Full-Bridge DMOS PWM Motor Drivers

A4952 and

A4953

7

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Application Information

Sense Pin (LSS)

In order to use PWM current control, a low-value resistor is

placed between the LSS pin and ground for current sensing pur-

poses. To minimize ground-trace IR drops in sensing the output

current level, the current sensing resistor should have an indepen-

dent ground return to the star ground point. This trace should be

as short as possible. For low-value sense resistors, the IR drops in

the PCB can be significant, and should be taken into account.

When selecting a value for the sense resistor be sure not to

exceed the maximum voltage on the LSS pin of ±500 mV at

maximum load. During overcurrent events, this rating may be

exceeded for short durations.

Ground

A star ground should be located as close to the A4952/ A4953

as possible. The copper ground plane directly under the exposed

thermal pad of the device makes a good location for the star

ground point. The exposed pad can be connected to ground for

this purpose.

Layout

The PCB should have a thick ground plane. For optimum electri-

cal and thermal performance, the A4952/A4953 must be soldered

directly onto the board. On the underside of the A4952/A4953

package is an exposed pad, which provides a path for enhanced

thermal dissipation. The thermal pad must be soldered directly to

an exposed surface on the PCB in order to achieve optimal ther-

mal conduction. Thermal vias are used to transfer heat to other

layers of the PCB.

The load supply pin, VBB, should be decoupled with an electro-

lytic capacitor (typically 100 μF) in parallel with a lower valued

ceramic capacitor placed as close as practicable to the device.

GND

RS

GND

GND

GND

C1

BULK

CAPACITANCE

VBB

OUT2

OUT1

C2

1

PAD

A4952

C1

C2

OUT2

LSS

OUT1

VBB

FLTn

RTRY

IN2

IN1

VREF

GND

PCB

Thermal Vias

Trace (2 oz.)

Signal (1 oz.)

Ground (1 oz.)

Thermal (2 oz.

Solder

A4952

Bill of Materials

Item

Reference

Value

Units

Description

1RS

0.25

Ω

2512, 1 W, 1% or better,

carbon film chip resistor

2

C1

0.22

μF

X5R minimum, 50 V or greater

3

C2

100

μF

Electrolytic, 50 V or greater

Layout for the A4952 (LY package)