JAJSPC6 November 2023 TPS61377
PRODUCTION DATA
The TPS61377 requires external compensation, which allows the loop response to be optimized for each application. The COMP pin is the output of the internal error amplifier. An external compensation network, comprised of resistor RC, and ceramic capacitors CC and CP, is connected to the COMP pin.
The power stage small signal loop response of constant off-time (COT) with peak current control can be modeled by Equation 11.
where
where
where
The COMP pin is the output of the internal transconductance amplifier. Equation 15 shows the small signal transfer function of compensation network.
where
The next step is to choose the loop crossover frequency, ƒC. The higher frequency that the loop gain stays above zero before crossing over, the faster the loop response is. It is generally accepted that the loop gain cross over no higher than the lower of either 1/10 of the switching frequency, ƒSW, or 1/5 of the RHPZ frequency, ƒRHPZ.
Then set the value of RC, CC, and CP (in Figure 8-1) by following these equations.
where
The value of CC can be set by Equation 17.
The value of CP can be set by Equation 18.
If the calculated value of CP is less than 10 pF, it can be left open.
Designing the loop for greater than 45° of phase margin and greater than 10-dB gain margin eliminates output voltage ringing during the line and load transient.