POWERSTEP01 datasheet(43/92 Pages) STMICROELECTRONICS

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powerSTEP01

Phase current control: current mode

When the current mode driving is selected (CM_VM bit in STEP_MODE register is set to 1),

the powerSTEP01 performs a new current control technique, named predictive current

control, allowing the device to obtain the target average phase current. This method is

described in detail in Section 9.1. Furthermore, the powerSTEP01 automatically selects the

better decay mode in order to follow the current profile.

Current control algorithm parameters can be programmed by T_FAST, TON_MIN,

TOFF_MIN and CONFIG registers (see Section 11.1.11 on page 56, 11.1.12 on page 56,

11.1.19 on page 59 and 11.1.27 on page 66 for details).

Different current amplitude can be set for acceleration, deceleration and constant speed

phases and when the motor is stopped through TVAL_ACC, TVAL_DEC, TVAL_RUN and

TVAL_HOLD registers (see Section 11.1.16 on page 58). The output current amplitude can

also be regulated by the ADCIN voltage value (see Section 9.4).

Each bridge is driven by an independent control system that shares with the other bridge the

control parameters only.

9.1

Predictive current control

Unlike classical peak current control systems, that make the phase current decay when the

target value is reached, this new method keeps the power bridge ON for an extra time after

reaching the current threshold.

At each cycle the system measures the time required to reach the target current (tSENSE).

After that the power stage is kept in a “predictive” ON state (tPRED) for a time equal to the

mean value of tSENSE in the last two control cycles (actual one and previous one), as shown

in Figure 19.

Figure 19. Predictive current control

At the end of the predictive ON state the power stage is set in OFF state for a fixed time, as

in a constant tOFF current control. During the OFF state both slow and fast decay can be

performed; the better decay combination is automatically selected by the powerSTEP01, as

described in Section 9.2.

predictive ON

state

OFF

state

SENSE (n-1)

OFF

tOFF

PRED (n) =

SENSE (n-1) + tSENSE(n)

Iref

Iout

PRED

(n-1)

SENSE (n)

PRED (n)

AM15048v1

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