AD5522
Data Sheet
Rev. E | Page 38 of 64
Table 14. References Suggested For Use with AD55221 Part No.
Voltage (V)
Initial
Accuracy %
Ref Out
TC (ppm/°C)
Ref Output
Current (mA)
SupplyVoltage
Range (V)
Package
ADR435
5
±0.04
1
30
+7 to +18
MSOP, SOIC
ADR445
5
±0.04
1
10
+5.5 to +18
MSOP, SOIC
ADR431
2.5
±0.04
1
30
+4.5 to +18
MSOP, SOIC
ADR441
2.5
±0.04
1
10
+3 to +18
MSOP, SOIC
1
Subset of the possible references suitable for use with the AD5522. Visit
www.analog.com for more options.
For other voltage and current ranges, the required reference
level can be calculated as follows:
1. Identify the nominal range required.
2. Identify the maximum offset span and the maximum gain
required on the full output signal range.
3. Calculate the new maximum output range, including the
expected maximum gain and offset errors.
4. Choose the new required VOUTMAX and VOUTMIN, keeping
the VOUT limits centered on the nominal values. Note that
AVDD and AVSS must provide sufficient headroom.
5. Calculate the value of VREF as follows:
VREF = (VOUTMAX VOUTMIN)/4.5
Reference Selection Example
If, given the following conditions:
Nominal output range = 10 V (2 V to +8 V)
Offset error = ±100 mV
Gain error = ±0.5%
REFGND = AGND = 0 V
Then, with gain error = ±0.5%, the maximum positive gain
error = +0.5%, and the output range including gain error =
10 V + 0.005(10 V) = 10.05 V.
With offset error = ±100 mV, the maximum offset error span =
2(100 mV) = 0.2 V, and the output range including gain error
and offset error = 10.05 V + 0.2 V = 10.25 V.
To calculate VREF with actual output range = 10.25 V, that is,
2.125 V to +8.125 V (centered),
VREF = (8.125 V + 2.125 V)/4.5 = 2.28 V
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 refer-
ence level.
Use a combination of these two approaches.
In this case, the optimum reference is a 2.5 V reference; the user
can use the M and C registers and the offset DAC to achieve the
required 2 V to +8 V range. Change the ISENSE amplifier gain to
5 to ensure a full-scale current range of the specified values (see
mization of power supplies and minimizes power consumption
within the device.
It is important to bear in mind when choosing a reference value
that values other than 5 V (MI gain = 10) and 2.5 V (MI gain = 5)
result in current ranges other than those specified. See the
CALIBRATION
Calibration involves determining the gain and offset of each
channel in each mode and overwriting the default values in the
M and C registers of the individual DACs. In some cases (for
example, FI mode), the calibration constants, particularly those
for gains, may be range dependent.
Reducing Zero-Scale Error
Zero-scale error can be reduced as follows:
1. Set the output to the lowest possible value.
2. Measure the actual output voltage and compare it to the
required value. This gives the zero-scale error.
3. Calculate the number of LSBs equivalent to the zero-scale
error and add/subtract this number to the default value of
the C register.
Reducing Gain Error
Gain error can be reduced as follows:
1. Measure the zero-scale error.
2. Set the output to the highest possible value.
3. Measure the actual output voltage and compare it to the
required value. This is the gain error.
4. Calculate the number of LSBs equivalent to the gain error
and subtract this number from the default value of the M
register. Note that only positive gain error can be reduced.