TSM931 TOUCHSTONE [Touchstone Semiconductor Inc], TSM931 Datasheet - Page 14

• Manufacturer Part Number: TSM931
• Description: Ultra Low-Power Single/Dual-Supply Comparators with Reference
• Manufacturer: TOUCHSTONE [Touchstone Semiconductor Inc]

TSM931-TSM934
feedback. The following procedure explains the
steps to design the circuit for a desired hysteresis:
Page 14
Figure 3. External Hysteresis
1. Choosing R3. As the leakage current at the
2. Next, the desired hysteresis band ( V
3. Calculating R1.
4. Choose the trip point for V
5. Calculating R2.
IN+ pin is less than 1nA, the current through
R3 should be at least 100nA to minimize
offset voltage errors caused by the input
leakage current. For R3
current through R3 is V
point. In this case, a 10MΩ resistor is a good
standard value for R3.
set. In this example, V
R1
In this example, a 100kΩ, 1% standard
value resistor is selected for R1.
which is the threshold voltage at which the
comparator switches its output from low to
high as V
example, choose V
100kΩ
10MΩ x
R3 x
IN
50mV
V
rises above the trip point. In this
V+
5V
H
THR
HB
= 3V.
is set to 50mV.
REF
IN
/R3 at the trip
11.8MΩ, the
rising (V
HB
THR
) is
),
Board Layout and 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
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.
TYPICAL APPLICATION CIRCUITS
Auto-Off Power Source
A timed auto power-off circuit can be designed as
shown in Figure 4 where the output of the TSM931
is the switched power-supply output. With an internal
reference, hysteresis, high current output, and a 2.5
μA supply current, the TSM931 provides a wealth of
features that make it perfect for this application.
While consuming only 3.5μA of quiescent current
with a 10mA load, the TSM931 is able to generate a
voltage of VBATT – 0.12V. As shown in the figure,
three resistors are used to generate a hysteresis
band of 100mV and sets the IN+ trip point to 50mV
when IN+ is going low. The maximum power-on
period of the OUT pin before power-down occurs
6. The last step is to verify the trip voltages and
R2
In this example, a 64.9kΩ, 1% standard
value resistor is selected for R2.
hysteresis
resistance values:
V
V
supply
THR
THF
65.44kΩ
1.182V x 100kΩ
V
V
V
THR
REF
REF
pins
V
3
THR
x R1 x
–
x R1
band
R1 x V+
when
1
R3
1
R1
R1
using
1
1
100kΩ
+
the
TSM931_34DS r1p0
R3
R2
1
1
1
+
power
the
R3
10MΩ
1
1
standard
supply
RTFDS