TPS54202H: ENable input pull down resistance.

Michael Biggs

Part Number: TPS54202H

When I put together a test circuit using the recommended 510k ohm pull up on the enable input, the regulator wouldn't turn on. I measured the resistance to ground at the enable pin and it measured about 14k ohms, rather than the 1 Meg typical specified in the data sheet . Based on that measurement I used a 24k ohm pullup to VIN, and the regulator turned on and worked properly. Is the data sheet value for the pull down wrong, or is my device defective?

over 6 years ago

0 Shawn Nie over 6 years ago

TI__Genius 10070 points

Hi,

Did you check another board? whether all the boards have the same issue?

Please double check the layout, there is no issue on the EVM. And could you please share the schematic?

Shawn

0 Michael Biggs over 6 years ago in reply to Shawn Nie

Prodigy 220 points

I only built one circuit, so I can't check against a different board. I just wanted to know if 1Meg was the correct value for the internal pull down. I have attached my circuit, which didn't work with R1 = 510k, but did work with R1 = 24k. Measured resistance from pin 5 to ground was 14k without R1.

0 Shawn Nie over 6 years ago in reply to Michael Biggs

TI__Genius 10070 points

Hi,

The EN pin is connected to VIN with R1 directly, and the range of input voltage is 12V to 24V, which exceeds the maximum voltage that EN can withstand. The voltage divider is needed to control the EN. Please refer to datasheet "6.3 Recommended Operating Conditions" and "7.3.6 Adjusting Under Voltage Lockout". Thanks.

Shawn

0 Michael Biggs over 6 years ago in reply to Shawn Nie

Prodigy 220 points

Thank you for your response.

Yes, as it says in 7.3.6, "To enable the device, connect a pull-up resistor R4 (typical 510 KΩ to limit the quiescent current) to the VIN pin. So there is a voltage divider consisting of the external 510k resistor and the internal Rpd "(typical 1Megohm)". But my question is whether Rpd is really 1Meg, because it wasn't on the one device I tested. Note that Figure 13 shows a zener diode on the EN input, so a supply voltage larger than 7 Volts can be used, so long as the current into the EN pin is limited (7.3.5 paragraph 2).

0 Shawn Nie over 6 years ago in reply to Michael Biggs

TI__Genius 10070 points

Hi,

Rpd is 1 Megohm, and as I have mentioned, there is no issue on the EVM, please change another IC to double check this issue. In my opinion, there may be two reasons:
1. The IC is damage.
2. There is some thing wrong with the layout or soldering.

BTW, what is output capacitors?

Shawn

0 Michael Biggs over 6 years ago in reply to Shawn Nie

Prodigy 220 points

Thanks. I have ordered another IC and I will report the results .

0 Jason Wang (BSR-MV) over 6 years ago in reply to Michael Biggs

TI__Genius 9550 points

hi,
please report your results in this thread or open a new one after you get new device for test. Before that, i am trying to close this thread firstly.

0 Michael Biggs over 6 years ago in reply to Shawn Nie

Prodigy 220 points

Apparently the chip was damaged. I replaced it, and then it worked correctly with a 510k ohm pullup to Vin. Thanks for the responses.

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TPS54202H: ENable input pull down resistance.