It is possible to use larger feedforward capacitors to further improve the transient response but take care to

ensure there is a minimum of -9-dB gain margin in all operating conditions. The feedforward capacitor injects

noise on the output into the FB pin. This added noise can result in increased on-time jitter at the switching node.

Too little gain margin can cause a repeated wide and narrow pulse behavior. Adding a 100-Ω resistor in series

with the feedforward capacitor can help reduce the impact of noise on the FB pin in case of non-ideal PCB

layout. The value of this resistor must be kept small as larger values bring the feedforward pole and zero closer

together degrading the phase boost the feedforward capacitor provides.

accounted for. The ESR zero can be calculated using Equation 20. If the ESR zero frequency is less than the

pin to ground can be used to add a pole into the control loop if necessary. All ceramic capacitors are used in this

design so the effect of the ESR zero is ignored.

ESR

OUT

ESR

1

f

2

C

R

u S u

u

(20)

8.2.1.2.13 MODE Pin

The MODE resistor is set to 4.87 kΩ to select the high current limit setting, 1.0-ms soft-start and the 2 pF ramp.

See Table 7-4 for the full list of the MODE pin settings.

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TPS543320

SLUSEE1 – DECEMBER 2020

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