LTC1154 Linear Technology, LTC1154 Datasheet - Page 8

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

LTC1154 OPERATIO
LTC1154
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.
Status Output Driver
The status circuitry continuously monitors the fault detec-
tion logic. This open-drain output is driven low when the
A
MOSFET and Load Protection
The LTC1154 protects the power MOSFET switch by
removing drive from the gate as soon as an over-current
condition is detected. Resistive and inductive loads can be
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.
Resistive Loads
Loads that are primarily resistive 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.
The drain sense circuitry has a built-in delay of approxi-
mately 10 s 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 (<1 F) 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.
Inductive Loads
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. The built-in 10 s delay will ensure that the over-
current protection is not false-triggered by a supply or
load transient. No external delay components are required
as shown in Figure 2.
Large inductive loads (>0.1mH) may require diodes con-
nected directly across the inductor to safely divert the
8
PPLICATI
O
U
S
I FOR ATIO
U
U
W
U
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.
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.
IN
EN
STATUS
GND
IN
EN
STATUS
GND
Figure 1. Protecting Resistive Loads
Figure 2. Protecting Inductive Loads
LTC1154
LTC1154
12V
DS
SD
V
G
S
12V
DS
SD
V
G
S
C
LOAD
+
1 F
+
1N5400
100 F
15V
15V
100 F
0.036
IRFZ24
LTC1154 • F01
0.036
R
12
IRFZ24
LOAD
12V, 1A
SOLENOID
LTC1154 • F02