OP4008B datasheet(3/6 Pages) MURATA

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Load Recommendations for the OP4008B

The Q and Q outputs of RFM's OPB-series of SAW clocks are AC-

coupled internally. This allows customers to set the DC level of the

outputs with a simple resistor pair on each output to drive most any

application.

VDC = VLOAD*R1/(R1 + R2)

and

50 = R1*R2/(R1 + R2)

The values of the resistors R2 and R1 are given directly as:

R2 = 50*VLOAD/VDC

R1 = 1/(0.02 - (1/R2))

3.3V

Load

OP4005B

LOAD

VDC

TUNE

Load Type

Vdc

Vload

10K 3.3 V PECL

1.95

120

3.3 V

100K 3.3 V PECL

1.88

120

3.3 V

10K 5 V PECL

3.65

180

5.0 V

100k 5 V PECL

3.58

180

5.0 V

10K -5 V NECL

-1.30

240

-5.0 V

100K -5 V NECL

-1.42

240

-5.0 V

Note that the OPB parts will drive negative ECL loads by applying negative voltage to the Vload points in the circuit.

Vdc is the DC level desired on the outputs.

Vload is the DC supply on the load resistors (typically 3.3 V).

The equations describe the voltage divider created by R1 & R2 and the equilivent load impedence set by the parrellel combination of R1 & R2.

A given load type will have specifications that set Vdc. Choose an available Vload that is 2x to 3x larger than the desired Vdc. This will allow R1 to be

expressed in terms of R2.

The following table has some typical values for Vdc & Vload for various ECL loads along with R1 & R2 values that are standard.

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