Step 6.
Compute the gain of the current amplifier.
The gain value must amplify the Vrsense input signal (the voltage across the Rsense resistor) so that
the Vout maximum and minimum output voltages (output voltage of the opamp) is measurable via the
ADC.
The following formulas were used to calculate the opamp gain when Imax = 250 mA.
VRSENSE = RSENSE ⋅ IMAX = 0.1V
VOUT = GAIN ⋅ VRSENSE
According to the previous formula, and with the constraint that Vout must not exceed 5 V, the opamp
gain is set to 50. This value has been selected between four possible gain values (25, 50, 75, and 100)
provided by the
TSC103IYPT
. The gain selection is implemented with the resistors connected to the
SEL1 and SEL2 pins.
VOUT = 50 ⋅ VRSENSE = 50 ⋅ 0.1 = 5V
Step 7.
Repeating the same approach used above, check that the gain = 50 is a good choice even when the
current flowing through the Rsense resistor is the mimimum possible (that is, Imin = 25 mA).
VRSENSE = RSENSE ⋅ IMIN = 0.01V
VOUT = GAIN ⋅ VRSENSE
VOUT = 50 ⋅ VRSENSE = 50 ⋅ 0.01 = 0.5V
Note:
The layout of the board can accommodate Rsense resistors with footprints compatible with 0603 to
2512 packages.
UM2995
How to customize the current sensing network
UM2995
-
Rev 1
page 27/47
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