The LTC®2937 is a power supply sequencer and supervisor with features that make it ideal for power supply management. It has features that enable seamless cooperation between any number of rails, including timing and sequencing, fast voltage supervision, fault handling, and debugging. Its EEPROM memory enables complete autonomy, and the I2C/SMBus interface allows it to be interactive in real time. With flexibility, however, comes some complexity, and there are design choices that need to be made in order to achieve success. This article walks through common scenarios and how to apply the features of the LTC2937 successfully.
At a minimum, we can implement a control mechanism using one of the supervisor channels to monitor the 12V voltage through a resistor divider, and cause a fault when it falls too low. The fault condition, while not ideal, at least causes all ENn pins to pull low simultaneously, shuttingoff the supplies before the 12V voltage collapses. This is a (minimal) improvement on uncoordinated collapse.
In this case, the LTC2937’s fault retry delay should be programmed longer than the expected time that it takes the 12V supply to collapse. This prevents the LTC2937 from trying to start again while the supply is falling. Setting FAULT_RESPONSE[7:5] = 3'b111 (13.1 seconds) will accomplish this.
To implement a full down-sequence there are several options. The best option is to use the ON pin to command the sequencer up or down. The ON pin controls when the supplies should be on or off with its logic level. Alternatively, an I2C command can force sequencing up and down, if there is a bus master to send that command. Both of these options require additional circuitry to command the LTC2937.