MAX20008AFOCVY datasheet(13/20 Pages) MAXIM

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To satisfy both LMIN1 and LMIN2, LMIN must be set to the

larger of the two as follows:

(

)

MIN

MIN1 MIN2

max L

, L

The maximum nominal inductor value recommended is 2

times the chosen value from the above formula:

MAX

MIN

2 L

Select a nominal inductor value based on the following

formula:

MIN

NOM

MAX

The best choice of inductor is usually the standard induc-

tor value closest to LNOM.

Input Capacitor

The input filter capacitor reduces peak currents drawn

from the power source and reduces noise and voltage

ripple on the input due to high speed switching.

Place a 0.1μF capacitor as close as possible to the

SUPSW and PGND pins, followed by a 4.7μF (or larger)

ceramic capacitor. A bulk capacitor with higher ESR

(such as an electrolytic capacitor) is normally required as

well to lower the Q of the front-end circuit and provide the

remaining capacitance needed to minimize input voltage

ripple.

The input capacitor RMS current requirement (IRMS) is

defined by the following equation:

(

)

OUT

SUP

OUT

RMS

LOAD(MAX)

SUP

×−

IRMS has a maximum value when the input voltage

equals twice the output voltage:

SUP

OUT

= ×

therefore:

(

)

LOAD MAX

RMS

Choose an input capacitor that exhibits less than +10°C

self-heating temperature rise at the RMS input current for

optimal long-term reliability.

The input-voltage ripple is composed of ∆VQ (caused by

the capacitor discharge) and ∆VESR (caused by the ESR

of the capacitor). Use low-ESR ceramic capacitors with

high ripple-current capability at the input. Calculate the

input capacitance and ESR required for a specified input

voltage ripple using the following equations:

ESR

∆

where:

(

)

SUP

OUT

SUP

−×

∆

××

and:

(

)

OUT

D1 D

×−

∆×

OUT

SUPSW

where:

IOUT is the maximum output current and D is the duty

cycle.

Output Capacitor

The output filter capacitor must have enough capacitance

and sufficiently low ESR to meet output-ripple require-

ments. In addition, the output capacitance must be high

enough to maintain the output voltage within specification

while the control loop responds to load changes.

When using high-capacitance, low-ESR capacitors, the

filter capacitor’s ESR dominates the output-voltage ripple,

so the size of the output capacitor depends largely on the

maximum ESR allowed to meet the output-voltage ripple

specifications as follows:

RIPPLE(P P)

−

×∆

When using low-ESR (e.g. ceramic) output capacitors,

size is usually determined by the capacitance required

to maintain the output voltage within specification during

load transients and can be estimated as follows:

OUT

∆

∆ × π×

where ∆I is the load change, ∆V is the allowed voltage

droop, and fC is the loop crossover frequency, which can

be assumed to be the lesser of fSW/10 or 100kHz. Any

calculations involving COUT should consider capacitance

tolerance, temperature, and voltage derating.

MAX20004/MAX20006/

MAX20008

36V, 220kHz to 2.2MHz, 4A/6A/8A

Fully Integrated Automotive

Step-Down Converters

www.maximintegrated.com

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