AD5522JSVDZ datasheet(39/60 Pages) AD

39 / 60 page

AD5522

Rev. A | Page 39 of 60

FORCE CURRENT (FI) MODE

In force current (FI) mode, the voltage at the FIN DAC is

converted to a current and is applied to the DUT. The feedback

path is the measure current amplifier, feeding back the voltage

measured across the sense resistor. MEASOUTx reflects the

voltage measured across the DUT (see Figure 52).

For the suggested current ranges, the maximum voltage drop

across the sense resistors is ±1 V. However, to allow for error

correction, there is some overrange available in the current

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

loaded to the FIN DAC is ±11.5 V. The forced current can be

calculated as follows:

FI = 4.5 × VREF × ((DAC_CODE − 32,768)/216)/(RSENSE ×

MI_Amplifier_Gain)

where:

FI is the forced current.

RSENSE is the selected sense resistor.

MI_Amplifier_Gain is the gain of the measure current

instrumentation amplifier. This gain can be set to 5 or

10 via the serial interface.

The ISENSE amplifier is biased by the offset DAC output voltage in

such a way as to center the measure current output regardless of

the voltage span used.

In the ±200 μA range with the 5 kΩ sense resistor and an ISENSE

gain of 10, the maximum current range possible is ±225 μA.

Similarly, for the other current ranges, there is an overrange of

12.5% to allow for error correction.

DUTGND

DUT

RSENSE

INTERNAL RANGE SELECT

(±5µA, ±20µA, ±200µA, ±2mA)

FIN

DAC

–

×5 or ×10

×1

AGND

VMID TO

CENTER

I RANGE

RSENSE

(UP TO

±80mA)

MEASVHx

EXTMEASIHx

EXTMEASILx

FOHx

EXTFOHx

CFFx

MEASOUTx

FORCE

AMPLIFIER

MEASURE CURRENT

AMPLIFIER

Ω

×1 OR

×0.2

Ω

Figure 52. Forcing Current, Measuring Voltage

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