LTC1153CS8 Linear Technology, LTC1153CS8 Datasheet - Page 9

• Manufacturer Part Number: LTC1153CS8
• Description: IC ELECTR CIRCUIT BREAKER 8-SOIC
• Manufacturer: Linear Technology

Specifications of LTC1153CS8

• Applications: Overvoltage Protection, Circuit Breaker
• Current - Supply: 180µA
• Voltage - Supply: 4.5 V ~ 18 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

A
should be connected across the load, as shown in Figure
2, to safely divert the stored energy.
Capacitive Loads
Large capacitive loads, such as complex electrical sys-
tems with large bypass capacitors, should be powered
using the circuit shown in Figure 3. The gate drive to the
power MOSFET switch 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 re-
duces the start-up current flowing into the supply capaci-
tor/s which, in turn, reduces supply transients and allows
for slower activation of sensitive electrical loads. (Diode,
D1, provides a direct path for the LTC1153 protection
circuitry to quickly discharge the gate).
The RC network, R
input should be set to trip based on the expected charac-
teristics of the load after start-up. With this circuit, it is
possible to power a large capacitive load and still react
quickly (10 s) to break the circuit if a short-circuit condi-
tion is encountered. The ramp rate at the output of the
switch as it lifts off ground is approximately:
And therefore the current flowing into the capacitor during
start-up is approximately:
PPLICATI
dV/dt = (V
I
START-UP
C
0.47 F
T
Figure 3. Powering Large Capacitive Loads
IN
C
STATUS
GND
T
= C
GATE
LTC1153
LOAD
O
– V
D
U
and C
12V
DS
SD
TH
V
S
G
S
dV/dt
)/(R1 C1)
D
I FOR ATIO
U
, in series with the drain sense
1OOk
C
0.01 F
R1
D
1N4148
D1
W
+
1OOk
C1
0.33 F
R2
470 F
1OOk
R
D
15V
+
U
MTP3055E
0.036
OUT
C
100 F
LTC1153 • F03
LOAD
Using the values shown in Figure 3, the start-up current is
less than 100mA and does not false-trip the breaker.
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 trip threshold up by
a factor of 11:1 (to 30A) for 100ms while the bulb is turned
on. The trip threshold then drops down to 2.7A after the
inrush current has subsided.
Selecting R
Figure 5 is a graph of normalized breaker trip time versus
breaker current. This graph is used to select the two delay
components, R
between the drain sense resistor and the drain sense input.
C
0.33 F
T
Figure 4. Lamp Driver with Delayed Protection
Figure 5. Trip Delay Time vs Breaker Current
0.01
IN
C
STATUS
GND
0.1
10
T
1
D
1
and C
LTC1153
D
BREAKER CURRENT (1 = SET CURRENT)
and C
D
12V
DS
SD
D
V
G
S
, which make up a simple RC delay
10
10k
100k
1M
LTC1153 • F05
+
VN2222LL
9.1V
LTC1153
470 F
100
0.1 F
MTP3055EL
0.036
12V/1A
BULB
LTC1153 • F04
9