LTC1154
U
LTC1154 OPERATIO
been set to minimize RFI and EMI emissions in normal
operation. If a short-circuit or current overload condition
is encountered, the gate is discharged very quickly (typi-
cally a few microseconds) by a large N-channel transistor.
gate of the MOSFET is driven low by the protection
circuitry. The status circuitry is reset along with the input
latch when the input, or ENABLE input, is cycled.
Status Output Driver
Thestatuscircuitrycontinuouslymonitorsthefaultdetec-
tion logic. This open-drain output is driven low when the
O U
W
U
PPLICATI
A
S I FOR ATIO
stored energy to ground. Many inductive loads have these
diodes included. If not, a diode of the proper current rating
should be connected across the load, as shown in Figure
2, to safely divert the stored energy.
MOSFET and Load Protection
The LTC1154 protects the power MOSFET switch by
removing drive from the gate as soon as an over-current
conditionisdetected. Resistiveandinductiveloadscanbe
protected with no external time delay in series with the
drain sense pin. Lamp loads, however, require that the
over-current protection by delayed long enough to start
the lamp but short enough to ensure the safety of the
MOSFET.
12V
+
100µF
IN
V
S
0.036Ω
EN
DS
G
LTC1154
STATUS
GND
IRFZ24
Resistive Loads
15V
Loadsthatareprimarilyresistiveshouldbeprotectedwith
asshortadelayaspossibletominimizetheamountoftime
that the MOSFET is subjected to an overload condition.
The drain sense circuitry has a built-in delay of approxi-
mately 10µs to eliminate false triggering by power supply
or load transient conditions. This delay is sufficient to
“mask” short load current transients and the starting of a
small capacitor (<1µF) in parallel with the load. The drain
sense pin can therefore be connected directly to the drain
current sense resistor as shown in Figure 1.
SD
R
LOAD
C
≤ 1µF
LOAD
12Ω
LTC1154 • F01
Figure 1. Protecting Resistive Loads
12V
+
100µF
IN
V
S
0.036Ω
Inductive Loads
EN
DS
G
Loads that are primarily inductive, such as relays, sole-
noids and stepper motor windings should be protected
with as short a delay as possible to minimize the amount
of time that the MOSFET is subjected to an overload
condition.Thebuilt-in10µsdelaywillensurethattheover-
current protection is not false-triggered by a supply or
load transient. No externaldelay components arerequired
as shown in Figure 2.
LTC1154
STATUS
IRFZ24
15V
GND
SD
12V, 1A
SOLENOID
1N5400
LTC1154 • F02
Large inductive loads (>0.1mH) may require diodes con-
nected directly across the inductor to safely divert the
Figure 2. Protecting Inductive Loads
8
Linear [ Linear ]
