Speed grades
Stratix V -2 vs -3: why the swap changes the core voltage
On most FPGAs a different speed grade is a timing question. On Stratix V it is also a power-supply question.
Updated 4 min readBased on the Stratix V Device Datasheet
Short answer
Stratix V C1, C2 and I2 parts run their core (VCC) at 0.90 V; C3, C4, I3, I4 and the low-power C2L, I2L and I3L parts run at 0.85 V.[1] The ranges don't overlap (0.87–0.93 V against 0.82–0.88 V), so a -3 on a -2 board, or a -2 on a -3 board, is outside its recommended operating conditions.
- 0.90 V grades
- C1, C2, I2 (0.87 to 0.93 V)
- 0.85 V grades
- C2L, C3, C4, I2L, I3, I3L, I4 (0.82 to 0.88 V)
- Exception
- C2L and I2L may also run at 0.90 V on C2/I2 boards
- Fastest grade
- 1 (C1); 4 is the slowest
Core voltage by speed grade
The Stratix V data sheet specifies VCC, the core and periphery supply, in two groups:[1]
| Grade | VCC (min – typ – max) | Junction temperature |
|---|---|---|
| C1 | 0.87 – 0.90 – 0.93 V | 0 to 85 °C |
| C2 | 0.87 – 0.90 – 0.93 V | 0 to 85 °C |
| I2 | 0.87 – 0.90 – 0.93 V | −40 to 100 °C |
| C2L | 0.82 – 0.85 – 0.88 V (or 0.90 V) | 0 to 85 °C |
| I2L | 0.82 – 0.85 – 0.88 V (or 0.90 V) | −40 to 100 °C |
| C3 | 0.82 – 0.85 – 0.88 V | 0 to 85 °C |
| I3, I3L | 0.82 – 0.85 – 0.88 V | −40 to 100 °C |
| C4 | 0.82 – 0.85 – 0.88 V | 0 to 85 °C |
| I4 | 0.82 – 0.85 – 0.88 V | −40 to 100 °C |
The data sheet also lists a special I3YY grade at 0.90 V. C2L and I2L “can also be run at 0.90 V for legacy boards” designed for C2 and I2.
What each swap means for the board
| Board designed for | Part fitted | Core supply |
|---|---|---|
| C2 / I2 (0.90 V) | C3, I3, C4, I4 | 0.90 V is above the 0.88 V maximum: change the regulator |
| C3 / I3 (0.85 V) | C2, I2, C1 | 0.85 V is below the 0.87 V minimum: change the regulator |
| C2 / I2 (0.90 V) | C2L, I2L | Allowed: the data sheet permits 0.90 V for these |
| C3 / I3 (0.85 V) | C2L, I2L, I3L | Same 0.85 V supply |
Voltage is only half of it
Finding the grade in the part number
In a Stratix V ordering code the FPGA fabric speed grade is the digit after the temperature letter; 1 is the fastest. The transceiver speed grade is a separate digit, earlier in the code. An optional suffix follows: L for the low-power profile, then N or G for RoHS (P for leaded).[2]
| Part number | Fabric grade | Core supply |
|---|---|---|
| 5SGXEA7N2F40C2N | C2 | 0.90 V |
| 5SGXEA7N2F40C2LN | C2L | 0.85 V (or 0.90 V) |
| 5SGXEA7N2F40C3N | C3 | 0.85 V |
| 5SGXEA7N2F40I2N | I2 | 0.90 V |
| 5SGXEA7N2F40I3N | I3 | 0.85 V |
| 5SGXEA7N3F40C4N | C4 | 0.85 V |
In 5SGXEA7N2F40C2N, N2 is the transceiver count and transceiver speed grade, F40 the package, C commercial temperature, 2 the fabric speed grade and N RoHS.
If VCC is shared with the transceiver supplies
The data sheet allows the transceiver supplies VCCR_GXB and VCCT_GXB to share the VCC core supply when they are set to 0.90 V or 0.85 V, but not at 1.0 V or 1.05 V.[1] On a board that shares them, changing VCC for a different speed grade changes the transceiver supplies too, so check the design against the transceiver supply requirements in the data sheet (Table 7) as well.
See the Stratix V GX family page for every device and part number, and Stratix IV vs Stratix V for a family comparison.
Frequently asked questions
What core voltage does a Stratix V -2 need?
0.90 V (0.87 to 0.93 V) for the C2 and I2 grades, the same as C1. The L versions, C2L and I2L, are specified at 0.85 V but can also run at 0.90 V on boards designed for C2 and I2.
What core voltage does a Stratix V -3 need?
0.85 V (0.82 to 0.88 V) for C3, I3 and I3L, and for the -4 grades C4 and I4.
Can I use a Stratix V -3 in place of a -2?
Not on the same core supply. A -2 board supplies 0.90 V, above the -3's 0.88 V maximum, and a -3 is also the slower grade, so timing must be re-closed. Changing the VCC regulator setpoint and re-running timing is a design change.
What does the L in a Stratix V part number mean?
L is the power profile option: a low-power device. It appears in the optional suffix, as in 5SGXEA7N2F40C2LN. C2L and I2L parts run at 0.85 V, or at 0.90 V on legacy C2/I2 boards.
References
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