TPS1211-Q1: RSNS location

Akihiro Hirata

Expert 6210 points

Part Number: TPS1211-Q1

Tool/software:

Hello team,

Are we able to put the RSNS resistor at the low side of the main FET Q1 like below?

Regards,

Hirata

over 1 year ago

0 Rakesh over 1 year ago

TI__Guru** 105561 points

Hi Hirata,

No.

TPS1211-Q1 does not support placing sense resistor on the source side of the MOSFET.

Best Regards,

Rakesh

0 Akihiro Hirata over 1 year ago in reply to Rakesh

TI__Expert 6210 points

Hi Rakesh-san,

Could you let me know the reason? I need to check but it might be critical.

Regards,

Hirata

0 Rakesh over 1 year ago in reply to Akihiro Hirata

TI__Guru** 105561 points

Hi Hirata,

The current sense amplifier is not designed to support rail-rail voltages.

Best Regards,

Rakesh

0 Akihiro Hirata over 1 year ago in reply to Rakesh

TI__Expert 6210 points

Rakesh

I don't understand what you mean. Please explain the reason clearly.

Regards,

Hirata

0 Rakesh over 1 year ago in reply to Akihiro Hirata

TI__Guru** 105561 points

Hi Hirata,

Please refer 5.4 Input Common Mode Voltage Range in https://www.ti.com/lit/an/sloa011b/sloa011b.pdf?ts=1719323047788&ref_url=https%253A%252F%252Fwww.google.com%252F

In this context, the current sense amplifier in TPS1211-Q1 does not work when the common-mode voltage is <3V i.e. a scenario where Rsns is placed at Vout. During startup Vout is close to zero, so, current sense amplifier does not able to detect any fault at the output.

Best Regards,

Rakesh

0 Akihiro Hirata over 1 year ago in reply to Rakesh

TI__Expert 6210 points

Rakesh

I don't find the description that TPS1211-Q1 current sense amplifier needs VCM > 3V. Where is this described in the datasheet?

or do you mean below?
1. Max V(IMON) voltage is always below the common mode voltage of the CS+.
2. The output current cannot be measured when common mode voltage is not high enough because of "1".
3. When RSNS is at the down stream of the FET, common mode voltage of CS+ is small during start up.
4. Because of "1", "2", and "3" above, There is a risk that output current cannot be measured accurately during startup if RSNS is located at the down stream of the FET.

Regards,

Hirata

0 Rakesh over 1 year ago in reply to Akihiro Hirata

TI__Guru** 105561 points

can you please elaborate your 1st point

Power management

Power management forum

TPS1211-Q1: RSNS location