Power Sequencer

Power Sequencer Tailored for Unique Systems

Successfully powering up a system can be tricky. So can powering one off. Timing, order of events, and power levels need to be just right for proper system functionality and stability. Using power sequencer can also prevent unnecessary current draw while portions of the design sit idle, waiting for prerequisite systems to be powered. Some FPGAs may require more than ten rails, which if sequenced using discrete components, could introduce extra power and board space overhead.

Using GreenPAK™ family of devices, it is easy to implement custom power sequencer designs in an extremely small area, using minimal power and board space. When paired with the tiny, ultra-low R_DSON GreenFET™ Integrated Power Switch, power sequencing with Dialog is an incredibly efficient solution.

Often in various combinations in a single system, some common methods for power sequencing include:

Fixed timing
Power Good
I2C Acknowledge
Voltage Sensing

GreenPAK Benefits for Power Sequencing

System Stability
- GreenPAK is Zero Code - Implementing features in hardware ensures stability
- GreenPAK can integrate many components ensuring fewer points of failure
Power Consumption
- GreenPAK is low-power - Can operate continuously without ruining power budget
Size
- GreenPAK is as small as 1.2 mm²
Flexibility
- GreenPAK GPIO are configurable - Pull-up/down resistors, Push-Pull, Open drain, etc.
- GreenPAK GPIO routing is flexible – Ensuring the least complexity in PCB routing
- GreenPAK integrates many common components – Generate custom timing and logic to fit the requirements of many power sequencer designs

Fixed Delay Sequencing

One method for sequencing multiple sub-systems is to allot a fixed amount of time for each start-up sequence. This is appropriate for systems which do not feature a Power Good signal. Finding a discrete solution with the exact delay timings needed can take hours, but with GreenPAK’s configurable logic and timing resources, developing a custom system is easy.

Example 1. Fixed Delay Sequencing

Key Design Considerations

Delay Time – Using GreenPAK’s internal oscillators and CNT/DLY blocks, it is possible to address a wide range of timing requirements
ON Signal Polarity – GreenPAK can be configured to output active high or low using integrated inverters and LUTs

Example 1. GreenPAK Implementation

Example 1. Timing Diagram

Power Good

Many ICs have the ability to produce a Power Good (PG) signal once the respective systems have finished their start-up routine. This can be useful in systems where start-up time is not fixed and may depend on multiple variables.

Example 2. Sequencing with Power Good

Key Design Considerations

ON and PG Signal Polarity – GreenPAK can be configured to output active high or low using integrated inverters and LUTs.

Example 2. GreenPAK Implementation

Example 2. Timing Diagram

I2C Acknowledge

Another option in programmable systems with I2C is to send a command to the power sequencer, in this case GreenPAK, to let it know start-up was completed successfully. Using GreenPAK's I2C virtual inputs, it is easy to treat an I2C command just like a digital Power Good signal.

Example 3. Power Sequencer with I2C Acknowledge

Key Design Considerations

I2C Speed – GreenPAK I2C supports up to 400 kHz
I2C Address – GreenPAK can have up to 16 unique I2C addresses

Example 3. Timing Diagram

Example 3. GreenPAK Implementation

Voltage Sensing

To ensure system stability, many SOCs, DSPs, and FPGAs require a minimum voltage for startup. Monitoring the power level of a rail can be done simply using GreenPAK’s configurable analog comparators.

Example 4. Power Sequencer with Voltage Sensing

Key Design Considerations

Over-voltage/Under-voltage Threshold – Supply tolerances vary, but using GreenPAK with integrated ACMPs enables reliable sequencing over a wide range of user specified conditions
Time Sensitive Voltage Limits – Varying periods of voltages outside the limit may be tolerable for some systems. GreenPAK’s configurable CNT/DLY blocks can be used to reject reset events below a wide range of time thresholds
Hysteresis – Nominal voltage requirements may incorporate hysteresis. GreenPAK’s ACMPs can be configured with 25, 50, or 200 mV hysteresis