LTC1154 查看數據表（PDF） - Linear Technology
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LTC1154 Datasheet PDF : 18 Pages
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LTC1154
APPLICATIONS INFORMATION
The Y axis of the graph is normalized to one RC time
constant. The X axis is normalized to the current. (The
set current is defined as the current required to develop
100mV across the drain sense resistor).
Note that the shutdown time is shorter for increasing levels
of MOSFET current. This ensures that the total energy
dissipated by the MOSFET is always within the bounds
established by the manufacturer for safe operation. (See
MOSFET data sheet for further information).
Using a Speed-Up Diode
To reduce the amount of time that the power MOSFET is
in a short-circuit condition, “bypass” the delay resistor
with a small signal diode as shown in Figure 6. The diode
will engage when the drop across the drain sense resistor
exceeds about 0.7V, providing a direct path to the sense pin
and dramatically reducing the amount of time the MOSFET
is in an overload condition. The drain sense resistor value
12V
IN
VS
EN
DS
LTC1154
STATUS
G
GND
SD
+
100μF
1N4148
0.01μF
100k
0.036Ω
IRF530
15V
LOAD
5V
5V
μP OR
CONTROL
LOGIC
+
120k 10k
10k
10k
12V
10μF
IN
VS
EN
DS
LTC1154
STATUS
G
GND
SD
300Ω
0.05Ω
MTP12N06
15V
10k LOAD
Figure 7. Reverse Battery Protection
LTC1154 • F07
Since the LTC1154 draws very little current while in normal
operation, the drop across the ground resistor is minimal.
The 5V μP (or control logic) is protected by the 10k resis-
tors in series with the input and status pins.
Current Limited Power Supplies
The LTC1154 requires at least 3.5V at the supply pin to
ensure proper operation. It is therefore necessary that the
supply to the LTC1154 be held higher than 3.5V at all times,
even when the output of the switch is short circuited to
ground. The output voltage of a current limited regulator
may drop very quickly during short-circuit and pull the
supply pin of the LTC1154 below 3.5V before the shutdown
circuitry has had time to respond and remove drive from
the gate of the power MOSFET. A supply filter should be
Figure 6. Using a Speed-Up Diode
LTC1154 • F06
is selected to limit the maximum DC current to 2.8A. The
diode conducts when the drain current exceeds 20A and
reduces the turn-off time to 15μs.
Reverse Battery Protection
The LTC1154 can be protected against reverse battery
conditions by connecting a resistor in series with the
ground lead as shown in Figure 7. The resistor limits the
supply current to less than 50mA with –12V applied.
>7V +
5V/2A
REGULATOR
100μF
IN
VS
EN
DS
LTC1154
STATUS
G
GND
SD
+
*20Ω
10μF
0.1Ω
+
0.1μF
47μF*
1N4148
100k
IRLR024
SHORT-
CIRCUIT
*SUPPLY FILTER COMPONENTS LTC1154 • F08
Figure 8. Supply Filter for Current Limited Supplies
1154fb
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