TPS2121: TPS2121 schematic review

Jimmy Lai

Expert 6845 points

Part Number: TPS2121
Other Parts Discussed in Thread: TPS22913, TLV62150

Dear Team,

Our customer have a project with dual input .

They use TPS2121 for oring circuit.

Power input as the below.

USB 5V@3A

2.Battery 6V~8.4V @2A

They hope default input is USB 5V when both input existing .

Please review the schematic. Thanks.

Jimmy

over 3 years ago

0 Kalin Burnside over 3 years ago

TI__Genius 13300 points

Hello Jimmy,

I've reviewed your schematic and MOST of your values line up. I have a few comments on this schematic:

1. There should not be capacitance on PR1 or CP2.

2. If you're aiming for Fast switch over in both directions you should use the control scheme on PR1 instead of CP2 since fast switchover only occurs when CP2 > 1.06V

3. The switch over voltage on PR1 is actually set to 3.18V which is a fairly low voltage to switch over at.

4. The input capacitance on both power supplies is fairly low to hold up each line during switch over with an output current of 3A. Some hysteresis may be needed- see the following application note for more information (section 2.2.2). The amount of input capacitances vs. output is a balancing act and may require some testing to get just right for your application.

https://www.ti.com/lit/ug/tidue50/tidue50.pdf

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1023453/faq-tps2121-how-do-i-achieve-a-seamless-power-switchover-using-ti-s-power-mux-devices

Also, Are you looking to have TPS22913 and the other devices reviewed as well? It may be easier to create additional posts to review those devices as the TLV62150 is not within our product line.

Regards,

Kalin Burnside

0 Kalin Burnside over 3 years ago in reply to Kalin Burnside

TI__Genius 13300 points

Hello Jimmy,

I have altered my post.

Regards,

Kalin Burnside

0 Jimmy Lai over 3 years ago in reply to Kalin Burnside

TI__Expert 6845 points

Hi Kalin,

We appreciated your great support!

1.The fast switch is only available when the both input are existing ,right?

I means the PR1 pin and CP2 pin that are only work when we have both input .

If we only have one input, the TPS2121 will auto select the right input ,right .

2. please check the schematic again. Thanks.

Many Thanks,

Jimmy

0 Kalin Burnside over 3 years ago in reply to Jimmy Lai

TI__Genius 13300 points

Hello Jimmy,

Fast switchover is when CP2 > 1.06V. If you use PR1 to switch then the device will use fast switchover to both inputs since if PR1 > CP2 it outputs IN1, but CP2 doesn't necessarily have to be below 1.06V in this case.

Can you please explain your use of a zener diode on the PR1 pin?

Regards,

Kalin Burnside

0 Jimmy Lai over 3 years ago in reply to Kalin Burnside

TI__Expert 6845 points

Hi Kalin,

When the USB 5V and battery 8.4V are both existing .

Normally [Input select ]net [D3] is pull high 3.3V to keep PR1 >3.125V when we using the USB 5V .

But to keep the battery health , we need to have charge and discharge recycle every one month ,

we need to keep [Input select ] net to 0V to enable PR1=0.7V , then we can use battery to discharge

Finally , Do you have any concern for the final schematic? Thanks a lot!

Many Thanks,

Jimmy

0 Timothy Logan over 3 years ago in reply to Jimmy Lai

TI__Mastermind 35005 points

Jimmy,

After all of the input/feedback from Kalin was addressed, everything looks good. Please do not hesitate to reach out if there are anymore questions.

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TPS2121: TPS2121 schematic review