TS12011 TOUCHSTONE [Touchstone Semiconductor Inc], TS12011 Datasheet - Page 9

• Manufacturer Part Number: TS12011
• Description: A 0.8V/1.5uA Nanopower Op Amp, Comparator, and Reference
• Manufacturer: TOUCHSTONE [Touchstone Semiconductor Inc]

Adding Hysteresis to the TS12012 Open-Drain
Option
The TS12012 has open-drain output and requires an
external pull-up resistor to V
Additional hysteresis can be generated using positive
feedback; however, the formulae differ slightly from
those of
procedure to calculate the resistor values for the
TS12012 is as follows:
TS12011_12DS r1p0
Figure 3. Using Four Resistors Introduces
Additional Hysteresis in the TS12012
1) As in the previous section, resistor R2 is
2) As before, the desired hysteresis band
3) Next, resistor R1 is then computed according
4) The trip point for V
5) With the V
chosen according to the formulae:
R2 = V
or
R2 = (V
where the smaller of the two resulting resistor
values is the best starting value.
(V
to the following equation:
R1 = (R2 + R4) x (V
chosen (again, remember that V
point for V
threshold voltage at which the comparator
switches its output from low to high as
V
is computed as follows:
COMPIN+
HYSB
the push-pull
) is set to 100mV.
REFOUT
DD
rises above the trip point.
- V
THR
REFOUT
/150nA
COMPIN+
from Step 4 above, resistor R3
)/150nA - R4
DD
HYSB
option TS12011. The
COMPIN+
falling). This is the
as shown in Figure 3.
/V
DD
)
rising (V
THF
is the trip
THR
) is
Pilot Light Flame Detector with Low-Battery
Lockout Circuit
The TS12011 can be used to create a pilot flame
detector with low-battery lockout circuit as shown in
Figure 4. The circuit is able to detect when the
thermocouple does not detect the pilot flame and
when the battery in the circuit drops to 1.39V. This
circuit makes use of the op-amp, comparator, and
0.58V reference in the TS12011. In this example, a
type R thermocouple is used. It generates a voltage
range from 9mV to 17mV that corresponds to a
temperature range of 900ºC to 1500ºC, which is
typical of a methane pilot flame. If the pilot flame is
removed, the temperature drops; hence, the output
voltage generated by the thermocouple is drops to a
minimum voltage of 0.1mV that is applied to the non-
inverting input of the op-amp. This switches the
output voltage of the op-amp to a LOW state and in
turn, switches Q1 off. If, however, the battery voltage
drops from 1.5V to 1.39V, the comparator output will
switch from an output HIGH to a LOW. This will turn
off Q2 and the output of the op-amp will turn Q1 off.
The complete circuit consumes approximately 95µA
of supply current at V
PC Board Layout and Power-Supply Bypassing
While power-supply bypass capacitors are not
typically required, it is good engineering practice to
use 0.1uF bypass capacitors close to the device’s
power supply pins when the power supply impedance
is high, the power supply leads are long, or there is
excessive noise on the power supply traces. To
reduce stray capacitance, it is also good engineering
practice to make signal trace lengths as short as
6) As before, the last step is to verify the trip
TS12011/TS12012
R3 = 1/[V
voltages and hysteresis band with the
standard resistor values used in the circuit:
For V
V
For V
V
-(R1/(R2+R4)) x V
and Hysteresis Band is given by V
THR
THF
= V
= V
COMPIN+
COMPIN+
REFOUT
REFOUT
THR
/(V
rising:
falling:
DD
x R1 x (1/R1+1/R2+1/R3)
x R1 x(1/R1+1/R3+1/(R2+R4))
REFOUT
= 1.5V.
DD
x R1) - (1/R1) - (1/R2)]
THR
– V
Page 9
RTFDS
THF