ML4895ES datasheet(9/10 Pages) MICRO-LINEAR

9 / 10 page

ML4895

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

ISENSE 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 ML4895

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 ML4895 ground pin

(pin 5) be made using a separate trace.

VOUT

3.3V

–

VIN

µF

IRF7406

IRF7403

µH

25m

Ω

10nF

154k

Ω

453k

Ω

100

µF

100

µF

100

µF

VIN

P DRV

N DRV

GND

ML4895

VREG

VFB

ISENSE

SHDN

Figure 6. 3.3V, 3A DC/DC Converter Circuit

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 VREG and bypass capacitor needs to be located

close to the ML4895 for adequate filtering of the IC’s

internal bias voltage.

6. Remote sensing the output for improved load

regulation can be implemented with the ML4895. The

output can be remote sensed by using the top of the

external resistor divider as the remote sense point.

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