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TPS61088: Calculating values for the loop compensation network

Paul Landini
Prodigy 145 points
Part Number: TPS61088

I am trying to calculate the values I would need for the loop compensation network for this part. Here are my calculations thus far:

f_RHPZ = (Ro * (1-D)^2)/(2*pi*L)

Ro = output load resistance = 10 Ohm

L = inductance = 1.2 uH

How do I calculate the duty cycle D of my system? The datasheet does not provide a way to calculate this.

Once I have f_RHPZ I can compare it to my switching frequency and from there I can select a loop crossover frequency fc. When I know fc I can calculate the resistance I will need, which is given by:

R = (2*pi*Vout*Rsense*fc*Co)/((1-D)*Vref*Gea)

The datasheet also does not provide a value for the amplifier's transconductance Gea. What is this value?

From here, the calculation of the capacitors I will need is straightforward. Are there any values TI recommends that work well for most systems? My input voltage will be between 2.7 and 4V and my output will be 12V, 1.2A

Thanks,

Paul

  • 0
    TI__Mastermind 40080 points

    Hi Paul,

    For your input and output range, you can directly use the parameters on the TPS61088 EVM if the output capacitance is  similar. If your output capacitance is only half of the EVM, then you can choose Rcomp=8.2k instead of 17.4k ohm.

    For the boost converter, D=(Vo-Vin)Vo ; Gea=0.00019A/V, which you can find in the TPS61088 datasheet.