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TPS2121: TPS Performance

Part Number: TPS2121

We are using the TPS2121 as given below in our project for switching between +12V_SPA0 and +12V_STBY and we did some measurements that does not meet design requirements as the output voltage DIP is seen when there is any switching at IN1/IN2 or small vol difference between IN1/IN2 .

Can you please review the below schematics and let me know your feedback?

  • Hi Amit, 

    What seems to be happening here is that the device is bouncing between two inputs. I see that you have expected this by adding some hysteresis with a 396kohm hysteresis resistor but I think you need a stronger pullup. Please retry this with a 100k resistor but note that by adding hysteresis, you may have to change the transition voltages because it will affect the voltage divider when IN2 is selected. Please look at this tech document for more information:

    Additionally, you may also need more input capacitance on the VBUS line to maintain the voltage. During fast switchover, there is no soft start or current clamping and your output capacitance is quite large. This means that an inrush will flow through the device which could cause the input voltage to dip noticeably.

    If you could provide a ST pin, PR1, and CP2 scopeshot, we could have a better idea of whether it's bouncing between the inputs 

    Best Regards,