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Auto Retry circuit for MAX1637 Step-Down Controller

2015-03-01 16:09  
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This article describes the Auto Retry circuit for MAX1637 Step-Down Controller. The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components:MAX1637.

On telecom applications, the MAX1637 is a popular device. This device offer a lot of advantages such as PWM operation, small size, high MOSFET-drive capability, wide VIN and VOUT ranges, and excellent protection against over- and under-voltage faults. An auto-retry controller that attempts to restart the system is often needed in telecom application. Here’s the circuit diagram:

Auto Retry Controller circuit schematic

Undervoltage is related to a short circuit:
When a short circuit is present and the controller cannot regulate the supply voltage, the Vout falls. IC2 latches and turns both device off if the voltage remains below 70% of it’s normal value for 6144 clock cycles. You must either turn off the power supply or toggle the active-low SHDN signal to restart IC2.

An internal power-fail comparator and manual-reset circuitry (MR) is included on microprocessor supervisor (IC1). When Vout (1.8V) is above the internal reference voltage (1.25V) will be detected by IC1′s PFI input. 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. 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.


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