L6258 STMicroelectronics, L6258 Datasheet - Page 23

• Manufacturer Part Number: L6258
• Manufacturer: STMicroelectronics

Specifications of L6258

• Operating Current: 15mA
• Motor Controller Type: PWM Motor Controller
• Package Type: PowerSO
• Operating Supply Voltage (min): 12V
• Operating Supply Voltage (typ): 34V
• Operating Supply Voltage (max): 5.25V
• Lead Free Status / Rohs Status: Not Compliant

L6258
Figure 10. Electrical model of the load
The schematic now shows the equivalent circuit of the stepper motor including a sine wave
voltage generator of the Bemf. The Bemf voltage of the motor is not constant, its value
changes depending on the speed of the motor.
Increasing the motor speed the Bemf voltage increases:
Bemf = Kt · ω
where:
Kt is the motor constant
ω is the motor speed in radiant per second
The formula defining the gain of the load considering the Bemf of the stepper motor
becomes:
we can see that the Bemf influences only the gain of the load block and does not introduce
any other additional pole or zero, so from the stability point of view the effect of the Bemf of
the motor is not critical because the phase margin remains the same.
Practically the only effect of the Bemf is to limit the gain of the total Aloop with a consequent
variation of the bandwidth of the system.
OUT+
OUT-
ACload
ACload dB
Acload
=
Vsense
---------------------
Vout
=
=
20
V S Bemf
---------------------------- -
⋅
=
log
–
V S
(
------------------------------------------------------------ -
⎛
⎜
⎝
V S Bemf
R
L
R
V S Bemf
---------------------------- -
Bemf
–
L
L
S
–
V S
⋅
----------------------
R L
V S
R S
+
)
⋅
⋅
R S
----------------------
R L
----------------------
R L
R
R S
+
+
PWM current control loop
S
R S
R S
⎞
⎟
⎠
to Sense
Amplifier
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