Detailed Description

LVDS is a signaling method for point-to-point and

multidrop data communication over a controlled-imped-

ance medium as defined by the ANSI TIA/EIA-644 and

IEEE 1596.3 standards. LVDS uses a lower voltage swing

than other common standards, achieving higher data

rates with reduced power consumption, while reducing

EMI emissions and system susceptibility to noise.

The MAX9169/MAX9170 are 630Mbps, four-port

repeaters for high-speed, low-power applications. The

MAX9169 accepts an LVDS input and has a fail-safe

input circuit. The MAX9170 features a +5V tolerant sin-

gle-ended LVTTL/LVCMOS input. Both devices repeat

the input at four LVDS outputs. The MAX9169 detects

differential signals as low as 50mV and as high as 1.2V

The MAX9170’s +5V tolerant LVTTL/LVCMOS input

includes circuitry to hold the decision threshold con-

stant at +1.5V over temperature and supply voltage.

The MAX9169/MAX9170 outputs use a current-steering

configuration to generate a 2.5mA to 4.5mA output cur-

rent. This current-steering approach induces less ground

bounce and shoot-through current, enhancing noise

margin and system speed performance. The outputs are

short-circuit current limited and are high impedance

when disabled or when the device is not powered.

The MAX9169/MAX9170 current-steering output requires

a resistive load to terminate the signal and complete the

transmission loop. Because the devices switch the direc-

tion of current flow and not voltage levels, the output volt-

age swing is determined by the value of the termination

resistor multiplied by the output current. With a typical

3.5mA output current, the MAX9169/MAX9170 produce

a 350mV output voltage when driving a transmission line

terminated with a 100

350mV). Logic states are determined by the direction of

current flow through the termination resistor.

Fail-Safe Circuitry

The fail-safe feature of the MAX9169 sets the outputs

high when the differential input is:

• Open

• Undriven and shorted

• Undriven and terminated

Without a fail-safe circuit, when the input is undriven,

noise at the input may switch the outputs and it may

appear to the system that data is being sent. Open or

undriven terminated input conditions can occur when a

cable is disconnected or cut, or when an LVDS driver

output is in high impedance. A shorted input can occur

because of cable failure.

When the input is driven with signals meeting the LVDS

standard, the input common-mode voltage is less than

(Figure 1). If the input is open, undriven and shorted, or

undriven and parallel terminated, an internal resistor in

0.3V, activating the fail-safe circuit and forcing the out-

puts high.

Applications Information

Supply Bypassing

ic 0.1µF and 0.001µF capacitors in parallel as close to

the device as possible, with the smaller value capacitor

imize parasitic inductance.

Traces, Cables, and Connectors

The characteristics of differential input and output con-

nections affect the performance of the MAX9169/

MAX9170. Use controlled-impedance traces, cables,

and connectors with matched characteristic impedance.

Ensure that noise couples as common mode by run-

ning the traces of a differential pair close together.

Reduce within-pair skew by matching the electrical

length of the traces of a differential pair. Excessive

skew can result in a degradation of magnetic field can-

cellation. Maintain a constant distance between traces

of a differential pair to avoid discontinuities in differen-

4-Port LVDS and LVTTL-to-LVDS Repeaters

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7

MAX9169

COMPARATOR

IN+

IN-

RECEIVER

OUT1+

OUT1-

OUT4+

OUT4-

Figure 1. MAX9169 Input Fail-Safe Circuit