AN 491: Power Sequence Auto Start Using Altera MAX Series

ID 683346
Date 9/22/2014

1.1. Power Saving

Many consumer and industrial application systems do not require the device to be powered on at all times. It is preferred to have a design in which the device powers on intermittently, remaining off for most of the cycle. This is especially useful in portable battery-operated systems which can function on a non-continuous periodic task.

Because MAX II and MAX V devices do not require a special power-on sequence, they can be switched on quickly (typically 200 μs, depending on the logic density). The ability to switch on and off quickly allows you to completely switch off the device and switch it back on using external circuitry. The external circuitry can be a simple RC timer designed for the required delay. The MAX 10 Single Supply devices are designed for customer to easily manage power-up sequence on the board. The instant-on feature is the fastest power-up mode for MAX 10 devices.

However, if you implement considerable power off time, such a simple RC timer circuit is not practical. This requires very large values of R & C. A counter utilizing capacitors as memory elements extends the power-down period. The device turns on for a very small duration during this power-down period, reads the value in these capacitors, increments the count, and stores them back again before powering down. This cycle repeats itself until the desired count is reached, at which time the device switches on completely. When it switches on in the power-on period, the device executes the task it was designed to accomplish.

Figure 1. Basic Block Diagram of an Auto Start System

The device uses the power down signals (power_dwn and its complement) to trigger the external circuit and power down the device. After the designed delay, the external circuit powers on the device. The memory capacitors are connected to the bidirectional pins of the device and are used as non-volatile memory elements.

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