Application information TSC101
14/18 Doc ID 13313 Rev 3
5 Application information
The TSC101 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 R
sense
resistor causing a voltage
drop equal to V
sense
across R
sense
. The amplifier 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 Rg1 so that the voltage drop across Rg1 exactly matches V
sense
.
Therefore, the drop across Rg1 is: V
Rg1
=V
sense
=R
sense
.I
load
If I
Rg1
is the current flowing through Rg1, then I
Rg1
is given by the formula: I
Rg1
=V
sense
/Rg1
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
Because the voltage across the R
g3
resistor is buffered to the Out pin, V
out
can be
expressed as:
V
out
=(R
g3
/R
g1
).V
sense
or V
out
=(R
g3
/R
g1)
.R
sense
.I
load
The resistor ratio R
g3
/R
g1
is internally set to 20V/V for TSC101A, to 50V/V for TSC101B and
to 100V/V for TSC101C.
The R
sense
resistor and the R
g3
/R
g1
resistor ratio (equal to A
v
) are important parameters
because they define the full scale output range of your application. Therefore, they must be
selected carefully.
6
6
SENSE
6
OUT
,OAD
)
LOAD
6TO6
2
SENSE
6
REG
6
P
6
M
/UT
'ND
6
##
2G 2G
2G
43#
-ICROCONTROLLER
!$#
'ND
6
##
!-
