AD5522JSVDZ datasheet(40/65 Pages) AD

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Data Sheet

AD5522

Rev. E | Page 39 of 64

Calibration Example

Nominal offset coefficient = 32,768

Nominal gain coefficient = 65,535

For example, the gain error = 0.5%, and the offset error = 100 mV.

Gain error (0.5%) calibration:

65,535 × 0.995 = 65,207

Therefore, load Code 1111 1110 1011 0111 to the M register.

Offset error (100 mV) calibration:

LSB size = 10.25/65,535 = 156 µV

Offset coefficient for 100 mV offset = 100/0.156 = 641 LSBs

Therefore, load Code 0111 1101 0111 1111 to the C register.

ADDITIONAL CALIBRATION

The techniques described in the Calibration section are usually

sufficient to reduce the zero-scale and gain errors. However,

there are limitations whereby the errors may not be sufficiently

reduced. For example, the offset (C) register can only be used to

reduce the offset caused by negative zero-scale error. A positive

offset cannot be reduced. Likewise, if the maximum voltage is

below the ideal value, that is, a negative gain error, the gain (M)

the error. These limitations can be overcome by increasing the

reference value.

SYSTEM LEVEL CALIBRATION

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

Following is an example of how to calibrate the FIN DAC of the

device without a DUT or DUT board connected.

The calibration procedure for the force and measure circuitry is

as follows:

1. Calibrate the force voltage (2 points).

In FV mode, write zero scale to the FIN DAC. Connect

SYS_FORCE to FOHx and SYS_SENSE to MEASVHx,

and close the internal force/sense switch (SW7).

Using the system PMU, measure the error between the

voltage at FOHx/MEASVHx and the desired value.

Similarly, load full scale to the FIN DAC and measure the

error between the voltage at FOHx/MEASVHx and the

desired value. Calculate the M and C values. Load these

values to the appropriate M and C registers of the FIN DAC.

2. Calibrate the measure voltage (2 points).

Connect SYS_FORCE to FOHx and SYS_SENSE to

MEASVHx, and close the internal force/sense switch (SW7).

Force voltage on FOHx via SYS_FORCE and measure the

voltage at MEASOUTx. The difference is the error between

the actual forced voltage and the voltage at MEASOUTx.

3. Calibrate the force current (2 points).

In FI mode, write zero scale to the FIN DAC. Connect

SYS_FORCE to an external ammeter and to the FOHx pin.

Measure the error between the ammeter reading and the

MEASOUTx reading. Repeat this step with full scale

loaded to the FIN DAC. Calculate the M and C values.

4. Calibrate the measure current (2 points).

In FI mode, write zero scale to the FIN DAC. Connect

SYS_FORCE to an external ammeter and to the FOHx pin.

Measure the error between the ammeter reading and the

MEASOUTx reading. Repeat this step with full scale

loaded to the FIN DAC.

5. Repeat this procedure for all four channels.

Similarly, calibrate the comparator and clamp DACs, and load

the appropriate gain and offset registers. Calibrating these

DACs requires some successive approximation to find where

the comparator trips or the clamps engage.

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