TPS65981: After setting minimum operating current to 2.5A (Sink) in the application tool, the chip still actively negotiates with 2A supply.

Jordan Collings

Part Number: TPS65981

Hi there,

I have a TPS65981 set up as a power sink. I have two PDOs set up as sink options. 5V 3A and 9V 2.5A. These are the minimum requirements for the given PDOs.

When i connect to a source capable of the following:
5V 3A
9V 2A

I expect the chip to reject the 9V as the source is only capable of 2A and use the 5V PDO option as this is to specification for that given PDO.

This is not happening. The negotiation picks the non compliant 9V2A.

Why may this be? i know power wise this may be the larger PDO, but it is still not able to meet the minimum requirements so it should use the 5V.

over 4 years ago

0 Emma Hoying over 4 years ago

TI__Genius 9630 points

Hello,

Sources can offer a max current, but current is always pulled by the sink. If your source offers a max current of 2A, and your sink is capable of pulling 2.5A, then it will choose the 9V 2A option, and the source will likely current limit to let the sink pull only 2A. If you connect a load to the TPS65981 and start pulling current, it should be current limited to 2A.

Regards,

Emma

0 Jordan Collings over 4 years ago in reply to Emma Hoying

Prodigy 140 points

Hi there,

i'm clear with the above, however, my minimum current and operational current of my sink is 2.5A @ 9V. It should reject the source 9V PDO as its only capable of supplying a maximum 9V 2A?

My other remaining source/sink profiles match so it should successfully negotiate to the 5V 3A PDO?

Regards,
Jordan

0 Emma Hoying over 4 years ago in reply to Jordan Collings

TI__Genius 9630 points

Hi Jordan,

The source will always select the PDO negotiated. If you are able, please check what your source's sink negotiation options. For example, when the TPS65981 is set up as a source, register 0x37 "Autonegotiate sink" sets up how the sink is selected.

Thanks,

Emma

0 Jordan Collings over 4 years ago in reply to Emma Hoying

Prodigy 140 points

'Choose Highest Current' solved this issue

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TPS65981: After setting minimum operating current to 2.5A (Sink) in the application tool, the chip still actively negotiates with 2A supply.