Datasheet

Data Sheet AD780
APPLYING THE AD780
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Figure 21. Precision 3 V Reference for the AD7884 16-Bit, High Speed ADC
The AD780 is also ideal for use with higher resolution converters,
such as the AD7710/AD7711/AD7712 (see Figure 22). While these
parts are specified with a 2.5 V internal reference, the AD780 in 3
V mode can be used to improve the absolute accuracy, temperature
stability, and dynamic range. It is shown in Figure 22 with the two
optional noise reduction capacitors.
Figure 22. Precision 2.5 V or 3.0 V Reference for the AD7710 High Resolution,
Σ-Δ ADC
4.5 V REFERENCE FROM 5 V SUPPLY
Some 5 V high resolution ADCs can accommodate reference vol-
tages up to 4.5 V. The AD780 can be used to provide a precision
4.5 V reference voltage from a 5 V supply using the circuit shown
in Figure 23. This circuit provides a regulated 4.5 V output from a
supply voltage as low as 4.7 V. The high quality tantalum 10 µF
capacitor, in parallel with the ceramic AD780 0.1 µF capacitor and
the 3.9 Ω resistor, ensures a low output impedance around 50 MHz.
Figure 23. 4.5 V Reference from a Single 5 V Supply
NEGATIVE (–2.5 V) REFERENCE
The AD780 can produce a negative output voltage in shunt mode
by connecting the input and output to ground, and connecting the
GND pin of the AD780 to a negative supply via a bias resistor, as
shown in Figure 25.
Figure 24. Negative (−2.5 V Shunt Mode Reference)
A precise –2.5 V reference capable of supplying up to 100 mA to a
load can be implemented with the AD780 in series mode, using the
bootstrap circuit shown in Figure 25.