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AN4158

Setup and optimization

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Figure 24. On-time measurement

In order to obtain the lowest current ripple possible, the TON_MIN value should be slightly

longer than the commutation time. Using longer TON_MIN increases the current ripple but

forces a higher minimum duty cycle value increasing the robustness of the control system.

5.1.2

TOFF

The off-time of the control system sets the maximum PWM frequency of the control system

Equation 11

control frequencies and then lower TOFF values. On the contrary, higher TOFF values and

inductive motor).

5.1.3

TOFF_FAST

The maximum fast decay duration should be set taking into account that its value is directly

proportional to the ripple of the current control algorithm.

High current ripple increases the noise, causes higher power dissipation and reduces the

positioning precision in microstepping operation. In general, the current ripple should be as

low as possible.

The minimum fast decay, which is one-eighth of TOFF_FAST, must be longer than

TON_MIN to avoid subsequent minimum on-time violations (see Figure 25).

V

BUS

OFF

ON

V

BUS

OFF

OFF

V

BUS

ON

OFF

V

BUS

ON

OFF

Power bridge

driving signal

t

on

Low side

High side

turn-on time

turn-

Dead time

Blanking time

Current sensing disabled

Commutation time

Current sensing

enabled

Even if the reference current is reached

the system cannot detect this condition

until the end of commutation

Reference current reached

AM15126v1

+

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=