3967 datasheet(6/16 Pages) ALLEGRO

6 / 16 page

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

3967

MICROSTEPPING DRIVER

WITH TRANSLATOR

RC Blanking. In addition to the fixed off time of the

PWM control circuit, the CT component sets the compara-

tor blanking time. This function blanks the output of the

current-sense comparator when the outputs are switched

by the internal current-control circuitry. The comparator

output is blanked to prevent false over-current detection

due to reverse recovery currents of the clamp diodes, and/

or switching transients related to the capacitance of the

load. The blank time tBLANK can be approximated by:

tBLANK = 1400CT

Enable Input (ENABLE). This active-low input

enables all of the outputs. When logic high the outputs are

disabled. Inputs to the translator (STEP, DIRECTION,

MS1, MS2) are all active independent of the ENABLE

input state.

Shutdown. In the event of a fault (excessive junction

temperature) the outputs of the device are disabled until

the fault condition is removed. At power up, and in the

event of low VCC, the under-voltage lockout (UVLO)

circuit disables the drivers and resets the translator to the

home state.

Sleep Mode (SLEEP). An active-low control input

used to minimize power consumption when not in use.

This disables much of the internal circuitry including the

outputs. A logic high allows normal operation and startup

of the device in the home position.

Percent Fast Decay Input (PFD). When a STEP

input signal commands a lower output current from the

previous step, it switches the output current decay to either

slow-, fast-, or mixed-decay depending on the voltage

level at the PFD input. If the voltage at the PFD input is

greater than 0.6VCC then slow-decay mode is selected. If

the voltage on the PFD input is less than 0.21VCC then

fast-decay mode is selected. Mixed decay is between

these two levels.

Mixed Decay Operation. If the voltage on the PFD

input is between 0.6VCC and 0.21VCC, the bridge will

operate in mixed-decay mode depending on the step

sequence (see figures). As the trip point is reached, the

device will go into fast-decay mode until the voltage on

the RC terminal decays to the voltage applied to the PFD

terminal. The time that the device operates in fast decay is

approximated by:

tFD = RTCTIn (0.6VCC/VPFD)

After this fast decay portion, tFD, the device will

switch to slow-decay mode for the remainder of the fixed

off-time period.

Functional Description (cont’d)

300

Dwg. GP-064-4

500

800

400

OUTPUT CURRENT IN MILLIAMPERES

2.0

1.0

0.5

1.5

2.5

600

700

TA = +25

°C

SOURCE DRIVER

SINK DRIVER

200

Typical output saturation

voltages showing Satlington™

sink-driver operation.

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