SNVSB87 November 2018 LM3880-Q1
The LM3880-Q1 simple power supply sequencer provides a simple solution for sequencing multiple rails in a controlled manner. Six independent timers are integrated to control the timing sequence (power up and power down) of three open-drain output flags. These flags permit connection to either a shutdown or enable pin of linear regulators and switchers to control the operation of the power supplies. This allows design of a complete power system without concern for large inrush currents or latch-up conditions that can occur.
The timing sequence of the device is controlled entirely by the enable (EN) pin. Upon power up, all the flags are held low until this precision enable is pulled high. When the EN pin is asserted, the power-up sequence starts. An internal counter delays the first flag (FLAG1) from rising until a fixed time period has expired. When the first flag is released, another timer will begin to delay the release of the second flag (FLAG2). This process repeats until all three flags have sequentially been released.
The power-down sequence is the same as power-up sequence, but in reverse. When the EN pin is deasserted a timer will begin that delays the third flag (FLAG3) from pulling low. The second and first flag will then follow in a sequential manner after their appropriate delays. The three timers that are used to control the power-down scheme can also be individually programmed and are completely independent of the power-up timers.