Datasheet

AD780
REV. B
–8–
LINE REGULATION
Line regulation is a measure of the change in output voltage due
to a specified change in input voltage. It is intended to simulate
worst case unregulated supply conditions and is measured in
µV/V. Figure 14 shows typical performance with 4.0 V < V
IN
<
15.0 V.
200
–200
415
100
–100
10
0
INPUT VOLTAGE – Volts
OUTPUT CHANGE – V
T = 25  C
Figure 14. Output Voltage Change vs. Input Voltage
PRECISION REFERENCE FOR HIGH RESOLUTION
+5 V DATA CONVERTERS
The AD780 is ideally suited to be the reference for most +5 V
high resolution ADCs. The AD780 is stable under any capaci-
tive load, it has superior dynamic load performance, and the
3.0 V output provides the converter with maximum dynamic
range without requiring an additional and expensive buffer am-
plifier. One of the many ADCs that the AD780 is suited for is
the AD7884, a 16-bit, high speed sampling ADC. (See Figure
15.) This part previously needed a precision 5.0 V reference, re-
sistor divider and buffer amplifier to do this function.
+5V
V
IN
V
OUT
GND
AD780
1F
V
REF
+F
V
REF
+S
AD7884
2.5/3.0V
SELECT
Figure 15. Precision 3.0 V Reference for the AD7884
16-Bit, High Speed ADC
The AD780 is also ideal for use with higher resolution convert-
ers such as the AD7710/AD7711/AD7712. (See Figure 16.)
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 ac-
curacy, temperature stability and dynamic range. It is shown fol-
lowing with the two optional noise reduction capacitors.
+5V
V
IN
V
OUT
GND
AD780
1F
REFIN+
REFIN–
AD7710
2.5/3.0V
SELECT
100F
100nF
Figure 16. Precision 2.5 V or 3.0 V Reference for the
AD7710 High Resolution, Sigma-Delta ADC
+4.5 V REFERENCE FROM +5 V SUPPLY
Some +5 V high resolution ADCs can accommodate reference
voltages 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 following in Figure 17. This circuit will provide 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 0.1 µF capacitor and the 3.9 Ω resistor ensure a low
output impedance up to around 50 MHz.
AD780
2N2907
10F
3.9
4k
0.01%
5k
0.01%
0.1F
0.1F
1k
V
SUPPLY
V
OUT
OP90
2.5k
0.1F
Figure 17. +4.5 V Reference from a Single +5 V Supply