TPS2116: TPS2116 for priority usage

Hossam Moghrabi

Intellectual 360 points

Part Number: TPS2116

Tool/software:

Hello,

I am interested in TPS2116 to switch between 2 power sources. one of them is priority, both are 3.3v.

here is my suggestion:

if i connect in1 to PR1 via resistor divider, it will make it always the priority, and when in1 is off then it will activate in2 (provided that in2 is on).

i find a potential problem where in1 itself is not connected which means pr1 will be ground and thus mode will be 0v. datasheet says it would go into shutdown but i don't want that, i want power to always be there but one of the inputs have priority when it is alive.

i do not have any other source besides these 2 sources, thus mode pin cannot get external high input. a possible hack i found is to connect both in1 and in2 to mode pin via a diode each... therefore mode pin is always getting about 3.1v (due to schottky diode drop)... while keeping in1 connected to pr1 via resistor divider as always.

is this correct?

please check and reply in details.

thanks

5 months ago

0 Kunal Goel 5 months ago

TI__Guru* 79181 points

Hi Hossam,

When mode is low, device will output higher input. So when VIN1=0, MODE=0 and VIN2 is >0V so output will be VIN2.

Regards

Kunal Goel

0 Hossam Moghrabi 5 months ago in reply to Kunal Goel

Intellectual 360 points

Hello Kunal,

so you think my circuit is ok?

I mean to connect IN1 to PR1 via resistor divider, and IN1 to MODE. so when IN1 is high, it is the delivered to output. while if IN1 is 0v, mode will be 0 and since IN2 is high it will be delivered to output.

notice that i don't have "external bias" to be delivered to mode but rather either in1 or in2, I choose in1 as explained in this post. is in1 here can be considered external bias or what?

please check this and respond to me in details showing each state and what is the expected output

I attached the circuit image here: https://i.slow.pics/UhGi7bp4.png

0 Kunal Goel 5 months ago in reply to Hossam Moghrabi

TI__Guru* 79181 points

Hi Hossam,

This will be called priority mode.

Schematic is fine. It is also shown in datasheet application section.

Regards

Kunal Goel

0 Hossam Moghrabi 5 months ago in reply to Kunal Goel

Intellectual 360 points

hello,

so if in1 became 0v or not connected at all, will this still work? i mean in2 be active?

then when in1 gets connected again, the chip will automatically switch to it?

regards,

0 Kunal Goel 5 months ago in reply to Hossam Moghrabi

TI__Guru* 79181 points

Hi Hossam,

so if in1 became 0v or not connected at all, will this still work? i mean in2 be active? YES

then when in1 gets connected again, the chip will automatically switch to it? YES

Regards

Kunal Goel

0 Hossam Moghrabi 5 months ago in reply to Kunal Goel

Intellectual 360 points

hello

that is what i needed to know.

just one more thing to finalize it: should i put pulldown resistors on both inputs or not? i mean to make them hard 0v when not connected instead of floating.

that would be the last question.

thanks

0 Kunal Goel 5 months ago in reply to Hossam Moghrabi

TI__Guru* 79181 points

Hi Hossam,

Yes you can do that. It should be fine.

Regards

Kunal Goel

0 Hossam Moghrabi 5 months ago in reply to Kunal Goel

Intellectual 360 points

hello

you mean it is ok to keep them floating without pulldown?

0 Kunal Goel 5 months ago in reply to Hossam Moghrabi

TI__Guru* 79181 points

HI Hossam,

No I meant, it would be good to keep some pulldown.

Regards

Kunal Goel

0 Kunal Goel 5 months ago in reply to Kunal Goel

TI__Guru* 79181 points

Also please keep some cap on VIN and VOUT pins.

0 Hossam Moghrabi 5 months ago in reply to Kunal Goel

Intellectual 360 points

hello,

please check the attached image for suggested pulldown and caps. notice that in1 has separate pulldown away from the voltage divider for pr1. is this ok?

as for caps, my application already have lots of output caps but i can add small 100nF caps on Vin and Vout of this chip, is that good?

+1 Kunal Goel 5 months ago in reply to Hossam Moghrabi

TI__Guru* 79181 points

Hi Hossam,

Design looks fine to me.

please check the attached image for suggested pulldown and caps. notice that in1 has separate pulldown away from the voltage divider for pr1. is this ok? YES.

as for caps, my application already have lots of output caps but i can add small 100nF caps on Vin and Vout of this chip, is that good? YES.

Regards

Kunal Goel

Power management

Power management forum

TPS2116: TPS2116 for priority usage