DAC8562 Datasheet, PDF (5/16 Pages) Analog Devices – +5 Volt, Parallel Input Complete 12-Bit DAC

DAC8562
OPERATION
The DAC8562 is a complete ready to use 12-bit digital-to-
analog converter. Only one +5 V power supply is necessary for
operation. It contains a voltage-switched, 12-bit, laser-trimmed
digital-to-analog converter, a curvature-corrected bandgap refer-
ence, a rail-to-rail output op amp, and a DAC register. The par-
allel data interface consists of 12 data bits, DB0–DB11, and a
active low CE strobe. In addition, an asynchronous CLR pin
will set all DAC register bits to zero causing the V_OUT to be-
come zero volts. This function is useful for power on reset or
system failure recovery to a known state.
current is provided by a P channel pull-up device that can sup-
ply GND terminated loads, especially important at the –5%
supply tolerance value of 4.75 volts.
V_DD
P-CH
N-CH
V_OUT
D/A CONVERTER SECTION
The internal DAC is a 12-bit voltage-mode device with an out-
put that swings from AGND potential to the 2.5 volt internal
bandgap voltage. It uses a laser trimmed R-2R ladder which is
switched by N channel MOSFETs. The output voltage of the
DAC has a constant resistance independent of digital input
code. The DAC output (not available to the user) is internally
connected to the rail-to-rail output op amp.
AMPLIFIER SECTION
The internal DAC’s output is buffered by a low power con-
sumption precision amplifier. This low power amplifier contains
a differential PNP pair input stage which provides low offset
voltage and low noise, as well as the ability to amplify the zero-
scale DAC output voltages. The rail-to-rail amplifier is config-
ured in a gain of 1.6384 (= 4.095 V/2.5 V) in order to set the
4.095 volt full-scale output (1 mV/LSB). See Figure 3 for an
equivalent circuit schematic of the analog section.
REFOUT
2.5V
BANDGAP
REFERENCE
VOLTAGE SWITCHED 12-BIT
R-2R D/A CONVERTER
2R
RAIL-TO-RAIL
OUTPUT
AMPLIFIER
BUFFER
R
V_OUT
R2
2R
R1
R
2R
AV = 4.096/2.5
= 1.636V/V
2R
SPDT
N ch FET
SWITCHES
2R
Figure 3. Equivalent DAC8562 Schematic of
Analog Portion
The op amp has a 16 µs typical settling time to 0.01%. There
are slight differences in settling time for negative slewing signals
versus positive. See the oscilloscope photos in the Typical Per-
formances section of this data sheet.
AGND
Figure 4. Equivalent Analog Output Circuit
Figures 5 and 6 in the typical performance characteristics sec-
tion provide information on output swing performance near
ground and full scale as a function of load. In addition to resis-
tive load driving capability, the amplifier has also been carefully
designed and characterized for up to 500 pF capacitive load
driving capability.
REFERENCE SECTION
The internal 2.5 V curvature-corrected bandgap voltage refer-
ence is laser trimmed for both initial accuracy and low tempera-
ture coefficient. The voltage generated by the reference is
available at the REFOUT pin. Since REFOUT is not intended
to drive external loads, it must be buffered–refer to the applica-
tions section for more information. The equivalent emitter fol-
lower output circuit of the REFOUT pin is shown in Figure 3.
Bypassing the REFOUT pin is not required for proper opera-
tion. Figure 7 shows broadband noise performance.
POWER SUPPLY
The very low power consumption of the DAC8562 is a direct
result of a circuit design optimizing use of the CBCMOS pro-
cess. By using the low power characteristics of the CMOS for
the logic, and the low noise, tight matching of the complemen-
tary bipolar transistors, good analog accuracy is achieved.
For power-consumption sensitive applications it is important to
note that the internal power consumption of the DAC8562 is
strongly dependent on the actual logic-input voltage-levels
present on the DB0–DB11, CE and CLR pins. Since these in-
puts are standard CMOS logic structures, they contribute static
power dissipation dependent on the actual driving logic V_OH and
V_OL voltage levels. The graph in Figure 9 shows the effect on to-
tal DAC8562 supply current as a function of the actual value of
input logic voltage. Consequently for optimum dissipation use
of CMOS logic versus TTL provides minimal dissipation in the
static state. A V_INL = 0 V on the DB0–DB11 pins provides the
lowest standby dissipation of 600 µA with a +5 V power supply.
OUTPUT SECTION
The rail-to-rail output stage of this amplifier has been designed
to provide precision performance while operating near either
power supply. Figure 4 shows an equivalent output schematic of
the rail-to-rail amplifier with its N channel pull down FETs that
will pull an output load directly to GND. The output sourcing
REV. A
–5–