LTC1153_15 Datasheet, PDF (10/16 Pages) Linear Technology – Auto-Reset Electronic Circuit Breaker

LTC1153
APPLICATI S I FOR ATIO
The Y axis of the graph is normalized to one RC time
constant. The X axis is normalized to the set current. (The
set current is defined as the current required to develop
100mV across the drain sense resistor).
Note that the trip delay 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 S.O.A. information).
Using a Speed-Up Diode
Another way to reduce the trip delay time is to “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 trip
delay time. The drain sense resistor value is selected to
limit the maximum DC breaker current to 4A.
12V
IN
V_S
C_T
DS
C_T
0.22µF
LTC1153
STATUS
G
GND
SD
+
100µF
1N4148
0.01µF
1OOk
0.036Ω
IRF530
15V
LOAD
5V
5V
µP OR
CONTROL
LOGIC
12V
+
120k _10k
10µF
IN
V_S
C_T
0.47µF
C_T
DS
LTC1153
10k
STATUS
G
GND
SD
300Ω
0.05Ω
MTP12N06
15V
10k ^LOAD
Figure 7. Reverse Battery Protection
LTC1153 • F07
Current Limited Power Supplies
The LTC1153 requires at least 3.5V at the supply pin to
ensure proper operation. It is therefore necessary that the
supply to the LTC1153 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 LTC1153 below 3.5V before the shut-
down circuitry has had time to respond and remove drive
from the gate of the power MOSFET. A supply filter should
be added as shown in Figure 8 which holds the supply pin
of the LTC1153 high long enough for the over-current
shutdown circuitry to respond and fully discharge the
gate, i.e., break the circuit.
Figure 6. Using a Speed-Up Diode
LTC1153 • F06
Reverse Battery Protection
The LTC1153 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. Since
the LTC1153 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
resistors in series with the input and status pins.
>7V ₊
5V/2A
REGULATOR
100µF
IN
V_S
C_T
DS
1µF
LTC1153
STATUS
G
GND
SD
+
*20Ω
10µF
0.1Ω
+
0.1µF
*47µF
1N4148
100k
IRLR024
SHORT
CIRCUIT
*SUPPLY FILTER COMPONENTS LTC1153 • F08
Figure 8. Supply Filter for Current Limited Supplies
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