AD5522 datasheet(24/45 Pages) AD

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AD5522

Preliminary Technical Data

Rev. PrL | Page 24 of 45

FORCE CURRENT, FI

In the force current mode, the voltage at FIN is now converted

to a current and applied to the DUT. The feedback path is now

the current measure amplifier, feeding back the voltage

measured across the sense resistor and MEASOUT reflects the

voltage measured across the DUT. See Figure 16.

For the suggested current ranges, the maximum voltage drop

across the sense resistors is ±1V, however, to allow for

correction of errors, there is some over range available in the

current ranges. The maximum full-scale voltage range that can

be loaded to the FIN DAC is ±11.5V; the forced current may be

calculated as follows:

Gain

RSENSE

VFIN

Where:

FI = Forced Current

VFIN = Voltage of the FIN DAC, See VOUT for DAC levels.

RSENSE = Selected Sense Resistor

Gain of Current Measure Instrumentation amplifier, it may be

set (via the serial interface) to 5 or 10.

The ISENSE amplifier is biased by the Offset DAC output

voltage, in such as way as to center the Measure current output

irrespective of the voltage span used.

Using the 5kΩ sense resistor and ISENSE gain of 10, the

maximum current range possible is ±225μA. Similarly for the

other current ranges, there is an over range of 12.5% to allow for

correction.

DUTGND

MEASVH

DUT

Rsense

up to

(64mA)

EXTMEASIH

EXTMEASIL

FOH

EXTFOH

CFF

FIN

MEASOUT

INTERNAL RANGE SELECT

(5uA, 20uA, 200uA, 2mA)

Rsense

DAC

x1/x0.2

x5 or x10

AGND

10k

Ω

OFFSET DAC

BIAS TO

CENTER

IRANGE

Figure 16. .Forcing current, measuring voltage

AD5522 Datasheet(PDF) 24 Page - Analog Devices

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