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MAX16909

36V, 220kHz to 1MHz Step-Down Converter

with Low Operating Current

PCB Layout Guidelines

Careful PCB layout is critical to achieve low switching

losses and clean, stable operation. Use a multilayer

board whenever possible for better noise immunity and

power dissipation. Follow these guidelines for good PCB

layout:

1) Use a large contiguous copper plane under the IC

package. Ensure that all heat-dissipating components

have adequate cooling. The bottom pad of the device

must be soldered down to this copper plane for effec-

tive heat dissipation and for getting the full power out

of the IC. Use multiple vias or a single large via in this

plane for heat dissipation.

2) Isolate the power components and high-current path

from the sensitive analog circuitry. This is essential to

prevent any noise coupling into the analog signals.

3) Keep the high-current paths short, especially at the

ground terminals. This practice is essential for stable,

jitter-free operation. The high-current path composed

of input capacitor, high-side FET, inductor, and output

capacitor should be as short as possible.

4) Keep the power traces and load connections short.

This practice is essential for high efficiency. Use

thick copper PCBs (2oz vs. 1oz) to enhance full-load

efficiency.

5) The analog signal lines should be routed away from

the high-frequency planes. This ensures integrity of

sensitive signals feeding back into the IC.

6) The ground connection for the analog and power

section should be close to the IC. This keeps the

ground current loops to a minimum. In cases where

only one ground is used, enough isolation between

analog return signals and high-power signals must

be maintained.

Figure 4. 1.8V/3A Configuration

D1

100µF

4.7µF

0.1µF

9.1kI

10kI

62kI

L1

15µH

1.8V AT 3A

0.1µF

LX

BST

OUT

FB

PGOOD

FOSC

1µF

12pF

BIAS

821pF

COMP

FSYNC

EN

SUPSW

SUP

GND

47µF

0.1µF

4.7µF

POWER GOOD

MAX16909

80.6kI

100kI