LTC2914 Linear Technology, LTC2914 Datasheet - Page 12

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

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LTC2914
At V
on. Therefore, an external pull-up resistor of no more than
100k is recommended on the OV pin if the state and pull-up
strength of the OV pin is crucial at very low V
Note however, by adding an external pull-up resistor, the
pull-up strength on the OV pin is increased. Therefore, if
it is connected in a wired-OR connection, the pull-down
strength of any single device must accommodate this
additional pull-up strength.
Output Rise and Fall Time Estimation
The UV and OV outputs have strong pull-down capabil-
ity. The following formula estimates the output fall time
(90% to 10%) for a particular external load capacitance
(C
where R
transistor, typically 50Ω at V
perature (25°C). C
on the pin. Assuming a 150pF load capacitance, the fall
time is 16.5ns.
The rise time on the UV and OV pins is limited by a 400k
pull-up resistance to V
output rise time (10% to 90%) at the UV and OV pins:
where R
APPLICATIO S I FOR ATIO
12
LOAD
t
t
FALL
RISE
CC
= 1V, the weak pull-up current on OV is barely turned
):
≈ 2.2 • R
≈ 2.2 • R
PD
PU
is the on-resistance of the internal pull-down
is the pull-up resistance.
PD
PU
LOAD
U
• C
• C
CC
LOAD
LOAD
is the external load capacitance
. A similar formula estimates the
U
CC
> 1V and at room tem-
W
CC
U
.
OV Latch (LTC2914-1)
With the LATCH pin held low, the OV pin latches low when
an OV condition is detected. The latch is cleared by raising
the LATCH pin high. If an OV condition clears while LATCH
is held high, the latch is bypassed and the OV pin behaves
the same as the UV pin with a similar timeout period at the
output. If LATCH is pulled low while the timeout period is
active, the OV pin latches as before.
Disable (LTC2914-2)
The LTC2914-2 allows disabling the UV and OV outputs
via the DIS pin. Pulling DIS high forces both outputs to
remain weakly pulled high, regardless of any faults that
occur on the inputs. However, if a UVLO condition oc-
curs, UV asserts and pulls low, but the timeout function
is bypassed. UV pulls high as soon as the UVLO condition
is cleared.
DIS has a weak 2µA (typical) internal pull-down current
guaranteeing normal operation with the pin left open.
2914f