AN2738 datasheet(13/54 Pages) STMICROELECTRONICS

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AN2738

L6390 op-amp

Doc ID 14589 Rev 2

13/54

L6390 op-amp

The L6390 integrates an operational amplifier optimized for field oriented control (FOC)

applications. In a typical FOC application a tri-phase power bridge is used and the currents

in the three half-bridges are sensed using a shunt resistor on the source of each low side

power switch. The analog current information is transformed in a discontinuous sense

voltage signal, available only when the current is flowing in the low side path and having the

same frequency of the PWM signal driving the bridge. The sense voltage is a bipolar analog

signal, which sign depends on the direction of the current (see Figure 10):

PWM frequency in a typical home appliance motor driver application is in the range of 5-20

kHz. The sense voltage signals must be provided to an A/D converter in order to perform the

matrix calculation related to a certain control technique. Those sense signals are usually

shifted and amplified by dedicated op-amps in order to exploit the full range of the A/D

converter. The typical scheme shown in Figure 11 is used.

Figure 10.

3-phase system

3-PHASE DRIVER

SINUSOIDAL VECTOR CONTROL

POWER

STAGE

3-PHASE

MOTOR

IPHASE

Iload x Rs

SENSING:

Discontinuos Voltage at fPWM frequency

-Iload x Rs

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