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This data sheet has been carefully checked and is believed to be reliable, however, no responsibility is assumed for possible inaccuracies or omissions. All specifications are subject to change without notice.

SA56U REV A FEBRUARY 2007 © 2007 Apex Microtechnology Corp.

4 QUADRANT DIGITAL MODE

During four-quadrant operation a single digital PWM input

includes magnitude and direction information. The digital PWM

input signal is applied to the DIR pin, as shown in Figure 4,

and the PWM pin is tied HIGH to V

MOSFETs will switch in a locked, complementary fashion.

With a 50% duty cycle the average voltage of outputs

A

average differential voltage over each period applied to the

load will therefore be zero.

Four-quadrant operation allows for smooth transitions

through zero current for low-speed applications. However,

power dissipation is slightly higher than in two-quadrant opera-

tion since all four output MOSFETs must switch every cycle.

BRAkING – DIGITAL MODE

Under digital control, the SA56 can rapidly decelerate the

motor by shunting the winding currents through the output

MOSFETs. Logic LOW on the PWM input both A and B out-

puts high. The motor winding current circulates through the on

resistance of the MOSFETs quickly slowing the motor.

The winding current can be monitored with the I

during the braking of the motor. However, the current during

braking circulates in the normal forward direction through one

output MOSFET and is in the reverse in the other MOSFET.

The current sense feature can measure only forward currents.

The logic input on the DIR pin dictates which output MOSFET

is used for sensing the forward current during braking.

PROTECTION CIRCUITS

The most severe condition for any power device is a direct,

hard-wired ("screwdriver") short from an output to ground.

While the short-circuit protection will latch the output MOSFETs

within 500 ns (typical), the die and package may be required to

dissipate up to 500 Watts of power until the protection circuits

are activated.

This energy can be destructive, particularly at higher operat-

ing voltages, so sound thermal design is critical if fault tolerance

is to be established in the design. The V

become very hot during this period of high current.

Thermal and short-circuit protection are included in the

SA56 to prevent damage in the event that faults occur as

described below:

OPERATING

CONSIDERATIONS

SA56

Short-circuit protection – The short-circuit protection circuits

will sense a direct short from either output (A

P

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.

Over-current protection – When the current on the high side

goes above 10 amperes peak, the over-current circuit tristates

so that the four MOSFETs go into a latched fault condition.

Thermal protection – The thermal protection circuits will en-

gage if the temperature of any of the four MOSFETs reaches

approximately 160°C. If this occurs, the FAULT output pin will

go HIGH. If the thermal protection circuit engages, it will place

all four MOSFETs in the tristate state (high-impedance output).

The T

not latch, thereby denoting which of the protection features

has been triggered.

PROGRAMMABLE CURRENT LIMIT

The I

output current of the active P channel output MOSFET. The

proportionality is approximately 200 microamperes per ampere

of output current. Note that the I

the switching transitions when current spikes are likely to be

significant.

To create a programmable current limit, connect a resistor

from I

an internally-generated 2.75V threshold, all four output MOS-

FETs will be turned off for the remainder of the switching cycle.

A 2.7k-Ohm resistor will set the current limit at approximately

5 amperes.

The I

control loop in torque motor applications.

CURRENT SENSE LINEARITY CALCULATION

The current sense linearity is specified in the table on page

2 and is calculated using the method described below:

a) Define a straight line (y = mx + b) joining the two end data

points where, m is the slope and b is the offset or zero

crossover. Calculate the slope m and offset c using the

extreme data points. Assume I

in the x axis.

b) Calculate linear I

the straight line equation derived in step (a) for the I

LOAD

data points.

c) Determine deviation from linear I

measured I

+