TS1002/TS1004
PIN FUNCTIONS
Pin
TS1002
TS1004
MSOP
TSSOP
1, 7
1, 7, 8, 14
4
3, 5
2, 6
8
7
3, 5, 10, 12
2, 6, 9, 13
14
Label
OUT
V
SS
+IN
-IN
V
DD
Function
Amplifier Outputs: A, B – TS1002; A, B, C, D – TS1004
Negative Supply or Analog GND. If applying a negative voltage to
this pin, connect a 0.1µF capacitor from this pin to analog GND.
Amplifier Non-inverting Inputs: A, B – TS1002; A, B, C, D – TS1004
Amplifier Inverting Inputs: A, B – TS1002; A, B, C, D – TS1004
Positive Supply Connection. Connect a 0.1µF bypass capacitor from
this pin to analog GND.
THEORY OF OPERATION
The TS1002 and the TS1004 are fully functional for
input signals from the negative supply (V
SS
or GND)
to the positive supply (V
DD
). Their input stages
consist of two differential amplifiers, a p-channel
CMOS stage and an n-channel CMOS stage that
are active over different ranges of the input common
mode voltage. The p-channel input pair is active for
input common mode voltages, V
INCM
, between the
negative supply to approximately 0.4V below the
positive supply. As the common-mode input voltage
moves closer towards V
DD
, an internal current mirror
activates the n-channel input pair differential pair.
The p-channel input pair becomes inactive for the
balance of the input common mode voltage range up
to the positive supply. Because both input stages
have their own offset voltage (V
OS
) characteristic, the
offset voltage of these amplifiers is a function of the
applied input common-mode voltage, V
INCM
. The V
OS
has a crossover point at ~0.4V from V
DD
(Refer to
the V
OS
vs. V
CM
curve in the Typical Operating
Characteristics section). Caution should be taken in
applications where the input signal amplitude is
comparable to the amplifiers’ V
OS
value and/or the
design requires high accuracy. In these situations, it
is necessary for the input signal to avoid the
crossover point. In addition, amplifier parameters
such as PSRR and CMRR which involve the input
offset voltage will also be affected by changes in the
input common-mode voltage across the differential
pair transition region.
The amplifiers’ second stage is a folded-cascode
transistor arrangement that converts the input stage
differential signals into a single-ended output. A
complementary drive generator supplies current to
the output transistors that swing rail to rail.
The amplifiers’ output stage voltage swings within
1.2mV from the rails at 0.8V supply when driving an
output load of 100kΩ - which provides the maximum
possible dynamic range at the output. This is
particularly important when operating on low supply
voltages. When driving a stiffer 10kΩ load, the
amplifiers’ output swings within 10mV of V
DD
and
within 5mV of V
SS
(or GND).
APPLICATIONS INFORMATION
Portable Gas Detection Sensor Amplifier
Gas sensors are used in many different industrial
and medical applications. Gas sensors generate a
current that is proportional to the percentage of a
particular gas concentration sensed in an air
sample. This output current flows through a load
resistor and the resultant voltage drop is amplified.
Depending on the sensed gas and sensitivity of the
sensor, the output current can be in the range of
tens of microamperes to a few milliamperes. Gas
sensor datasheets often specify a recommended
load resistor value or a range of load resistors from
which to choose.
There are two main applications for oxygen sensors
– applications which sense oxygen when it is
abundantly present (that is, in air or near an oxygen
tank) and those which detect traces of oxygen in
parts-per-million
concentration.
In
medical
applications, oxygen sensors are used when air
quality or oxygen delivered to a patient needs to be
monitored. In fresh air, the concentration of oxygen
TS1002_4DS r1p0
Page 7
RTFDS
TOUCHSTONE [ TOUCHSTONE SEMICONDUCTOR INC ]
