AD5412ACPZ AD [Analog Devices], AD5412ACPZ Datasheet - Page 24

• Manufacturer Part Number: AD5412ACPZ
• Description: Single Channel, 12/16-Bit, Serial Input, Current Source & Voltage Output DAC
• Manufacturer: AD [Analog Devices]

AD5412/AD5422
THEORY OF OPERATION
The AD5412/AD5422 is a precision digital to current loop and
voltage output converter designed to meet the requirements of
industrial process control applications. It provides a high
precision, fully integrated, low cost single-chip solution for
generating current loop and unipolar/bipolar voltage outputs.
The current ranges available are; 0 to 20mA, 0 to 24mA and 4 to
20mA, the voltage ranges available are; 0 to 5V, ±5V, 0 to 10V
and ±10V, a 10% over-range is available on all voltage output
ranges. The current and voltage outputs are available on
separate pins and only one is active at any one time. The desired
output configuration is user selectable via the CONTROL
register.
ARCHITECTURE
The DAC core architecture of the AD5412/AD5422 consists of
two matched DAC sections. A simplified circuit diagram is
shown in Figure 57. The 4 MSBs of the 12/16-bit data word are
decoded to drive 15 switches, E1 to E15. Each of these switches
connects 1 of 15 matched resistors to either ground or the
reference buffer output. The remaining 8/12 bits of the data-
word drive switches S0 to S7/S11 of a 8/12-bit voltage mode R-
2R ladder network.
V
The voltage output from the DAC core is either converted to a
current (see diagram, Figure 58) which is then mirrored to the
supply rail so that the application simply sees a current source
output with respect to ground or it is buffered and scaled to
output a software selectable unipolar or bipolar voltage range
(See diagram, Figure 59). The current and voltage are output on
separate pins and cannot be output simultaneously.
12/16-BIT
REF
DAC
2R
Figure 58. Voltage to Current conversion circuitry
8/12-BIT R-2R LADDER
2R
S0
Figure 57. DAC Ladder Structure
A1
2R
S1
T1
R1
R2
S7/S11
2R
FOUR MSBs DECODED INTO
A2
15 EQUAL SEGMENTS
2R
E1
T2
AV
DD
2R
E2
R3
I
OUT
2R
E15
Rev. PrF | Page 24 of 38
V
OUT
Voltage Output Amplifier
The voltage output amplifier is capable of generating both
unipolar and bipolar output voltages. It is capable of driving a
load of 1 kΩ in parallel with 1 µF (with addition of external
compensation capacitor) to AGND. The source and sink
capabilities of the output amplifier can be seen in Figure 22. The
slew rate is 1 V/µs with a full-scale settling time of 10 µs, (10V
step). Figure 59 shows the voltage output driving a load, R
top of a common mode voltage, (V
In output module applications where a cable could possibly
become disconnected from +V
loop being broken and possibly resulting in large destructive
voltages on V
included as shown to ensure the amplifier loop is kept closed. If
remote sensing of the load is not required, +V
connected to V
When changing ranges on the voltage output a glitch may
occur, for this reason it is recommended that the output is
disabled by setting the OUTEN bit of the Control register to
logic low before changing the output voltage range, this will
prevent a glitch from occuring.
Driving Large Capacitive Loads
The voltage output amplifier is capable of driving capacitive
loads of up to 1uF with the addition of a non-polarised 4nF
compensation capacitor between the C
Without the compensation capacitor, up to 20nF capacitive
loads can be driven.
Reference Buffers
The AD5412/AD5422 can operate with either an external or
internal reference. The reference input has an input range of 4 V
to 5 V, 5 V for specified performance. This input voltage is then
buffered before it is applied to the DAC.
SERIAL INTERFACE
The AD5412/AD5422 is controlled over a versatile 3-wire serial
interface that operates at clock rates up to 30 MHz. It is
compatible with SPI®, QSPI™, MICROWIRE™, and DSP
standards.
12/16-BIT
REFIN
DAC
OUT
OUT
, a resistor, R
and -V
RANGE
SCALING
Preliminary Technical Data
Figure 59. Voltage Output
SENSE
1
, of value 2kΩ to 5kΩ should be
should be connected to GND.
SENSE
CM
resulting in the amplifier
) of -1V to +3V.
COMP
and V
+V
-V
V
SENSE
SENSE
OUT
SENSE
OUT
should be
pins.
V
CM
R
R
-1V to +3V
L
1
L
on