12

ML4411/ML4411A

BRAKE

VCC

PH3

PH2

PH1

RC

+5V

ENABLE E/A

PWR FAIL

RESET

VCO/TACH OUT

GND

P1

P2

VCC2

P3

DIS PWR

N1

N2

N3

0.01

1.2K

0.5

Ω

+V

+V

10K

10K

10K

+5

+12

+5

+5

+12

+

–

+12

3.3K

10K

1M

+5

+5

1M

2.2

+12

0.01

28

27

26

25

24

23

22

21

20

19

18

17

16

15

1

2

3

4

5

6

7

8

9

10

11

12

13

14

0.02

Figure 15. ML4411 Unipolar Drive Application

In unipolar operation, the motor‘s windings must be

allowed to drive freely to:

Therefore, there can be no diodes to clamp the inductive

however, to avoid an over-voltage condition on the

voltage is created to provide the clamping voltage. The

inductive energy may either be dissipated (Figure 16) or

alternately efficiently regenerated back to the system

supply (Figure 17).

The circuit in Figure 15 is designed to minimize the

external components necessary, at some compromise to

performance. The 3 resistors from the motor phase

windings to the PH inputs work with the ML4411‘s 8Ký

internal resistance to ground to divide the motor‘s

phase voltage down, providing input signals that do not

exceed 12V.

12V

BATTERY

C1

0.1

+12V TO

VCC AND VCC2

+12V

5V

REG

12V

LDO

0.1

1000

10

0.1

+5V

Figure 16. Dissipative Clamping Technique

This circuit uses analog speed regulation. The 1Mý

resistor from Pin 20 to the speed regulation op amp

provides the function of injecting current into the VCO

loop filter for the open loop stepping phase of start-up

operation. The “one shot” circuitry to time the reset is

replaced by a diode and RC delay from the rising edge or

the POWERFAIL signal. The error amplifier is left enabled

continuously since at low speeds its current contribution

is negligible. The current injected into the loop filter must

be greater than the leakage current from the phase

detector amplifier for the motor to start reliably.

5V

REG

12V

LDO

0.1

D1

L1

12V

BATTERY

50% DUTY

CYCLE

Figure 17. Non-Dissipative Clamping Technique