ML4894 Просмотр технического описания (PDF) - Micro Linear Corporation

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ML4894

Synchronous Buck Controller

Micro Linear Corporation 

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 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.

ML4894

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 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

C4

VIN

1µF

1 VREG

2 VFB

3 ISENSE

4 SHDN

VIN 8

P DRV 7

N DRV 6

GND 5

Q1

IRF7406

Q2

IRF7403

L1

39µH

R1

25mΩ

C6

C7

100µF 100µF

C8

100µF

+

VOUT

5V

–

Figure 6. 5V, 3A DC/DC Converter Circuit

9

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