TPS65982: Current limit behavior

Aaron Jones

Part Number: TPS65982

Hi TI,

I need to drive an inductive load at 3-3.5A, 20V, around 3-4ms duration, rms measured around 1A (20W). How will the TPS65982 respond to the peak current values if both the source and sink both use the TPS65982 with a 2A negotiated contract?

over 6 years ago

0 Eric Beljaars over 6 years ago

TI__Mastermind 36751 points

Hi Aaron,

The Peak Current behavior will depend on the configuration of your Source TPS65982. You can adjust the Peak Current in the Source PDO's from 100% to 200%. Since you have a 2A contract and need to pass through a 3-3.5A load, I would set the peak current setting for your 20V/ 2A PDO at 200% to pass this current through without triggering OCP.

Thank you,

Eric

0 Aaron Jones over 6 years ago in reply to Eric Beljaars

TI__Intellectual 760 points

Hey Eric,

This might be documented in the datasheet and I'm missing it, but the sink PDO would behave similarly, correct?

The datasheet states

"The current through PP_HV to VBUS is current limited to ILIMPPHV (only when operating as a source) and is controlled automatically by the digital core. When the current exceeds ILIMPPHV, the current-limit circuit activates. Depending on the severity of the over-current condition, the transient response will react in one of two ways: Figure 27 shows the approximate response time and clamping characteristics of the circuit for a hard short while Figure 28 shows the approximate response time and clamping characteristics for a soft short of 7"

So, the sink doesn't power limit. However, I can set a sink PDO peak current in settings--does this mean the sink PDO peak current would be used by the source? Which value would the source limit by?

In other words, if my source is set to 200% peak, and my sink is set to 150% sink, the peak current before OCP would be 150%, but because the source would then limit the current to 150% correct? Or would it be 200%?

0 Eric Beljaars over 6 years ago in reply to Aaron Jones

TI__Mastermind 36751 points

Hi Aaron,

The Sink does not implement any OCP per USB PD Spec. The Sink setting in the Sink PDO is only used when matching to the Source PDOs of the connected device. If your Source is set to 200% and your Sink is set to 150%. OCP would trip at the 200% mark.

Thank you,
Eric

0 Aaron Jones over 6 years ago in reply to Eric Beljaars

TI__Intellectual 760 points

Eric,

As a final question, the TPS65982 should be able to support any of the below profiles, given that they are type-C compliant?

0 Eric Beljaars over 6 years ago in reply to Aaron Jones

TI__Mastermind 36751 points

Yes, that is correct.

Thank you,
Eric

0 Aaron Jones over 6 years ago in reply to Eric Beljaars

TI__Intellectual 760 points

Hi Eric,

I've attached my settings. I've set my PDO sink to accept 3A ONLY, but I'm still negotiating a contract with a 2.25A source. What's going on here?

PDO.7z

0 Eric Beljaars over 6 years ago in reply to Aaron Jones

TI__Mastermind 36751 points

Hi Aaron,

I'm assuming you're using a 45W Type-C adapter that is offering 20V/2.25A to the TPS65982-EVM that you are using. Although you set your source PDO to sink only 3A, it will still accept lower contracts. In this scenario, the capabilities mismatch in the PD communication will be set to 1:

You can find more information about the capabilities mismatch in the USB PD Spec.

Thank you,

Eric

0 Aaron Jones over 6 years ago in reply to Eric Beljaars

TI__Intellectual 760 points

Eric,

Is there any way to configure the sink to not accept the PDO and stick to 5V?

0 Eric Beljaars over 6 years ago in reply to Aaron Jones

TI__Mastermind 36751 points

Hi Aaron,

You could try changing the setting in the Autonegotiate Sink register (0x37) If you disable the Autonegotiate Sink Register, the TPS65982 will only sink the 5V contract.

Thank you,
Eric

0 Aaron Jones over 6 years ago in reply to Eric Beljaars

TI__Intellectual 760 points

Eric,

Just to clarify,

I'd need to send a command to then negotiate a 20V,3A contract with a compatible source, correct?

0 Eric Beljaars over 6 years ago in reply to Aaron Jones

TI__Mastermind 36751 points

Hi Aaron,

That is correct.

Thank you,
Eric

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TPS65982: Current limit behavior