APPLICATIONS • High-Voltage Current Sensing • Battery Cell Voltage Monitoring • Power-Supply Current Monitoring • Motor Controls • Replacement for Isolation Circuits
DESCRIPTION 2 The INA149 is a precision unity-gain difference • Common-Mode Voltage Range: ±275 V amplifier with a very high input common-mode • Minimum CMRR: 90 dB from –40°C to +125°C voltage range. It is a single, monolithic device that • DC Specifications: consists of a precision op amp and an integrated thin- – Maximum Offset Voltage: 1100 μV film resistor network. The INA149 can accurately measure small differential voltages in the presence of – Maximum Offset Voltage Drift: 15 μV/°C common-mode signals up to ±275 V. The INA149 – Maximum Gain Error: 0.02% inputs are protected from momentary common-mode – Maximum Gain Error Drift: 10 ppm/°C or differential overloads of up to 500 V. – Maximum Gain Nonlinearity: 0.001% FSR In many applications, where galvanic isolation in not required, the INA149 can replace isolation amplifiers. • AC Performance: This ability can eliminate costly isolated input side – Bandwidth: 500 kHz power supplies and the associated ripple, noise, and – Typical Slew Rate: 5 V/μs quiescent current. The excellent 0.0005% nonlinearity • Wide Supply Range: ±2.0 V to ±18 V and 500-kHz bandwidth of the INA149 are superior to those of conventional isolation amplifiers. – Maximum Quiescent Current: 900 μA – Output Swing on ±15-V Supplies: ±13.5 V The INA149 is pin-compatible with the INA117 and INA148 type high common-mode voltage amplifiers • Input Protection: and offers improved performance over both devices. – Common-Mode: ±500 V The INA149 is available in the SOIC-8 package with – Differential: ±500 V operation specified over the extended industrial temperature range of –40°C to +125°C.
COMMON-MODE RANGE The high common-mode range of the INA149 is achieved by dividing down the input signal with a high precision resistor divider. This resistor divider brings both the positive input and the negative input within the input range of the internal operational amplifier. This input range depends on the supply voltage of the INA149. Both Figure 2 and Figure 3 can be used to determine the maximum common-mode range for a specific supply voltage. The maximum common-mode range can also be calculated by ensuring that both the positive and the negative input of the internal amplifier are within 1.5 V of the supply voltage. In case the voltage at the inputs of the internal amplifier exceeds the supply voltage, the internal ESD diodes start conducting current. This current must be limited to 10 mA to make sure not to exceed the absolute maximum ratings for the device.
COMMON-MODE REJECTION Common-mode rejection (CMR) of the INA149 depends on the input resistor network, which is laser-trimmed for accurate ratio matching. To maintain high CMR, it is important to have low source impedance driving the two inputs. A 75-Ω resistance in series with pins 2 or 3 decreases the common-mode rejection ratio (CMRR) from 100 dB (typical) to 74 dB. Resistance in series with the reference pins also degrades CMR. A 4-Ω resistance in series with pins 1 or 5 decreases CMRR from 100 dB to 74 dB. Most applications do not require trimming. Figure 45 shows an optional circuit that may be used for trimming offset voltage and common-mode rejection.
MEASURING CURRENT The INA149 can be used to measure a current by sensing the voltage drop across a series resistor, RS. Figure 46 shows the INA149 used to measure the supply currents of a device under test. The sense resistor imbalances the input resistor matching of the INA149, thus degrading its CMR. Also, the input impedance of the INA149 loads RS, causing gain error in the voltage-to-current conversion. Both of these errors can be easily corrected. The CMR error can be corrected with the addition of a compensation resistor (RC), equal to the value of RS, as shown in Figure 46. If RS is less than 5 Ω, degradation in the CMR is negligible and RC can be omitted. If RS is larger than approximately 1 kΩ, trimming RC may be required to achive greater than 90-dB CMR. This error is caused by the INA149 input impedance mismatch.
NOISE PERFORMANCE The wideband noise performane of the INA149 is dominated by the internal resistor network. The thermal or Johnson noise of these resistors measures approximately 550 nV/√Hz. The internal op amp contributes virtually no excess noise at frequencies above 100 Hz. Many applications may be satisfied with less than the full 500-kHz bandwidth of the INA149. In these cases, the noise can be reduced with a low-pass filter on the output. The two-pole filter shown in Figure 47 limits bandwidth and reduces noise. Because the INA149 has a 1/f noise corner frequency of approximately 100 Hz, a cutoff frequency below 100 Hz does not further reduce noise. Component values for different filter frequencies are shown in Table 1.

Product name:INA149AID
Manufacturer: Texas Instruments	Product Category: Differential Amplifier
Series: INA149	Number of channels: 1 Channel
GBP-Gain Bandwidth Product: 500 kHz	SR - Slew Rate : 5 V/us
CMRR - Common Mode Rejection Ratio: 90 dB	Vos - Input Bias Voltage : 1000 uV
Supply voltage - max: 36 V	Supply Voltage - Min: 4 V
Operating Supply Current: 775 uA	Minimum operating temperature: - 40 C
Maximum operating temperature: + 125 C	Installation style: SMD/SMT
Package/Case: SOIC-8 Package: Tube	Input Voltage Range—Max: 300 V
Operating supply voltage: 4 V to 36 V	Product: Differential Amplifiers
Product Type: Differential Amplifiers	Factory Packing Quantity: 150
Vcm - Common Mode Voltage: - 275 V	Unit weight: 540 mg