TPS25942A: MUX With Automatic and Seamless Switchover Not working Properly

Hi Vishal,

Thanks for reaching out!
I will look into this and reply back.

Best Regards,
Rakesh

Hello Rakesh,

Kindly Reply back ASAP.

Regards

Hi Vishal,

FLT pin will assert due to reverse voltage condition for the second channel (please refer block diagram Figure 48). But FLT output fluctuation will only happen if there is changeover from one channel to other and vice-versa.
Can you please share test waveforms of
1. Vin1, Vout, PGOOD of 1st channel, FLT of 2nd channel
2. Vin1, Vout, input current of 2nd channel and FLT of 2nd channel

OVLO pin can be used for the second channel to set OV threshold.


Best Regards,
Rakesh

Hello Rakesh,

I have done the simulation. It is showing good results. find the attachment for simulation and the waveforms.

Regards

Vishal kakadeTPS25942_automatic and seamless power muxing for almost same rail - autosave 19-04-05 16_37.TSC

Hi Vishal,

Thank you!
Looks like the reverse current blocking is not working as expected. But, I wonder why I_IN_2 is NOT equal to I_OUT_2. I see I_IN_2 = -6A where as I_OUT_2= 0A.
I will check on the reverse current blocking function. In the meanwhile can you cross check why I_IN_2 is NOT equal to I_OUT_2

Best Regards,
Rakesh

Hello Rakesh,

There was a mistake from side in the previous simulation which I sent. I used a different voltage source at the input. 

Please check my new simulation. (All results are good).

TPS25942_automatic and seamless power muxing.TSC

hello Rakesh,

Please reply ASAP. This is urgent.

Regards
Vishal Kakade

Hi Vishal,

Looks good.
what is your max load current? If it is ~4.5A, I suggest to go for new device TPS2121.
Let me know if you have any questions.

Best Regards,
Rakesh

Hello Rakesh,

My Board is already fabricated. The maximum load current is 3A-4A But I am getting this issue with No load.

Regards

. 

Hi Vishal,

The ~FLT pin fluctuation is because of Reverse Current Protection as defined in Section 9.3.5 in datasheet.
Looks your issue is similar to e2e.ti.com/.../2163835

Can you share test waveforms
Vin1, Vin2, Vout, FLT1
Vin1, Vout, PGOOD1, FLT1

Best Regards,
Rakesh

Hello Rakesh,

Please find the attachment for my Complete schematic. 

Expt: Primary supply is generated from AC (230V to VCC_12V1) and secondary supply is generated from DC (48V to VCC_12V2).

I tried powering the muxing circuit independently from a separate 12V supply. It is working fine.

Then I tried VCC_12V1 is generated from Ac AND vcc_12V2 is directly powered by 12V external. At this time I am getting the same issue.

From Above observation, it is clear that AC to DC supply is making causing some issues because of which FLT pin is fluctuating.

Now I wanna Know is it because of layout? because My both 12V are generated properly. When both are on simultaneously, I am getting huge ripple at the output and is the LEGACY 10G POWER_080319_14PM.pdfsame reason for FLT flickering.

Hi Vishal,

The reverse voltage threshold is only 10mV, so any low frequency voltage ripple on VCC_12V1 coming from AC to DC supply create these kind of fluctuations.
Test waveforms can give me more insight on the issue. Can you provide
Vin1, Vin2, Vout, FLT1
Vin1, Vout, PGOOD1, FLT1

Best Regards,
Rakesh

Hello Rakesh,

We are getting a 12V square wave at VCC_12V1. But After I removed the TPS25942, my 12V is good. why is this happening?

Meanwhile I'll try to share the waveforms.

Regards

Hi Vishal,

Please share the waveforms to close this issue.
Thanks!

Best Regards,
Rakesh