INA821IDRGT.B

Part: INA821 — Texas Instruments

Type: Precision Instrumentation Amplifier

Description: 35 μV (max) offset, 7 nV/√Hz noise, 650 μA (max) supply current precision instrumentation amplifier with gain of 1 to 10,000 set by one external resistor, ±40 V input protection and a 4.5–36 V supply range.

Operating Conditions:

• Supply voltage: 4.5–36 V single supply, or ±2.25 to ±18 V dual supply
• Specified operating temperature: -40 to +125 °C
• Gain range: 1 to 10,000 V/V, G = 1 + 49.4 kΩ / RG

Absolute Maximum Ratings:

• Max supply voltage: ±20 V (-20 to 20 V)
• Signal input pin voltage: ±40 V
• REF pin voltage: ±20 V
• Output short-circuit: continuous
• Max junction temperature: 175 °C
• Storage temperature: -65 to 150 °C

Key Specs:

• Input stage offset voltage: 10 μV typ, 35 μV max (D, DRG); 40 μV max (DGK) at 25 °C, VS = ±15 V
• Input bias current: 0.15 nA typ, 0.5 nA max at 25 °C
• Input voltage noise: 7 nV/√Hz at 1 kHz, G = 100; 0.14 μVPP (0.1–10 Hz)
• CMRR (DC to 60 Hz): 92 dB min at G = 1, 112 dB min at G = 10, 132 dB min at G = 100, 140 dB min at G = 1000
• PSRR: 110 dB min at G = 1, 136 dB min at G = 1000
• Bandwidth (-3 dB): 4.7 MHz at G = 1, 970 kHz at G = 10, 290 kHz at G = 100, 30 kHz at G = 1000
• Slew rate: 2.0 V/μs (G = 1)
• Gain error: ±0.005% typ, ±0.025% max (G = 1); gain drift ±5 ppm/°C max (G = 1), ±35 ppm/°C max (G > 1)
• Quiescent current: 600 μA typ, 650 μA max at 25 °C; 870 μA max over -40 to +125 °C
• Output short-circuit current: ±20 mA typ; stable with 1000 pF load capacitance

Features:

• Low offset voltage and drift, super-beta input transistors
• Inputs protected up to ±40 V
• RFI input filter (45 MHz, -3 dB)
• Stable with 1-nF capacitive loads
• Single or dual supply operation
• Available in SOIC, VSSOP and WSON packages

Applications:

• Analog input module
• Flow transmitter
• Battery test
• LCD test
• Electrocardiogram (ECG)
• Surgical equipment
• Process analytics (pH, gas, concentration, force and humidity)

Package:

• SOIC-8 (D): 4.90 mm × 3.91 mm
• VSSOP-8 (DGK): 3.00 mm × 3.00 mm
• WSON-8 (DRG): 3.00 mm × 3.00 mm

• 1 · Low offset voltage: 10 μV (typ), 35 μV (max)
• Gain drift: 5 ppm/°C (G = 1), 35 ppm/°C (G > 1) (max)
• Noise: 7 nV/ √ Hz
• Bandwidth: 4.7 MHz (G = 1), 290 kHz (G = 100)
• Stable with 1-nF capacitive loads
• Inputs protected up to ±40 V
• Common-mode rejection: 112 dB, G = 10 (min)
• Power supply rejection: 110 dB, G = 1 (min)
• Supply current: 650 μA (max)
• Supply range:
• -Single-supply: 4.5 V to 36 V
• -Dual-supply: ±2.25 V to ±18 V
• Specified temperature range: -40°C to +125°C
• Packages: 8-pin SOIC, VSSOP, and WSON

• Analog input module
• Flow transmitter
• Battery test
• LCD test
• Electrocardiogram (ECG)
• Surgical equipment
• Process analytics (pH, gas, concentration, force and humidity)

at TA = 25°C, VS = ±15 V, RL = 10 k Ω , VREF = 0 V, and G = 1 (unless otherwise noted)

over operating free-air temperature range (unless otherwise noted) (1)

over operating free-air temperature range (unless otherwise noted)

The parasitic resistance at the reference pin (RREF) creates an imbalance in the four resistors of the internal difference amplifier that results in a degraded common-mode rejection ratio (CMRR). Figure 66 shows the degradation in CMRR of the INA821 as a result of the increased resistance at the reference pin. For the best performance, keep the source impedance to the REF pin (RREF) less than 5 Ω .

Figure 66. The Effect of Increasing Resistance at the Reference Pin

Voltage reference devices are an excellent option for providing a low-impedance voltage source for the reference pin. However, if a resistor voltage divider generates a reference voltage, buffer the divider by an op amp, as shown in Figure 67, to avoid CMRR degradation.

Figure 67. Use an Op Amp to Buffer Reference Voltages

Figure 66. The Effect of Increasing Resistance at the Reference Pin