Datasheet

Data Sheet AD5412/AD5422
Rev. I | Page 29 of 44
Readback Operation
Readback mode is invoked by setting the address byte and
read address when writing to the input register (see Table 9 and
Table 11). The next write to the AD5412/AD5422 should be a
NOP command, which clocks out the data from the previously
addressed register as shown in Figure 3.
By default the SDO pin is disabled after having addressed the
AD5412/AD5422 for a read operation; a rising edge on LATCH
enables the SDO pin in anticipation of data being clocked out.
After the data has been clocked out on SDO, a rising edge on
LATCH disables (tristate) the SDO pin. To read back the data
register, for example, implement the following sequence:
1. Write 0x020001 to the input register. This configures the
part for read mode with the data register selected.
2. Follow this with a second write: a NOP condition, which is
0x000000. During this write, the data from the register is
clocked out on the SDO line.
Table 9. Read Address Decoding
Read Address Function
00 Read status register
01
Read data register
10 Read control register
POWER-ON STATE
During power-on of the AD5412/AD5422, the power-on-reset
circuit ensures that all registers are loaded with zero-code. As
such, both outputs are disabled; that is, the V
OUT
and I
OUT
pins
are in tristate. The +V
SENSE
pin is internally connected to ground
through a 40 kΩ resistor. Therefore, if the V
OUT
and +V
SENSE
pins
are connected together, V
OUT
is effectively clamped to ground
through a 40 kΩ resistor. Also upon power-on, internal
calibration registers are read, and the data is applied to internal
calibration circuitry. For a reliable read operation, there must be
sufficient voltage on the AV
DD
supply when the read event is
triggered by the DV
CC
power supply powering up. Powering up
the DV
CC
supply after the AV
DD
supply ensures this. If DV
CC
and
AV
DD
are powered up simultaneously or the internal DV
CC
is
enabled, the supplies should be powered up at a rate greater
than, typically, 500 V/sec or 24 V/50 ms. If this cannot be
achieved, issue a reset command to the AD5412/AD5422 after
power-on; this performs a power-on-reset event, reading the
calibration registers and ensures specified operation of the
AD5412/AD5422. To ensure correct calibration and to allow the
internal reference to settle to its correct trim value, 40 µs should
be allowed after a successful power on reset.
Voltage Output
For a unipolar voltage output range, the output voltage can be
expressed as






×=
N
REFIN
OUT
D
GainVV
2
For a bipolar voltage output range, the output voltage can be
expressed as
22
REFIN
N
REFIN
OUT
VGain
D
Gain
VV
×
−






×
=
where:
D is the decimal equivalent of the code loaded to the DAC.
N is the bit resolution of the DAC.
V
REFIN
is the reference voltage applied at the REFIN pin.
Gain is an internal gain whose value depends on the output
range selected by the user as shown in Table 10.
Table 10. Internal Gain Value
Output Range Gain Value
+5 V 1
+10 V 2
±5 V 2
±10 V 4
Current Output
For the 0 mA to 20 mA, 0 mA to 24 mA, and 4 mA to 20 mA
current output ranges, the output current is respectively
expressed as
DI
N
OUT
×






=
2
mA20
DI
N
OUT
×






=
2
mA24
mA4
2
mA16
+×






=
DI
N
OUT
where:
D is the decimal equivalent of the code loaded to the DAC.
N is the bit resolution of the DAC.
Table 11. Input Shift Register Contents for a Read Operation
MSB LSB
D23 D22 D21 D20 D19 D18 D17 D16 D15 to D2 D1 D0
0
0
0
0
0
0
1
0
X
1
Read address
1
X = don’t care.