AMIS-30521 Micro-stepping Motor Driver

Data Sheet

8.4 Programmable Peak-Current

The amplitude of the current waveform in the motor coils (coil peak current = Imax) is adjusted by means of an SPI parameter

"CUR[4:0]" (Table 13: SPI Control Register 0). Whenever this parameter is changed, the coil-currents will be updated immediately at

the next PWM period. More information can be found in Table 24: SPI Control Parameter Overview CUR[4:0].

8.5 Speed and Load Angle Output

The SLA-pin provides an output voltage that indicates the level of the Back-e.m.f. voltage of the motor. This Back-e.m.f. voltage is

sampled during every so-called "coil current zero crossings". Per coil, two zero-current positions exist per electrical period, yielding in

total four zero-current observation points per electrical period.

ZOOM

t

Voltage Transient

Next

Micro-step

Previous

Micro-step

Coil Current Zero Crossing

Current Decay

Zero Current

t

t

PC20070604.7

Figure 12: Principle of Bemf Measurement

As this transient is not always desired in application software, two operating modes can be selected by means of the bit <SLAT> (see

"SLA-transparency" in Table 15: SPI Control Register 2). The SLA pin shows in "transparent mode" full visibility of the voltage transient

behavior. This allows a sanity-check of the speed-setting versus motor operation and characteristics and supply voltage levels. If the bit

“SLAT” is cleared, then only the voltage samples at the end of each coil current zero crossing are visible on the SLA-pin. Because the

transient behavior of the coil voltage is not visible anymore, this mode generates smoother Back e.m.f. input for post-processing, e.g.

by software.

divider is set through an SPI bit <SLAG>. (Table 15: SPI Control Register 2)

Table 12: Parameter Table SLA Pin

Symbol

Pin(s)

Parameter

Remark/Test Conditions

Min.

Typ.

Max.

Unit

Output voltage range

0.5

4.5

V

Output offset the SLA pin

0.2V < Vsla < Vdd - 0,2V

-20

20

mV

Output resistance SLA pin

1

k

Ω

Load capacitance SLA pin

50

pF

SLA

SLAG=0

SLAG=1

0,5

0,25

13

AMI Semiconductor

– June 2007, M-20683-001

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