PBL3775-1NS 데이터 시트보기 (PDF) - Ericsson

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PBL3775-1NS

Dual Stepper Motor Driver

Ericsson  

PBL 3775/1

Functional Description

Each channel of the PBL 3775/1

consists of the following sections: an

output H-bridge with four transistors and

four recirculation diodes, capable of

driving up to 750 mA continuous current

to the motor winding,

a logic section that controls the output

transistors, an S-R flip-flop, and a com-

parator. The clock-oscillator is common

to both channels.

Constant current control is achieved

by switching the output current to the

windings. This is done by sensing the

peak current through the winding via a

current-sensing resistor RS, effectively

connected in series with the motor

winding. As the current increases, a

voltage develops across the sensing

resistor, which is fed back to the

comparator. At the predetermined level,

defined by the voltage at the reference

input VR, the comparator resets the flip-

flop, which turns off the upper output

transistor. The turn-off of one channel is

independent of the other channel. The

current decreases until the clock

oscillator triggers the flip-flops of both

channels simultaneously, which turns on

the output transistors again, and the

cycle is repeated.

To prevent erroneous switching due to

switching transients at turn-on, the

PBL 3775/1 includes a digital filter. The

clock oscillator provides a blanking

pulse which is used for digital filtering of

the voltage transient across the current

sensing resistor during turn-on.

The current paths during turn-on, turn-

off and phase shift are shown in figure 5.

Applications Information

Current control

The regulated output current level to the

motor winding is determined by the

voltage at the reference input and the

value of the sensing resistor, RS. The

peak current through the sensing

resistor (and the motor winding) can be

expressed as:

IM,peak = 0.1•VR / RS [A]

With a recommended value of 0.5 ohm

for the sensing resistor R , a 2.5 V

S

reference voltage will produce an output

current of approximately 500 mA. RS

should be selected for maximum motor

current. Be sure not to exceed the

absolute maximum output current which

is 850 mA. Chopping frequency, winding

inductance and supply voltage also

affect the current, but to much less

extent.

For accurate current regulation, the

sensing resistor should be a 0.5 - 1.0 W

precision resistor, i. e. less than 1%

tolerance and low temperature

coefficient.

Current sense filtering

At turn-on a current spike occurs, due to

the recovery of the recirculation diodes

and the capacitance of the motor

winding. To prevent this spike from

reseting the flip-flops through the

current sensing comparators, the clock

oscillator generates a blanking pulse at

turn-on. The blanking pulse pulse

disables the comparators for a short

time. Thereby any voltage transient

across the sensing resistor will be

ignored during the blanking time.

V MM

1

2

3

RS

Motor Current

1

2

Fast Current Decay

Slow Current Decay

3

Time

+5 V

0.1 µF

0.1 µF

V MM

+

10 µF

12

4

19

V

9 Phase1 CC

V

MM1

V

MM2

MA1

3

10 Dis1

7 VR1

14 Phase 2

13 Dis2

16 V R2

RC GND

PBL 3775/1

C1

E1 C2

MB1 1

20

MA2

MB2 22

E2

11 5, 6, 8

2 15

21

+5 V 12 kΩ

17, 18

STEPPER

MOTOR

4 700 pF

GND (VCC )

RS

0.47 Ω

RS

0.47 Ω

Pin numbers refer

to DIL package.

GND (VMM )

Figure 5. Output stage with current paths Figure 6. Typical stepper motor driver application with PBL 3775/1.

during turn-on, turn-off and phase shift.

5

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