AD5361 Analog Devices, AD5361 Datasheet - Page 18

• Manufacturer Part Number: AD5361
• Description: 16-Channel, 14-Bit, Serial Input, Voltage-Output DAC
• Manufacturer: Analog Devices

Specifications of AD5361

• Resolution (bits): 14bit
• Dac Update Rate: 540kSPS
• Dac Settling Time: 20µs
• Max Pos Supply (v): +16.5V
• Single-supply: No
• Dac Type: Voltage Out
• Dac Input Format: Ser,SPI

AD5360/AD5361
4.
5.
Reference Selection Example
VREF calculation
If the solution yields an inconvenient reference level, the user
can adopt one of the following approaches:
•
•
•
CALIBRATION
The user can perform a system calibration on the AD5360 and
AD5361 to reduce gain and offset errors to below 1 LSB. This is
achieved by calculating new values for the M and C registers and
reprogramming them.
Reducing Zero-Scale and Full-Scale Error
Zero-scale error can be reduced as follows:
1.
2.
3.
Choose the new required VOUT
the VOUT limits centered on the nominal values. Note that
V
Calculate the value of VREF as follows:
VREF = (VOUT
Nominal output range = 20 V (−10 V to +10 V)
Offset error = ±100 mV
Gain error = ±3%
SIGGND = AGND = 0 V
Gain error = ±3%
Offset error = ±100 mV
Actual output range = 20.6 V, that is, −10.3 V to +10.3 V
VREF = (10.3 V + 10.3 V)/4 = 5.15 V
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 conven-
ient reference level but may reduce the performance by
overcompaction of the transfer function.
Use a combination of these two approaches.
Set the output to the lowest possible value.
Measure the actual output voltage and compare it with the
required value. This gives the zero-scale error.
Calculate the number of LSBs equivalent to the error and
add this from the default value of the C register. Note that
only negative zero-scale error can be reduced.
DD
Maximum positive gain error = +3%
Output range including gain error = 20 + 0.03 (20) =
20.6 V
Maximum offset error span = 2 (100 mV) = 0.2 V
Output range including gain error and offset error =
20.6 V + 0.2 V = 20.8 V
(centered);
and V
SS
must provide sufficient headroom.
MAX
− VOUT
MIN
MAX
)/4
and VOUT
MIN
, keeping
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Full-scale error can be reduced as follows:
1.
2.
3.
4.
The M and C registers should not be programmed until both
zero-scale errors and full-scale errors have been calculated.
AD5360 Calibration Example
This example assumes that a −10 V to +10 V output is required.
The DAC output is set to −10 V but is measured at −10.03 V.
This gives a zero-scale error of −30 mV.
The full-scale error can now be removed. The output is set
to +10 V, and a value of +10.02 V is measured. The full-scale
error is +20 mV. The span error is +20 mV − (−30 mV) =
+50 mV.
The errors can now be removed.
1.
2.
3.
4.
Additional Calibration
The techniques described in the previous section are usually
enough to reduce the zero-scale errors and full-scale errors in
most applications. However, there are limitations whereby the
errors may not be sufficiently removed. For example, the offset
(C) register can only be used to reduce the offset caused by the
negative zero-scale error. A positive offset cannot be reduced.
Likewise, if the maximum voltage is below the ideal value, that
is, a negative full-scale error, the gain (M) register cannot be
used to increase the gain to compensate for the error.
These limitations can be overcome by increasing the refer-
ence value. With a 2.5 V reference, a 10 V span is achieved.
The ideal voltage range, for the AD5360 or AD5361, is
−5 V to +5 V. Using a 2.6 V reference increases the range
to −5.2 V to +5.2 V. Clearly, in this case, the offset and gain
errors are insignificant and the M and C registers can be
used to raise the negative voltage to −5 V and then reduce
the maximum voltage down to +5 V to give the most
accurate values possible.
Measure the zero-scale error.
Set the output to the highest possible value.
Measure the actual output voltage and compare it with the
required value. Add this error to the zero-scale error. This
is the span error, which includes full-scale error.
Calculate the number of LSBs equivalent to the span error
and subtract it from the default value of the M register.
Note that only positive full-scale error can be reduced.
1 LSB = 20 V/65,536 = 305.176 μV
30 mV = 98 LSBs
+50 mV = 164 LSBs
98 LSBs should be added to the default C register value;
(32,768 + 98) = 32,866.
32,866 should be programmed to the C register.
164 LSBs should be subtracted from the default M register
value; (65,535 − 164) = 65,371.
65,371 should be programmed to the M register.