AD7397ARU-REEL7 Analog Devices Inc, AD7397ARU-REEL7 Datasheet - Page 11

• Manufacturer Part Number: AD7397ARU-REEL7
• Description: IC DAC 10BIT PARALLEL 3V 24TSSOP
• Manufacturer: Analog Devices Inc

Specifications of AD7397ARU-REEL7

• Rohs Status: RoHS non-compliant
• Settling Time: 60µs
• Number Of Bits: 10
• Data Interface: Parallel
• Number Of Converters: 2
• Voltage Supply Source: Single Supply
• Power Dissipation (max): 1mW
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 24-TSSOP

allowing any new Input Register data updates to directly control
the DAC output voltages for single-buffered applications. For
doubled-buffered applications where both DAC outputs, V
and V
the two inputs, LDA and LDB, can be tied together and pulsed
active low in a synchronous manner.
RESET (RS) PIN
Forcing the asynchronous RS pin low will set the Input and
DAC registers to all zeros and the DAC output voltage will be
zero volts. The reset function is useful for setting the DAC
outputs to zero at power-up or after a power supply interrup-
tion. Test systems and motor controllers are two of many appli-
cations that benefit from powering up to a known state. The
external reset pulse can be generated by the microprocessor’s
power-on RESET signal, from the microprocessor, or by an
external resistor and capacitor. RESET has a Schmitt trigger
input which results in a clean reset function when using external
resistor/capacitor generated pulses. See Table I, Control-Logic
Truth.
POWER SHUTDOWN (SHDN)
Maximum power savings can be achieved by using the power
shutdown control function. This hardware-activated feature is
controlled by the active low input SHDN pin. This pin has a
Schmitt trigger input which helps to desensitize it to slowly
changing inputs. By placing a logic low on this pin the internal
consumption of the AD7397 or AD7397 is reduced to nanoamp
levels, guaranteed to 1.5 A maximum over the operating tem-
perature range. If power is present at all times on the V
while in the shutdown mode, the internal DAC register will
retain the last programmed data value. This data will be used
when the part is returned to the normal active state by placing
the DAC back to its programmed voltage setting. Shutdown
recovery time measures 80 s. In the shutdown state the DAC
output amplifier exhibits an open-circuit high-resistance state.
Any load connected will stabilize at its termination voltage. If
the power shutdown feature is not needed then the user should
tie the SHDN pin to the V
function.
UNIPOLAR OUTPUT OPERATION
This is the basic mode of operation for the AD7396. As shown
in Figure 29, the AD7396 has been designed to drive loads as
low as 5 k in parallel with 100 pF. The code table for this
operation is shown in Table II.
REV. 0
0.01 F
OUTB
EXT
REF
, need to be changed simultaneously to a new value,
Figure 29. Unipolar Output Operation
C
16/14
R
V
DIGITAL
REF
+2.7V TO +5.5V
DGND
AD7396
DD
V
DD
DAC A
DAC B
voltage thereby disabling this
AGND
DIGITAL INTERFACE
CIRCUITRY OMITTED
FOR CLARITY.
75k
75k
0.1 F
100pF
100pF
V
V
10 F
OUTA
OUTB
DD
pin
OUTA
–11–
Hexadecimal
Number
In DAC Register
FFF
801
800
7FF
000
The circuit can be configured with an external reference plus
power supply, or powered from a single dedicated regulator or
reference, depending on the application performance requirements.
BIPOLAR OUTPUT OPERATION
Although the AD7397 has been designed for single supply op-
eration, the output can easily be configured for bipolar opera-
tion. A typical circuit is shown in Figure 30. This circuit uses a
clean regulated +5 V supply for power, which also provides
the circuit’s reference voltage. Since the AD7397 output span
swings from ground to very near +5 V, it is necessary to choose
an external amplifier with a common-mode input voltage range
that extends to its positive supply rail. The micropower con-
sumption OP196 has been designed just for this purpose and
results in only 50 A of maximum current consumption. Con-
nection of the equal-value 470 k resistors results in a differen-
tial amplifier mode of operation with a voltage gain of two,
which produces a circuit output span of ten volts, that is,
–5 V to +5 V. As the AD7397 DAC is programmed from zero-
code 000
put voltage V
output voltage V
Equation 3.
where D is the decimal code loaded in the AD7397 DAC regis-
ter. Note that the LSB step size is 10/1024 = 10 mV. This
circuit has been optimized for micropower consumption includ-
ing the 470 k gain setting resistors, which should have low
temperature coefficients to maintain accuracy and matching
(preferably the same resistor material, such as metal film). If
better stability is required, the power supply could be substi-
tuted with a precision reference voltage such as the low dropout
REF195, which can easily supply the circuit’s 262 A of current
and still provide additional power for the load connected to V
The micropower REF195 is guaranteed to source 10 mA output
drive current, but consumes only 50 A internally. If higher
resolution is required, the AD7396 can be used with the addi-
tion of two more bits of data inserted into the software coding,
which would result in a 2.5 mV LSB step size. Table III shows
examples of nominal output voltages, V
lar operation circuit application.
V
OUT
H
= [(D/512)–1]
to midscale 200
O
is set at –5 V, 0 V and +5 V (–1 LSB). The
Table II. Unipolar Code Table
O
is coded in offset binary according to
Decimal
Number
2047
In DAC Register
4095
2049
2048
0
H
5
to full-scale 3FF
AD7396/AD7397
O
, provided by the bipo-
H
, the circuit out-
Output
Voltage (V)
(V
2.4994
1.2506
1.2500
1.2494
0
REF
= 2.5 V)
(4)
O
.