2.4.2. Power-Down Sequence Recommendations and Requirements for Intel® Stratix® 10 Devices
Intel's FPGAs need to follow certain requirements during a power-down sequence. The power-down sequence can be a controlled power-down event via an on/off switch or an uncontrolled event as with a power supply collapse. In either case, you must follow a specific power-down sequence. Below are four power-down sequence specifications. They are either Recommended (one), Required (two), or Relaxed (one). To comply with Intel® ’s FPGA Power-Down requirements, the Recommended option is best.
Recommended Power-Down Ramp Specification
This is the best option to minimize power supply currents.
- Power down all power rails fully within 100 ms.
- Power down power supplies within the same Group in any order.
- Before Group 3 supplies power down, power down all Group 4 supplies within 10% of GND.
- Before Group 2 supplies power down, power down all Group 3 supplies within 10% of GND.
- Before Group 1 supplies power down, power down all Group 2 supplies within 10% of GND.
- The maximum voltage differential between any Group 3 supply and any Group 2 supply is 1.92 V, and only applicable for the 1.8V voltage rails in Group 2.
- Ensure that the newly combined power rails do not cause any driving of unpowered GPIO or transceiver pins.
- Ensure that the newly combined power rails do not violate any power-down sequencing specification due to device (third party) leakage; maintain the Required Voltage Differential Specification.
During the power-up/down sequence, the device output pins are tri-stated. To ensure long term reliability of the device, Intel recommends that you do not drive the input pins during this time.
Required Power-Down Ramp Specification
In cases where power supply is collapsing or if the recommended specification cannot be met, the following PDS sequence is required.
- Power down all power rails fully within 100 ms.
- As soon as possible, disable all power supplies.
- Tri-state Group 1 supplies, and do not drive them actively to GND.
- If possible, drive or terminate Group 2, Group 3, and Group 4 supplies to GND.
- Ensure no alternative sourcing of any power supply exists during the power-down sequence; reduce all supplies monotonically and with a consistent RC typical decay.
- By the time any Group 1 supply goes under 0.35 V, all Group 2, Group 3, and Group 4 supplies must be under 1.0 V.
Required Voltage Differential Specification
To not excessively overstress device transistors during power-down, there is an additional voltage requirement between any two power supplies between different power groups during power-down:
ΔV < ΔVnom + 500 mV
- Power down all power rails fully within 100 ms.
- For example, if Group 1 Voltage = 0.9 V, Group 2 Voltage = 1.8 V, and Group 3 Voltage = 3.0 V, then:
G3Vnom = 3.0 V
G2Vnom = 1.8 V
G2Vnom = 1.8 V
G1Vnom = 0.9 V
G3Vnom = 3.0 V
G1Vnom = 0.9 V
(G3V – G2V)nom = 1.2 V (G2V – G1V)nom = 0.9 V (G3V – G1V)nom = 2.1 V (G3V – G2V) <= 1.2 V + .5 V (G2V – G1V) <= 0.9 V + .5 V (G3V – G1V) <= 2.1 V + .5 V (G3V – G2V) <= 1.7 V (G2V – G1V) <= 1.4 V (G3V – G1V) <= 2.6 V - To meet this voltage differential requirement, ramp down all power supplies as soon as possible according to the Required Power-Down Ramp Specification.
Relaxed Power-Down Duration Specification
For supplies being powered down with no active termination, voltage reduction to GND slows down as supply approaches 0 V. In this case, the 100 ms power requirement is relaxed - measure it when supply reaches near GND.
- Ensure all Group 1 supplies reach < 100 mV within 100 ms.
- Ensure all Group 2, Group 3, and Group 4 supplies reach < 200 mV within 100 ms.