LTC1153 Datasheet, PDF (8/16 Pages) Linear Technology – Auto-Reset Electronic Circuit Breaker

LTC1153
U
LTC1153 OPERATIO
Controlled Gate Rise and Fall Times
When the input is switched ON and OFF, the gate is
charged by the internal charge pump and discharged in a
controlled manner. The charge and discharge rates have
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 input and
the gate charge control logic. The open-drain output is
driven low when the input is turned ON and the breaker is
latched off. The status circuitry is reset along with the input
latch when the auto-reset circuitry retries the breaker or
the input is cycled low.
APPLICATI S I FOR ATIO
MOSFET and Load Protection
The LTC1153 protects the power MOSFET switch by
removing drive from the gate as soon as an over-current
condition is detected and breaking the circuit to the load.
Resistive and inductive loads can be protected with no
external time delay in series with the drain sense pin. High
inrush current loads, however, require that the trip delay
time be set long enough to start the load 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 switch or the load is subjected to an
overload condition. The drain sense circuitry has a built-
in trip delay of approximately 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.
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 10µs trip delay will ensure that the
breaker is not false-tripped by a supply or load transient.
No external delay components are required as shown in
Figure 2.
12V
IN
V_S
C_T
0.22µF
C_T
DS
LTC1153
STATUS
G
GND
SD
+
100µF
0.036Ω
IRFZ24
15V
C_LOAD ≤ 1µF
R_LOAD
12Ω
LTC1153 • F01
Figure 1. Protecting Resistive Loads
12V
IN
V_S
C_T
0.22µF
C_T
DS
LTC1153
STATUS
G
GND
SD
+
100µF
0.036Ω
IRFZ24
15V
1N5400
12V, 1A
SOLENOID
Figure 2. Protecting Inductive Loads
LTC1153 • F02
Large inductive loads (>0.1mH) may require diodes con-
nected directly across the inductor to safely divert the
stored energy to ground. Many inductive loads have these
diodes included. If not, a diode of the proper current rating
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