Datasheet

MAX16935
36V, 3.5A, 2.2MHz Step-Down Converter
with 28µA Quiescent Current
15Maxim Integrated
Typical Application Circuit
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 compo-
nents have adequate cooling. The bottom pad of the
IC must be soldered down to this copper plane for
effective 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. Doing so 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 the input capacitor, high-side FET, inductor, and
the 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. Doing so 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.
D1
C
OUT
22µF
C
IN2
R
COMP
20kI
R
PGOOD
10kI
R
SYNCOUT
100I
R
FOSC
12kI
L1
2.2µH
V
OUT
5V AT 3.5A
C
BST
0.22µF
LX
BST
V
OUT
V
BIAS
OUT
V
BAT
FB
V
BIAS
V
OUT
PGOOD
SYNCOUT
FOSC
C
BIAS
1µF
C
COMP2
12pF
BIAS
C
COMP1
1000pF
COMP
FSYNC
OSC SYNC PULSE
EN
SUPSWSUP
C
IN1
POWER-GOOD OUTPUT
180° OUT-OF-PHASE OUTPUT
AGNDPGND
MAX16935
R
SNUB*
C
SNUB*
*R
FILTER
= 1I and C
FILTER
= 220pF required for the following
operating conditions:
V
BAT
R 25V, V
OUT
P 5V, f
SW
R 1.8MHz, FPWM mode enabled