Datasheet

TSC103 Application information
Doc ID 16873 Rev 2 19/26
7 Application information
The TSC103 can be used to measure current and to feed back the information to a
microcontroller.
Figure 22. Single-supply configuration schematic
The current from the supply flows to the load through the R
sense
resistor, causing a voltage
drop equal to V
sense
across R
sense
. The amplifier’s input currents are negligible, therefore its
inverting input voltage is equal to V
m
. 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 R
g1
so that the voltage drop across R
g1
matches V
sense
exactly.
Therefore, the drop across R
g1
is:
V
Rg1
=V
sense
=R
sense
.I
load
If I
Rg1
is the current flowing through R
g1
, then I
Rg1
is given by the formula:
I
Rg1
=V
sense
/R
g1
The I
Rg1
current flows entirely into resistor R
g3
(the input bias current of the buffer is
negligible). Therefore, the voltage drop on the R
g3
resistor can be calculated as follows.
V
Rg3
=R
g3
.I
Rg1
=(R
g3
/R
g1
).V
sense
=K1.V
sense
with K1=R
g3
/R
g1
.
The voltage across the R
g3
resistor is buffered to the Out pin by the voltage buffer, featuring
a gain equal to K2. Therefore V
out
can be expressed as:
V
out
=K1.K2.V
sense
= Av.V
sense
with Av= K1.K2
or: V
out
= Av .R
sense
.I
load
AM04517
5 V
Vsense
load
Iload
Rsense
Common-mode voltage: 2.9 V to 70 V
Vp Vm
Rg1
Rg2
Vcc+
Vcc
SEL1
Vout
load
Iload
Rsense
Rg3
Vp Vm
Out
Rg1
Rg2
Voltage
buffer
Sense
amplifier
Vcc+
TSC103
Gnd
Vcc-
K2
µ Controller
ADC
Vcc
GPIO2
Gnd
SEL1
SEL2
GPIO1