參數(shù)資料
型號(hào)： LTC1645CS
廠商： LINEAR TECHNOLOGY CORP
元件分類(lèi)： 電源管理
英文描述： Low Power Timer 8-SOIC 0 to 70
中文描述： 2-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO14
封裝： 0.150 INCH, PLASTIC, SO-14
文件頁(yè)數(shù)： 15/24頁(yè)
文件大小： 312K
代理商： LTC1645CS
15
LTC1645
V
5V/DIV
V
5V/DIV
V
5V/DIV
V
5V/DIV
TIMER
2V/DIV
RESET
5V/DIV
Figure 16. Ramping 3.3V and 2.5V Up and Down Together
APPLICATIOU
W
U
U
This circuit guarantees that: (1) V
OUT1
never exceeds
V
OUT2
by more than 1.2V, and (2) V
OUT2
is never greater
than V
OUT1
by more than 0.4V. On power-up, V
OUT1
and
V
OUT2
ramp up together. On power-down, the LTC1645
turns off Q1 and Q2 simultaneously. Charge remains
stored on C
LOAD1
and C
LOAD2
and the output voltages will
vary depending on the loads. D1 and D2 turn on at
≈
1V
(
≈
0.5V each), ensuring condition 1 is satisfied, while D3
prevents violations of condition 2. Different diodes may be
necessary for different output voltage configurations.
Barring an overvoltage condition at the input(s), the only
time these diodes might conduct current is during a
power-down event, and then only to discharge C
LOAD1
or
C
LOAD2
. In the case of an input overvoltage condition that
causes excess current to flow, the circuit breaker will trip
if the current limit level is set appropriately.
Figure 17 shows an application circuit where V
OUT1
ramps up before V
OUT2
. V
OUT1
is initially discharged and
D1 is reverse-biased, thus the voltage at the ON pin is
determined only by V
CC1
through the resistor divider R1
and R2. The voltage at the ON pin exceeds 0.8V if V
CC1
is
above 4.6V and V
OUT1
begins to ramp up after a timing
cycle. As V
OUT1
ramps up, D1 becomes forward-biased
and pulls the ON pin above 2V when V
OUT1
≈
4.5V. This
turns on GATE2 and V
OUT2
ramps up. The FB comparator
monitors V
OUT2
, and the spare comparator monitors
V
OUT1
with R
HYST
creating
≈
50mV of hysteresis.
Power Supply Multiplexer
Using back-to-back FETs, the LTC1645 can Hot Swap two
supplies to the same output, automatically selecting the
primary supply if present or the secondary supply if the
primary supply is not available. Referring to Figure 18, a
diode-or circuit provides power to the LTC1645 if either
supply is up. Schottky diodes are used to prevent the
voltage at V
CC1
from approaching the undervoltage lock-
out threshold. This application assumes that if a supply is
not present, the supply input is floating.
If only the 3.3V supply is present, the voltage at the COMP
+
pin is below the trip point and COMPOUT pulls the base of
Q3 low, allowing the GATE1 pin to ramp up normally. The
voltage at the ON pin exceeds 0.8V if the 3.3V supply is
greater than 3V, ramping up GATE1 and turning on Q1A and
Q1B. The ON pin does not exceed 2V (unless the 3.3V supply
exceeds 7.5V!), keeping GATE2 low and Q2A and Q2B off.
If only the 5V supply is present or if both supplies are
present, the COMP
+
pin is above 1.238V and COMPOUT
allows the base of Q3 to be pulled high by R2. This turns
Q3 on, keeping GATE1 low and Q1A and Q1B off. The
voltage at the ON pin is pulled above 2V by R1 and GATE2
turns Q2A and Q2B on.
相關(guān)PDF資料
PDF描述
LTC1645CS8 Low Power Timer 8-SOIC 0 to 70
LTC1645I Low Power Timer 8-SOIC 0 to 70
LTC1645IS Low Power Timer 8-SOIC 0 to 70
LTC1645IS8 Low Power Timer 8-PDIP 0 to 70
LTC1649 Low Power Timer 8-SOIC -40 to 85
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