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TPS62826: Resistor Divider, Cf, Slew Rate

d_zero
Genius 4815 points
Part Number: TPS62826


Dear *,

we would like to use TPS6282x in our design but have few questions.

1)  In the DS stated that the R2 should not be higher than 100kOhm, and then is 100k chosen for the application.

If we lover the R2, then the benefit is that the system is more robuster regarding noise but we loose efficiency? 

2) Do we always calculate the Cf (C3) as 12uF/R2 ? what if there is a larger Load Capacitor?

3) We need or rail to be Vout = 1.1V, Ioutmax =2A, Iouttyp = 1.4A and the Max Slew rate  is 25mV/us

what is the connection between the SS time of 1.25ms to the slew rate, will the TPS6282x support the 25mV/us slew rate?

Best Regards,

David.

  • 0
    TI__Expert 3645 points
    Hello,
    About your first question, the value reported in the datasheet is the efficiency at light (low) load. You can use a lower value for R2 to improve noise rejection but affecting the efficiency. The feedforward cap acts on the compensation network so you can choose the output cap for your application, check the stability and eventually add the feedforward cap. In theory, the feedforward cap introduces a pole and a zero and playing with its value you can modify the phase margin. Finally, the scenario described seems ok; the slew rate refers to the input voltage? In this case, you can evaluate the SR in your situation dividing 1.1 V by the soft start time (1.25ms), and you will see that you are mainly under 25mV/us.
  • 0 in reply to Alfonso Furio
    TI__Expert 3645 points
    Hello,
    due to inactivity, I am going to close this post but you can re-open it and I will be glad to give further support.