Phase current control: current mode
powerSTEP01
Figure 22. Adaptive decay - switch from normal to slow+ fast decay mode and vice
versa
2nd fast decay
1st fast decay
switch to fast + slow decay mode
reference current
Time
tOFF,FAST
tOFF
tOFF
tOFF,SLOW
tFAST
Target current is increased (raising step)
system returns to slow decay mode and tFAST vaule is halved
reference current
Time
AM15051v1
9.3
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. However,
exceeding the fast duration could cause a strong ripple on the step change. The
powerSTEP01 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 (see Section 11.1.18). 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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STMICROELECTRONICS [ ST ]
