3 Recommendations for Microchip Devices

Microchip defines SSOs as any outputs that transition in phase within a 1 ns window. The measurements made by Microchip are based on the following worst-case conditions:

  • The switching outputs are adjacent to the quiet outputs on either side.
  • All unused I/O buffers are tristated so they do not help either GND or VCC.
  • A worst-case package is used.

The following table lists the recommendations for Microchip devices under typical conditions. The recommendations give the number of adjacent I/Os that can be switched simultaneously around an I/O required to be quiet. For legacy products, see Table 3-2.

Important: For SSO recommendations on ProASIC® 3/E and ProASIC PLUS®, see ProASIC3/E SSO and Pin Placement Guidelines and AC264: ProASICPLUS SSO and Pin Placement Guidelines.
Table 3-1. SSOs Around a Quiet Output for SX-A, RTSX-SU, Axcelerator, and RTAX-S Devices

Device and I/O Supply Voltage

SSOs

At High Slew

At Low Slew

RTAX-S (2.5V/3.3V)1

402

Unrestricted2

Axcelerator (2.5V/3.3V)

402

Unrestricted2

SX-A/RTSX-SU 5.0V

243

> 403

SX-A/RTSX-SU 3.3V

322

> 402

Important:
  1. Applies to RTAX2000S and smaller devices.
  2. The observed ground bounce is less than 1.25V with a pulse width of less than 2 ns.
  3. The observed ground bounce is less than 1.5V with a pulse width of less than 2 ns.
Table 3-2. Recommended SSO Limits for Microchip Legacy FPGAs

Device

Package

Maximum Recommended SSOs for Loads

20 pF

35 pF

50 pF

42MX (5V)

PQ160

—

—

101

42MX (3.3V)

PQ160

—

—

75

40MX (5V)

PQ160

—

—

292

40MX (3.3V)

PQ160

—

—

56

A1010A/A1020A

44 PLCC

40

22

16

A1010A/1020A

68 PLCC

60

34

24

A1020A

84 PLCC

80

45

32

A1010A/1020A

84 PGA

80

45

32

A1010A/A1020A

100 PQFP

80

45

32

A1280/A1280XL

PG176, PQ160

160

90

64

A1240/A1240XL

PG132, PQ144

120

68

48

A1240/A1225/A1225XL

84 PLCC

80

45

32

A1225/A1225XL

100 PGA, PQFP

80

45

32

A1400 family3

84 PLCC

64

48

42

A1400 family3

All other packages

128

64

58
Note:
  1. If one or more pins exist between the SSOs and quiet output, the recommendation increases to 100.
  2. If one or more pins exist between the SSOs and quiet output, the recommendation increases to 46.
  3. The recommended SSO value for the A1400 family can be doubled for outputs using low slew drivers.