SMA7029 データシートの表示（PDF） - Allegro MicroSystems

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SMA7029

HIGH-CURRENT PWM, UNIPOLAR STEPPER MOTOR CONTROLLER/DRIVERS

Allegro MicroSystems 

SLA7024M, SLA7026M, AND SMA7029M

HIGH-CURRENT PWM,

UNIPOLAR STEPPER MOTOR

CONTROLLER/DRIVERS

For given values of R1, R2, and Vb (VREF ≈ 0.82 V), Figure 3 illustrates

output current as a function of current-sensing resistance (RS).

3.0

SLA7026M MAX.

2.5

R1 = 510 Ω

R2 = 100 Ω

2.0

RX = ∞

Vb = 5 V

1.5

SLA7024M & SMA7029M MAX.

1.0

0.5

0

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

CURRENT-SENSING RESISTANCE in OHMS

Dwg. GK-014

FIGURE 3. CURRENT-SENSING RESISTANCE

Reduced/Holding Current Mode

Additional circuitry (Figure 4) enables reducing motor current. The

external transistor changes the voltage-divider ratio, VREF, and reduces the

output current. IHOLD is determined by resistors R2 and RX in parallel:

IHOLD

≈

R1 R2

+

R2 RX

R1 RX +

R2 RX

•

Vb

RS

(3)

or

IHOLD

≈

R2Õ

R1 + R2Õ

•

Vb

RS

(4)

where R2Õ= the equivalent value of R2 and RX in parallel.

Vb

HOLD

R1

RX

R5

R2

C3

VREF

SENSE

RS

Dwg. EK-010

FIGURE 4. HOLD CURRENT MODE

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