DAC8803 Datasheet, PDF (22/30 Pages) Texas Instruments – Quad, Current Output, Serial Input 14-Bit Multiplying Digital-to-Analog Converter

DAC8803
SBAS340A – JANUARY 2005 – REVISED APRIL 2005
www.ti.com
The DAC is designed to operate with both negative or positive reference voltages. The V_DD power pin is only
used by the logic to drive the DAC switches on and off. Note that a matching switch is used in series with the
internal 5 kΩ feedback resistor. If users are attempting to measure the value of R_FB, power must be applied to
V_DD in order to achieve continuity. An additional V_SS bias pin is used to guard the substrate during high
temperature applications to minimize zero-scale leakage currents that double every 10°C. The DAC output
voltage is determined by V_REF and the digital data (D) according to Equation 1:
V_OUT + *V_REF
D
16384
(1)
Note that the output polarity is opposite to the V_REF polarity for dc reference voltages.
V_REFX
RRR
2R
2R
V_DD
R_FBX
2R
R 5 kW
S2
From Other DACS A_GND
S1
I_OUTX
A_GNDF
A_GNDX
V_CC
DGND
Digital interface connections omitted for clarity.
Switches S1 and S2 are closed, V_DD must be powered.
Figure 54. Typical Equivalent DAC Channel
The DAC is also designed to accommodate ac reference input signals. The DAC8803 accommodates input
reference voltages in the range of -12 V to +12 V. The reference voltage inputs exhibit a constant nominal input
resistance of 5 kΩ, ± 20%. On the other hand, the DAC outputs I_OUTA, B, C, D are code-dependent and produce
various output resistances and capacitances.
The choice of external amplifier should take into account the variation in impedance generatedby the DAC8803
on the amplifiers' inverting input node. The feedback resistance, in parallel with the DAC ladder resistance,
dominates output voltage noise. For multiplying mode applications, an external feedback compensation capacitor
(C_FB) may be needed to provide a critically damped output response for step changes in reference input
voltages.
Figure 5 and Figure 6 show the gain vs frequency performance at various attenuation settings using a 23 pF
external feedback capacitor connected across the I_OUTX and R_FBX terminals. In order to maintain good analog
performance, power supply bypassing of 0.01 µF, in parallel with 1 µF, is recommended. Under these conditions,
clean power supply with low ripple voltage capability should be used. Switching power supplies is usually not
suitable for this application due to the higher ripple voltage and PSS frequency-dependent characteristics. It is
best to derive the DAC8803 5-V supply from the system analog supply voltages. (Do not use the digital 5-V
supply.) See Figure 55.
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