AD420 Data Sheet
AD420 PROTECTION
TRANSIENT VOLTAGE PROTECTION
The AD420 contains ESD protection diodes, which prevent
damage from normal handling. The industrial control envir-
onment can, however, subject I/O circuits to much higher
transients. To protect the AD420 from excessively high voltage
transients, such as those specified in IEC 801, external power
diodes and a surge current limiting resistor may be required, as
shown in Figure 15. The constraint on the resistor is that during
normal operation the output voltage level at I
OUT
must remain
within its voltage compliance limit
(I
OUT
× (Rp + R
LOAD
) ≤ V
CC
− 2.75 V)
and the two protection diodes and resistor must have
appropriate power ratings.
00494-015
AD420
I
OUT
V
CC
V
CC
R
LOAD
R
P
GND
Figure 15. Output Transient Voltage Protection
BOARD LAYOUT AND GROUNDING
The AD420 ground pin, designated GND, is the high quality
ground reference point for the device. Any external loads on the
REF OUT and V
OUT
pins of the AD420 should be returned to
this reference point. Analog and digital ground currents should
not share a common path. Each signal should have an appropriate
analog or digital signal return routed close to it. Using this
approach, signal loops enclose a small area, minimizing the
inductive coupling of noise. Wide PC tracks, large gauge wire,
and ground planes are highly recommended to provide low
impedance signal paths.
POWER SUPPLIES AND DECOUPLING
The AD420 supply pins, V
CC
(Pin 23) and V
LL
(Pin 2), should be
decoupled to GND with 0.1 µF capacitors to eliminate high
frequency noise that may otherwise get coupled into the analog
system. High frequency ceramic capacitors are recommended.
The decoupling capacitors should be located in close proximity
to the pins and the ground line to have maximum effect. Further
reductions in noise, and improvements in performance, may be
achieved by using a larger value capacitor on the V
LL
pin.
Rev. I | Page 14 of 16
