TPS25750: Access the ADC measurements of VBUS and the current on VBUS through the I2Cs network.

Shane Kent

Part Number: TPS25750
Other Parts Discussed in Thread: LMZ21701

Hello -

I'm working on an application that requires redundant measurement of VBUS and the current on VBUS. The TPS25750 has been a great part for our needs for a year now and I'm diving in now to see if I can utilize the internal VBUS and current measurements of the internal ADC of the TPS25750 as one of the redundant measurements for those values. The other measurement is via external measurement.

Chuck Branch had some discussions regarding this topic here: https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1034381/tps25750-question-of-tps25750

I haven't seen any further discussion on this topic. The datasheet and user manual for the TPS25750 suggest that the VBUS and I_VBUS measurements through the ADC can be accessed via the I2Cs interface of the part, but there doesn't seem to be any information on how to do that ("The output from the ADC is available to read and used by application firmware.").

I look forward to hearing back on this topic.

10 months ago

0 Raymond Lin 10 months ago

TI__Mastermind 25556 points

Hi Shane,

Let me check up on this and get back to you by midweek.

Thanks and Regards,
Raymond Lin

0 Shane Kent 10 months ago in reply to Raymond Lin

Prodigy 75 points

Thank you, Raymond Lin.

0 Raymond Lin 10 months ago in reply to Shane Kent

TI__Mastermind 25556 points

Hi Shane,

I_VBUS is intended for reading the current on PP5V, are you looking to read the measurements through PP5V or PPHV?

Thanks and Regards,

Raymond Lin

0 Shane Kent 10 months ago in reply to Raymond Lin

Prodigy 75 points

Hi Raymond -

Ah, I was thinking that I_VBUS was the current through PPHV. In this case, just having the ADC measurement for VBUS would be useful. I'll have to come up with an alternative way to measure the current through VBUS.

-Shane

0 Raymond Lin 10 months ago in reply to Shane Kent

TI__Mastermind 25556 points

Hi Shane,

Let me check internally on PPHV ADC and get back to you tomorrow.

Thanks and Regards,

Raymond Lin

0 Shane Kent 10 months ago in reply to Raymond Lin

Prodigy 75 points

Sounds great, Raymond. Thank you for the quick support thus far.

-Shane

0 Raymond Lin 10 months ago in reply to Shane Kent

TI__Mastermind 25556 points

Hi Shane,

What kind of DCDC is attached to the PPHV pin of TPS25750D? Are you using one of the supported BQ Battery Charger devices to pair with TPS25750?

Thanks and Regards,

Raymond Lin

0 Shane Kent 10 months ago in reply to Raymond Lin

Prodigy 75 points

Hi Raymond -

No, I'm not utilizing a BQ battery charger device in this application. Instead, we're utilizing a few distributed LMZ21701 buck regulator modules as well as some TI inductive load drivers.

-Shane

+1 Raymond Lin 10 months ago in reply to Shane Kent

TI__Mastermind 25556 points

Hi Shane,

To read the VBUS voltage, you can read register 0x6A (ADC_RESULTS) and the specified bits below:

This register is readily available to read without any changes to the configuration, we're working on adding this into the technical reference manual in a future release of the document.

Let us know if there's any questions or concerns!

Thanks and Regards,

Raymond Lin

0 Shane Kent 9 months ago in reply to Raymond Lin

Prodigy 75 points

Hi Raymond -

This is extremely helpful, thank you! Here's a read of register 0x6A in my application:

In this configuration the TPS25750 has an I2C address of 0x21 and the negotiated supply voltage should be 15V, but it really is 15.39V.

I might be misunderstanding, but bits 31:24 of this sequential 9-byte read is 0xF6 which is ~24V if I use the PA_VBUS conversion listed.
However, the 39:32 bits of this read is 0x9C which converts to ~15.28V if I use that conversion.

Am I misunderstanding something? Should I be using that 0x9C measurement?

Lastly, are you able to share the rest of the mapping for this 9-byte sequence and have you determined if there is a current measurement being reported back to the ADC?

Thanks again for the help, Raymond!

-Shane

+1 Raymond Lin 9 months ago in reply to Shane Kent

TI__Mastermind 25556 points

Hi Shane,

The register setup is shown below:

It seems like the first byte in the read (0x0D) is the length of the I2C read. Following 0x0D there are two 0x00 (I assume both of your ADCIN1 and ADCIN2 are tied to GND). 0xF6 is then mapped to LDO_3V3 which calculates to roughly 3.44V. Finally for PA_VBUS (31:24) which is 0x9C this will give you 15.29V.

TPS25750 does not support current sensing on PPHV so unfortunately there's no way to read the measurement. However if the LMZ21701 has a current ADC register, you can use "I2Cw" through the TPS25750 to read back the current values.

Thanks and Regards,

Raymond Lin

0 Shane Kent 9 months ago in reply to Raymond Lin

Prodigy 75 points

Great! Thank you, Raymond. This is helpful to have - thank you for verifying the numbers for me.

We can close out this topic now.

-Shane

0 Raymond Lin 9 months ago in reply to Shane Kent

TI__Mastermind 25556 points

Hi Shane,

No problem, if you have any additional questions please open a new thread so we can have better tracking!

Thanks and Regards,

Raymond Lin

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TPS25750: Access the ADC measurements of VBUS and the current on VBUS through the I2Cs network.