TIDA-01513: Why does ISO_NEG go high while only POS_SW is on-state?

Yoshiki Ochi

Part Number: TIDA-01513

Hi team,

Could you tell me why ISO_NEG goes high while only POS_SW is on-state with HV positive error test?

I referred to figure.22. I thought ISO_NEG would keep Vref because there is no current path via lower side resistors but it didn't. Could you show me the current path in that state and equation about ISO_NEG in this state?

Or did I misunderstand the switching state?

Best regards,
Ochi

over 4 years ago

0 David Dong over 4 years ago

TI__Prodigy 610 points

Hi Ochi-San,

I think you are right. The ISO_NEG should be keep equal to VREF as there is no current flow at all.

I guess this might be caused by the supply isolation of 400V and 12V during the test.

How about testing it again by us?

0 Yoshiki Ochi over 4 years ago in reply to David Dong

TI__Expert 7585 points

Hi David,

I would like to do that. But I could not test that board with high voltage, such 400V.

Is it OK to test with 12V and 40V, which imitate HV, with modified isolated resistor ladders and isolation leakage resistor?

Regards,
Ochi

0 David Dong over 4 years ago in reply to Yoshiki Ochi

TI__Prodigy 610 points

Hi Ochi-San,

I think 40V is enough for the test as the reference voltage is small as only 2.5V.

Do you have board in hand? If yes, it's quite quick to do so.

I'd like to see the result once you finished.

0 Yoshiki Ochi over 4 years ago in reply to David Dong

TI__Expert 7585 points

Hi David,

There is no latest board. I will order and test it.

I will let you know when test is finished.

Regards,
Ochi

0 Yoshiki Ochi over 4 years ago in reply to Yoshiki Ochi

TI__Expert 7585 points

I found that the test board but I should confirm it works or not.

I will update the status by this Friday.

Regards,
Ochi

0 Yoshiki Ochi over 4 years ago in reply to Yoshiki Ochi

TI__Expert 7585 points

Hi David,

The board I had was bad condition due to short circuit between R10 and C7 in the schematic in page 12.

On the other hand , I found that it is possibility to misunderstand the pin location of RELAY_POS as RELAY_NEG. The measurement pin location looks confused because the order of RELAY_POS and RELAY_NEG is opposite compared with the order of ISO_POS and ISO_NEG.

I cannot actual test because there is no board with being able to operate, but this assumption makes sense for figure 22.

Regards,
Ochi

0 David Dong over 4 years ago in reply to Yoshiki Ochi

TI__Prodigy 610 points

Hi Ochi-San,

Thanks for you explanation.

Yes, if the RELAY_POS as RELAY_NEG are opposite, the test result can be explained. Actually in the test, the RELAY_NEG is firstly turned on, ISO_NEG changes to be higher than VREF.

Now we are planning to update the design and let's test it again to verify your assumption.

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TIDA-01513: Why does ISO_NEG go high while only POS_SW is on-state?