AD5360 Analog Devices, AD5360 Datasheet - Page 17

• Manufacturer Part Number: AD5360
• Description: 16-Channel, 16-Bit, Serial Input, Voltage-Output DAC
• Manufacturer: Analog Devices

Specifications of AD5360

• Resolution (bits): 16bit
• 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

SIGGND
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
connections 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 SIGGND. 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
initialization sequence has finished. The outputs then go to
their power-on default values.
TRANSFER FUNCTION
The output voltage of a DAC in the AD5360/AD5361 is dependent
on the value in the input register, the value of the M and C
registers, and the value in the offset DAC. The transfer functions
for the AD5360/AD5361 are shown in the following sections.
AD5360 Transfer Function
The input code is the value in the X1A or X1B register that is
applied to DAC (X1A, X1B default code = 32,768)
DAC output voltage
where:
DAC_CODE should be within the range of 0 to 65,535.
V
V
M = code in gain register − default code = 2
C = code in offset register − default code = 2
REF
REF
DAC_CODE = INPUT_CODE × (M + 1)/2
V
= 3.0 V, for a 12 V span.
= 5.0 V, for a 20 V span.
OFFSET
OUT
DAC
= 4 × V
60kΩ
R4
2
16
Figure 23. Output Amplifier and Offset DAC
+ V
CHANNEL
20kΩ
REF
R3
SIGGND
DAC
× (DAC_CODE − (OFFSET_CODE × 4))/
60kΩ
DD
20kΩ
R2
20kΩ
R5
R1
> 6 V and V
CLR
S2
CLR
S1
SS
< −4 V and the
16
15
SIGGND
.
– 1.
R6
10kΩ
S3
16
+ C − 2
CLR
OUTPUT
15
Rev. A | Page 17 of 28
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
offset DAC is 8192 (0x2000). With a 10 V reference, this gives
a span of −10 V to +10 V.
AD5361 Transfer Function
The input code is the value in the X1A or X1B register that is
applied to DAC (X1A, X1B default code = 8192)
DAC output voltage
where:
DAC_CODE should be within the range of 0 to 16,383.
V
V
M = code in gain register − default code = 2
C = code in offset register − default code = 2
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 AD5360/AD5361 have two reference input pins. The
voltage applied to the reference pins determines the output
voltage span on VOUT0 to VOUT15. VREF0 determines the
voltage span for VOUT0 to VOUT7 (Group 0), and VREF1
determines the voltage span for VOUT8 to VOUT15 (Group 1).
The reference voltage applied to each VREF pin can be different,
if required, allowing each group of eight channels to have a
different voltage span. The output voltage range and span can
be adjusted by programming the offset register and gain register
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 AD5360/AD5361 are used,
the required output range is slightly different. The chosen
output range should take into account the system offset and
gain errors that need to be trimmed out. Therefore, the chosen
output range should be larger than the actual, required range.
The required reference levels can be calculated as follows:
1.
2.
3.
REF
REF
= 3.0 V, for a 12 V span.
= 5.0 V, for a 20 V span.
DAC_CODE = INPUT_CODE × (M + 1)/2
V
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.
OUT
= 4 × V
V
SIGGND
REF
× (DAC_CODE − OFFSET_CODE)/2
MAX
− VOUT
MIN
)/4
AD5360/AD5361
14
13
.
− 1.
14
+ C − 2
13
14
+