概要

The AD8211 is a high voltage, precision current shunt amplifier. It features a set gain of 20 V/V, with a typical ±0.35% gain error over the entire temperature range. The buffered output voltage directly interfaces with any typical converter. Excellent commonmode rejection from −2 V to +65 V is independent of the 5 V supply. The AD8211 performs unidirectional current measurements across a shunt resistor in a variety of industrial and automotive applications, such as motor control, solenoid control, or battery management.
Special circuitry is devoted to output linearity being maintained throughout the input differential voltage range of 0 mV to 250 mV, regardless of the common-mode voltage present. The AD8211 has an operating temperature range of −40°C to +125°C and is offered in a small 5-lead SOT package.

 

特徴

自動車用途に適合
±4000 V human body model (HBM) electrostatic discharge (ESD)
High common-mode input voltage range: −2 V to +65 V
Continuous input voltage range: −3 V to +68 V
Buffered output voltage
Wide operating temperature range 5-lead SOT: −40°C to +125°C
Excellent ac and dc performance
5 µV/°C typical offset drift
−13 ppm/°C typical gain vs. temperature
120 dB typical common-mode rejection ratio (CMRR) at dc

 

アプリケーション

High-side current sensing
Motor controls
Transmission controls
Engine management
Suspension controls
Vehicle dynamic controls
DC-to-dc converters

 

動作理論

In typical applications, the AD8211 amplifies a small differential input voltage generated by the load current flowing through a shunt resistor. The AD8211 rejects high common-mode voltages (up to 65 V) and provides a ground referenced, buffered output that interfaces with an analog-to-digital converter (ADC).
A load current flowing through the external shunt resistor produces a voltage at the input terminals of the AD8211. The inverting terminal, which has very high input impedance, is held to the following because negligible current flows through Resistor R:
(VCM) − (ISHUNT × RSHUNT)
This current (IIN) is converted back to a voltage via ROUT. The output buffer amplifier has a gain of 20 V/V and offers excellent accuracy because the internal gain setting resistors are precision trimmed to within 0.01% matching. The resulting output voltage is equal to:
VOUT = (ISHUNT × RSHUNT) × 20

 

OUTPUT LINEARITY

In all current sensing applications, and especially in automotive and industrial environments where the common-mode voltage can vary significantly, it is important that the current sensor maintain the specified output linearity, regardless of the input differential or common-mode voltage. The AD8211 contains specific circuitry on the input stage, which ensures that even when the differential input voltage is very small, and the common-mode voltage is also low (below the 5 V supply), the input-to-output linearity is maintained.
Regardless of the common mode voltage, the AD8211 provides a correct output voltage when the input differential is at least 2 mV, which is due to the voltage range of the output amplifier that can go as low as 33 mV typical. The specified minimum output amplifier voltage is 100 mV to provide sufficient guard bands. The ability of the AD8211 to work with very small differential inputs, regardless of the common-mode voltage, allows for additional dynamic range, accuracy, and flexibility in any current sensing application.

 

HIGH-SIDE CURRENT SENSING

In this configuration, the shunt resistor is referenced to the battery. High voltage is present at the inputs of the current sense amplifier. In this mode, the recirculation current is again measured and shorts to ground can be detected. When the shunt is battery referenced, the AD8211 produces a linear ground referenced, analog output. An AD8214 can also provide an overcurrent detection signal in as little as 100 ns. This feature is useful in high current systems where fast shutdown in overcurrent conditions is essential.

 

LOW-SIDE CURRENT SENSING

In systems where low-side current sensing is preferred, the AD8211 provides an integrated solution with great accuracy. Ground noise is rejected, CMRR is typically higher than 90 dB, and output linearity is not compromised, regardless of the input differential voltage.