LTC2914 Linear Technology, LTC2914 Datasheet - Page 10

• Manufacturer Part Number: LTC2914
• Description: Quad UV/OV Positive/Negative Voltage Monitor
• Manufacturer: Linear Technology

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LTC2914
Power-Up/Power-Down
As soon as V
asserts low and the OV output weakly pulls to V
The LTC2914 is guaranteed to assert UV low and OV high
under conditions of low V
2V (2.1V maximum) the VH and VL inputs take control.
Once all VH inputs and V
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 specifi ed margin.
All LTC2914 inputs have a relative threshold accuracy of
±1.5% over the full operating temperature range.
For example, when the LTC2914 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 LTC2914, 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 R
R
ing 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 fol-
lowing calculations.
The UV trip point is given as:
The two extreme conditions, with a relative accuracy of
1.5% and resistance accuracy of 1%, result in:
APPLICATIO S I FOR ATIO
10
B
V
and R
UV
=
C
0 5
.
affect the UV and OV trip points as well. Us-
CC
V
reaches 1V during power-up, the UV output
⎛
⎝ ⎜
1
+
U
R
A
R
+
C
CC
CC
R
U
, down to V
B
become valid an internal timer
⎞
⎠ ⎟
W
CC
= 1V. Above V
U
CC
.
CC
A
=
,
Therefore,
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 LTC2914 lowpass fi lters
the output of the fi rst stage comparator at each input. This
fi lter integrates the output of the comparator before as-
serting the UV or OV logic. A transient at the input of the
comparator of suffi cient magnitude and duration triggers
the output logic. The Typical Performance Characteristics
section shows a graph of the Transient Duration vs Com-
parator Overdrive.
For a desired trip point of 4.5 5 V,
and
a
n n d
V
V
V
V
UV MIN
UV MAX
UV MIN
UV MAX
(
(
(
(
)
)
)
)
=
=
=
=
0 5
0 5
0 5
0 5
.
.
.
.
V
V
V
V
• .
• .
• .
• .
0 985
0 985
1 015
1 015
•
•
•
•
⎛
⎜ ⎜
⎝
⎛
⎝
⎛
⎜
⎝
⎛
⎝
1
1 8 0 99
1
1 8 1 01
+
+
+
+
(
(
R
R
R
1 01
0 99
A
A
A
.
.
R
R
.
.
R
+
+
C
+
C
C
R
R
⎞
⎠
• .
R
⎞
⎠
B
• .
B
0 99
B
=
)
1 01
=
) )
= 8
• .
4 354
• . 0 99
4 650 0 V
1 01
.
.
⎞
⎟
⎠
V
⎞
⎟
⎠
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