AD5363 Analog Devices, AD5363 Datasheet - Page 18

• Manufacturer Part Number: AD5363
• Description: 8-Channel, 14-Bit, Serial Input, Voltage-Output DAC
• Manufacturer: Analog Devices

Specifications of AD5363

• Resolution (bits): 14bit
• Dac Settling Time: 20µs
• Single-supply: No
• Dac Type: Voltage Out
• Dac Input Format: Ser,SPI

AD5362/AD5363
OUTPUT AMPLIFIER
Because the output amplifiers can swing to 1.4 V below the
positive supply and 1.4 V above the negative supply, this limits
how much the output can be offset for a given reference voltage.
For example, it is not possible to have a unipolar output range
of 20 V, because the maximum supply voltage is ±16.5 V.
Figure 23 shows details of a DAC output amplifier and its connec-
tions to the offset DAC. On power-up, S1 is open, disconnecting
the amplifier from the output. S3 is closed, so the output is pulled
to SIGGNDx (R1 and R2 are greater than R6). S2 is also closed to
prevent the output amplifier from being open-loop. If CLR is low at
power-up, the output remains in this condition until CLR is taken
high. The DAC registers can be programmed, and the outputs
assume the programmed values when CLR is taken high. Even if
CLR is high at power-up, the output remains in this condition
until V
finished. The outputs then go to their power-on default value.
TRANSFER FUNCTION
The output voltage of a DAC in the AD5362/AD5363 is depen-
dent on the value in the input register, the value of the M and C
registers, and the value in the offset DAC.
AD5362 Transfer Function
The input code is the value in the X1A or X1B register that is
applied to the DAC (X1A, X1B default code = 32,768).
where:
M = code in gain register − default code = 2
C = code in offset register − default code = 2
The DAC output voltage is calculated as follows:
where:
DAC_CODE should be within the range of 0 to 65,535.
For 12 V span, VREF = 3.0 V.
For 20 V span, VREF = 5.0 V.
OFFSET_CODE is the code loaded to the offset DAC. It is
multiplied by 4 in the transfer function because this DAC is a
14-bit device. On power-up, the default code loaded to the
SIGGNDx
DAC_CODE = INPUT_CODE × (M + 1)/2
VOUT = 4 × VREF × (DAC_CODE − (OFFSET_CODE ×
4))/2
DD
OFFSET
DAC
> 6 V and V
16
60kΩ
+ V
R4
Figure 23. Output Amplifier and Offset DAC
SIGGND
CHANNEL
20kΩ
R3
DAC
SS
< −4 V and the initialization sequence has
60kΩ
20kΩ
R2
20kΩ
R5
R1
CLR
S2
CLR
S1
16
15
SIGGNDx
– 1.
.
16
R6
10kΩ
S3
+ C − 2
CLR
OUTPUT
15
Rev. A | Page 18 of 28
offset DAC is 8192 (0x2000). With a 5 V reference, this gives
a span of −10 V to +10 V.
AD5363 Transfer Function
The input code is the value in the X1A or X1B register that is
applied to the DAC (X1A, X1B default code = 8192).
where:
M = code in gain register − default code = 2
C = code in offset register − default code = 2
The DAC output voltage is calculated as follows:
where:
DAC_CODE should be within the range of 0 to 16,383.
For 12 V span, VREF = 3.0 V.
For 20 V span, VREF = 5.0 V.
OFFSET_CODE is the code loaded to the offset DAC. On power-
up, the default code loaded to the offset DAC is 8192 (0x2000).
With a 5 V reference, this gives a span of −10 V to +10 V.
REFERENCE SELECTION
The AD5362/AD5363 have two reference input pins. The
voltage applied to the reference pins determines the output
voltage span on VOUT0 to VOUT7. VREF0 determines the
voltage span for VOUT0 to VOUT3 (Group 0), and VREF1
determines the voltage span for VOUT4 to VOUT7 (Group 1).
The reference voltage applied to each VREF pin can be differ-
ent, if required, allowing each group of four channels to have a
different voltage span. The output voltage range and span can
be adjusted further by programming the offset and gain
registers for each channel as well as programming the offset
DAC. If the offset and gain features are not used (that is, the M
and C registers are left at their default values), the required
reference levels can be calculated as follows:
If the offset and gain features of the AD5362/AD5363 are used,
the required output range is slightly different. The selected
output range should take into account the system offset and
gain errors that need to be trimmed out. Therefore, the selected
output range should be larger than the actual, required range.
The required reference levels can be calculated as follows:
1.
2.
3.
4.
5.
DAC_CODE = INPUT_CODE × (M + 1)/2
VOUT = 4 × VREF × (DAC_CODE − OFFSET_CODE)/
2
VREF = (VOUT
Identify the nominal output range on VOUT.
Identify the maximum offset span and the maximum gain
required on the full output signal range.
Calculate the new maximum output range on VOUT,
including the expected maximum offset and gain errors.
Choose the new required VOUT
ing the VOUT limits centered on the nominal values. Note
that V
Calculate the value of VREF as follows:
VREF = (VOUT
14
+ V
DD
SIGGND
and V
SS
MAX
MAX
must provide sufficient headroom.
− VOUT
− VOUT
MIN
MIN
)/4
)/4
MAX
and VOUT
14
13
– 1.
.
14
+ C − 2
MIN
, keep-
13