TS1005
Configuring the TS1005 as Microwatt Analog
Comparator
design, therefore, was to set the feedback resistor
R3:
Although optimized for use as an operational
amplifier, the TS1005 can also be used as a rail-to-
rail I/O comparator as illustrated in Figure 7.
R3 = 10MΩ
Calculating a value for R1 is given by the following
expression:
R1 = R3 x (VHYB/VDD)
Substituting VHYB = 100mV, VDD = 3.0V, and R3 =
10MΩ into the equation above yields:
R1 = 333kΩ
The following expression was then used to calculate
a value for R2:
Figure 7: A MicroWatt Analog Comparator with User-
Programmable Hysteresis.
R2 = 1/[VHI/(VREF x R1) – (1/R1) – (1/R3)]
External hysteresis can be employed to minimize the
risk of output oscillation. The positive feedback
circuit causes the input threshold to change when
the output voltage changes state. The diagram in
Figure 8 illustrates the TS1005’s analog comparator
Substituting VHI = 1V, VREF = 1.5V, R1 = 333kΩ, and
R3 = 10MΩ into the above expression yields:
R2 = 909kΩ
Printed Circuit Board Layout Considerations
Even though the TS1005 operates from a single
0.8V to 5.5V power supply and consumes very little
supply current, it is always good engineering
practice to bypass the power supplies with a 0.1μF
ceramic capacitor placed in close proximity to the
VDD and VSS (or GND) pins.
Figure 8: Analog Comparator Hysteresis Band and Output
Switching Points.
hysteresis band and output transfer characteristic.
Good pcb layout techniques and analog ground
plane management improve the performance of any
analog circuit by decreasing the amount of stray
capacitance that could be introduced at the op amp's
inputs and outputs. Excess stray capacitance can
easily couple noise into the input leads of the op
amp and excess stray capacitance at the output will
add to any external capacitive load. Therefore, PC
board trace lengths and external component leads
should be kept a short as practical to any of the
TS1005’s package pins. Second, it is also good
engineering practice to route/remove any analog
ground plane from the inputs and the output pins of
the TS1005.
The design of an analog comparator using the
TS1005 is straightforward. In this application, a 3.0V
power supply (VDD) was used and the resistor divider
network formed by RD1 and RD2 generated a
convenient reference voltage (VREF) for the circuit at
½ the supply voltage, or 1.5V, while keeping the
current drawn by this resistor divider low. Capacitor
C1 is used to filter any extraneous noise that could
couple into the TS1005’s inverting input.
In this application, the desired hysteresis band was
set to 100mV (VHYB) with a desired high trip-point
(VHI) set at 1V and a desired low trip-point (VLO) set
at 0.9V.
Since the TS1005 is a low supply current amplifier
(1.3µA, typical), it is desired that the design of an
analog comparator using the TS1005 should also
use as little current as practical. The first step in the
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TS1005DS r1p0
RTFDS
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