AD5522 datasheet(17/45 Pages) AD

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Preliminary Technical Data

AD5522

Rev. PrL | Page 17 of 45

CURRENT RANGE SELECTION

Integrated thin film resistors minimize external components

and allow easy selection of current ranges from 5 µA (200kΩ),

20μA (50kΩ), 200μA (5kΩ) and 2mA (500Ω). Per channel, one

current range up to 64mA may be accommodated by

connecting an external sense resistor. For current ranges in

excess of 64mA, it is recommended an external amplifier be

used.

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 full-scale voltage range that can be loaded

to the 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.

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.

Also, the forced current range will only be the quoted full scale

range with an applied reference of 5V or 2.5V (with ISENSE

AMP gain = 5). 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.

When using the EXTFOHx outputs for current ranges up to

64mA, there is no switch in series with the EXTFOHx line,

ensuring minimum capacitance presented at the output of the

force amplifier. This is also an important feature if using a Pin

electronics driver to provide high current ranges.

HIGH CURRENT RANGES

With the use of an external high current amplifier, one high

current range in excess of 64mA is possible. The high current

amplifier simply buffers the force output and provides the drive

for the required current.

DUTGND

MEASVH

DUT

Rsense

EXTMEASIH

EXTMEASIL

FOH

EXTFOH

CFF

FIN

INTERNAL RANGE SELECT

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

10k

Ω

Rsense

DAC

HIGH CURRENT

BUFFER

x5 or x10

AGND

MEASOUT

x1/x0.2

OFFSET DAC

BIAS TO

CENTER

IRANGE

Figure 10. Addition of high current amplifier for wider current range(>64mA)

DEVICE UNDER TEST GROUND (DUTGND)

By default, there is one DUTGND input available for all four

PMU channels. In some applications of a PMU, it is necessary

that each channel operate from its own DUTGND level. There

is a shared pin in the form of the GUARDIN(0-3)/DUTGND(0-

3) which may be shared as either the input to the GUARD

amplifier (GUARDIN), or as a DUTGND per channel function.

This should be configured through the serial interface on power

on as per required operation. The default connection is SW13b

and SW14b. When configured as DUTGND per channel, this

multifunction pin is no longer connected to the input of the

guard amplifier, it is instead connected to the low end of the

instrumentation amplifier (SW14a), and the input of the Guard

amplifier is not connected internally to MEASVH (SW13a).

DUTGND

MEASVH (0-3)

GUARD (0-3)

GUARDIN (0-3)/

DUTGND (0-3)

AGNDx

MEASURE

VOLTAGE

IN AMP

DUT

GUARD AMP

SW 14

SW 13

SW 16

Figure 11. Using the DUTGND per channel Feature

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