LM628 datasheet(19/24 Pages) NSC

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Typical Applications (Continued)

propriate move via the LM628, but with no feedback from the

system encoder. When the all-zeros code is present, adjust

the pot for 0V at Pin 6 of the LF356.

A Monolithic Linear Drive Using LM12 Power Op Amp

Figure 15 shows a motor-drive amplifier built using the LM12

Power Operational Amplifier. This circuit is very simple and

can deliver up to 8A at 30V (using the LM12L/LM12CL). Re-

sistors R1 and R2 should be chosen to set the gain to pro-

vide maximum output voltage consistent with maximum input

voltage. This example provides a gain of 2.2, which allows

for amplifier output saturation at ±22V with a ±10V input, as-

suming power supply voltages of ±30V. The amplifier gain

should not be higher than necessary because the system is

non-linear when saturated, and because gain should be con-

trolled by the LM628. The LM12 can also be configured as a

current driver, see 1987 Linear Databook, Vol. 1, p. 2–280.

Typical PWM Motor Drive Interfaces

Figure 16 shows an LM18298 dual full-bridge driver inter-

faced to the LM629 PWM outputs to provide a switch-mode

power amplifier for driving small brush/commutator motors.

Incremental Encoder Interface

The incremental (position feedback) encoder interface con-

sists of three lines: Phase A (Pin 2), Phase B (Pin 3), and In-

dex (Pin 1). The index pulse output is not available on some

encoders. The LM628 will work with both encoder types, but

commands SIP and RDIP will not be meaningful without an

index pulse (or alternative input for this input … be sure to tie

Pin 1 high if not used).

Some consideration is merited relative to use in high

Gaussian-noise environments. If noise is added to the en-

coder inputs (either or both inputs) and is such that it is not

sustained until the next encoder transition, the LM628 de-

coder logic will reject it. Noise that mimics quadrature counts

or persists through encoder transitions must be eliminated

by appropriate EMI design.

Simple digital “filtering” schemes merely reduce susceptibil-

ity to noise (there will always be noise pulses longer than the

filter can eliminate). Further, any noise filtering scheme re-

duces decoder bandwidth. In the LM628 it was decided

(since simple filtering does not eliminate the noise problem)

to not include a noise filter in favor of offering maximum pos-

sible decoder bandwidth. Attempting to drive encoder signals

too long a distance with simple TTL lines can also be a

source of “noise” in the form of signal degradation (poor rise-

time and/or ringing). This can also cause a system to lose

positional integrity. Probably the most effective countermea-

sure to noise induction can be had by using balanced-line

drivers and receivers on the encoder inputs.

Figure 17

shows circuitry using the DS26LS31 and DS26LS32.

DS009219-14

Note:

FIGURE 12. Host Interface and Minimum System Configuration

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