Functional Description

The MAX3785 6.25Gbps PC board equalizer consists

of an equalizer, limiting amplifier, offset driver, and off-

set cancellation circuit (see Figure 2). The equalizer

block compensates for the attenuation caused by the

PC board. The limiting amplifier squares up the signal

at the output of the equalizer block. The offset cancella-

tion circuit corrects for internal offset in the limiting

amplifier to minimize pulse-width distortion. This intro-

duces a low-frequency cutoff. The data must achieve a

50% mark/space ratio in less than 100µs. The specified

minimum differential input must be maintained to avoid

oscillation.

Input and Output Structures

An equivalent DC input circuit is shown in Figure 3. It

has an equivalent DC differential input resistance of

100

Ω. The output buffer is implemented using current-

mode logic (CML), as shown in Figure 4.

Package Description

The chip-scale package (UCSP) has a bump pitch of

0.5mm (19.7 mils) and a bump diameter of 0.3mm (12

mils). Lay out the solder pad spacing on 0.5mm (19.7

mils), a pad size of 0.25mm (10 mils) and a solder

mask opening of 0.33mm (13 mils). Round or square

pads are permissible. For detailed information on UCSP

layout and handling, go to Maxim’s website,

www.maxim-ic.com. The enclosed package description

was accurate at the time of publication. For the

MAX3785, all the balls shown in row B of the drawing

are unpopulated. See the

Package Information section

for the latest package information.

6.25Gbps, 1.8V PC Board Equalizer

6

_______________________________________________________________________________________

PIN

NAME

FUNCTION (MAX3785UBL)

A1

IN-

Negative Data Input, CML

A2

GND

Supply Ground

A3

OUT-

Negative Data Output, CML

C1

IN+

Positive Data Input, CML

C2

Supply Voltage

C3

OUT+

Positive Data Input, CML

MAX3785UBL Pin Description

PIN

NAME

FUNCTION (MAX3785UTT)

1

IN-

Negative Data Input (CML)

2

GND

Supply Ground

3

OUT-

Negative Data Output (CML)

4

OUT+

Positive Data Output (CML)

5

Supply Voltage

6

IN+

Positive Data Input (CML)

—

EP

Exposed Pad

MAX3785UTT Pin Description

Figure 2. Functional Diagram of the MAX3785

EQUALIZER

OFFSET

ADJUST

LIMITER

OUTPUT

BUFFER

MAX3785

OUT+

OUT-

IN+

IN-