TS1005
PIN FUNCTIONS
Pin
1
2
3
4
5
Label
OUT
V
SS
+IN
-IN
V
DD
Function
Amplifier Output.
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 Input.
Amplifier Inverting Input.
Positive Supply Connection. Connect a 0.1µF bypass capacitor
from this pin to analog GND.
THEORY OF OPERATION
The TS1005 is fully functional for an input signal
from the negative supply (V
SS
or GND) to the
positive supply (V
DD
). The input stage consists 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 the TS1005 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 TS1005’s 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 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 TS1005 output stages voltage swings within
3.5mV from the rails at 1.8V 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
TS1005 swings within 30mV of V
DD
and within 13mV
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
is 20.9% and air samples containing less than 18%
oxygen are considered dangerous. In industrial
applications, oxygen sensors are used to detect the
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TS1005DS r1p0
RTFDS
TOUCHSTONE [ TOUCHSTONE SEMICONDUCTOR INC ]
