AMIS-30521 데이터 시트보기 (PDF) - ON Semiconductor

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AMIS-30521

Micro-Stepping Motor Driver

ON Semiconductor 

AMIS−30521, NCV70521

through the inherent parasitic drain−bulk diode of the

transistor.

Depending on the desired current range and the

micro−step position at hand, the RDS(on) of the low−side

transistors will be adapted such that excellent current−sense

accuracy is maintained. The RDS(on) of the high−side

transistors remain unchanged, see also the DC−parameter

table for more details.

PWM Current Control

A PWM comparator compares continuously the actual

winding current with the requested current and feeds back

the information to a digital regulation loop. This loop then

generates a PWM signal, which turns on/off the H−bridge

switches. The switching points of the PWM duty−cycle are

synchronized to the on−chip PWM clock.

The frequency of the PWM controller can be doubled to

reduce the over−all current−ripple with a factor of two.

Icoil

To further reduce the emission, an artificial jitter can be

added to the PWM frequency. (see Table 12, SPI Control

Register 1). The PWM frequency will not vary with changes

in the supply voltage. Also variations in motor−speed or

load−conditions of the motor have no effect. There are no

external components required to adjust the PWM frequency.

Automatic Forward & Slow−Fast Decay

The PWM generation is in steady−state using a

combination of forward and slow−decay. The absence of

fast−decay in this mode, guarantees the lowest possible

current−ripple “by design”. For transients to lower current

levels, fast−decay is automatically activated to allow

high−speed response. The selection of fast or slow decay is

completely transparent for the user and no additional

parameters are required for operation.

Set value

Actual value

0

t

T PWM

Forward & Slow Decay

Forward & Slow Decay

Fast Decay & Forward

Figure 7. Forward & Slow/Fast Decay PWM

PC20070604.1

Automatic Duty Cycle Adaptation

In case the supply voltage is lower than 2*Bemf, then the

duty cycle of the PWM is adapted automatically to >50% to

maintain the requested average current in the coils. This

process is completely automatic and requires no additional

parameters for operation.

Icoil

Duty Cycle

< 50 %

Duty Cycle > 50 %

Duty Cycle < 50 %

Actual value

Set value

TPWM

Figure 8. Automatic Duty Cycle Adaptation

t

PC20070604.2

http://onsemi.com

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