AD780
APPLYING THE AD780
COMPENSATION CAPACITOR, C2 (nF)
Data Sheet
100
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.
A bypass capacitor of 1 µF (+V
IN
to GND) should be used if the
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
I
q
at 5 V. This increases by ~2 µA/V up to 36 V.
2
7
10
1
+V
IN
NC
V
OUT 6
1
NC
0.1
0.1
R
NULL
1µF
AD780
TRIM
5
3
TEMP
1
10
LOAD CAPACITOR, C1 (µF)
100
R POT
Figure 6. Compensation and Load Capacitor Combinations
GND
4
O/P SELECT
2.5V – NC
3.0V – GND
8
00841-005
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
AMPLIFIER GAIN = 100
100µV
100
90
NC = NO CONNECT
Figure 5. Optional Fine-Trim Circuit
1s
The external null resistor affects the overall temperature
coefficient by a factor equal to the percentage of V
OUT
nulled.
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).
0.1 TO 10Hz
Figure 7. Standalone Noise Performance
NO AMPLIFIER
20µV
100
90
10ms
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.
10
0%
10Hz TO 10kHz
Figure 8. Standalone Noise Performance
Rev. F | Page 6 of 12
00841-008
00841-007
Initial error can be nulled using a single 25 kΩ potentiometer
connected between V
OUT
, TRIM, and GND. This is a coarse
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
is simply greater than or equal to 2.1 kΩ/R
NULL
for either the
2.5 V or 3.0 V mode.
10
0%
00841-006
AD [ ANALOG DEVICES ]
