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Circuitry
5
SBOU196 – December 2017
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Copyright © 2017, Texas Instruments Incorporated
INA381EVM
4
Circuitry
This section summarizes the INA381EVM components. For the following instructions, x = A to D.
4.1
Cx1, Cx2
Cx1 and Cx2 are 10-
μ
F and 0.1-
μ
F supply bypass capacitors respectively.
4.2
Cx3, Rx2, Rx4
Cx3, Rx2, and Rx4 footprints are for customizing the input pi-filter to the INA381 device. Default values
are 0
Ω
and 1000 pF. However, no capacitor is installed.
4.3
Cx4, Rx3
Cx4 and Rx3 are footprints for a customizable output filter. Default values are 0
Ω
and 1000 pF. However,
no capacitor is installed.
4.4
Ux1
Ux1 is the test-device location. Four device boards are supplied with the INA381EVM. Each board is
populated with one of the available device gains: 20 V/V, 50 V/V, 100 V/V, or 200 V/V. This option enables
users to test the devices and determine the gain setting best suited for a given application. The following
list of factors is involved in selecting the appropriate device:
•
Select INA381 for unidirectional applications only.
•
The differential input voltage is applied across the inputs, or developed based on the load current that
flows through the shunt resistor connected across the inputs.
•
The most limiting factor that requires attention to be given to device selection is the output voltage.
•
The selected device must allow the output voltage to remain within the acceptable range after the
Vsense voltage (IN+ – IN–) is amplified by the respective device gain. The max output voltage must
remain within the range of 10 mV above ground to 100 mV below the supply voltage.
•
Choose an appropriate gain and sense resistor to create the largest appropriate output swing possible
and to minimize error.
4.5
Rx5, Cx5
Rx5 is a 50-k
Ω
trimming potentiometer that allows the user to set the CMPREF voltage without having to
use an additional power supply. Cx5 is a bypass capacitor that is meant to absorb any transients that
would otherwise feed into the CMPREF pin.
4.6
Rx1, Rx7, Qx1, Dx1
Rx1 serves as a pull-up resistor that keeps the ALERT pin voltage around VS+ when the ALERT pin is
open drain (inactive) and as an impedance path that prevents VS+ from shorting to GND when the ALERT
pin goes low (active). Qx1 serves as a switch controlled by the ALERT pin. When Qx1 switches on
(ALERT goes active low), Dx1 turns on, which notifies the user that voltage at VOUT exceeded the
voltage at CMPREF. Rx7 limits the current through Dx1.
4.7
Jx
Jx controls whether the device uses continuous mode or latch mode. RST shorted to VS+ puts the device
in latch mode. RST shorted to GND puts the device in continuous mode.
4.8
Voltages Inputs
The IN+ (TPx3 or TPxV3) and IN– (TPx5 or TPxV5) inputs accept a differential voltage that is amplified by
the selected device gain and is presented at the VOUT test point (TPx04 or TPx14). These inputs can
also be used to connect the differential voltage developed across an external shunt in an existing circuit.
The acceptable differential input voltage range and polarity are determined by the supply voltage and gain
of the selected device.
