Data Sheet

AD780

Rev. F | Page 7 of 12

NC

TEMP

TRIM

GND

O/P SELECT

2.5V – NC

3.0V – GND

NC

1

F

AD780

NC = NO CONNECT

1

7

6

5

8

4

2

3

C2

C1

Figure 9. Noise Reduction Circuit

NOISE COMPARISON

The wideband noise performance of the AD780 can also be

expressed in ppm. The typical performance with C1 and C2 is

0.6 ppm; without external capacitors, typical performance is

1.2 ppm.

This performance is, respectively, 7× and 3× lower than the

specified performance of the LT1019.

10Hz TO 10kHz

NO AMPLIFIER

10ms

20

V

100

90

10

0%

Figure 10. Reduced Noise Performance with C1 = 100 μF, C2 = 100 nF

TEMPERATURE PERFORMANCE

The AD780 provides superior performance over temperature by

means of a combination of patented circuit design techniques,

precision thin-film resistors, and drift trimming. Temperature

performance is specified in terms of ppm/°C; because of

nonlinearity in the temperature characteristic, the box test

method is used to test and specify the part. The nonlinearity

takes the form of the characteristic S-shaped curve shown in

Figure 11. The box test method forms a rectangular box around

this curve, enclosing the maximum and minimum output

voltages over the specified temperature range. The specified

drift is equal to the slope of the diagonal of this box.

2.0

–0.8

–0.4

0

0.4

0.8

1.2

1.6

–60

–40

–20

0

20

40

60

80

100

120

140

TEMPERATURE (

C)

Figure 11. Typical AD780BN Temperature Drift

TEMPERATURE OUTPUT PIN

The AD780 provides a TEMP output (Pin 3) that varies linearly

with temperature. This output can be used to monitor changes

in system ambient temperature, and to initiate calibration of the

temperature coefficient is approximately 2 mV/°C.

temperature taken at the output of the op amp with a

noninverting gain of 5.

4.25

4.00

3.75

3.50

3.25

3.00

2.75

2.50

2.25

2.00

–75

–50

–25

0

25

50

75

100

125

150

TEMPERATURE (

C)

CIRCUIT CALIBRATED AT 25

C

REFER TO FIGURE 13

10mV PER

C

Figure 12. Temperature Pin Transfer Characteristic

Since the TEMP voltage is acquired from the band gap core

circuit, current pulled from this pin has a significant effect on

suitable op amp, e.g., an OP07, AD820, or AD711 (all of which

would result in less than a 100 μV change in VOUT). The

or