TS1102
or
S
L A
x R
SE
R
A
SE
Table 1: Internal Gain Setting Resistors (Typical
Values)
GAIN (V/V)
25
50
100
200
R
GAIN
(Ω)
400
200
100
100
R
OUT
(Ω)
10k
10k
10k
20k
Part Number
TS1102-25
TS1102-50
TS1102-100
TS1102-200
Since the FET’s drain terminal is connected to R
OUT
,
the output voltage of the TS1102 at the OUT
terminal is, therefore;
V
T
L A
x R
SE
SE
x
R
T
R
A
The current-sense amplifier’s gain accuracy is
therefore the ratio match of R
OUT
to R
GAIN
. For each
of the four gain options available, Table 1 lists the
values for R
OUT
and R
GAIN
. The TS1102’s output
stage is protected against input overdrive by use of
an output current-limiting circuit of
3mA
(typical) and
a
7V
internal clamp protection circuit.
To achieve its very-low input offset voltage
performance over temperature, VSENSE voltage,
and power supply voltage, the design of the
TS1102’s amplifier is chopper-stabilized, a
commonly-used technique to reduce significantly the
input offset voltage of amplifiers. This method,
however, does employ the use of sampling
techniques and therefore residue of the TS1102’s
10kHz internal clock is contained in the TS1102’s
output voltage spectrum.
APPLICATIONS INFORMATION
Therefore,
Choosing the Sense Resistor
V
OUT(max)
= V
RS+(min)
- V
SENSE(max)
– V
OH(max)
Selecting the optimal value for the external RSENSE
is based on the following criteria and for each
commentary follows:
1) RSENSE Voltage Loss
2) V
OUT
Swing vs. Applied Input Voltage at V
RS+
and Desired V
SENSE
3) Total I
LOAD
Accuracy
4) Circuit Efficiency and Power Dissipation
5) RSENSE Kelvin Connections
6) Sense Resistor Composition
1) RSENSE Voltage Loss
For lowest IR voltage loss in RSENSE, the smallest
usable value for RSENSE should be selected.
2) V
OUT
Swing vs. Applied Input Voltage at V
RS+
and Desired V
SENSE
As there is no separate power supply pin for the
TS1102, the circuit draws its power from the applied
voltage at both its RS+ and RS- terminals.
Therefore, the signal voltage at the OUT terminal is
bounded by the minimum supply voltage applied to
the TS1102.
and
R
SE
V
SE
T
A
max
L A
max
where the full-scale V
SENSE
should be less than
V
OUT(MAX)
/ A
at the application’s minimum RS+
terminal voltage. For best performance with a 3.6V
power supply, RSENSE should be chosen to
generate a V
SENSE
of: a) 120mV (for the 25V/V GAIN
option), b) 60mV (for the 50V/V GAIN option), c)
30mV (for the 100V/V GAIN option), or d) 15mV (for
the 200V/V GAIN option) at the full-scale I
LOAD(MAX)
current in each application. For the case where the
minimum power supply voltage is higher than 3.6V,
each of the four full-scale V
SENSE
s above can be
increased.
3) Total I
LOAD
Accuracy
In
the
TS1102’s
linear
region
where
V
OUT
< V
OUT(MAX)
, there are two specifications related
to the circuit’s accuracy: a) the TS1102’s input offset
voltage (V
OS
= 200μV, max) and b) its gain error
(GE(max) = 0.5%).
Page 8
TS1102DS r1p0
RTFDS
TOUCHSTONE [ TOUCHSTONE SEMICONDUCTOR INC ]
