TSM931-TSM934
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
performed:
1. As described in the section “Hysteresis
(TSM931-TSM933)”, 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.
2. Selecting 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.
Figure 4. Auto-Off Power Switch Operates on 2.5µA
quiescent current.
can be determined by the RC time constant as
follows:
R x C ꢃ 4.6 s
The period value will change depending on the
leakage current and the voltage applied to the
circuit. For instance: 2MΩ x 10μF x 4.6 s = 92 s.
3. Calculating R2 + R3. As the input voltage
VIN rises, the overvoltage threshold should
be 5.5V. Choose R2 + R3 as follows:
Window Detector
VOTH
R2 + R3 ꢀ R1 x ꢃ
ꢂ 1ꢄ
The schematic shown in Figure 5 is for a 4.5V
VREF+VHYS
undervoltage threshold detector and
a
5.5V
overvoltage threshold detector using the TSM933.
Resistor components R1, R2, and R3 can be
5.5V
ꢀ 294kΩ x ꢃ
ꢂ 1ꢄ
1.182V +5mV
ꢀ 1.068MΩ
4. Calculating R2. As the input voltage VIN
falls, the undervoltage threshold should be
4.5V. Choose R2 as follows:
ꢀ
VREFꢂVHYS
VUTH
R2 ꢀ (R1 + R2+ R3) x
ꢂ 294k
ꢀ
1.182Vꢂ5mV
ꢀ (294kΩ + 1.068MΩ) x
ꢀ 62.2kΩ
ꢂ 294k
4.5
Figure 5. Window Detector
In this example, a 61.9kΩ, 1% standard
value resistor is selected for R2.
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,
5. Calculating R3.
R3 ꢀ (R2 + R3) ꢂ R2
TSM931_34DS r1p0
Page 15
RTFDS
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