Data Sheet ADN8810
Rev. B | Page 11 of 16
FUNCTIONAL DESCRIPTION
The ADN8810 is a single 12-bit current output digital-to-analog
converter with a 3-wire SPI interface. Up to eight devices can be
independently programmed from the same SPI bus.
The full-scale output current is set with two external resistors.
The maximum output current can reach 300 mA. Figure 17
shows the functional block diagram of the ADN8810.
DVDD
SB
CS
VREF
BIAS
GEN
SCLK
SDI
PVDD
PVDD
IOUT
IOUT
AVSS
AVDD
DGND ADDR2 ADDR1 ADDR0 DVSSRESET
15k
1.5k
FAULT
FAULT
DETECTION
12-BIT
DATA LATCH
ADDRESS
DECODER
12-BIT
DAC
CONTROL
LOGIC
R
SN
1.5k
FB ENCMP
03195-0-017
Figure 17. Functional Block Diagram
SETTING FULL-SCALE OUTPUT CURRENT
Two external resistors set the full-scale output current from the
ADN8810. These resistors are equal in value and are labeled R
SN
in Figure 1. Use 1% or better tolerance resistors to achieve the
most accurate output current and the highest output impedance.
Equation 1 shows the approximate full-scale output current.
The exact output current is determined by the data register code
as shown in Equation 2. The variable code is an integer from 0
to 4095, representing the full 12-bit range of the ADN8810.
SN
FS
R
I
10
096.4
(1)
1.0
15
1
1000 k
R
R
Code
I
SN
SN
OUT
(2)
REFERENCE VOLTAGE SOURCE
The ADN8810 is designed to operate with a 4.096 V reference
voltage connected to VREF. The output current is directly
proportional to this reference voltage. A low noise precision
reference should be used to achieve the best performance. The
ADR292, ADR392, or REF198 is recommended.
POWER SUPPLIES
There are three principal supply current paths through the
ADN8810:
AVDD provides power to the analog front end of the
ADN8810 including the DAC. Use this supply line to
power the external voltage reference. For best performance,
AVDD should be low noise.
DVDD provides power for the digital circuitry. This includes
the serial interface logic, the
SB
and
RESET
logic inputs,
and the FAULT output. Tie DVDD to the same supply line
used for other digital circuitry. It is not necessary for
DVDD to be low noise.
PVDD is the power pin for the output amplifier. It can
operate from as low as 3.0 V to minimize power dissipation
in the ADN8810. For best performance, PVDD should be
low noise.
Current is returned through three pins:
AVSS is the return path for both AVDD and PVDD. This
pin is connected to the substrate of the die as well as the
slug on the bottom of the LFCSP. For single-supply
operation, this pin should be connected to a low noise
ground plane.
DVSS returns current from the digital circuitry powered by
DVDD. Connect DVSS to the same ground line or plane
used for other digital devices in the application.
DGND is the ground reference for the digital circuitry. In a
single-supply application, connect DGND to DVSS.
For single-supply operation, set AVDD to 5 V, set PVDD from
3.0 V to 5 V, and connect AVSS, AGND, and DGND to ground.
SERIAL DATA INTERFACE
The ADN8810 uses a serial peripheral interface (SPI) with three
input signals: SDI, CLK, and
CS
. Figure 2 shows the timing
diagram for these signals.
Data applied to the SDI pin is clocked into the input shift
register on the rising edge of CLK. After all 16 bits of the data-
word have been clocked into the input shift register, a logic high
on
CS
loads the shift register byte into the ADN8810. If more
than 16 bits of data are clocked into the shift register before
CS
goes high, bits are pushed out of the register in first-in first-out
(FIFO) fashion.
