Reduced EMI and Reflections

(MAX3293/MAX3294)

The MAX3293/MAX3294 are slew-rate limited, minimiz-

ing EMI and reducing reflections caused by improperly

terminated cables. Figure 12 shows Fourier analysis of

the MAX3295 transmitting a 125kHz signal. High-fre-

quency harmonics with large amplitudes are evident.

Figure 13 shows the same information, but for the slew-

rate-limited MAX3293, transmitting the same signal.

The high-frequency harmonics have much lower ampli-

tudes, and the potential for EMI is significantly reduced.

To minimize reflections, the line should be terminated at

both ends in its characteristic impedance, and stub

lengths off the main line should be kept as short as

possible. The slew-rate-limited MAX3293 and MAX3294

are more tolerant of imperfect termination.

Driver-Output Protection

Two mechanisms prevent excessive output current and

power dissipation caused by faults or by bus contention.

The first, a foldback current limit on the output stage,

provides immediate protection against short circuits over

the whole common-mode voltage range (see the

Typical

Operating Characteristics). The second, a thermal-shut-

down circuit, forces the driver outputs into a high-imped-

ance state if the die temperature exceeds +160°C.

20Mbps, +3.3V, SOT23 RS-485/

RS-422 Transmitters

10

______________________________________________________________________________________

Figure 12. Driver-Output Waveform and FFT Plot of MAX3295

Transmitting a 125kHz Signal

Figure 13. Driver-Output Waveform and FFT Plot of MAX3293

Transmitting a 125kHz Signal

DRIVER-OUTPUT WAVEFORM AND

FFT PLOT OF MAX3293

10dB/div

Chip Information

PROCESS: BiCMOS

DRIVER-OUTPUT WAVEFORM AND

FFT PLOT OF MAX3295

10dB/div

Z

DE

16

Y

+

5

GND

DI

MAX3293

MAX3294

MAX3295

SOT23-6

TOP VIEW

2

34

Pin Configuration

Package Information

For the latest package outline information and land patterns

“+”, “#”, or “-” in the package code indicates RoHS status only.

Package drawings may show a different suffix character, but

the drawing pertains to the package regardless of RoHS status.

PACKAGE

TYPE

PACKAGE

CODE

OUTLINE

NO.

LAND

PATTERN NO.

6 SOT23

U6CN+2

21-0058

90-0175