TS9002
1. As described below, determine the desired
hysteresis and select resistors R4 and R5
accordingly. This circuit has ±5mV of
hysteresis at the input where the input
voltage VIN will appear larger due to the
input resistor divider.
VHB
R1 ꢀ
R2 ꢀ
ꢀ
2 x ꢁREF
VHB
2
1.1ꢂ2 ꢃ
ꢁREF
where IREF is the primary source of current out of the
reference pin and should be maintained within the
maximum current the reference can source. It is safe
to maintain the current within 20µA. It is also
important to ensure that the current from reference is
much larger than the HYST pin input current. Given
R2 = 2.4MΩ, the current sourced by the reference is
0.5μA. This allows the hysteresis band and R1 to be
approximated as follows:
R1(kΩ) ꢀ VHB(mv)
Figure 3. Window Detector
Note the hysteresis is the same for both
comparators.
2. Choosing R1. As the leakage current at the
INB- pin is less than 1nA, the current
through R1 should be at least 100nA to
minimize offset voltage errors caused by the
input leakage current. Values within 100kΩ
and 1MΩ are recommended. In this
example, a 294kΩ, 1% standard value
resistor is selected for R1.
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 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.
3. Calculating R2 + R3. As the input voltage
VIN rises, the overvoltage threshold should
be 5.5V. Choose R2 + R3 as follows:
VOTH
R1 + Rꢄ ꢀ R1 x ꢁ
ꢃ 1ꢂ
VREF+VHYS
Window Detector
5.5V
ꢀ 294kΩ x ꢁ
ꢃ 1ꢂ
1.1ꢂ2V + 5mV
The schematic shown in Figure 3 is for a 4.5V
undervoltage threshold detector and
a
5.5V
ꢀ 1.0ꢅꢂMΩ
overvoltage threshold detector using the TS9002.
Resistor components R1, R2, and R3 can be
selected based on the threshold voltage desired
while resistors R4 and R5 can be selected based on
the hysteresis desired. Adding hysteresis to the
circuit will minimize chattering on the output when
the input voltage is close to the trip point. OUTA and
OUTB generate the active low undervoltage
indication and active-low overvoltage indication,
respectively. If both OUTA and OUTB signals are
ANDed together, the resulting output of the AND
gate is an active-high, power-good signal. To design
the circuit, the following procedure needs to be
followed:
4. Calculating R2. As the input voltage VIN falls,
the undervoltage threshold should be 4.5V.
Choose R2 as follows:
ꢀ
VREFꢃVHYS
VUTH
R2 ꢀ (R1 + R2+ Rꢄ) x
ꢃ 294k
ꢀ
1.1ꢂ2Vꢃ5mV
ꢀ (294kΩ + 1.0ꢅꢂMΩ) x
ꢀ ꢅ2.2kΩ
ꢃ 294k
4.5
TS9002DS r1p0
Page 9
RTFDS
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