8

SY58021U

Micrel, Inc.

M9999-062405

hbwhelp@micrel.com or (408) 955-1690

Part Number

Function

Data Sheet Link

SY58020U

6GHz, 1:4 CML Fanout Buffer/Translator

http://www.micrel.com/product-info/products/sy58020u.shtml

Internal I/O Termnations

SY58021U

4GHz, 1:4 LVPECL Fanout Buffer/Translator

http://www.micrel.com/product-info/products/sy58021u.shtml

with Internal Termination

SY58022U

5.5GHz, 1:4 Fanout Buffer/Translator

http://www.micrel.com/product-info/products/sy58022u.shtml

w/400mV LVPECL Outputs and Internal Terminations

16-MLF™ Manufacturing Guidelines

www.amkor.com/products/notes_papers/MLF_AppNote_0902.pdf

Exposed Pad Application Note

M-0317

HBW Solutions

http://www.micrel.com/product-info/as/solutions.shtml

RELATED MICREL PRODUCTS AND SUPPORT DOCUMENTATION

R2

82

Ω

R2

82

Ω

*Note. For +2.5V systems,

R1 = 250

Ω, R2 = 62.5Ω

+3.3V*

+3.3V*

R1

130

Ω

R1

130

Ω

+3.3V*

SY58021U

Figure 4. Parallel Termination-Thevenin Equivalent

LVPECL OUTPUT

Z = 50

Ω

Z = 50

Ω

50

Ω

50

Ω

50

Ω

+3.3V

+3.3V

“source”

“destination”

C1 (optional)

0.01

µF

* For +2.5V, Rb = 19Ω

* For +3.3V, Rb = 46Ω to 50Ω

Notes:

1. Power saving alternative to Thevenin termination.

2. Place termination resistors as close to destination inputs as possible.

3. Rb resistor sets the DC bias voltage, equal to VT.

SY58021U

Figure 5. Parallel Termination (3-Resistor)

LVPECL output have very low output impedance (open

emitter), and small signal swing which results in low EMI.

LVPECL is ideal for driving 50

Ω and 100Ω controlled

impedance transmission lines. There are several techniques

in terminating the LVPECL output, as shown in Figures 4

through 6.

R2

82

Ω

R2

82

Ω

*Note:

For +2.5V systems,

R1 = 250

Ω, R2 = 62.5Ω

+3.3V*

+3.3V*

R1

130

Ω

R1

130

Ω

+3.3V*

SY58021U

Figure 6. Terminating Unused I/O