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UC1638

UC2638

UC3638

The UC3638 is designed to provide pulse width modula-

tion control of DC brush motors in applications requiring

precision torque, velocity, or position control. Due to its

high frequency capability, other high power applications

such as switch mode audio amplifiers can also be ad-

dressed. Through a combination of circuit sophistication

and integration, the designer can maintain a high level

of flexibility, while reducing cost compared to solutions

using other PWM ICs.

Figure 1 shows a typical application circuit for the

UC3638. By taking advantage of the UC3638's many in-

tegrated functions, a low cost and compact average cur-

rent mode motor controller can be designed. Depending

on the level of complexity, as many as 15 discrete com-

ponents and an additional high bandwidth amplifier can

be saved compared to a similar circuit using the

UC3637 PWM controller.

Oscillator Section and Modulation Scheme

Figure 2 depicts the UC3638 oscillator and PWM wave-

forms for the condition where the output of the voltage

amplifier (COMP) is at the null point (same voltage as

AREF). For applications using split voltage supply rails,

AREF will normally be tied to system ground. This re-

sults in a voltage null point of zero volts. For this condi-

tion, AREFIN should be tied to the negative voltage sup-

ply rail (VEE), which disables the internal voltage buffer,

allowing AREF to be tied to ground. For a single supply

system, AREFIN should be left open circuit, and AREF

should be decoupled to VEE (system ground) with at

least 0.1

µF. The resulting voltage null point for this case

APPLICATION INFORMATION

Figure 1. Average Motor Current Control Loop

UDG-95049-2

Figure 2. Oscillator and PWM Waveforms

UDG-95068-1