TSM9117 TOUCHSTONE [Touchstone Semiconductor Inc], TSM9117 Datasheet - Page 14

• Manufacturer Part Number: TSM9117
• Description: 1.6V Nanopower Comparators with/without Internal References
• Manufacturer: TOUCHSTONE [Touchstone Semiconductor Inc]

Figure 4: Using Four Resistors Introduces Additional
TSM9117-TSM9120
Adding Hysteresis to the TSM9118/TSM9120
The TSM9118/TSM9120 have a 4mV internal
hysteresis band. Both products have open-drain
outputs and require an external pullup resistor to V
as shown in Figure 4. Additional hysteresis can be
generated using positive feedback; however, the
formulae
TSM9117/TSM9119. The procedure to calculate the
resistor values for the TSM9118/TSM9120 is as
follows:
Page 14
6)
1) As in the previous section, resistor R2 is
In this example, a 137kΩ, 1% standard
value resistor is selected for R3.
and hysteresis band using the standard
resistance values:
For
V
= 3V
and, for V
V
and Hysteresis Band = V
chosen according to the formulae:
R2 = V
or
R2 = (V
The last step is to verify the trip voltages
Hysteresis in the TSM9118 & TSM9120.
THR
THF
differ
VIN
= V
= V
REF
rising:
CC
THR
REF
IN
/0.2µA
- V
slightly
falling:
x R1 [(1/R1) + (1/R2) + (1/R3)]
- (R1 x V
REF
)/0.2μA - R4
CC
from
/R2) = 2.9V
THR
those
– V
THF
= 100mV
of
the
CC
PC Board Layout and Power-Supply Bypassing
While power-supply bypass capacitors are not
typically required, it is good engineering practice to
use 0.1µF 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 possible. Also recommended are a ground
plane and surface mount resistors and capacitors.
2) As before, the desired hysteresis band
3) Next, resistor R1 is then computed
4) The trip point for V
5) With the V
6) As before, the last step is to verify the trip
where the smaller of the two resulting
resistor values is the best starting value.
(V
according to the following equation:
R1 = (R2 + R4) x (V
(again, remember that V
for V
at which the comparator switches its output
from low to high as V
point.
is computed as follows:
R3 = 1/[V
voltages and hysteresis band with the
standard resistor values used in the circuit:
For V
V
and, for V
V
-[R1/(R2+R4)] x V
and Hysteresis Band is given by V
THR
THF
HYSB
IN
= V
= V
IN
) is set to 100mV.
falling). This is the threshold voltage
rising:
REF
REF
THR
IN
THR
falling:
x R1 x [1/R1+1/R3+1/(R2+R4)]
x R1 x (1/R1+1/R2+1/R3)
/(V
from Step 4 above, resistor R3
REF
CC
IN
x R1) - (1/R1) - (1/R2)]
HYSB
rising (V
IN
TSM9117_20DS r1p0
rises above the trip
/V
THF
CC
is the trip point
)
THR
) is chosen
THR
- V
RTFDS
THF