ML4894
LAYOUT
A typical application circuit is shown in Figure 6.
Proximity of passive devices and adequate power and
ground planes are critical for reliable operation of the
circuit. In general, use the top layer for the high current
connections and the bottom layer for the quiet
connections such as GND, feedback and current sense.
Some more specific guidelines follow.
1. The connection from the current sense resistor to the
I
SENSE
pin should be made by a separate trace and
located as close to the lead of the resistor as possible.
The trace length from the sense resistor to the ML4894
should be kept as short as possible and away from
switching components and their traces.
2. The trace lengths from the buck regulator’s input
capacitor to the switching MOSFET, from the MOSFETs
to the inductor, from the synchronous rectifier MOSFET
to the sense resistor, and from the inductor to the
output capacitor should all be as short as possible.
3. The high current ground paths need to be kept separate
from the signal ground paths. The GND connection
should be made at a single-point star ground. It is very
important that the ground for the ML4894 ground pin
(pin 5) be made using a separate trace.
4. Concentrating on keeping the current sense and high
current connections short as well as keeping the
switching components and traces away from the
sensitive analog components and traces during layout
will eliminate the majority of problems created by a
poor layout.
5. The V
REG
and bypass capacitor needs to be located
close to the ML4894 for adequate filtering of the IC’s
internal bias voltage.
6. Remote sensing the output for improved load
regulation can be implemented with the ML4894. The
output can be remote sensed by using the top of the
external resistor divider as the remote sense point.
C1
22µF
C2
22µF
C3
22µF
ML4894
1
VIN
C4
1µF
2
3
4
Q1
IRF7406
L1
39µH
Q2
IRF7403
C6
100µF
R1
25mΩ
–
C7
100µF
C8
100µF
+
VREG
VFB
ISENSE
SHDN
VIN
8
P DRV
7
N DRV
6
GND
5
VOUT
5V
Figure 6. 5V, 3A DC/DC Converter Circuit
9
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
