AMIS30421C4211G ONSEMI [ON Semiconductor], AMIS30421C4211G Datasheet - Page 21

• Manufacturer Part Number: AMIS30421C4211G
• Description: Micro-Stepping Stepper Motor Bridge Controller
• Manufacturer: ONSEMI [ON Semiconductor]

transient behavior. This transient behavior (which is not the
BEMF) can be made visible or invisible on the SLA−pin by
means of SPI bit <SLAT>. When set to transparent
(<SLAT> = ‘1’), the coil voltage is sampled every PWM
cycle and updated on the SLA−pin (see Figure 19). When set
to not−transparent (<SLAT> = ‘0’), only the last sample
(taken right before leaving the “coil current zero crossing”)
will be copied to the SLA−pin (see Figure 20).
SLA−pin and the coil voltage is:
offset of 0.6 V. Five different SLA gain values can be set by
means of SPI bits <SLAG[2:0]>.
zero crossing”. If NXT pulses are applied too fast it’s
possible that the “coil current zero crossing” is too short
making it impossible to measure the real BEMF (see
The relationship between the voltage measured on the
V
SPI bit <SLA_OFFS> can be used to add an additional
AMIS−30421 has the ability to stretch the “coil current
SLA
Transparent
Figure 19. Principle of BEMF Measurement in
I
= 0.6 + (0.6 x <SLA_OFFS>) + (V
coil
V
V
V
NXT
I
SLA
Remark: V
coil
coil
Microstep
Previous
V
Bemf of previous
coil
zero crossing
BB
is only drawn during the coil current zero crossing
+ 0.6V
Transparent Mode
Current Decay
Zero Crossing
Coil Current
V
BEMF
Microstep
coil
Next
x <SLAG>)
t
t
t
t
http://onsemi.com
t
21
Not− transparent
keep in mind that there is a delay between applying the NXT
pulse (to leave the “coil current zero crossing”) and the
updated voltage on the SLA−pin (see t
Figure 20 and Table 5).
Figure 20. Principle of BEMF Measurement in
Figure 21). By using SPI bits <MIN_SLA_TIME[1:0]> one
can stretch the “coil current zero crossing” without changing
the speed of the motor (see Figure 21). AMIS−30421 will
ignore but keep track of the NXT pulses applied during the
“stretched coil current zero crossing” and compensate the
ignored pulses when leaving the “coil current zero
crossing”.
application note AND8399. Although this application note
refers to AMIS−305xx, it is also valid for AMIS−30421.
When working in not−transparent mode (<SLAT> = ‘0’)
More information on using the SLA−pin can be found in
I
coil
V
V
V
NXT
I
SLA
Remark: V
coil
coil
Microstep
Previous
Bemf of previous
V
coil
zero crossing
BB
is only drawn during the coil current zero crossing
+ 0.6V
Not−Transparent Mode
Current Decay
Zero Crossing
Coil Current
V
BEMF
Microstep
Last sample before leaving
zero crossing is retained.
t
SLA _DELAY
Next
SLA_DELAY
t
t
t
t
t
in