PTN78020A: Output voltage set-poitn resistor values isssues

Hi John,

Can you please share a snippet of your schematic so that we can review all your pin connections to the PTN78020A?

Did you mean 22uF input cap? The minimum stated in the datasheet is 18.8uF.

Regards,
Kris

Here is the design. 

Condition:

Vin: 12 V

C1/C2: 2.2 uF

Cout: 330 uF

Rset: (Required 1%, 0.05 W) I have 13.1 kΩ.

RESULT:

At Vout/GND, I am reading approximately 5 V, which is completely fine because that's what I am trying to achieve.

However, with Rset being 13.1 kΩ, theoretically with the TI datesheet(Table 3 of PTN78020W), it should be 21 kΩ to get 5V. 

EVEN THOUGH it is working fine, it is still a mystery how this is operating in the manner i described above. Did not make any sense to me.

Could you give me an idea?

Thank you. 

Hi John,

One of my colleagues tested an EVM with your exact board schematic except he was following table 3 of the datasheet. He had  RSET  to be 21kΩ  and the result of an output voltage of 5Vout. From this I have a few questions and suggestions for testing:

1. How many of your parts exhibit this issue where Rset was 13.1kΩ and resulted in 5Vout?
2. Can you test on a different PTN78020WAH device to see if the issue follows a new device? 
3. What is the result if you populated the Rset with 21kΩ instead of 13.1kΩ?

Regards,

Jimmy 

Hello Jimmy,

Thank you very much for testing on your side and verifying that the board follows the datasheet.

1. Currently, we only have 1 board and I will have to order some to test.

2. I will order PTN78020WAH to verify that.

3. We are currently out of 21 kOhm SMD or T-H, that we have to order to test.

Do you guys take any requests for a sample? (PTN78020WAH board).

Thank you, 

John. 

Hi John,

Take a look at the schematic below. The image demonstrates resistor values internal to the device. We don't see how that resistor value is causing such strange phenomenon.
Lets try a few more things:

1. Populate Rset with another value of your choice. For example, Rset = 79.3kΩ results Vout = 3.3V
2. Leave Vo Adj (Pin 4) open, which should result a Vout = 2.5V

Is there a reason why you chose a 13.1kΩ? How did you come across this value? Did you try different resistor values before 13.1kΩ? (I'm assuming you were following table 3 in the datasheet.)

Thanks,
Alejandro

Hi John,

Any updates on this? Just checking in to see if you were able to perform the tests. If so, what were the results?

Regards,
Alejandro

I will have to get the board and parts to try.

Please keep this open, I will eventually write the test result.

Thank you.

Sincerely,

John

Hi John,

Any updates? Are you still experiencing the odd results?

Regards,
Alejandro

Hi John,

We have not heard back from you. We want to make sure your concern has been resolved.
Is there any update or anything I can do further to help? When should we expect to receive these test results?

Regards,
Alejandro

Hi John,

I understand you want to keep the thread open, but due to the inactivity the thread closes automatically. May we contact you at the email address you provided in your E2E profile? Therefore, we can have direct contact and have any follow up conversation. I would not want the system assuming the problem has been resolved on your end due to inactivity.

Regards,
Alejandro