LTC1154 Linear Technology, LTC1154 Datasheet - Page 10

• Manufacturer Part Number: LTC1154
• Description: High-Side Micropower MOSFET Driver
• Manufacturer: Linear Technology

LTC1154
A
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 opera-
tion. (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 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 15 s.
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.
10
PPLICATI
IN
EN
STATUS
GND
LTC1154
Figure 6. Using a Speed-Up Diode
O
U
12V
DS
SD
V
G
S
S
I FOR ATIO
U
0.01 F
+
100 F
W
1N4148
100k
15V
LOAD
LTC1154 • F06
IRF530
0.036
U
5V
Since the LTC1154 draws very little current while in
normal operation, the drop across the ground resistor is
minimal. The 5V P (or control logic) is protected by the
10k resistors 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 shut-
down circuitry has had time to respond and remove drive
from the gate of the power MOSFET. A supply filter should
CONTROL
>7V
LOGIC
P OR
5V
Figure 8. Supply Filter for Current Limited Supplies
+
IN
EN
STATUS
GND
120k
100 F
Figure 7. Reverse Battery Protection
LTC1154
10k
10k
10k
REGULATOR
+
5V/2A
300
10 F
DS
SD
V
G
S
IN
EN
STATUS
GND
*SUPPLY FILTER COMPONENTS
*20
0.1 F
LTC1154
12V
+
+
47 F*
DS
SD
V
G
S
10 F
1N4148
10k
100k
15V
LOAD
MTP12N06
IRLR024
0.05
0.1
LTC1154 • F08
SHORT
CIRCUIT
LTC1154 • F07