TPS62821: Power OFF behavior

Akihisa Tamazaki

Part Number: TPS62821

Hello team，

My customer is checking TPS62821EVM-005 behavior and has a question about Power Off behavior. The customer connected EVM with the only load at output and DC supply at input. He did not modify the circuit in EVM.

Then, under high load condition of Iout=90%, Vout went down once and then rose again when the input power was turned off as shown in the following attachment.

/cfs-file/__key/communityserver-discussions-components-files/196/TPS62821EVM_2D00_005--Power-OFF-behavior.pptx

Is this behavior normal? If yes, would you please tell me why TPS62821 operate like this?

Your advise is appreciated.

Best Regards,
Akihisa Tamazaki

over 1 year ago

+1 Febin over 1 year ago

TI__Mastermind 19250 points

Hi Tamazaki-san,

- The test setup does not look correct to me. It's a bit confusing for me...

- Case Vin=3.3V/5V, Vin reading on scope plot is not in accordance with the scale on the plot.

- Is the EN pin connected externally or the jumper on the EVM was used? If jumper was used, why is the Vin and EN not having the same value in all cases?

- Case 3.3Vin: You said Vin drops from 3.3V to 0V. From the scope plot something is not right. Same for Case 5Vin.

- For higher loads, Vin seems to be unstable...

- Can you please repeat in the following way:

Vin= 3.3V or 5V, Vout= 1.8V, Iout = 0.1A and 0.9A. EN pin externally triggered using a function generator. This is the correct method to plot Power-off. You will see examples in the datasheet.

Please share the updated scope plots.

Regards,

Febin

0 Akihisa Tamazaki over 1 year ago in reply to Febin

TI__Genius 10875 points

Febin-san,

As you pointer out to me, when EN state is OFF(Low), the output decrease to 0V clearly as below link.

/resized-image/__size/1746x878/__key/communityserver-discussions-components-files/196/TPS62821_6E30FB96906ECB7A0B4E8A30797227602800_EN_9230_OFF_2900_.png

The customer set EN=ON while Vin drops from 3.3V/5V to 0V. Because the voltage from 0V to 6V at EN pin is acceptable in TPS62821 absolute maximum rating. I do not believe that TPS62821 will be broken even if EN voltage(up to 6V) is larger than Vin.
Should the customer avoid having VIN 0 V with EN on? Customer says that It is OK to be unstable like waveforms (/cfs-file/__key/communityserver-discussions-components-files/196/6175.TPS62821EVM_2D00_005--Power-OFF-behavior.pptx)

Your advice is apprediated.

Best Regards,
Akihisa Tamazaki

+1 Febin over 1 year ago in reply to Akihisa Tamazaki

TI__Mastermind 19250 points

Hi Tamazaki-san,

I do not see a problem if Vin=0V, EN=High

However, if Vin drops (typically less than 2.2V) then the device will enter UVLO condition.

So, if you want to measure Vout discharge during Power-off, EN must be pulled low and Vin must be present, otherwise Output discharge cannot function. I am confused what you're trying to do with this measurement.

Regards,

Febin

0 Akihisa Tamazaki over 1 year ago in reply to Febin

TI__Genius 10875 points

Febin-san,

Thank you for your comment. I understand. I will share output discharge function during power off with the customer.

Best Regards,
Akihisa Tamazaki

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TPS62821: Power OFF behavior