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参数资料
| 型号： | LTC2919HDDB-3.3#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 电源管理 |
| 英文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO10 |
| 封装： | 3 X 2 MM, LEAD FREE, PLASTIC, MO-229WECD-1, DFN-10 |
| 文件页数： | 15/16页 |
| 文件大小： | 195K |
| 代理商： | LTC2919HDDB-3.3#PBF |
LTC2919
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2919f
APPLICATIO S I FOR ATIO
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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 congured for positive polarity,
below threshold if congured 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 as-
serts 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 oat 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 VCCpassestheUVLOthreshold,polarityselectionand
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 VCCdropsbelowtheUVLOthreshold
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:
V
S(MAX) – 6.2V
10mA
≤ RCC ≤
V
S(MIN) – 6.8V
200A + IREF
where VS(MIN) and VS(MAX) are the operating minimum and
maximum of the supply, and IREF is the maximum current
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 sufciently
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 polarities
of the LTC2919 adjustable inputs. SEL may be connected
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
SEL
Positive Polarity
(+) UV or (–) OV
Positive Polarity
(+) UV or (–) OV
VCC
Positive Polarity
(+) UV or (–) OV
Negative Polarity
(–) UV or (+) OV
Open
Negative Polarity
(–) UV or (+) OV
Negative Polarity
(–) UV or (+) OV
Ground
Note: Open = open circuit or driven by a three-state buffer in high impedance
state with leakage current less than 5μA.
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