TPS548A20: NC on pins 27 and 28?

Sepeedah Zadeh

Part Number: TPS548A20
Other Parts Discussed in Thread: TPS549A20, TPS53915, TPS53515

Hi team,

Customer is trying to see if they can use TPS548A20 in place of TPS549A20 due to shortage issue. Looks like HW wise the main difference is on the I2C line (pin 27 and 28). Can we float these pins on TPS548A20 instead of grounding it? Thanks1

over 4 years ago

+1 Kadeem Samuel over 4 years ago

TI__Mastermind 22210 points

Sepeedah,

These pins can be left floating. If you refer to page four of the TPS548A20EVM datasheet (www.ti.com/.../sluubc0, you will see that these pins are left floating on the EVM with no issues.

0 Sepeedah Zadeh over 4 years ago in reply to Kadeem Samuel

TI__Expert 3100 points

Kadeem,

If I reference that schematic, I see the pins are pulled to ground with R14 and R15 when there isn't a PMBUS connection is that not correct?

0 Lishuang Zhao over 4 years ago in reply to Sepeedah Zadeh

TI__Expert 7500 points

Hi Sepeedah,

Yes, these two pins are connected to GND through R14 and R15. I don't think they can be left floating. But I am not pretty sure.

Let's wait for David response who is the expert of this part.

Thanks,

Lishuang

0 Kadeem Samuel over 4 years ago in reply to Lishuang Zhao

TI__Mastermind 22210 points

Lishuang,

My sincerest apologies, I was looking at the incorrect pins. Yes, those pins do need to be pulled to GND, per page 3 of the TPS548A20 datasheet.

0 David_Daniels over 4 years ago in reply to Kadeem Samuel

TI__Mastermind 23660 points

See https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1010502/tps53515-pins-27-and-28/3759440?tisearch=e2e-sitesearch&keymatch=tps53515#3759440

The TPS548A20 and the TPS549A20 use the same controller as the TPS53515 and TPS53915 as the guidance would be the same

0 Sepeedah Zadeh over 4 years ago in reply to David_Daniels

TI__Expert 3100 points

Thanks team for the responses here. So if I understand correctly, we don't even need to cut traces when swapping TPS549A20 (with I2C) with TPS548A20 (no I2C), we can just leave pin 27 and 28 (SDA and SCL) connected on TPS548A20 as is, correct?

0 David_Daniels over 4 years ago in reply to Sepeedah Zadeh

TI__Mastermind 23660 points

As long as you do not write or read the address of the TPS58A20, I2C is still there but does not function like the TPS549A20. The pin 1 sets the switching frequency for TPS548A20 and it sets the address for the TPS549A20 when used according to the datasheet. But when not grounding the pin 27 and pin 28, the TPS548A20 will respond with an ACK at the address based on the pin 1 resistors.

0 Sepeedah Zadeh over 4 years ago in reply to David_Daniels

TI__Expert 3100 points

I see, so it will need some provisioning on the address etc. Can we leave those pins floating?

+1 David_Daniels over 4 years ago in reply to Sepeedah Zadeh

TI__Mastermind 23660 points

I would recommend connecting the TPS548A20 as though it was a TPS549A20 and not writing to the address.

In general, it is not a good idea to leave inputs floating, tie pin 27 and pin 28 low would be preferred, high is acceptable. The 27 and 28 pins are inputs to the I2C.

0 Sepeedah Zadeh over 4 years ago in reply to David_Daniels

TI__Expert 3100 points

OK, makes sense, thanks David!

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TPS548A20: NC on pins 27 and 28?