TSM9117 TOUCHSTONE [Touchstone Semiconductor Inc], TSM9117 Datasheet - Page 13

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

Figure 3: Using Three Resistors Introduces Additional
Figure 2: TSM9117-TSM9120 Threshold Hysteresis
hysteresis effectively forces one comparator input to
move quickly past the other input, moving the input
out of the region where oscillation occurs. out of the
region where oscillation occurs. Figure 2 illustrates
the case in which an IN- input is a fixed voltage and
an IN+ is varied. If the input signals were reversed,
the figure would be the same with an inverted
output. To save cost and external pcb area, an
internal 4mV hysteresis circuit was added to the
TSM9117–TSM9120.
Adding Hysteresis to the TSM9117/TSM9119
The
hysteresis
hysteresis can be generated with three external
resistors using positive feedback as shown in Figure
3. Unfortunately, this method also reduces the
hysteresis
procedure to calculate resistor values.
TSM9117_20DS r1p0
`
TSM9117/TSM9119
Hysteresis in the TSM9117 & TSM9119.
Band
response
band
(V
HYSB
time.
)
exhibit
of
Use
4mV.
the
an
Additional
following
internal
TSM9117-TSM9120
1) Setting R2. As the leakage current at the IN
2) Next, the desired hysteresis band (V
3) Resistor R1 is calculated according to the
4) The trip point for V
5) With the V
pin is less than 2nA, the current through R2
should be at least 0.2μA to minimize offset
voltage errors caused by the input leakage
current. The current through R2 at the trip
point is (V
In solving for R2, there are two formulas –
one each for the two possible output states:
R2 = V
or
R2 = (V
From the results of the two formulae, the
smaller of the two resulting resistor values is
chosen. For example, when using the
TSM9117 (V
and if I
formulae above produce two resistor values:
6.26MΩ and 10.24MΩ - the 6.2MΩ standard
value for R2 is selected.
set. In this example, V
following equation:
R1 = R2 x (V
and substituting the values selected in 1)
and 2) above yields:
R1 = 6.2MΩ x (100mV/3.3V) = 187.88kΩ.
The 187kΩ standard value for R1 is chosen.
such that V
is the trip point for V
threshold voltage at which the comparator
switches its output from low to high as V
rises above the trip point. In this example,
V
is then computed as follows:
R3 = 1/[V
R3 = 1/[3V/(1.252V x 187kΩ)
- (1/187kΩ) - (1/6.2MΩ)] = 136.9kΩ
THR
is set to 3V.
R2
REF
CC
= 0.2μA is chosen, then the
THR
/I
REF
- V
THR
R2
THR
/(V
REF
HYSB
REF
- V
from Step 4 above, resistor R3
> V
REF
)/I
= 1.252V) at a V
OUT
/V
R2
REF
IN
x R1) - (1/R1) - (1/R2)]
CC
)/R2.
IN
rising (V
)
x (R1 + R2)/R2 (V
HYSB
falling). This is the
is set to 100mV.
THR
) is chosen
CC
= 3.3V
Page 13
HYSB
RTFDS
THF
IN
) is