AN4144 datasheet(22/28 Pages) STMICROELECTRONICS

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Supply voltage compensation guidelines

AN4144

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DocID023491 Rev 3

Supply voltage compensation guidelines

The effectiveness of the compensation is strongly dependent on the actual duty cycle value

because the system is not able to overcome the maximum duty cycle of 100%. When the

variations of the application supply voltage make the use of the compensation system

essential, the maximum target current is limited by the lower voltage value which is

expected from the power supply output.

For this reason, the application setup, i.e. motor characteristics and phase currents, should

be chosen considering the minimum expected supply voltage.

For example, suppose 85% of the 24 V bus is needed in order to reach the target current at

1000 step/s. If the bus voltage is reduced by 20% (i.e. the actual voltage is:

24 V

 0.8 = 19.2 V), the compensation system increases the duty cycle by a factor of

1/0.8 = 1.25. In this case the resulting duty cycle is 106.25%, which is greater than the

maximum available value (100%).

Example 3

VBUS = VBUS,nom = 24 V -> DutyCyclePWM at 1000 step/s = 85%

VBUS = 0.8  VBUS,nom = 19.2 V -> DutyCyclePWM at 1000 step/s = 85% / 0.8 = 106.25%.

AN4144 Datasheet(PDF) 22 Page - STMicroelectronics