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L6712A L6712

CURRENT READING AND OVER CURRENT

transconductance ratio is issued by the external resistor Rg placed outside the chip between ISENx and

PGNDSx pins toward the reading points. The differential current reading rejects noise and allows to place

sensing element in different locations without affecting the measurement's accuracy. The current reading

circuitry reads the current during the time in which the low-side mosfet is on (OFF Time). During this time,

the reaction keeps the pin ISENx and PGNDSx at the same voltage while during the time in which the

reading circuitry is off, an internal clamp keeps these two pins at the same voltage sinking from the ISENx

imum rating overcome on ISENx pin).

The proprietary current reading circuit allows a very precise and high bandwidth reading for both positive

and negative current. This circuit reproduces the current flowing through the sensing element using a high

speed Track & Hold transconductance amplifier. In particular, it reads the current during the second half

of the OFF time reducing noise injection into the device due to the mosfet turn-on (See fig. 4-left). Track

time must be at least 200ns to make proper reading of the delivered current.

This circuit sources a constant 50

µA current from the PGNDSx pin: it must be connected through the Rg

resistor to the ground side of the sensing element (See Figure 4-right). The two current reading circuitries

use this pin as a reference keeping the ISENx pin to this voltage.

The current that flows in the ISENx pin is then given by the following equation:

carried by the relative phase. The current information reproduced internally is represented by the second

term of the previous equation as follow:

Since the current is read in differential mode, also negative current information is kept; this allow the de-

vice to check for dangerous returning current between the two phases assuring the complete equalization

between the phase's currents. From the current information of each phase, information about the total cur-

current carried by the two phases.

Figure 4. Current reading timing (left) and circuit (right)

I

ISENx

50

µA

R

SENSE

I

PHASEx

⋅

R

g

-------------------------------------------------

50

µAI

INFOx

+

=

+

=

I

INFOx

R

SENSE

I

PHASEx

⋅

R

g

-------------------------------------------------

=

Rg

50

µA

Rg

LGATEx

ISENx

PGNDSx

Track & Hold