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