L6474PD View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6474PD' PDF : 53 Pages View PDF
L6474
Phase current control
Figure 11. Adaptive decay - switch from normal to slow + fast decay mode and vice versa
1st fast decay
reference current
nd fast decay
switch to fast + slow decay mode
2
t
OFF
t
FAST
t
OFF
tOFF,SLOW
Time
t
OFF,FAST
Target current is increased (raising step)
system returns to slow decay mode and tFAST value is halved
reference current
Time
7.3
Auto-adjusted fast decay during the falling steps
When the target current is decreased by a microstep change (falling step), the device
performs a fast decay in order to reach the new value as fast as possible. Anyway,
exceeding the fast duration could cause a strong ripple on the step change. The L6474
automatically adjusts these fast decays reducing the current ripple.
At reset, the fast decay value (tFALL) is set to FALL_STEP/4 (T_FAST register). The tFALL
value is doubled every time, within the same falling step, an extra fast decay is necessary to
obtain an ON time greater than TON_MIN. The maximum tFALL value is equal to
FALL_STEP.
At the next falling step, the system uses the last tFALL value of the previous falling step.
Stopping the motor or reaching the current sinewave zero crossing causes the current
control system to return to the reset state.
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