AD7398BR Analog Devices Inc, AD7398BR Datasheet - Page 14

• Manufacturer Part Number: AD7398BR
• Description: D/A Converter (D-A) IC
• Manufacturer: Analog Devices Inc

Specifications of AD7398BR

• Resolution (bits): 12bit
• Digital Ic Case Style: SOIC
• No. Of Pins: 16
• Operating Temperature Range: -40°C To +125°C
• Update Rate: 0.167MSPS
• Mounting Type: Surface Mount
• Peak Reflow Compatible (260 C): No
• Rohs Status: RoHS non-compliant
• Settling Time: 6µs
• Number Of Bits: 12
• Data Interface: Serial
• Number Of Converters: 4
• Voltage Supply Source: Dual ±
• Power Dissipation (max): 16mW
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 16-SOIC (0.300", 7.5mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

AD7398/AD7399
THEORY OF OPERATION
The AD7398/AD7399 contain four 12-bit and 10-bit,
respectively, voltage output, digital-to-analog converters. Each
DAC has its own independent multiplying reference input. Both
the AD7398 and AD7399 use a 3-wire, SPI-compatible serial
data interface, with an asynchronous RS pin for zero-scale reset.
In addition, an LDAC strobe enables four-channel simultaneous
updates for hardware-synchronized output voltage changes.
DAC OPERATION
The internal R-2R ladder of the AD7398/AD7399 operates in
the voltage switching mode, maintaining an output voltage that
is the same polarity as the input reference voltage. A proprietary
scaling technique is used to attenuate the input reference voltage in
the DAC. The output buffer amplifies the internal DAC output to
achieve a V
REF
V
REF
to V
Figure 26. Simplified DAC Channel
OUT
gain of unity.
AD7398/AD7399
CLK
SDI
R
CS
GND
R
REGISTER
SERIAL
V
V
DD
SS
ON RESET
AD7398/AD7399
V
12/10
POWER
4
OUT
A
ADDRESS
DECODE
Figure 25. Simplified Block Diagram
RS
Rev. C | Page 14 of 24
V
DD
REGISTER
REGISTER
REGISTER
REGISTER
INPUT
INPUT
INPUT
INPUT
The nominal DAC output voltage is determined by the
externally applied V
where:
D is the 12-bit or 10-bit decimal equivalent of the data word.
V
In order to maintain good analog performance, the user should
bypass power supplies with 0.01 μF ceramic capacitors (mount
them close to the supply pins) and 1 μF to 10 μF tantalum
capacitors in parallel. In addition, clean power supplies with low
ripple voltage capability should be used. Switching power supplies
can be used for this application, but beware of its higher ripple
voltage and PSS frequency-dependent characteristics. It is also
best to supply power to the AD7398/AD7399 from the system’s
analog supply voltages. Do not use the digital 5 V supply.
The reference input resistance is code dependent, exhibiting
worst case 35 kΩ for AD7398 when the DAC is loaded with
alternating codes 010101010101. Similarly, the reference input
resistance is 40 kΩ for AD7399 when the DAC is loaded with
0101010101.
REF
GND
V
is the externally applied reference voltage.
V
V
REF
OUT
OUT
REGISTER
REGISTER
REGISTER
REGISTER
A
LDAC
= V
= V
V
DAC
DAC
DAC
DAC
REF
B V
REF
REF
× D/4096 (For AD7398)
× D/1024 (For AD7399)
REF
C V
DAC A
DAC B
DAC C
DAC D
REF
V
SS
REF
and the digital data (D) as
D
V
V
V
V
OUT
OUT
OUT
OUT
A
B
C
D
(1)
(2)