INA225-Q1 Datasheet, PDF (15/33 Pages) Texas Instruments – High-Speed Current-Shunt Monitor

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INA225-Q1
SBOS728 – FEBRUARY 2015
Changing the gain setting from 25 V/V to 100 V/V, as shown in Table 2, decreases the maximum differential
input voltage from 160 mV down to 40 mV, thus requiring only a 4-mΩ current-sensing resistor to achieve the
4-V output at the 10-A current level. The power dissipated across this resistor at the 10-A current level is
400 mW, significantly increasing the availability of component options to select from.
The increase in gain by a factor of four reduces the power dissipation requirement of the current-sensing resistor
by this same factor of four. However, with this smaller full-scale signal, the measurement uncertainty resulting
from the device fixed input offset voltage increases by the same factor of four. The measurement error resulting
from the device input offset voltage is approximately 0.1% at the 160-mV full-scale input signal for the 25-V/V
gain setting. Increasing the gain to 100 V/V and decreasing the full-scale input signal to 40 mV increases the
offset induced measurement error to 0.38%.
I_MAX
V_OUT
Gain
V_DIFF
R_SENSE
P_RSENSE
V_OS Error
Table 2. Accuracy and R_SENSE Power Dissipation vs Gain Setting
PARAMETER
EQUATION
Full-scale current
Full-scale output voltage
Gain selected
Ideal maximum differential input voltage
Current-sense resistor value
Current-sense resistor power dissipation
Offset voltage error
V_Diff = V_OUT / Gain
R_SENSE = V_Diff / I_MAX
R_SENSE x I_MAX ²
(V_OS / V_DIFF ) x 100
RESULT
10 A
4V
100 V/V
40 mV
4 mΩ
0.4 W
0.375%
7.3.2 Programmable Gain Select
The device features a terminal-controlled gain selection in determining the device gain setting. Four discrete gain
options are available (25 V/V, 50 V/V, 100 V/V, and 200 V/V) on the device and are selected based on the
voltage levels applied to the gain-select terminals (GS0 and GS1). These terminals are typically fixed settings for
most applications but the programmable gain feature can be used to adjust the gain setting to enable wider
dynamic input range monitoring as well as to create an automatic gain control (AGC) network.
Table 3 shows the corresponding gain values and gain-select terminal values for the device.
GAIN
25 V/V
50 V/V
100 V/V
200 V/V
Table 3. Gain Select Settings
GS0
GND
GND
V_S
V_S
GS1
GND
V_S
GND
V_S
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