LTC1154 查看數據表（PDF） - Linear Technology
零件编号
产品描述 (功能)
生产厂家
LTC1154 Datasheet PDF : 18 Pages
| |||
LTC1154
APPLICATIONS INFORMATION
Capacitive Loads
Large capacitive loads, such as complex electrical systems
with large bypass capacitors, should be powered using
the circuit shown in Figure 3. The gate drive to the power
MOSFET is passed through an RC delay network, R1 and
C1, which greatly reduces the turn-on ramp rate of the
switch. And since the MOSFET source voltage follows the
gate voltage, the load is powered smoothly and slowly from
ground. This dramatically reduces the start-up current
flowing into the supply capacitor(s) which, in turn, reduces
supply transients and allows for slower activation of sensi-
tive electrical loads. (Diode, D1, provides a direct path for
the LTC1154 protection circuitry to quickly discharge the
gate in the event of an overcurrent condition).
12V
IN
VS
EN
DS
LTC1154
STATUS
G
GND
SD
+
470μF
CD
0.01μF
RD
100k
0.036Ω
D1
1N4148
R1
R2
100k
100k
MTP3055E
C1
0.33μF
15V
+
OUT
CLOAD
100μF
LTC1154 • F03
Figure 3. Powering Large Capacitive Loads
The RC network, RD and CD, in series with the drain sense
input should be set to trip based on the expected character-
istics of the load after start-up. With this circuit, it is possible
to power a large capacitive load and still react quickly to
an overcurrent condition. The ramp rate at the output of
the switch as it lifts off ground is approximately:
dV/dt = (VGATE – VTH)/(R1 • C1)
And therefore the current flowing into the capacitor during
start-up is approximately:
ISTART-UP = CLOAD • dV/dt
Using the values shown in Figure 3, the start-up current
is less than 100mA and does not false-trigger the drain
sense circuitry which is set at 2.7A with a 1ms delay.
Lamp Loads
The inrush current created by a lamp during turn-on can be
10 to 20 times greater than the rated operating current. The
circuit shown in Figure 4 shifts the current limit threshold
up by a factor of 11:1 (to 30A) for 100ms when the bulb
is first turned on. The current limit then drops down to
2.7A after the inrush current has subsided.
12V
IN
VS
EN
DS
LTC1154
STATUS
G
GND
SD
+
10k
100k
470μF
0.036Ω
VN2222LL
0.1μF
1M
MTP3055EL
9.1V
12V/1A
BULB
LTC1154 • F04
Figure 4. Lamp Driver with Delayed Protection
Selecting RD and CD
Figure 5 is a graph of normalized overcurrent shutdown
time versus normalized MOSFET current. This graph is
used to select the two delay components, RD and CD,
which make up a simple RC delay between the drain sense
resistor and the drain sense input.
10
1
0.1
0.01
1
10
100
MOSFET CURRENT (1 = SET CURRENT)
LTC1154 • F05
Figure 5. Overcurrent Shutdown Time vs MOSFET Current
1154fb
9
Share Link: 