AD7937AR Analog Devices Inc, AD7937AR Datasheet - Page 7

• Manufacturer Part Number: AD7937AR
• Description: IC,D/A CONVERTER,DUAL,12-BIT,CMOS,SOP,24PIN
• Manufacturer: Analog Devices Inc

Specifications of AD7937AR

• Rohs Status: RoHS non-compliant
• Settling Time: 1µs
• Number Of Bits: 12
• Data Interface: Parallel
• Number Of Converters: 2
• Voltage Supply Source: Single Supply
• Power Dissipation (max): 24mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (7.5mm Width)

APPLICATION HINTS
Output Offset: CMOS D/A converters in circuits such as Fig-
ures 4 and 5 exhibit a code-dependent output resistance which
in turn can cause a code-dependent error voltage at the output
of the amplifier. The maximum amplitude of this error, which
adds to the D/A converter nonlinearity, depends on V
V
operation, it is recommended that V
(25
Suitable op amps are the AD711C and its dual version, the
AD712C. These op amps have a wide bandwidth and high slew
rate and are recommended for wide bandwidth ac applications.
AD711/AD712 settling time to 0.01% is typically 3 µs.
Temperature Coefficients: The gain temperature coefficient
of the AD7937 has a maximum value of 5 ppm/°C and typical
value of 1 ppm/°C. This corresponds to worst case gain shifts of
2 LSBs and 0.4 LSBs respectively over a 100°C temperature range.
When trim resistors R1 (R3) and R2 (R4) are used to adjust full
scale range as in Figure 4, the temperature coefficient of R1 (R3)
and R2 (R4) should also be taken into account.
High Frequency Considerations: AD7937 output capacitance
works in conjunction with the amplifier feedback resistance to
add a pole to the open-loop response. This can cause ringing or
oscillation. Stability can be restored by adding a phase compen-
sation capacitor in parallel with the feedback resistor. This is
shown as C1 and C2 in Figures 4 and 5.
Feedthrough: The dynamic performance of the AD7937 depends
upon the gain and phase stability of the output amplifier, together
with the optimum choice of PC board layout and decoupling
components.
OS
is the amplifier input offset voltage. To maintain specified
10
–6
) (V
REF
) over the temperature range of operation.
OS
be no greater than
OS
, where
MICROPROCESSOR INTERFACING
The byte loading structure of the AD7937 makes it very easy to
interface the device to any 8-bit microprocessor system. Figure
8 shows an example 8-bit interface between the AD7937 and a
generic 8-bit microcontroller/DSP processor. Pins D7 to D0 of
the processor are connected to pins D7 to D0 of the AD7937.
When writing to the DACs, the lower 8 bits must be written
first, followed by the upper four bits. The upper four bits should
be output on data lines D0 to D3.
DSP PROCESSOR
CONTROLLER/
*
ADDITIONAL PINS OMITTED FOR CLARITY
OF ADDRESS
UPPER BITS
DATA
BUS
BUS
R/W
D7
D0
A0
A1
*
ADDRESS
DECODE
SYSTEM
RESET
FROM
CLR
D7
D0
CS
UPD
A0
A1
WR
AD7937
AD7937*