When it comes to protecting sensitive circuitry from potentially damaging over-voltage spikes and supply surges we usually resort to networks of coils, capacitors, resistors and suppression diodes to iron out the transients. The LTC4380 low quiescent current surge stopper IC from Linear Technology goes about it in a different way; it looks out for over-voltage nasties and switches a fast N-channel external series-connected MOSFET to limit the surge. The chip is just 3 mm square and draws very little quiescent current.

Versions are available or fixed gate clamp voltages are selectable for 12V and 24/28 V and adjustable gate-clamp voltages for systems using any voltage up to 72 V systems. The IC is particularly suitable for vehicular electrical systems which are notoriously noisy environments. An internal voltage multiplier circuit takes care of the MOSFET gate control voltage. In addition to over-voltage the IC also detects over current and under-voltage conditions.
Key features:
• 8 μA operating current
• Resists surge voltages up MOSFET limit
• Operating voltage range: 4 to 72 V
• Over-current protection
• Gate-Clamp voltage selectable between 31.5 V and 50 V
• Reverse voltage protection to -60 V
• Adjustable switching threshold
• Adjustable error timer
• Controls an external N-channel MOSFET
• 10-pin. DFN (3 × 3mm) and MSOP packages