TPS2121: TPS2121 IN2 load switch output

Radhakrishnan Mathachetty2

Part Number: TPS2121

We are using TPS2121 in one of our design and the circuit connection is as shown below

We are hoping that always IN1 takes priority. The circuit works but always we see IN1 is selected irrespective of other conditions. When only IN2 is present we don't see any output. I have tried removing R50, VBUS is power by 5V source and 5V_IN floating or no connection. I was expecting to VBUS voltage at the output but no voltage.

Is there anything wrong in the circuit connection. The operating condition we are looking at is that when both 5V_IN and VBUS is present, 5V_IN should be switched to the output when only VBUS is present then we want the VBUS to be switched to the output.

Please let us know what is missing in our circuit.

Regards

Radha

over 6 years ago

0 Alpha H over 6 years ago

TI__Genius 10855 points

Hi Radha,

Thanks for reaching out on E2E!

Can you reattach the image? Unfortunately, it looks like I can't see the schematic right now.

Thanks,
Arthur Huang

0 Radhakrishnan Mathachetty2 over 6 years ago in reply to Alpha H

Prodigy 50 points

Hi Arthur

Please find the schematics attached.

0 Alpha H over 6 years ago in reply to Radhakrishnan Mathachetty2

TI__Genius 10855 points

Hi Radha,

Taking a look at the schematic, it looks like the resistors connected to PR1 and CP2 are configured incorrectly. The switchover between IN1 and IN2 is dependent on the voltage on the PR1 and CP2 pins. If PR1 > CP2, then IN1 is the output. If PR1 < CP2, then IN2 is the output. I recommend configuring the device similar to the configuration on page 25. You can change the resistor dividers and follow the calculations in the datasheet, but the voltage on PR1 should be higher than CP2 to give IN1 priority.

Thanks,
Arthur Huang

0 Radhakrishnan Mathachetty2 over 6 years ago in reply to Alpha H

Prodigy 50 points

Hi Arthur
Thanks for the quick reply. When there is no voltage at IN1 then the output should switch to IN2 if there is voltage(5V) at IN2 right ?
But it is not happening. when the IN1 is not present, there is no output voltage whether IN2 voltage source present or not.

If IN1 is not present and IN2 is present then CP2> PR1, expect IN2 -> OUT ?

Regards
Radha

0 Radhakrishnan Mathachetty2 over 6 years ago in reply to Radhakrishnan Mathachetty2

Prodigy 50 points

Hi Arthur

Our goal is to have IN1 switch to OUTput when IN1 is ON and IN2 ON or OFF. IN2 to switch to OUTput when IN1 is OFF and IN2 is ON.

Regards
Radha

0 Alpha H over 6 years ago in reply to Radhakrishnan Mathachetty2

TI__Genius 10855 points

Hi Radha,

Can you provide any oscilliscope shots of the behavior? If IN1 is not present, then the device should switch over to IN2, as you mentioned.

What is your downstream load and operating conditions? What is your load current? Can you try repeated the same test with the downstream load disconnected?

Thanks,
Arthur

0 Radhakrishnan Mathachetty2 over 6 years ago in reply to Alpha H

Prodigy 50 points

Hi Arthur,

The output current is < 200mA. I don't have oscilloscope shots.

Regards
Radha

0 Alpha H over 6 years ago in reply to Radhakrishnan Mathachetty2

TI__Genius 10855 points

Hi Radha,

I wanted to follow up on this thread. Were you able to collect oscilloscope shots of the behavior? Has the issue been resolved?

Thanks,
Arthur

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TPS2121: TPS2121 IN2 load switch output