9

PRELIMINARY

Precision Edge™

SY89834U

Micrel

TERMINATION RECOMMENDATIONS

R2

82

Ω

R2

82

Ω

+3.3V

+3.3V

R1

130

Ω

R1

130

Ω

+3.3V

Figure 4a. Parallel Termination–Thevenin Equivalent

Note 1.

For +2.5V systems: R1 = 250

Ω, R2 = 62.5Ω

For +3.3V systems: R1 = 130

Ω, R2 = 82Ω

Z = 50

Ω

Z = 50

Ω

50

Ω

50

Ω

50

Ω

+3.3V

+3.3V

source

destination

Rb

C1

0.01

µF

(optional)

Figure 4b. Three-Resistor “Y–Termination”

Note 1.

Power-saving alternative to Thevenin termination.

Note 2.

Place termination resistors as close to destination inputs as possible.

Note 3.

+3.3V

+3.3V

R2

82

Ω

+3.3V

+3.3V

R1

130

Ω

R1

130

Ω

R2

82

Ω

Q

/Q

R3

1k

Ω

R4

1.6k

Ω

Figure 4c. Terminating Unused LVPECL I/O

Note 1.

Unused output (/Q) must be terminated to balance the output.

Note 2.

For +2.5V systems: R1 = 250

Ω, R2 = 62.5Ω, R3 = 1.25kΩ, R4 = 1.2kΩ.

Note 3.

Unused output pairs (Q and /Q) may be left floating.