AD5522JSVD datasheet(25/48 Pages) AD

25 / 48 page

Preliminary Technical Data

AD5522

Rev. PrM | Page 25 of 48

Reference Selection Example

Nominal Output Range = 10V (-2V to +8V)

Offset Error = ±100mV

Gain Error = ±0.5%

REFGND = AGND = 0V

Gain Error = ±0.5%

=> Maximum Positive Gain Error = +0.5%

=> Output Range incl. Gain Error

= 10 + 0.005(10)=10.05V

Offset Error = ±100mV

=> Maximum Offset Error Span = 2(100mV)=0.2V

=> Output Range including Gain Error and Offset Error =

10.05V + 0.2V = 10.25V

VREF Calculation

Actual Output Range = 10.25V, that is -2.125V to +8.125V

(centered);

VREF = (8.125V + 2.125V)/4.5 = 2.28V

If the solution yields an inconvenient reference level, the user

can adopt one of the following approaches:

Use a resistor divider to divide down a convenient,

higher reference level to the required level.

Select a convenient reference level above VREF and

modify the Gain and Offset registers to digitally

downsize the reference. In this way the user can use

almost any convenient reference level.

Use a combination of these two approaches

In this case, the optimum reference to choose is a 2.5V

reference, then use the m and c registers and the OFFSET DAC

to achieve the required -2V to +8V range. The ISENSE

amplifier gain should be changed to a gain of 5. This ensures a

full scale current range of the specified values and also allows

optimization of power supplies and minimizes power

consumption within the device.

CALIBRATION

The user can perform a system calibration by overwriting the

default values in the m and c registers for any individual DAC

channels as follows:

Calculate the nominal offset and gain coefficients for the new

output range (see previous example)

Calculate the new m and c values for each channel based on

the specified offset and gain errors

Calibration Example

Nominal Offset Coefficient = 32768

Nominal Gain Coefficient = 10/10.25x 65535 = 63937

12/12.26× 65535 = 64145

Example 1: Gain Error = +0.5%, Offset Error = +100mV

1) Gain Error (0.5%) Calibration: 63937 × 0.995 = 63617

=> Load Code “0b1111 1000 1000 0001” to m register

2) Offset Error (100mV) Calibration:

LSB Size = 10.25/65535 = 156 µV;

Offset Coefficient for 100mV Offset = 100/0.156 = 641 LSBs

=> Load Code “0b0111 1101 0111 1111” to c register

SYSTEM LEVEL CALIBRATION

There are many ways to calibrate the device on power on. The

following gives an example of how to calibrate the FIN DAC of

the device without a DUT or DUT board connected.

Calibration Procedure for Force and Measure circuitry:

Calibrate Force Voltage (2 point)

Write zero scale to the Force DAC (FIN), connect

SYS_FORCE to FOHx and SYS_SENSE to MEASVHx,

close the internal Force/Sense Switch (SW 7). Using the

System PMU, measure the error between voltage at FOHx,

MEASVHx and desired value.

Similarly, load Full scale to the Force DAC, and measure

the error between FOHx , MEASVH and the desired value.

Work out m and c values. Load these values to appropriate

m and c registers for Force DAC.

Calibrate Measure Voltage (2 point)

Connect SYS_FORCE to FOH, SYS_SENSE to MEASVHx

Close Internal Force/Sense switch (SW 7). Force voltage on

FOH via SYS_FORCE and measure voltage at MEASOUT.

The difference is the error between the actual forced

voltage and the voltage at MEASOUT.

Calibrate Force current (2 point)

In Force current mode, write zero and fullscale to the Force

DAC. Connect SYS_FORCE to external ammeter and to

FOH pin. Measure error on zero and fullscale current and

calculate m and c values.

Calibrate Measure Current (2 Point)

Write zero scale to the Force DAC in Force Current mode.

Connect SYS_FORCE to an external ammeter and to the

FOH pin. Measure the error between ammeter reading and

MEASOUT reading. Repeat with Full scale loaded to the

Force DAC.

Repeat for all four channels.

Similarly, calibrate the comparators and clamp DACs and load

the appropriate gain and offset registers. Calibrating these

DACs will require some successive approximation to find where

the comparator trips or the clamps engage.

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