tao

0 Qingquan Tang over 5 years ago in reply to TaoTao

TI__Expert 3525 points

Hi Tao,

I assume you registered on TI.com, then I thought you should be able to download the datasheet from online product page? You may try different browsers if you have issues, but IE should work.

If you couldn't for some reason, you may request to who you bought the product.

Best,

Qingquan

0 TaoTao over 5 years ago in reply to Qingquan Tang

Intellectual 255 points

Hi Qingquan,

Thanks for your reply.

Yes, I had registered on TI.COM, and I can download the datasheet from online product page, but this datasheet is not full datasheet, It only contains a very simple introduction without many information about CSD95490Q5MC, for example, the chart of Lset value in figure 17 from the datasheet. It is not browsers issue.

And, the product is a sample obtained through TI.COM.

Thanks again.

Tao

0 Qingquan Tang over 5 years ago in reply to TaoTao

TI__Expert 3525 points

Hi Tao,

I understand now.

There are some information not for public disclosure, we require NDA to share.

Would you check if your company or organization has NDA with us?

Best,

Qingquan

0 TaoTao over 5 years ago in reply to Qingquan Tang

Intellectual 255 points

Hi Qingquan,

Thanks for your reply.

I got it, I am a student. so maybe can't get the full datasheet.

Fortunately, it didn’t greatly affect the progress of my experiment.

Appreciate your patience answer.

Tao

Power management

Power management forum

CSD95490Q5MC: There is a undershoot on Vsw( with Buck converter), when i used CSD95490Q5MC.