MC3479

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5

APPLICATION INFORMATION

General

The MC3479 integrated circuit is designed to drive a

stepper positioning motor in applications such as disk drives

and robotics. The outputs can provide up to 350 mA to each

of two coils of a two−phase motor. The outputs change state

with each low−to−high transition of the clock input, with the

new output state depending on the previous state, as well as

the input conditions at the logic controls.

Outputs

The outputs (L1−L4) are high current outputs (see

Figure 5), which when connected to a two−phase motor,

provide two full−bridge configurations (L3 and L4 are not

shown in Figure 5). The polarities applied to the motor coils

which in turn depends on the inputs and the decoding

circuitry.

input signals are

p 10 ns.

1.5 V

1.5 V

Phase A

Output

F/HS,

CW/CCW

Inputs

0

L1 − L4

Outputs

3.0 V

0

Clk

3.0 V

Figure 4. Clock Timing (Refer to Figure 2)

6.0 V

1.5 V

Current

Drivers

and

Logic

L2

Parasitic

Diodes

L1

Motor Coil

B/S

I

To L3, L4

Transistors

CW / CCW

OIC

Clk

F/HS

Inputs

Logic Decoding

Circuit

Figure 5. Output Stages

The maximum sink current available at the outputs is a

function of the resistor connected between Pin 6 and ground

(see section on Bias/Set operation). Whenever the outputs