CS30 datasheet(15/18 Pages) STMICROELECTRONICS

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CS30

Application information

The CS30 can be used to measure current and to feed back the information to a

microcontroller, as shown in Figure 23.

Figure 23. Typical application schematic

The current from the supply flows to the load through the Rsense resistor causing a voltage

drop equal to Vsense across Rsense. The amplifier input currents are negligible, therefore its

inverting input voltage is equal to Vm. The amplifier's open-loop gain forces its non-inverting

input to the same voltage as the inverting input. As a consequence, the amplifier adjusts

current flowing through Rg1 so that the voltage drop across Rg1 exactly matches Vsense.

Therefore, the drop across Rg1 is: VRg1=Vsense=Rsense.Iload

If IRg1 is the current flowing through Rg1, then IRg1 is given by the formula: IRg1=Vsense/Rg1

The IRg1 current flows entirely into resistor Rg3 (the input bias current of the buffer is

negligible). Therefore, the voltage drop on the Rg3 resistor can be calculated as follows:

VRg3=Rg3.IRg1=(Rg3/Rg1).Vsense

Because the voltage across the Rg3 resistor is buffered to the Out pin, Vout can be

expressed as:

Vout=(Rg3/Rg1).Vsense or Vout=(Rg3/Rg1).Rsense.Iload

The resistor ratio Rg3/Rg1 is internally set to 20V/V for CS30A, to 50V/V for CS30B and to

100V/V for CS30C.

The Rsense resistor and the Rg3/Rg1 resistor ratio (equal to Av) are important parameters

because they define the full scale output range of your application. Therefore, they must be

selected carefully.

5 V

Vsense

Vout

Load

Iload

2.8 V to 30 V

Rsense

Vreg

Out

Gnd

VCC

Rg1

Rg2

Rg3

CS30

Microcontroller

ADC

Gnd

VCC

AM06163v1

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