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5

OPERATING

CONSIDERATIONS

SA56

GENERAL

Please read "SA56 Design Ideas" that covers the various

SA56 applications in considerable detail. Also see Application

Note 1 "General Operating Considerations" which covers stabil-

ity, power supplies, heat sinking, mounting, and specification

interpretation. Visit www.apexmicrotech.com for design tools

that help automate tasks such as calculations for stability,

internal power dissipation, current limit, heat sink selection,

Apex's complete Application Notes library, Technical Seminar

Workbook and Evaluation Kits.

GROUND PINS

The two SIG

Pins 1 and 23, P

pins are connected at one point inside the IC. It is also recom-

mended the user connect both pins at a single point on the board

in a way that no current flows through that connection.

POWER SUPPLY BYPASSING

Bypass capacitors to power supply terminals V

be connected physically close to the pins to prevent erratic,

low-efficiency operation and excessive ringing at the outputs.

Electrolytic capacitors, at least 10 μF per output ampere are

required for suppressing V

capacitors (X7R) 1 μF or greater should also be used. Only ca-

pacitors rated for switching applications should be considered.

The bypass capacitors must be located as close to the power

supply pins as possible. Due to the very fast switching times

of the outputs, the inductance of 1 inch of circuit trace could

cause noticeable degradation in performance. The bypassing

requirements of V

0.1 μF to 0.47 μF capacitor connected directly between the

V

PIN DESCRIPTIONS

Pin # Name

Description

1,23 P

GND

Power high current ground return path of the

motor.

2,3

B

OUT

Half bridge output B

4,5,

V

S

High voltage supply

19,20

6

SC

The short-circuit protection circuits will sense

a direct short from either output (A

B

load. If the high-current protection circuit

engages it will place all four MOSFETs in the

tristate state (high-impedance output). The

SC output, pin 6, will go HIGH though not

latch, thereby denoting that this protection

feature has been triggered.

7

T

LIM

Temperature limit, CMOS. This pin can be

used as a flag for an over-temperature con-

dition. Under normal operation this pin will

be logic low. When a junction temperature

exceeds approximately 160°C this pin will

change to logic high and the output will be

latched off. Grounding this pin disables over

temperature protection. This pin should be

left open if over temperature protection is

desired but the flag is not used.

8

I

SEN

Current Sense output and programmable

current limit. A current proportional to the

output current is sourced by this pin. Typi-

cally this pin is connected to a resistor for

programmable current limit or transconduc-

tance operation.

9,10 SIG

GND

Ground connection for all internal digital and

low-current analog circuitry.

11

FAULT

This pin latches high whenever the four

MOSFETs have been placed in the tristate

condition which occurs when either the

high-current or the thermal protection has

engaged.

12

C

PWM

An external timing capacitor is connected to

this pin to set the frequency of the internal

oscillator and ramp generator for analog

control mode. The capacitor value (pF)

switching frequency. This pin is grounded

for digital control mode.

13,14 V

DD

5V supply for input logic and low voltage

analog circuitry.

15

V

REF

Reference voltage. Can be used at low cur-

rent for biasing analog loop circuits.

16

DIR

Direction of rotation control; In 2 quadrant,

digital control, determines the active output

FETs. This pin should be grounded in analog

control mode.

17

PWM

CMOS/TTL input for digital PWM control, or

1-4V analog input for duty cycle control in

analog control mode.

18

DISABLE Following a fault, pulling the DISABLE pin

HIGH and then LOW will reset a latched

fault condition. (When pulled HIGH, all four

output MOSFETs are disabled. A logic LOW

on this pin allows the four output FETs to

function normally.) When the DISABLE and

FAULT pins are tied to a microcontroller, the

FAULT pin will generate an interrupt in the

microcontroller, so that the interrupt, can in

turn, generate a pulse on the DISABLE pin.

When a fault occurs, the SA56 fault circuitry

will be reset.

21,22 A

OUT

Half bridge output A