REV. F

–10–

AD420

AD420 PROTECTION

TRANSIENT VOLTAGE PROTECTION

The AD420 contains ESD protection diodes which prevent

damage from normal handling. The industrial control environ-

ment can, however, subject I/O circuits to much higher tran-

sients. In order 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 re-

quired, as shown in Figure 14. The constraint on the resistor is

must remain within its voltage compliance limit

× (Rp + R

≤ V

and the two protection diodes and resistor must have appropri-

ate power ratings.

GND

AD420

Figure 14. 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

this reference point. Analog and digital ground currents should

not share a common path. Each signal should have an appropri-

ate 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

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