DAC8043 Datasheet, PDF (6/7 Pages) Analog Devices – 12-Bit Serial Input Multiplying CMOS D/A Converter

DISCUSSION OF
SPECIFICATIONS
RELATIVE ACCURACY
This term, also known as end point linearity or integral
linearity, describes the transfer function of analog output to
digital input code. Relative accuracy describes the deviation
from a straight line, after zero and full scale errors have been
adjusted to zero.
DIFFERENTIAL NONLINEARITY
Differential nonlinearity is the deviation from an ideal 1LSB
change in the output when the input code changes by 1LSB.
A differential nonlinearity specification of 1LSB maximum
guarantees monotonicity.
GAIN ERROR
Gain error is the difference between the full-scale DAC
output and the ideal value. The ideal full scale output value
for the DAC8043 is –(4095/4096)V_REF. Gain error may be
adjusted to zero using external trims as shown in Figure 4.
OUTPUT LEAKAGE CURRENT
The current which appears at I_OUT with the DAC loaded with
all zeros.
OUTPUT CAPACITANCE
The parasitic capacitance measured from I_OUT to GND.
FEEDTHROUGH ERROR
The AC output error due to capacitive coupling from V_REF to
I_OUT with the DAC loaded with all zeros.
OUTPUT CURRENT SETTLING TIME
The time required for the output current to settle to within
+0.01% of final value for a full scale step.
DIGITAL-TO-ANALOG GLITCH ENERGY
The integrated area of the glitch pulse measured in nanovolt-
seconds. The key contributor to digital-to-analog glitch is
charge injected by digital logic switching transients.
CIRCUIT DESCRIPTION
Figure 1 shows a simplified schematic of a DAC8043. The
current from the V_REF pin is switched between I_OUT and GND
by 12 single-pole double-throw CMOS switches. This main-
V_REF
R
2R
R
R
2R
2R
2R
2R ^{R RFB}
Bit 1
(MSB)
Bit 2
Bit 3
Bit 12
(LSB)
I_OUT
GND
tains a constant current in each leg of the ladder regardless of
the input code. The input resistance at V_REF is therefore
constant and can be driven by either a voltage or current, AC
or DC, positive or negative polarity, and have a voltage range
up to ±20V.
A CMOS switch transistor, included in series with the ladder
terminating resistor and in series with the feedback resistor,
R_FB, compensates for the temperature drift of the ON resis-
tance of the ladder switches.
Figure 2 shows an equivalent circuit for the DAC. C_OUT is the
output capacitance due to the N-channel switches and varies
from about 80pF to 110pF with digital input code. The current
source I_LKG is the combination of surface and junction leak-
ages to the substrate. I_LKG approximately doubles every 10°C.
R_O is the equivalent output resistance of the D/A and it varies
with input code.
V_REF
R
D_{IN x} V_REF
4096 R
R_O
I_LKG
R
R_FB
I_OUT
C_OUT
GND
FIGURE 2. Equivalent Circuit for the DAC.
INSTALLATION
ESD PROTECTION
All digital inputs of the DAC8043 incorporate on-chip ESD
protection circuitry. This protection is designed to withstand
2.5kV (using the Human Body Model, 100pF and 1500Ω).
However, industry standard ESD protection methods should
be used when handling or storing these components. When
not in use, devices should be stored in conductive foam or
rails. The foam or rails should be discharged to the destina-
tion socket potential before devices are removed.
POWER SUPPLY CONNECTIONS
The DAC8043 is designed to operate on V_DD = +5V ±5%.
For optimum performance and noise rejection, power supply
decoupling capacitors C_D should be added as shown in the
application circuits. These capacitors (1µF tantalum recom-
mended) should be located close to the D/A. Output op amp
analog common (+ input) should be connected as near to the
GND pins of the DAC8043 as possible.
WIRING PRECAUTIONS
To minimize AC feedthrough when designing a PC board,
care should be taken to minimize capacitive coupling be-
tween the V_REF lines and the I_OUT lines. Coupling from any
of the digital control or data lines might degrade the glitch
performance. Solder the DAC8043 directly into the PC board
without a socket. Sockets add parasitic capacitance (which
can degrade AC performance).
FIGURE 1. Simplified Circuit Diagram for the DAC.
®
DAC8043
6