LTC2913CDD-2(RevA) データシートの表示（PDF） - Linear Technology
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LTC2913CDD-2 Datasheet PDF : 12 Pages
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LTC2913
APPLICATIONS INFORMATION
Power-Up/Power-Down
As soon as VCC reaches 1V during power-up, the UV output
asserts low and the OV output weakly pulls to VCC.
The LTC2913 is guaranteed to assert UV low and OV high
under conditions of low VCC, down to VCC = 1V. Above
VCC = 2V (2.1V maximum), the VH and VL inputs take
control.
Once both VH inputs and VCC are valid, an internal timer
is started. After an adjustable delay time, UV weakly pulls
high.
Threshold Accuracy
Reset threshold accuracy is important in a supply-sensitive
system. Ideally, such a system resets only if supply voltages
fall outside the exact thresholds for a specified margin.
All LTC2913 inputs have a relative threshold accuracy of
±1.5% over the full operating temperature range.
For example, when the LTC2913 is programmed to moni-
tor a 5V input with a 10% tolerance, the desired UV trip
point is 4.5V. Because of the ±1.5% relative accuracy of
the LTC2913, the UV trip point is between 4.433V and
4.567V which is 4.5V ±1.5%.
Likewise, the accuracy of the resistances chosen for RA,
RB and RC can affect the UV and OV trip points as well.
Using the example just given, if the resistances used to
set the UV trip point have 1% accuracy, the UV trip range
is between 4.354V and 4.650V. This is illustrated in the
following calculations.
The UV trip point is given as:
VUV
=
0.5V
1+
RC
RA + RB
The two extreme conditions, with a relative accuracy of
1.5% and resistance accuracy of 1%, result in:
VUV(MIN)
=
0.5V
•
0.985
•
1+
RC
(RA +
• 0.99
RB) • 1.01
and
VUV(MAX)
=
0.5V
•
1.015
•
1+
RC • 1.01
(RA + RB) • 0.99
For
a desired
trip
point
of 4.5V,
RC
RA + RB
=8
Therefore,
VUV(MIN)
=
0.5V
•
0.985
•
1+
8
0.99
1.01
=
4.354V
and
VUV(MAX)
=
0.5V
• 1.015
•
1+
8
1.01
0.99
=
4.650V
Glitch Immunity
In any supervisory application, noise riding on the moni-
tored DC voltage causes spurious resets. To solve this
problem without adding hysteresis, which causes a new
error term in the trip voltage, the LTC2913 lowpass filters
the output of the first stage comparator at each input. This
filter integrates the output of the comparator before as-
serting the UV or OV logic. A transient at the input of the
comparator of sufficient magnitude and duration triggers
the output logic. The Typical Performance Characteristics
show a graph of the Transient Duration vs. Comparator
Overdrive.
2913fa
8
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