AD5522JSVDZ datasheet(30/60 Pages) AD

30 / 60 page

AD5522

Rev. A | Page 30 of 60

CURRENT RANGE SELECTION

Integrated thin film resistors minimize the need for external

components and allow easy selection of any of these current

ranges: ±5 μA (200 kΩ), ±20 μA (50 kΩ), ±200 μA (5 kΩ), and

±2 mA (500 Ω). One current range up to ±80 mA can be

accommodated per channel by connecting an external sense

resistor. For current ranges in excess of ±80 mA, it is necessary

that an external amplifier be used.

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 (±12.5% or ±0.125 V across RSENSE). The 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.

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.

Also, the forced current range is the quoted full-scale range only

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

gain = 5). The ISENSE amplifier is biased by the VMID DAC

voltage in such a way as to center the measure current output

irrespective of the voltage span used.

When using the EXTFOHx outputs for current ranges up to

±80 mA, there is no switch in series with the EXTFOHx line,

ensuring minimum capacitance present at the output of the

force amplifier. This feature is important when 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 ±80 mA is possible. The high current

amplifier buffers the force output and provides the drive for the

required current. The AD8397 is a dual high current output

amplifier (300 mA depending on supply conditions). To achieve

full swing from this amplifier, it should be used with a gain of 2

or more, thus requiring a voltage divider at the output of

EXTFOHx. This amplifier is available in an SOIC exposed pad

package which is well-suited to high power applications.

To eliminate any timing concerns when switching between the

internal ranges and the external high current range, there is a

mode where the internal ±80 mA stage can be enabled at all

times. See Table 25 for more information.

DUTGND

MEASVHx

DUT

RSENSE

EXTMEASIHx

EXTMEASILx

FOHx

EXTFOHx

HIGH

CURRENT

AMPLIFIER

CFFx

FIN

INTERNAL RANGE SELECT

(±5µA, ±20µA, ±200µA, ±2mA)

DAC

–

×5 or ×10

×1

AGND

MEASOUTx

×1 OR

×0.2

Ω

VMID TO

CENTER

I RANGE

Ω

Figure 44. Addition of High Current Amplifier for Wider Current Range (>±80 mA)

AD5522JSVDZ датащи(PDF) 30 Page - Analog Devices

AD5522JSVDZ датащи(HTML) 30 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

датащи скачать

ссылки URL