Maxim’s MAX1637 is a very popular device on telecommunication applications. It offers a lot of advantages which are the small size, PWM operation, wide Vin and Vout range, high MOSFET drive capability, and excellent protection against over and under voltage faults. In telecom operation, an auto-retry controller that attempts to restart the system is often needed. Here is the circuit :
The Vout falls if a short circuit is present and the controller can not regulate the supply voltage. Undervoltage is related to short circuit. If the voltage remains below 70% of its normal value for 6144 clock cycles, IC2 latches and turns both device off. To restart the IC2, you must either toggle the active-low SHDN signal or turn off the power supply.
On microprocessor supervisor (IC1), an internal power-fail comparator and manual-reset circuitry (MR) is included. IC1′s PFI input will detect when Vout(1.8V) is above the internal reference voltage (1.25V). Active-low RESET and active-low SHDN go high after a timeout delay of 140ms, re-enabling IC2. The other way to re-enabling IC2 is when the supply voltage is first switched on : the 3.5V rail stabilizes after 140ms will cause active-low RST to go high and activate IC2.The active-low PFO output produces a pulse using the internal 60k pull-up resistor and external 0.1 uF capacitor if Vout falls below 1.25V (due to a short circuit, for instance). The pulse will makes active-low MR low, causing active-low RST to assert and pull active-low SHDN low. [Source : Maxim Semiconductor Application Note]