link to page 3 link to page 4 Data SheetAD8420SPECIFICATIONS +VS = +5 V, −VS = 0 V, VREF = 0.5 V, V+IN = 0.5 V, V−IN = 0.5 V, TA = 25°C, G = 1 to 1000, RL = 20 kΩ, specifications referred to input, unless otherwise noted. All Table 2 limits are valid from VS = 3 V to VS = ±5 V, unless otherwise specified. Table 2. Parameter TestConditions/CommentsMinTypMaxUnit COMMON-MODE REJECTION RATIO (CMRR) VCM = 0 V to 2.7 V CMRR DC to 60 Hz 100 dB CMRR at 1 kHz 100 dB NOISE Voltage Noise Spectral Density f = 1 kHz, VDIFF ≤ 100 mV 55 nV/√Hz Peak to Peak f = 0.1 Hz to 10 Hz, VDIFF ≤ 100 mV 1.5 μV p-p Current Noise Spectral Density f = 1 kHz 80 fA/√Hz Peak to Peak f = 0.1 Hz to 10 Hz 3 pA p-p VOLTAGE OFFSET Offset VS = 3 V to VS = 5 V 125 μV VS = ±5 V 150 μV Average Temperature Coefficient TA = −40°C to +85°C 1 μV/°C Offset RTI vs. Supply (PSR) VS = 2.7 V to 5 V 86 dB INPUTS Valid for REF and FB pair, as well as +IN and −IN Input Bias Current1 TA = +25°C 20 27 nA TA = +85°C 24 nA TA = −40°C 30 nA Average Temperature Coefficient TA = −40°C to +85°C 30 pA/°C Input Offset Current TA = +25°C 1 nA TA = +85°C 1 nA TA = −40°C 1 nA Average Temperature Coefficient TA = −40°C to +85°C 0.5 pA/°C Input Impedance Differential 130||2 MΩ||pF Common Mode 1000||2 MΩ||pF Differential Input Operating Voltage TA = –40°C to +85°C −1 +1 V Input Operating Voltage (+IN, −IN, REF, or FB) TA = +25°C −VS − 0.15 +VS − 2.2 V TA = +85°C −VS − 0.05 +VS − 1.8 V TA = –40°C −VS − 0.2 +VS − 2.7 V DYNAMIC RESPONSE Small Signal −3 dB Bandwidth G = 1 250 kHz G = 10 25 kHz G = 100 2.5 kHz G =1000 0.25 kHz Settling Time 0.01% VS = ±5 V G = 1 −1 V to +1 V output step 3 μs G = 10 −4.5 V to +4.5 V output step 130 μs G = 100 −4.5 V to +4.5 V output step 1 ms Slew Rate 1 V/μs Rev. A | Page 3 of 26 Document Outline FEATURES APPLICATIONS PIN CONFIGURATION GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION ARCHITECTURE SETTING THE GAIN GAIN ACCURACY INPUT VOLTAGE RANGE INPUT PROTECTION Input Voltages Beyond the Rails Large Differential Input Voltage LAYOUT Common-Mode Rejection Ratio over Frequency Power Supplies Reference DRIVING THE REFERENCE PIN INPUT BIAS CURRENT RETURN PATH RADIO FREQUENCY INTERFERENCE (RFI) OUTPUT BUFFERING APPLICATIONS INFORMATION AD8420 IN ELECTROCARDIOGRAPHY (ECG) CLASSIC BRIDGE CIRCUIT 4 mA TO 20 mA SINGLE-SUPPLY RECEIVER OUTLINE DIMENSIONS ORDERING GUIDE