AN2836 datasheet(24/57 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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24 / 57 page

Designing an application with L6225, L6226, L6227

AN2836

24/57

Doc ID 15084 Rev 1

4.13

Overcurrent protection

To implement an overcurrent protection, a dedicated overcurrent detection (OCD) circuitry

(see Figure 21 and 22 for a simplified schematic) senses the current in each high side.

Power DMOS are actually made of thousands of individual identical cells, each carrying a

fraction of the total flowing current. The current sensing element, connected in parallel to the

power DMOS, is made only of a few such cells, having a 1:N ratio compared to the power

DMOS. The total drain current is split between the output and the sense element according

to the cell ratio. Sensed current is, then, a small fraction of the output current and does not

contribute significantly to power dissipation.

Figure 21.

L6225 and L6227 overcurrent detection simplified circuitry

Figure 19.

PWM controller loses the current

regulation due to minimum on-time

(L6227 only)

Figure 20.

PWM controller loses the current

regulation due to minimum on-time

(L6227 only) - detail

AN2836 Datasheet(PDF) 24 Page - STMicroelectronics