L6207 datasheet(18/53 Pages) STMICROELECTRONICS

18 / 53 page

AN1762 APPLICATION NOTE

18/53

3.12 Over Current Protection

To implement an Over Current (i.e. short circuit) Protection, a dedicated Over Current Detection (OCD) circuitry

(see Figure 19 for a simplified schematic) senses the current in each high side. Power DMOS are actually made

up with thousands of individual identical cells, each carrying a fraction of the total current flowing. The current

sensing element, connected in parallel to the Power DMOS, is made only with 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 ac-

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

significantly to power dissipation.

Figure 19. Over Current Detection simplified circuitry.

OVER

TEMPERATURE

IREF

(I1A+I2A) / n

I1A / n

POWER SENSE

1 cell

POWER SENSE

1 cell

POWER DMOS

n cells

POWER DMOS

n cells

HIGH SIDE DMOSs OF

THE BRIDGE A

OUT1A

OUT2A

VSA

I1A

I2A

I2A / n

OCD

COMPARATOR

TO GATE

LOGIC

INTERNAL

OPEN-DRAIN

RDS(ON)

Ω TYP.

CENA

RENA

RCLA.

ENA

OCDA

PROGCLA,

+5V

1.2V

µC or LOGIC

OVER TEMPERATURE

IREF

(I1A+I2A) / n

I1A / n

POWER SENSE

1 cell

POWER SENSE

1 cell

POWER DMOS

n cells

POWER DMOS

n cells

HIGH SIDE DMOSs OF

THE BRIDGE A

OUT1A

OUT2A

VSA

I1A

I2A

I2A / n

OCD

COMPARATOR

TO GATE

LOGIC

INTERNAL

OPEN-DRAIN

RDS(ON)

Ω TYP.

CEN

REN

ENA

+5V

µC or LOGIC

L6206

L6205, L6207

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