Application Bulletin «Input Overload Protection For The RCV420 4-20 mA Current-Loop Receiver» (Texas Instruments) - 3

Since the overload protection circuitry interrupts the current loop, a logic gate is needed to prevent a false indication of open circuit. The 2N3904 transistor is wire-ORed to the underrange comparator output, assuring it will go high only during actual underload conditions. The 1µF capacitor con- nected to the 470Ω relay drive resistor delays relay turn-on to prevent possible logic race conditions which could pro- duce a false underrange output logic “sliver”. The capacitor can be omitted if this is not a concern. The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems. 3