Circuitry
5
SBOU167 – March 2019
Copyright © 2019, Texas Instruments Incorporated
INA185EVM
4
Circuitry
This section summarizes the INA185EVM components. For the following circuits, x = A to D.
4.1
C1x, J1x, R1x, and TP1x
C1x and R1x form a low-pass RC filter to the source that supplies the INA185 REF pin. By default, no
filter is installed, with R1x shorted by a 0-
Ω
resistor, and C1x not populated. J1x is a jumper that
conveniently allows the user to short the INA185 reference to ground, connect directly to an external
power supply, or short to a voltage set by a buffered voltage divider.
4.2
C2x and C3x, and TP2x
C2x is a 0.1-µF supply bypass capacitor for the INA185, U1x. The C2x footprint size, 0201, was chosen in
order to reduce overall layout size. A 0.1-µF capacitor is required for proper operation of the INA185, and
the user typically will not need to replace or adjust C2x. C3x is a footprint for an additional supply bypass
capacitor that the user can populate to further stabilize the supply. TP2x allows the user to connect an
external supply to the INA185 VS pin.
4.3
C4x
C4x is a 0.1-µF supply bypass capacitor for the optional INA185 reference pin buffer, U2x.
4.4
C5x, R2x, and R4x
C4x, R2x, and R4x form a differential mode filter to the input of the INA185, U1x. By default, this filter is
not installed, with R2x and R4x shorted by a 0-
Ω
resistor, and C4x not populated. If this filter is installed,
R2x and R4x must be less than 10
Ω
with low tolerance (
≤
1%) in order to minimize measurement error.
4.5
C6x, R3x, TP4x, and TP5x
C3x and R3x form a low-pass filter on the output of the INA185, U1x. By default, no filter is installed with
R3x shorted by a 0-
Ω
resistor, and C6x not populated. TP4x shows unfiltered output. By default, TP5x
also shows unfiltered output, but with R3 and C6 populated, TP5x shows filtered output.
4.6
C7x, R5x, and R6x
C7x and R5x form a low-pass filter to the input of the optional reference buffer. R5x and R6x form a
voltage divider that sets a desired reference voltage.
4.7
U1x
U1x is the INA185 current shunt monitor. Four gain-option segments are supplied within the INA185EVM
board. Each segment is populated with one of the available device gains. This configuration enables users
to test the devices and determine the best gain setting for a given application. For x = A to D, the gain is
20 V/V, 50 V/V, 100 V/V, and 200 V/V, respectively.
The following is a list of the factors involved in selecting the appropriate device:
•
The differential input voltage is applied across the inputs, or developed based on the load current that
flows through the shunt resistor.
•
The 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
developed input voltage is amplified by the respective device gain. The output voltage must remain
within the range of 10 mV greater than ground to 100 mV less than the supply voltage.
•
An output less than the minimum allowable output requires a device with a higher gain. Likewise, an
output greater than the maximum allowable output requires a device with a lower gain.
4.8
U2x
U2x is a SOT-23 footprint for a buffer amplifier. By default, this part is not populated.