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L6474PD View Datasheet(PDF) - STMicroelectronics

Part Name
Description
MFG CO.
L6474PD
ST-Microelectronics
STMicroelectronics ST-Microelectronics
'L6474PD' PDF : 53 Pages View PDF
Phase current control
L6474
7.2
Auto-adjusted decay mode
During the current control, the device automatically selects the best decay mode in order to
follow the current profile reducing the current ripple.
At reset, the OFF time is performed by turning on both the low-side MOS of the power stage
and the current recirculates in the lower half of the bridge (slow decay).
If, during a PWM cycle, the target current threshold is reached in a time shorter than the
TON_MIN value, a fast decay of TOFF_FAST/8 (T_FAST register) is immediately
performed, turning on the opposite MOS of both half bridges and the current recirculates
back to the supply bus.
After this time, the bridge returns to the ON state: if the time needed to reach the target
current value is still less than TON_MIN, a new fast decay is performed with a period twice
the previous one. Otherwise, the normal control sequence is followed as described in
Section 7.1. The maximum fast decay duration is set by TOFF_FAST value.
Figure 10. Adaptive decay - fast decay tuning
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When two or more fast decays are performed with present target current, the control system
adds a fast decay at the end of every OFF time, keeping the OFF state duration constant
(tOFF is split into tOFF,SLOW and tOFF,FAST). When the current threshold is increased by
a microstep change (rising step), the system returns to normal decay mode (slow decay
only) and the tFAST value is halved.
Reaching the current sinewave zero crossing causes the current control system to return to
the reset state.
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DocID022529 Rev 4
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