MAXIM MAX3785 Technical data

MAX3785

6.25Gbps, 1.8V PC Board Equalizer

________________________________________________________________

Maxim Integrated Products

1

19-2630; Rev 4; 10/08

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.

General Description

The MAX3785 6.25Gbps equalizer operates from a sin­gle 1.8V supply and compensates for transmission­medium losses encountered with FR-4 transmission
lines. Optimized for low-voltage, high-density, DC-cou­pled interconnections between the line card and switch
card, the MAX3785 enables a system upgrade path
while maintaining a legacy rate of 2.5Gbps to

3.125Gbps. Roughly the size of two 0603 passive com­ponents, the MAX3785 easily provides placement and
routing flexibility.

The MAX3785 is composed of an equalizer, limiting
amplifier, and output driver. For data rates of 3.2Gbps
and lower, the MAX3785 equalizes signals for spans up
to 40in of FR-4 board material. For data rates up to

6.25Gbps, the MAX3785 compensates for 30in of FR-4
board material. The MAX3785 is coding independent,
functioning equally well for 8b/10b or scrambled signals.

The MAX3785 features DC-coupled current-mode logic
(CML) data inputs and outputs. It is packaged in a tiny

1.5mm ×1.5mm chip-scale package (UCSP™) and a
6-pin TDFN package.

Applications

HSBI for ≤ 6.4Gbps

Double IEEE 802.3ae XAUI

Double STM-16/OC-48

Features

♦ Single 1.8V Supply

♦ Very Low Power, 60mW

♦ Spans 30in with FR-4 at 6.25Gbps

♦ Operates from 1.0Gbps to 6.4Gbps

♦ Coding Independent, 8b/10b or Scrambled

♦ DC-Coupled CML Inputs and Outputs

♦ Small 1.5mm × 1.5mm Footprint

Ordering Information

Typical Application Circuit

UCSP is a trademark of Maxim Integrated Products, Inc.

+

Denotes a lead-free/RoHS-compliant package.

*

EP = Exposed pad.

Pin Configurations

PART TEMP RANGE PIN-PACKAGE

MAX3785UBL 0°C to +85°C 6 UCSP (3  3)

MAX3785UWL+ 0°C to +85°C 6 WLP

MAX3785UTT 0°C to +85°C 6 TDFN-EP*

MAX3785UTT+ 0°C to +85°C 6 TDFN-EP*

MAX3785ITT -20°C to +85°C 6 TDFN-EP*

MAX3785ITT+ -20°C to +85°C 6 TDFN-EP*

TOP VIEW (BUMPS ON BOTTOM OF DIE)

Δ

A1 A2 A3
IN- GND OUT-

MAX3785UBL

C1 C2 C3

IN+ V

3 x 3 UCSP TDFN

OUT+

CC

1 6 IN+

IN-

MAX3785UTT

2

GND

34

5V

CC

OUT+OUT-

LINE CARD

MAC

RxRxTx

1.8V

V

CC

Tx

OUT IN

MAX3785

BACKPLANE

6.25Gbps

IN OUT

MAX3785

30in (0.75m)

1.8V

V

CC

SWITCH CARD

SWITCH

ASIC WITH

SERDES

Rx

Tx

MAX3785

6.25Gbps, 1.8V PC Board Equalizer

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

Supply Voltage, V

CC

to GND.................................-0.5V to +6.0V

Continuous Output Current (OUT+, OUT-) .......-25mA to +25mA

Input Voltage (IN+, IN-) ..............................-0.5V to (V

CC

+ 0.5V)

Operating Ambient Temperature Range

(UBL, UTB)......................................................... 0°C to +85°C

Operating Ambient Temperature Range (ITT).....-20°C to +85°C

Storage Ambient Temperature Range...............-55°C to +150°C

Continuous Power Dissipation (T

A

= +70°C)

6-Pin TDFN (derate 24.4mW above +70°C)..................1.95W

ELECTRICAL CHARACTERISTICS

(Typical values measured at VCC= 1.8V and TA= +25°C. Specifications guaranteed over specified operating conditions.)
(See

Operating Conditions

table.)

Note 1: Guaranteed by design and characterization.
Note 2: Using input pattern 0000011111 at 6.25Gbps.
Note 3: Difference in deterministic jitter between data source and equalizer output, evaluated at 2.5Gbps, 3.2Gbps, 5Gbps, and

6.25Gbps. Pattern used: PRBS (2

7

), ninety-six 0s, 1, 0, 1, 0, PRBS (27), ninety-six 1s, 0, 1, 0, 1.

Note 4: Signal is applied differentially at input to a 6-mil wide, loosely coupled stripline. Deterministic jitter at the output of the

transmission line is from media-induced loss, not from clock source modulation (see Figure 1).

Supply Current 35 55 mA

Input Swing (IN)

Input Common-Mode Voltage Range (Note 1)

Input Return Loss 100MHz to 3.2GHz, power off 15 dB

Differentia l Input Resistance IN+ and IN- 85 100 115 

Output Swing

Output Resistance OUT+ or OUT- 42 50 58 

Output Return Loss 100MHz to 3.2GHz, IN+ = high 14 dB

Output Transition Time (tr, tf) 20% to 80% (Note 2) 30 40 55 ps

Residual Deterministic Jitter
(Notes 1, 3, 4)

Output Random J itter (Notes 1, 2) 0.75 1.0 ps

Low-Frequency Cutoff Frequenc y 50 kHz

Latency 200 ps

Max imum B it Rate (Note 1) 6.25 6.4 Gbps

Min imum Bit Rate (Note 1) 1.0 2.5 Gbps

PARAMETER CONDITIONS MIN TYP MAX UNITS

Measured differentially at data source before
encountering loss (Point A in Figure 1) (Note 1)

Measured differentially at OUT+ and OUT- with 50
±1% load at each side

2.5Gbps, 3.2Gbps, 5.0Gbps; 0in to 30in FR-4
400mV

2.5Gbps, 3.2Gbps; 40in FR-4
400mV

6.25Gbps; 0in to 30in FR-4
600mV

6.25Gbps; 0in to 30in FR-4
IN = 400mV

 IN  1600mV

P-P

 IN  1600mV

P-P

 IN  1600mV

P-P

P-P

P-P

P-P

P-P

400 1600 mV

(IN

V

CC

MIN

-

/4)

V

-

CC

/4)

(IN

MAX

450 800 mV

0.10 0.15

0.15 0.20

0.15 0.25

0.20 0.30

P-P

V

P-P

UI

RMS

MAX3785

6.25Gbps, 1.8V PC Board Equalizer

_______________________________________________________________________________________ 3

Operating Conditions

Typical Operating Characteristics

(VCC= +1.8V, TA= +25°C, unless otherwise noted. Measurements done at 6.25Gbps, 500mV

P-P

at the source with a test pattern:

PRBS (2

7

), ninety-six 0s, 1, 0, 1, 0, PRBS (27), ninety-six 1s, 0, 1, 0, 1. Deterministic jitter of the MAX3785 and the board was mea­sured using Tektronix’s FrameScan™. Deterministic jitter of the system was subtracted from the measured value. Eye diagrams were
acquired by FrameScan, which includes system jitter but eliminates random jitter.)

Figure 1. Conditions of Testing

FrameScan is a trademark of Tektronix.

EYE DIAGRAM OF UNEQUALIZED

SIGNAL AFTER 30in OF FR-4

MAX3785 toc01

30ps/div

70mV/div

TEST PATTERN, 6.25Gbps,
WITHOUT RANDOM JITTER,
INCLUDING 13ps SYSTEM JITTER

EYE DIAGRAM OF EQUALIZED

SIGNAL AFTER 30in OF FR-4

MAX3785 toc02

30ps/div

70mV/div

TEST PATTERN, 6.25Gbps,
WITHOUT RANDOM JITTER,
INCLUDING 13ps SYSTEM JITTER

EYE DIAGRAM OF EQUALIZED

SIGNAL AFTER 30in OF FR-4

MAX3785 toc03

30ps/div

70mV/div

2

10

- 1 PRBS, 6.25Gbps,
WITHOUT RANDOM JITTER,
INCLUDING 13ps SYSTEM JITTER

PARAMETER CONDITIONS MIN TYP MAX UNITS

Supply Voltage (VCC) 1.71 1.8 1.89 V

Operating Ambient Temperature (UBL, UTT) 0 25 85 °C

10Hz ≤ f < 100Hz 100

100Hz ≤ f < 1MHz 40Supply Noise Tolerance

1MHz ≤ f ≤ 1GHz 10

Bit Rate NRZ data 2.50 6.25 Gbps

Operating Ambient Temperature (ITT) -20 25 85 °C

PC BOARD

SIGNAL SOURCE

AB

<1.0pF SMA
CONNECTOR

3in ≤ L ≤ 30in

<1.0pF SMA

CONNECTOR

IN OUT

MAX3785

FR-4

< 4.4

4.0 < ε

r

tanδ = 0.022

C

mV

P-P