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INA214-Q1 Datasheet(PDF) 11 Page - Texas Instruments |
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INA214-Q1 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 20 page INA21x V+ OUT GND IN- IN+ PRODUCT R and R 3 4 INA213 20 kW C BYPASS NOTE: 1-MW paths from shunt inputs to reference and INA21x outputs. Shutdown Control REF Reference Voltage 1 MW R 3 R 2 R 4 Supply Load R SHUNT Output INA213 10 kW INA213-Q1 INA214-Q1 www.ti.com SBOS475B – MARCH 2009 – REVISED JUNE 2010 SHUTTING DOWN While the INA21x does not have a shutdown pin, its low power consumption allows powering from the output of a logic gate or transistor switch that can turn on and turn off the INA21x power-supply quiescent current. However, in current shunt monitoring applications. there is also a concern for how much current is drained from the shunt circuit in shutdown conditions. Evaluating this current drain involves considering the simplified schematic of the INA21x in shutdown mode shown in Figure 25. Figure 25. Basic Circuit for Shutting Down INA21x With Grounded Reference Note that there is typically slightly more than 1-M Ω impedance (from the combination of 1-MΩ feedback and 5-k Ω input resistors) from each input of the INA21x to the OUT pin and to the REF pin. The amount of current flowing through these pins depends on the respective ultimate connection. For example, if the REF pin is grounded, the calculation of the effect of the 1-M Ω impedance from the shunt to ground is straightforward. However, if the reference or op amp is powered while the INA21x is shut down, the calculation is direct; instead of assuming 1 M Ω to ground, however, assume 1 MΩ to the reference voltage. If the reference or op amp is also shut down, some knowledge of the reference or op amp output impedance under shutdown conditions is required. For instance, if the reference source behaves as an open circuit when it is unpowered, little or no current flows through the 1-M Ω path. Regarding the 1-M Ω path to the output pin, the output stage of a disabled INA21x does constitute a good path to ground; consequently, this current is directly proportional to a shunt common-mode voltage impressed across a 1-M Ω resistor. As a final note, when the device is powered up, there is an additional, nearly constant, and well-matched 25 µA that flows in each of the inputs as long as the shunt common-mode voltage is 3 V or higher. Below 2-V common-mode, the only current effects are the result of the 1-M Ω resistors. REF INPUT IMPEDANCE EFFECTS As with any difference amplifier, the INA21x common-mode rejection ratio is affected by any impedance present at the REF input. This concern is not a problem when the REF pin is connected directly to most references or power supplies. When using resistive dividers from the power supply or a reference voltage, the REF pin should be buffered by an op amp. In systems where the INA21x output can be sensed differentially, such as by a differential input analog-to-digital converter (ADC) or by using two separate ADC inputs, the effects of external impedance on the REF input can be cancelled. Figure 26 depicts a method of taking the output from the INA21x by using the REF pin as a reference. Copyright © 2009–2010, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Link(s): INA213-Q1 INA214-Q1 |
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