Circuit description

L6227Q

12/27

4.3

Truth table

4.4

PWM current control

The L6227Q includes a constant off time PWM current controller for each of the two bridges.

The current control circuit senses the bridge current by sensing the voltage drop across an

external sense resistor connected between the source of the two lower power MOS

transistors and ground, as shown in Figure 9. As the current in the load builds up the voltage

across the sense resistor increases proportionally. When the voltage drop across the sense

resistor becomes greater than the voltage at the reference input (VREF

sense comparator triggers the monostable switching the low-side MOS off. The low-side

MOS remain off for the time set by the monostable and the motor current recirculates in the

upper path. When the monostable times out the bridge will again turn on. Since the internal

dead time, used to prevent cross conduction in the bridge, delays the turn on of the power

MOS, the effective off time is the sum of the monostable time plus the dead time.

Figure 9.

PWM current controller simplified schematic

Table 7.

Truth table

Inputs

Outputs

1.

Valid only in case of load connected between OUT1 and OUT2

EN

IN1

IN2

OUT1

OUT2

2.

X = don't care

X

3.

High Z = high impedance output

High Z

Disable

H

L

L

GND

GND

Brake mode (lower path)

H

H

L

Vs

GND (Vs)

Forward

H

L

H

4.

GND (Vs) = GND during Ton, Vs during Toff

Vs

Reverse

H

H

H

Vs

Vs

Brake mode (upper path)