POWERSTEP01 datasheet(46/92 Pages) STMICROELECTRONICS

46 / 92 page

Phase current control: current mode

powerSTEP01

46/92

DocID025022 Rev 5

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 on page 59). 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.

Figure 22. Adaptive decay - switch from normal to slow+ fast decay mode and vice

versa

Time

reference current

st fast decay

Target current is increased (raising step)

2nd fast decay

system returns to slow decay mode and tFAST vaule is halved

switch to fast + slow decay mode

FAST

OFF,FAST

OFF,SLOW

OFF

reference current

AM15051v1

POWERSTEP01 Datasheet(PDF) 46 Page - STMicroelectronics