PBL3770A 데이터 시트보기 (PDF) - Ericsson

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PBL3770A

High Performance Stepper Motor Drive Circuit

Ericsson  

PBL 3770A

voltage across the sensing resistor is

below the comparator threshold level.

The sinking transistor then turns on

and the motor current starts to increase

again, The cycle is repeated until the

current is turned off via the logic inputs.

When both I1 and I0 are high, all four

transistors in the output H-bridge are

turned off, which means that inductive

current recirculates through two opposite

free-wheeling diodes (see figure 6, arrow

3). this method of turning off the current

results in a faster current decay than if

only one transistor was turned off and

will therefore improve speed

performance in half-stepping mode.

Heatsinking

The junction temperature of the chip

highly effects the lifetime of the circuit. In

high-current applications, the

heatsinking must be carefully conside-

red.

The Rthj-a of the PBL 3770A can be

reduced by soldering the ground pins to

a suitable copper ground plane on the

printed circuit board (see figure 14) or by

applying an external heatsink type V7 or

V8, see figure 14.

The diagram in figure 13 shows the

maximum permissible power dissipation

versus the ambient temperature in °C,

for heatsinks of the type V7, V8, or a 20

cm2 copper area respectively. Any

external heatsink or printed circuit board

copper must be connected to electrical

ground.

For motor currents higher than approx

600 mA, some form of heatsinking is

recommended to assure optimal

reliability.

The diagrams in figures 12 and 13 can

be used to determine the required

heatsinking of the circuit. In some

systems, forced-air cooling may be

available to reduce the temperature rise

of the circuit.

Applications Information

Motor selection

Some stepper motors are not designed

for continuous operation at maximum

current. As the circuit drives a constant

current through the motor, its tempera-

ture can increase, both at low- and high-

speed operation.

Some stepper motors have such high

core losses that they are not suited for

switched-mode operation.

200 mA/div

1 ms/div

0

100µs/div

Figure 5. Motor current (IM ),

Vertical : 200 mA/div,

Horizontal: 1 ms/div,

expanded part 100 µs/div.

I

0A

I

1A

Ph

A

Ph

B

I

0B

I

1B

I

MA

100%

60%

–20%

–60%

–100%

I

MB

100%

60%

20%

–60%

–100%

Full step position

Half step position

Stand by mode

at 20 %

Half step mode at 100 %

Figure 7. Principal operating sequence.

External recirculation

diodes

21

3

RS

Motor Current

1

2

3

Fast Current Decay

Slow Current Decay

Time

Figure 6. Output stage with current paths

for fast and slow current decay.

Full step mode at 60 %

6

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