SMP Surface Mount Power Cross Protection Fuses are primarily intended for use in telecommunication circuit applications requiring low current protection with high surge tolerance.
They are typically used to replace heat coil type devices.
They are designed to be placed between the line input and the surge arresting components (mov. gas tube, zenor diode, air gaps, etc.)
These fuses will withstand transient surge currents generated by lightning in accordance with the attached table.
SMP Fuses guard protected circuitry against sustained overload or short circuit conditions. Such sustained overloads may be generated by accidental contact between utility cables and phone lines (power line cross).
SMP Fuse are used in circuits to obtain compliance with the test requirements specified in UL 1950/60950 and Bellcore GR 1089.

SMP 500
SMP 1.25

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The ZXCT1032 is a high-side current monitor that drives a PMOS or PNP transistor to provide in-rush current limit and over-current protection. The ZXCT1032 includes a high accuracy high-side current monitor, a start-up timer and a re-try inhibit timer.
The ZXCT1032 takes the voltage developed across a current shunt resistor and compares
this with an externally set trip point. It works in three modes:
- Linear soft-start
- Over-current detector
- Over-current disconnect/fuse

Linear soft-start
Upon power up the ZXCT1032 enters a linear soft-start mode. During which the output current ramps up from zero to a maximum user defined trip point. The trip point is set by the voltage on ISET pin and RSENSE.
The ramp rate is determined by capacitor CT. The soft start ensures that capacitive loads are
smoothly charged without causing excessive power supply startup transients.

Over-current detectior
When external capacitor CT has charged up above the VISET the ZXCT1032 switches from its
soft-start mode to its over-current detection mode. During this mode the external MOSFET
will be fully enhanced reducing the its voltage drop and power dissipation.

• Accurate high-side current sensing
• User defined and dynamically adjustable trip current
• Load switch control
• Fault flag logic output
• User defined ramp and inhibit timers
• SO8 package
• Temperature range -40 to 85°C
While in this mode the internal current monitor continually checks the output current and compares it to the trip-current level determined by VISET.

Over-current disconnect/fuse
If the trip current limit is exceeded at any time the ZXCT1032 enters its Over-current disconnect
mode. The drive pin is driven high, turning the pass MOSFET off; the flag output goes low
indicating a fault.
The drive and flag outputs are latched in these states for a period determined by CT, VISET and the internally set discharge current (3µA typical). After CT has discharged to 80mV the ZXCT1032 will restart into its linear soft-start mode.
The CT charge and discharge times have been ratioed to so that the power dissipation in the
pass MOSFET should allow indefinite operation in the event of a continuous load failure.

Pin 3 description:
Determines the load current trip level or constant current level. ISET can be left open circuit (internal 2.1V reference) or driven via a DC voltage or µC PWM output. Its source impedance is 50k ohm

• Electronic fuse
• Short circuit protected supply feed
• Hot swap
• Power over twisted pair


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