L6238S View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6238S' PDF : 31 Pages View PDF
Figure 4-11: Bemf Amplifier.
L6238S
VoBEMF
-35
-25
0
SLOPE=0
25
35
SLOPE=1
ViBEMF(mV)
D95IN316
sistive network as shown in figure 4.12 can be
used to emulate the Bemf of the motor.
The actual Bemf zero-crossing is 30 electrical de-
grees (50% of a commutation interval) away from
the optimal switch point. A digital counter circuit
measures 50% of the previous interval to deter-
mine the next interval’s commutation delay from
the zero crossing. During the low RPM stages of
start up the long commutation intervals may
cause the counter to overflow, in which case 50%
of the max count will be less than 50% of the
ideal commutation interval. Therefore, the torque
Figure 4-12: Bemf Emulator
will not be optimal until the desired commutation
interval is less than the dynamic range of the
counter.
4.9 Center Tap Protection
Spindle Motors with a high number of windings
exhibit a transformer coupling effect that in some
cases can cause relatively high currents to flow
through the center tap input.
Current flowing out of the center tap pin as high
as 25mA has been observed with certain motors.
Figure 4-13
R1 1K
TO CENTER
TAP INPUT
D95IN317
DS1
21/31
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