In normal operation, internal charge pump generates voltage 11,5V above Vout which turning MOSFET fully on and providing a low impedance path from input to the load.
During an overvoltage event input voltage rises. Output voltage rises in the same way up to the point where the output approaches the gate clamp minus MOSFET threshold voltage (LTC4380-1, 2) or 13,5V above voltage on the VCC pin (LTC4380-3, 4).Thus input surge is blocked from reaching the load.
Even during overvoltage event like load dump the load circuitry may continue operating throughout this interval, but only at the expense of dissipation in the MOSFET pass device. MOSFET dissipation or stress is a function of the input voltage waveform, output voltage and load current. The MOSFET must be sized to survive this stress.
LTC4380 adaptive timer protects MOSFET against working outside of SOA (Safe Operating Area) by turning it off at user defined conditions and simultaneously turns pull low FLTn output.
LTC43080-1,3 stays off until and can be reset by cycling power or by pulling the ON pin low for at least 100µs. LTC4380-2,4 enters a cool down phase, allowing time for the MOSFET temperature to equalize with its surroundings before automatically restarting.
During cold crank the battery potential can drop from the 12V nominal to as low as 3V for up to 40ms. Very low current consumption 8uA and minimum operating voltage 4V allow using of simple RC filter with reasonable values (10k, 4,7uF) placed at VCC pin to provide supply for LTC4380 during this event.
LTC4380is reverse input protected up to -60V (pins VCC, SEL and ON). To protect load against negative input voltages schottky diode or better N-channel MOSFET (lower voltage drop) can be added in series.
• Automotive/Avionic/Industrial Surge Protection
• Hot Swap/ Live Insertion
• High Side Switch for Battery Powered Systems
• Intrinsic Safety Applications
Latch off (LTC4380-1,3) or Automatic Retry (LTC4380-2, 4) Options
Low 0.1% Retry Duty Cycle During Persistent Input Overvoltage or Output Overcurrent (LTC4380-2, 4)
–40°C to 125°C Operating Temperature Range
10-Pin MSOP & 3mm x 3mm DFN Packages
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Date of publishing 08/17/2016. When you issue article on your website, please give its source: https://www.soselectronic.com/en/articles/linear-technology/ltc4380-surge-stopper-for-always-on-electronics-1886
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