LTC2919HDDB-3.3-TRPBF View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
LTC2919HDDB-3.3-TRPBF Datasheet PDF : 20 Pages
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LTC2919
APPLICATIONS INFORMATION
The LTC2919 is a low power, high accuracy triple/dual
supply monitor with two adjustable inputs and an accurate
UVLO that can monitor a third supply. Reset timeout may
be selected with an external capacitor, set to an internally
generated 200ms, or disabled entirely.
The three-state polarity select pin (SEL) chooses one of
three possible polarity combinations for the adjustable
input thresholds, as described in Table 1. An individual
output is released when its corresponding ADJ input is
valid (above threshold if configured for positive polarity,
below threshold if configured for negative polarity).
Both input voltages (VADJ1 and VADJ2) must be valid and
VCC above the UVLO threshold for longer than the reset
timeout period before RST is released. The LTC2919
asserts the reset output during power-up, power-down
and brownout conditions on any of the voltage inputs.
Power-Up
The LTC2919 uses proprietary low voltage drive circuitry
for the RST, OUT1 and OUT2 pins which holds them low
with VCC as low as 200mV. This helps prevent indeter-
minate voltages from appearing on the outputs during
power-up.
In applications where the low voltage pull-down capabil-
ity is important, the supply to which the external pull-up
resistor connects should be the same supply which pow-
ers the part. Using the same supply for both ensures that
RST, OUT1 and OUT2 never float above 200mV during
power-up, as the pull-down ability of the pin will then
increase as the required pull-down current to maintain a
logic low increases.
Once VCC passes the UVLO threshold, polarity selection
and timer initialization will occur. If the monitored ADJ
input is valid, the corresponding OUT will be released.
When both ADJ1 and ADJ2 are valid, the appropriate
timeout delay will begin, after which RST will be released.
Power-Down
On power-down, once VCC drops below the UVLO thresh-
old or either VADJ becomes invalid, RST asserts logic low.
VCC of at least 0.5V guarantees a logic low of 0.15V at RST.
Shunt Regulator
The LTC2919 contains an internal 6.5V shunt regulator on
the VCC pin to allow operation from a high voltage supply.
To operate the part from a supply higher than 6V, the VCC
pin must have a current-limiting series resistor, RCC, to
the supply. This resistor should be sized according to the
following equation:
VS(MAX) – 6.2V
10mA
≤ R CC
≤
VS(MIN) – 6.8V
200µA + IREF
where VS(MIN) and VS(MAX) are the operating minimum
and maximum of the supply, and IREF is the maximum cur-
rent the user expects to draw from the reference output.
As an example, consider operation from an automobile bat-
tery which might dip as low as 10V or spike to 60V. Assume
that the user will be drawing 100μA from the reference. We
must then pick a resistance between 5.4k and 10.7k.
When the VCC pin is connected to a low impedance supply,
it is important that the supply voltage never exceed 6V,
or the shunt regulator may begin to draw large currents.
Some supplies may have a nominal value sufficiently
close to the shunt regulation voltage to prevent sizing of
the resistor according to the above equation. For such
supplies, a 470Ω series resistor may be used.
Adjust Polarity Selection
The external connection of the SEL pin selects the polari-
ties of the LTC2919 adjustable inputs. SEL may be con-
nected to GND, connected to VCC or left unconnected
during normal operation. When left unconnected, the
maximum leakage allowable from the pin is ±5µA. Table 1
shows the three possible selections of polarity based on
SEL connection.
Table 1. Voltage Threshold Selection
ADJ1 INPUT
ADJ2 INPUT
Positive Polarity
(+) UV or (–) OV
Positive Polarity
(+) UV or (–) OV
Positive Polarity
(+) UV or (–) OV
Negative Polarity
(–) UV or (+) OV
Negative Polarity
(–) UV or (+) OV
Negative Polarity
(–) UV or (+) OV
SEL
VCC
Open
Ground
Note: Open = open circuit or driven by a three-state buffer in high impedance
state with leakage current less than 5μA.
Rev. A
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