MIC2132 datasheet(32/48 Pages) MICROCHIP

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MIC2132

DS20006654B-page 32

 2022 Microchip Technology Inc. and its subsidiaries

EQUATION 5-11:

The maximum value of the overall ESR of the output

capacitor in steady state is calculated in Equation 5-12.

EQUATION 5-12:

The maximum overall ESR value of the output capacitor

must also meet the load transient requirement and is

calculated in Equation 5-13. Then, the lower value must

be chosen for the output capacitor ESR.

EQUATION 5-13:

As described in Section 4.1 “Control Architecture” of

the MIC2132 “Functional Description”, it requires at least

20 mV peak-to-peak ripple at the FBS pin to make the

gm amplifier and the error comparator behave properly.

Also, the output voltage ripple should be in phase with

the inductor current.

Therefore, the output voltage ripple caused by the

output capacitor’s value should be much smaller than

the ripple caused by the output capacitor’s ESR. If

low-ESR capacitors, such as ceramic capacitors, are

selected as the output capacitors, a ripple injection

method must be applied to provide enough feedback

voltage ripple. Please refer to Section 4.4 “Ripple

Injection Circuit Components Selection” for more

details.

The voltage rating of the output capacitor should be

25% greater than the maximum output voltage. The

output capacitor RMS current is calculated in

Equation 5-14:

EQUATION 5-14:

The power dissipated in the output capacitor is

calculated in Equation 5-15.

EQUATION 5-15:

5.3

Input Capacitor Selection

In addition to high-frequency ceramic capacitors, a

larger bulk capacitance, either ceramic or aluminum

electrolytic, should be used to help attenuate ripple on

the input and to supply current to the input during large

output current transients. The input capacitor for the

power stage input VIN should be selected for ripple volt-

age at VIN, capacitance, ESR, ripple current rating and

voltage rating. Tantalum input capacitors may fail when

subjected to high inrush currents caused by turning the

input supply on. A tantalum input capacitor’s voltage

rating must be at least two times the maximum input

voltage to maximize reliability. Aluminum electrolytic,

OS-CON and multilayer polymer film capacitors can

handle the higher inrush currents without voltage

derating. Due to the ripple cancellation effect of the

two-phase buck converter, the input ripple voltage and

ripple current are smaller than those of the

single-phase converter, and the effective ripple

frequency seen by the input capacitor is twice the

switching frequency. The input ripple voltage depends

on the IOUT and input capacitor’s capacitance and

ESR. The steady state input voltage ripple can be esti-

mated by Equation 5-16.

EQUATION 5-16:

The capacitance of the input capacitor can be

determined in Equation 5-17:

EQUATION 5-17:

Where:

ΔILOAD = Output Load Current Step in Load

Transient

ΔVOUT(TRANS) = Output Voltage Change in Load

Transient

fCO = Crossover Frequency, Equal to

About fSW/10

COUT ≥

ILOAD

VOUT(TRANS) × π × fCO

ESRCOUT ≤

VOUT(PP)

IOPP

ESRCOUT ≤

VOUT(TRANS)

ILOAD

ICOUT(RMS) =

IOPP

√

PDISS(COUT) = ICOUT(RMS)2 × ESRCOUT

Where:

IOUT = Total Output Current

D = Duty Cycle per Phase

n = Total Number of Phases (n = 2,4,6,8)

k = 0,1,2,3... for D > k/n and k < n

fSW

Switching Frequency per Phase

CIN = Total Input Capacitance

ESRCIN = Equivalent Series Resistance of Input

Capacitor

VIN ≈

n × fSW × CIN









IOUT × D –×

[]









– D –

× ESRCIN

IOUT

Where:

k = 0,1,2,3,.... for D > k/n and k < n

n = Total Number of Phases (n = 2,4,6,8)

CIN ≥

n × fSW × VIN









IOUT × D –×

[]









– D –

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