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

15.0 V.

200

–200

415

100

–100

10

0

INPUT VOLTAGE – Volts

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

GND

AD780

1 F

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

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

OP90

2.5k

0.1 F

Figure 17. +4.5 V Reference from a Single +5 V Supply