L8229 datasheet(16/42 Pages) STMICROELECTRONICS

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L6219_HI mode

L8229

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Note that Iout max is 1.2A and the wide range allowed for Vref requires the choice of a

suitable sense resistor to prevent current range over the maximum.

6.4

Single-pulse Generator

The pulse generator is a monostable circuit triggered on the positive going edge of the

comparator output. The circuit output is high during the pulse time Toff that is determined by

the time components Rt and Ct.

Toff =~ 1.1 x RtCt

(including switching dead time)

The single pulse turns off the power switch connected to the motor winding, causing the

winding current to decrease during Toff. If a new trigger signal should occur during Toff it will

be ignored.

6.5

Output Stage

Each of the two outputs stage contains four LDMOS transistors (P and N channel)

connected in two H Bridges. The intrinsic body diode of the LDMOS serve as recirculation

diode for flyback current.

The LDMOS are used to switch the power supply to the motor winding, thus driving a

constant current through the winding. It should be noted however, that is not permitted to

short-circuit the outputs. Internal circuitry is added in order to increase the accuracy of the

motor current particularly with low current levels.

6.6

Vs, Vcc, Vref

The circuit will stand any order of turn-on or turn-off of the supply voltages Vs and Vcc.

Normal dV/dt values are then assumed.

Preferably, Vref should be tracking Vcc during power-on and power-off if Vs is established.

Figure 3.

Ton and Toff

Normalized

output current

Ton

Toff

Tdelay

VSense

Vref

VRC

0.5

1.0

Normalized

output current

Ton

Toff

Tdelay

VSense

Vref

VRC

0.5

1.0

Ton

Toff

Tdelay

VSense

Vref

VRC

0.5

1.0

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