AD780

Data Sheet

Rev. F | Page 6 of 12

APPLYING THE AD780

The AD780 can be used without any external components to

achieve specified performance. If power is supplied to Pin 2 and

Pin 4 is grounded, Pin 6 provides a 2.5 V or 3.0 V output

depending on whether Pin 8 is left unconnected or grounded.

load capacitance in the application is expected to be greater

than 1 nF. The AD780 in 2.5 V mode typically draws 700 µA of

NC

TEMP

TRIM

GND

O/P SELECT

2.5V – NC

3.0V – GND

NC

R POT

1

µF

AD780

NC = NO CONNECT

1

7

6

5

8

4

2

3

Figure 5. Optional Fine-Trim Circuit

Initial error can be nulled using a single 25 kΩ potentiometer

trim with an adjustment range of 4%, and is only included here

for compatibility purposes with other references. A fine trim

can be implemented by inserting a large value resistor (e.g., 1

MΩ to

5 MΩ) in series with the wiper of the potentiometer (see

Figure 5). The trim range, expressed as a fraction of the output,

2.5 V or 3.0 V mode.

The external null resistor affects the overall temperature

For example, a 1 mV (0.03%) shift in the output caused by the

trim circuit, with a 100 ppm/°C null resistor, adds less than

0.06 ppm/°C to the output drift (0.03% × 200 ppm/°C, since the

resistors internal to the AD780 also have temperature

coefficients of less than 100 ppm/°C).

NOISE PERFORMANCE

The impressive noise performance of the AD780 can be further

improved, if desired, by adding two capacitors: a load capacitor

(C1) between the output and ground, and a compensation

capacitor (C2) between the TEMP pin and ground. Suitable

values are shown in Figure 6.

100

10

1

0.1

0.1

1

10

100

LOAD CAPACITOR, C1 (

µF)

Figure 6. Compensation and Load Capacitor Combinations

C1 and C2 also improve the settling performance of the AD780

when subjected to load transients. The improvement in noise

performance is shown in Figure 7, Figure 8, Figure 9, and

Figure 10.

0.1 TO 10Hz

AMPLIFIER GAIN = 100

1s

100

µV

100

90

10

0%

Figure 7. Standalone Noise Performance

10Hz TO 10kHz

NO AMPLIFIER

10ms

20

µV

100

90

10

0%

Figure 8. Standalone Noise Performance