AN2836 datasheet(23/57 Pages) STMICROELECTRONICS

Part #	AN2836

Description	Modern motion control applications need more flexibility that can be addressed

PDF	57 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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23 / 57 page

AN2836

Designing an application with L6225, L6226, L6227

Doc ID 15084 Rev 1

23/57

Figure 18.

Slow decay mode output stage configurations

In some conditions (short off-time, very low regulated current, high motor winding L / R) the

system may need an on-time shorter than 1.5 µs in which case the PWM current controller

can lose the regulation.

Figure 19 shows the operation of the circuit in this condition. When the current first reaches

the threshold, the bridge is turned off for a fixed time and the current decays. During the

following on-time, the current increases above the threshold, but the bridge cannot be

turned off until the minimum 1.5 µs on-time expires. Since the current increases more in

each on-time than it decays during the off-time, it keeps growing during each cycle, with a

steady state asymptotic value set by the duty cycle and load DC resistance. The resulting

peak current is:

Equation 12

where D = tON / (tON + tOFF) is the duty cycle and RLOAD is the load DC resistance.

LOAD

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AN2836 Datasheet(PDF) 23 Page - STMicroelectronics