ltc1154cs8-trpbf Linear Technology Corporation, ltc1154cs8-trpbf Datasheet - Page 10

• Manufacturer Part Number: ltc1154cs8-trpbf
• Description: High-side Micropower Mosfet Driver
• Manufacturer: Linear Technology Corporation

LTC1154
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 defi ned 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
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.
APPLICATIONS INFORMATION
10
IN
EN
STATUS
GND
LTC1154
Figure 6. Using a Speed-Up Diode
12V
DS
SD
V
G
S
0.01μF
+
100μF
1N4148
100k
15V
LOAD
LTC1154 • F06
IRF530
0.036Ω
5V
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 fi lter should be
CONTROL
>7V
μP OR
LOGIC
5V
Figure 8. Supply Filter for Current Limited Supplies
+
IN
EN
STATUS
GND
120k
100μF
Figure 7. Reverse Battery Protection
LTC1154
10k
10k
10k
REGULATOR
+
5V/2A
300Ω
10μF
DS
SD
V
G
S
IN
EN
STATUS
GND
*SUPPLY FILTER COMPONENTS
*20Ω
0.1μF
LTC1154
12V
+
+
47μF*
DS
SD
V
G
S
10μF
1N4148
10k
100k
15V
LOAD
MTP12N06
0.05Ω
IRLR024
0.1Ω
LTC1154 • F08
SHORT-
CIRCUIT
LTC1154 • F07
1154fa