AD5443 Analog Devices, AD5443 Datasheet - Page 15

• Manufacturer Part Number: AD5443
• Description: High Bandwidth CMOS 12-Bit Serial Interface Multiplying D/A Converter
• Manufacturer: Analog Devices

Specifications of AD5443

• Resolution (bits): 12bit
• Dac Update Rate: 2.47MSPS
• Dac Settling Time: 90ns
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: Ser,SPI

THEORY OF OPERATION
The AD5426, AD5432, and AD5443 are 8-, 10-, and 12-bit
current output DACs consisting of a standard inverting R-2R
ladder configuration. A simplified diagram for the 8-bit
AD5426 is shown in Figure 40. The matching feedback resistor,
R
(minimum 8 kΩ and maximum 12 kΩ). If I
kept at the same potential, a constant current flows in each
ladder leg, regardless of digital input code. Therefore, the input
resistance presented at V
value R. The DAC output (I
various resistances and capacitances. External amplifier choice
should take into account the variation in impedance generated
by the DAC on the amplifiers inverting input node.
Access is provided to the V
the DAC, making the device extremely versatile and allowing it
to be configured in several different operating modes. For
example, it can be configured to provide a unipolar output,
4-quadrant multiplication in bipolar or single-supply modes of
operation. Note that a matching switch is used in series with the
internal R
power must be applied to V
CIRCUIT OPERATION
Unipolar Mode
Using a single op amp, these devices can easily be configured to
provide 2-quadrant multiplying operation or a unipolar output
voltage swing, as shown in Figure 41.
When an output amplifier is connected in unipolar mode, the
output voltage is given by
where D is the fractional representation of the digital word
loaded to the DAC, and n is the number of bits.
FB
, has a value of R. The value of R is typically 10 kΩ
D = 0 to 255 (8-bit AD5426)
V
V
REF
OUT
= 0 to 1023 (10-bit AD5432)
= 0 to 4095 (12-bit AD5443)
FB
=
feedback resistor. If users attempt to measure R
−
S1
2R
V
R
DAC DATA LATCHES
REF
AND DRIVERS
×
S2
Figure 40. Simplified Ladder
2R
2
D
R
n
REF
S3
2R
REF
OUT
DD
is always constant and nominally of
, R
to achieve continuity.
) is code-dependent, producing
R
FB
, I
S8
2R
OUT
1, and I
2R
OUT
R
OUT
1 and I
2 terminals of
R
I
I
OUT
OUT
FB
OUT
A
1
2
2 are
FB
Rev. C | Page 15 of 28
,
Note that the output voltage polarity is opposite to the V
polarity for dc reference voltages.
These DACs are designed to operate with either negative or
positive reference voltages. The V
the internal digital logic to drive the DAC switches’ on and off
states.
These DACs are also designed to accommodate ac reference
input signals in the range of −10 V to +10 V.
With a fixed 10 V reference, the circuit shown in Figure 41 gives
a unipolar 0 V to −10 V output voltage swing. When V
signal, the circuit performs 2-quadrant multiplication. Table 5
shows the relationship between digital code and expected
output voltage for unipolar operation (AD5426, 8-bit device).
Table 5. Unipolar Code Table
Digital Input
1111 1111
1000 0000
0000 0001
0000 0000
V
REF
NOTES
1. R1 AND R2 USED ONLY IF GAIN ADJUSTMENT IS REQUIRED.
2. C1 PHASE COMPENSATION (1pF TO 2pF) MAY BE REQUIRED
IF A1 IS A HIGH SPEED AMPLIFIER.
R1
MICROCONTROLLER
SYNC
V
REF
SCLK SDIN GND
AD5426/
AD5432/
AD5443
Figure 41. Unipolar Operation
V
V
Analog Output (V)
−V
−V
−V
−V
DD
DD
REF
REF
REF
REF
AD5426/AD5432/AD5443
(255/256)
(128/256) = −V
(1/256)
(0/256) = 0
R
FB
I
I
OUT
OUT
DD
R2
1
2
power pin is used by only
C1
AGND
REF
/2
A1
A1
V
TO –V
OUT
IN
= 0
REF
REF
is an ac