SLA7024M Ver la hoja de datos (PDF) - Allegro MicroSystems

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Fabricante

SLA7024M

HIGH-CURRENT PWM, UNIPOLAR STEPPER MOTOR CONTROLLER/DRIVERS

Allegro MicroSystems 

SLA7024M, SLA7026M, AND SMA7029M

HIGH-CURRENT PWM,

UNIPOLAR STEPPER MOTOR

CONTROLLER/DRIVERS

DETERMINING THE MOTOR PWM FREQUENCY

The modules function asynchronously, with PWM OFF time fixed by R3

and

C1

at input td.

tOFF ≈ -R3

The

• C1

OFF time

• logn (1 -

can

V2 b)

be

calculated

as:

(5)

Recommended circuit constants and tOFF are:

Vb = 5 V

R3 = 47 kΩ

C1 = 470 pF

tOFF = 12 µs

50

40

20

RS = 1 Ω

L/R = 1 to 3 ms

VCC = 24 V

30

25

20

30

VCC = 36 V

35

40

10

0

0

2

4

6

8

10

12

14

MOTOR RESISTANCE in OHMS

Dwg. GK-016

FIGURE 7.

PWM FREQUENCY vs MOTOR RESISTANCE

POWER DISSIPATION CALCULATIONS

Excepting high-current applications utilizing the SLA7026M above

approximately 2.0 A at +65°C (with 2-phase operation), the need for heat

sinks is rare. The basic constituents of conduction losses (internal power

dissipation) include:

(a) FET output power dissipation (IOUT2 • rDS(on) or IOUT • VDS(ON)),

(b) FET body diode power dissipation (VSD • IOUT), and

(c) control circuit power dissipation (VCC • ICC).

Device conduction losses are calculated based on the operating mode

(wave drive, half-step, or 2-phase). Assuming a 50% output duty cycle:

Wave Drive = 0.5 (IOUT2 • rDS(on)) + 0.5 (VSD • IOUT) + (VCC • 15 mA)

Half-Step = 0.75 (IOUT2 • rDS(on)) + 0.75 (VSD • IOUT) + (VCC • 15 mA)

2-Phase = (IOUT2 • rDS(on)) + (VSD • IOUT) + (VCC • 15 mA)

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