Detailed Description

Connecting CML Outputs to 50

Ω

Oscilloscopes

CML outputs have a common-mode voltage near VCC.

To avoid changing this optimum common-mode volt-

age, all CML outputs are AC-coupled on-board with

0.1µF capacitors. The CML outputs should not be con-

nected directly through 50

Ω to ground.

Terminating Unused Outputs

The MAX3781 EV kit has 100

Ω differential resistors

placed across all outputs. These resistors must be

removed before connecting the outputs to a 50

Ω oscil-

loscope. For best performance, keep all outputs termi-

nated, either to a 50

Ω measurement device or to the

100

Ω differential resistor.

Control Lines

Jumpers JU1, JU2, and JU3 are provided to set the

operating mode of the MAX3781. Shorting these

jumpers pulls the corresponding TTL control line to a

logical zero. All TTL control lines are internally pulled

high through 15k

Ω resistors. See Table 1 for more infor-

mation regarding setting operating modes.

Exposed-Pad Package

The exposed paddle (EP) 48-pin TQFP has features

that provide a very low thermal resistance path for heat

removal from the IC. The paddle is electrical ground on

the MAX3781 and should be soldered to the circuit

board for proper thermal and electrical performance.

MAX3781 Evaluation Kit

2

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Table 1. Operating Modes

SEL_

PD

LO1_

LO2_

SO_

0

0

SI_

SI_

LI2_

01

−

SI_

LI2_

1

0

SI_

SI_

LI1_

1

1

SI_

−

LI1_