DAC8812 Datasheet, PDF (14/29 Pages) Texas Instruments – Dual, Serial Input 16-Bit Multiplying Digital-to-Analog Converter

DAC8812
SBAS349D – AUGUST 2005 – REVISED JANUARY 2016
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Feature Description (continued)
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. The DAC output voltage is determined by V_REF and the digital data (D)
according to Equation 1:
D
V_OUT = V_REF ´ _{65 536}
(1)
Note that the output polarity is opposite of the V_REF polarity for dc reference voltages.
The DAC is also designed to accommodate ac reference input signals. The DAC8812 accommodates input
reference voltages in the range of –15 V to 15 V. The reference voltage inputs exhibit a constant nominal input
resistance of 5 kΩ, ±20%. On the other hand, DAC outputs I_OUTA and B are code-dependent and produce
various output resistances and capacitances.
The choice of external amplifier should take into account the variation in impedance generated by the DAC8812
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 (4 pF to 20 pF typical), may be needed to provide a critically damped output response for step
changes in reference input voltages.
Figure 15 shows the gain vs frequency performance at various attenuation settings using a 3 pF external
feedback capacitor connected across the I_OUTX and R_FBX pins. 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 P_SS frequency-dependent characteristics. It is best to derive the
DAC8812 5-V supply from the system analog supply voltages (do not use the digital 5-V supply); see Figure 31.
15 V
Analog
2R
Power
+
5V
Supply
R
V_DD
V_REFX
2R
R
2R
R
2R
R
R
5 kW
R_FBX
S2
S1
I_OUTX
A_GNDX
15 V
V_CC
A1
+
V_EE
DGND
Digital interface connections omitted for clarity.
Switches S1 and S2 are closed, V_DD must be powered.
DGND
Figure 31. Recommended Kelvin-Sensed Hookup
V_OUT
Load
14
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