MAXIM MAX3293, MAX3294, MAX3295 User Manual

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General Description

The MAX3293/MAX3294/MAX3295 low-power, high­speed transmitters for RS-485/RS-422 communication
operate from a single +3.3V power supply. These
devices contain one differential transmitter. The
MAX3295 transmitter operates at data rates up to
20Mbps, with an output skew of less than 5ns, and a
guaranteed driver propagation delay below 25ns. The
MAX3293 (250kbps) and MAX3294 (2.5Mbps) are
slew-rate limited to minimize EMI and reduce reflections
caused by improperly terminated cables.

The MAX3293/MAX3294/MAX3295 output level is guar­anteed at +1.5V with a standard 54Ω load, compliant
with RS-485 specifications. The transmitter draws 5mA
of supply current when unloaded, and 1µA in low­power shutdown mode (DE = GND).

Hot-swap circuitry eliminates false transitions on the data
cable during circuit initialization or connection to a live
backplane, and short-circuit current limiting and thermal­shutdown circuitry protect the driver against excessive
power dissipation.

The MAX3293/MAX3294/MAX3295 are offered in a
6-pin SOT23 package, and are specified over the
automotive temperature range.

Applications

RS-485/RS-422 Communications
Clock Distribution
Telecom Equipment
Automotive
Security Equipment
Point-of-Sale Equipment
Industrial Control

Features

♦ Space-Saving 6-Pin SOT23 Package

♦ 250kbps/2.5Mbps/20Mbps Data Rates Available

♦ Operate from a Single +3.3V Supply

♦ ESD Protection

±9kV—Human Body Model

♦ Slew-Rate Limited for Errorless Data

Transmission (MAX3293/MAX3294)

♦ 1µA Low-Current Shutdown Mode

♦ -7V to +12V Common-Mode Input Voltage Range

♦ Current Limiting and Thermal Shutdown for

Driver-Overload Protection

♦ Hot-Swap Inputs for Telecom Applications

♦ Automotive Temperature Range (-40°C to +125°C)

MAX3293/MAX3294/MAX3295

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

RS-422 Transmitters

________________________________________________________________ Maxim Integrated Products 1

Selector Guide

Ordering Information

19-2770; Rev 1; 2/03

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

PART TEMP RANGE

PIN­PACKAGE

MAX3293AUT-T -40°C to +125°C 6 SOT23-6
MAX3294AUT-T -40°C to +125°C 6 SOT23-6
MAX3295AUT-T -40°C to +125°C 6 SOT23-6

Typical Operating Circuit

MAX3293
MAX3294
MAX3295

D

DI

DE

MAX3280E
MAX3281E
MAX3283E
MAX3284E

R

RO

120Ω

Z

Y

Pin Configuration

MAXIMUM

PART

MAX3293AUT-T 0.25 Yes ABNI
MAX3294AUT-T 2.5 Yes ABNJ
MAX3295AUT-T 20 No ABNK

DATA RATE

(Mbps)

SLEW-RATE

LIMITED

MARK

TOP

TOP VIEW

16Y

DI

V

CC

MAX3293

2

MAX3294
MAX3295

34

SOT23-6

5 GND

ZDE

MAX3293/MAX3294/MAX3295

20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= +3.3V ±5%, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at VCC= +3.3V and TA= +25°C.) (Notes 1, 2)

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.

(All voltages referenced to GND, unless otherwise noted.)
Supply Voltage (V

CC

).............................................................+6V

DE, DI .......................................................................-0.3V to +6V

Y, Z .........................................................................-7V to +12.5V

Maximum Continuous Power Dissipation (T

A

= +70°C)

6-Pin SOT23 (derate 6.25mW/°C above +70°C).........500mW

Operating Temperature Ranges

MAX32_ _AUT...............................................-40°C to +125°C

Storage Temperature Range .............................-65°C to +160°C

Junction Temperature .....................................................+160°C

Lead Temperature (soldering, 10s) .................................+300°C

PARAMETER

CONDITIONS

UNITS

POWER SUPPLY

Supply Voltage V

CC

V

Supply Current in Normal
Operation

I

Q

No load, DI = VCC or GND, DE = V

CC

5mA

I

SHDN

No load, DE = GND 1 10 µA

DRIVER

R = 50Ω (RS-422),
T

A

≤ +85°C

2.0

Differential Driver Output V

OD

Figure 1, DE = VCC,
DI = GND or V

CC

R = 27Ω (RS-485),
T

A

≤ +85°C

1.5

V

Change in Magnitude of
Differential Output Voltage

∆V

OD

Figure 1, R = 27Ω or 50Ω,
DE = V

CC

(Note 3)

0.2 V

Driver Common-Mode Output
Voltage

V

OC

Figure 1, R = 27Ω or 50Ω,
DE = V

CC

, DI = VCC or GND

-1 +3 V

Change in Magnitude of Common­Mode Voltage

∆V

OC

Figure 1, R = 27Ω or 50Ω (Note 3) 0.2 V

DRIVER LOGIC

Input High Voltage V

IH

DE, DI 2.0 V

Input Low Voltage V

IL

DE, DI 0.8 V

Input Current I

IN

DE, DI -2 +2 µA

VIN = +12V -20

Output Leakage I

O

Y, Z
DE = GND,
V

CC

= GND or

+3.3V

VIN = -7V -20

µA

(VCC - 1V) ≤ V

OUT

≤ +12V, output high

Driver Short-Circuit Foldback
Output Current

I

OSFD

-7V ≤ V

OUT

≤ 1V, output high -25

mA

0 ≤ V

OUT

≤ +12V, output low

Driver Short-Circuit
Output Current

I

OSD

-7V ≤ V

OUT

≤ VCC, output high

mA

Thermal-Shutdown Threshold T

TS

°C

Thermal-Shutdown Hysteresis T

TSH

40 °C

ESD Protection Y, Z Human Body Model ±9 kV

Supply Current in Shutdown Mode

SYMBOL

MIN TYP MAX

3.135 3.300 3.465

V

CC

V

CC

+20

+20

+250

+25

-250

160

MAX3293/MAX3294/MAX3295

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

RS-422 Transmitters

_______________________________________________________________________________________ 3

SWITCHING CHARACTERISTICS (MAX3293)

(VCC= +3.3V ±5%, TA= +25°C, unless otherwise noted. Typical values are at VCC= +3.3V.)

SWITCHING CHARACTERISTICS (MAX3294)

(VCC= +3.3V ±5%, TA= +25°C, unless otherwise noted. Typical values are at VCC= +3.3V.)

PARAMETER

CONDITIONS

UNITS

t

PLH

Driver Propagation Delay

t

PHL

Figures 2, 3; R

DIFF

= 54Ω,

C

L

= 50pF

ns

t

R

Driver Differential Output Rise
or Fall Time

t

F

Figures 2, 3; R

DIFF

= 54Ω,

C

L

= 50pF

ns

Driver Output Skew t

SKEW

Figures 2, 3; R

DIFF

= 54Ω, CL = 50pF,

t

SKEW

= | t

PLH

- t

PHL

| (Note 5)

ns

Differential Driver Output Skew

Figures 2, 3; R

DIFF

= 54Ω, CL = 50pF

ns

Maximum Data Rate Figures 2, 3; R

DIFF

= 54Ω, CL = 50pF

kbps

Driver Enable to Output High t

ZH

Figures 4, 5; S2 closed, RL = 500Ω,
C

L

= 100pF

ns

Driver Enable to Output Low t

ZL

Figures 4, 5; S1 closed, RL = 500Ω,
C

L

= 100pF

ns

Driver Disable Time from Low t

LZ

Figures 4, 5; S1 closed, RL = 500Ω,
C

L

= 100pF

ns

Driver Disable Time from High t

HZ

Figures 4, 5; S2 closed, RL = 500Ω,
C

L

= 100pF

ns

Device-to-Device Propagation
Delay Matching

Same power supply, maximum temperature

900 ns

SYMBOL

t

DSKEW

difference between devices = +30°C (Note 5)

MIN TYP MAX

400 1300
400 1300
400 1200
400 1200

-400 +400

-100 +100
250

2000

2000

1000

1000

Driver Propagation Delay

Driver Differential Output Rise
or Fall Time

Driver Output Skew t

Differential Driver Output Skew t
Maximum Data Rate Figures 2, 3; R

Driver Enable to Output High t

Driver Enable to Output Low t

Driver Disable Time from Low t

Driver Disable Time from High t

Device-to-Device Propagation
Delay Matching

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

t

PLH

t

PHL

t

R

t

F

SKEW

DSKEW

ZH

ZL

LZ

HZ

Figures 2, 3; R
C

= 50pF

L

Figures 2, 3; R
C

= 50pF

L

Figures 2, 3; R

= | t

t

SKEW

Figures 2, 3; R

Figures 4, 5; S2 closed, RL = 500Ω,

= 100pF

C

L

Figures 4, 5; S1 closed, RL = 500Ω,

= 100pF

C

L

Figures 4, 5; S1 closed, RL = 500Ω,

= 100pF

C

L

= 54Ω,

DIFF

= 54Ω,

DIFF

= 54Ω, CL = 50pF,

DIFF

- t

PLH

| (Note 5)

PHL

= 54Ω, CL = 50pF -6 +6 ns

DIFF

= 54Ω, CL = 50pF 2.5 Mbps

DIFF

Figures 4, 5; S2 closed, RL = 500Ω,

= 100pF

C

L

Same power supply, maximum temperature
difference between devices = +30°C (Note 5)

24 70
24 70
10 70
10 70

ns

ns

-40 +40 ns

400 ns

400 ns

100 ns

100 ns

46 ns

MAX3293/MAX3294/MAX3295

20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters

4 _______________________________________________________________________________________

Note 1: Devices production tested at +25°C. Limits over the operating temperature range are guaranteed by design.
Note 2: All currents into the device are positive; all currents out of the device are negative. All voltages are referenced to device

ground, unless otherwise noted.

Note 3: ∆V

OD

and ∆VOCare the changes in VODand VOC, respectively, when the DI input changes state.

Note 4: The maximum current applies to peak current just prior to foldback current limiting.
Note 5: Not production tested. Guaranteed by design.

SWITCHING CHARACTERISTICS (MAX3295)

(VCC= +3.3V ±5%, TA= +25°C, unless otherwise noted. Typical values are at VCC= +3.3V.)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

t

PLH

25

Driver Propagation Delay

t

PHL

Figures 2, 3; R

DIFF

= 54Ω, CL = 50pF

25

ns

t

R

TA < +85°C 15

Driver Differential Output Rise
or Fall Time

t

F

Figures 2, 3;
R

DIFF

= 54Ω,

C

L

= 50pF

T

A

< +85°C 15

ns

Driver Output Skew t

SKEW

Figures 2, 3; R

DIFF

= 54Ω, CL = 50pF,

t

SKEW

= | t

PLH

- t

PHL

|

5ns

Differential Driver Output Skew

Figures 2, 3; R

DIFF

= 54Ω, CL = 50pF 5 ns

Figures 2, 3; R

DIFF

= 54Ω, CL = 50pF,

T

A

≤ +85°C

20

Maximum Data Rate

Figures 2, 3; R

DIFF

= 54Ω, CL = 50pF 16

Mbps

Driver Enable to Output High t

ZH

Figures 4, 5; S2 closed, RL = 500Ω,
C

L

= 100pF

ns

Driver Enable to Output Low t

ZL

Figures 4, 5; S1 closed, RL = 500Ω,
C

L

= 100pF

ns

Driver Disable Time from Low t

LZ

Figures 4, 5; S1 closed, RL = 500Ω,
C

L

= 100pF

ns

Driver Disable Time from High t

HZ

Figures 4, 5; S2 closed, RL = 500Ω,
C

L

= 100pF

ns

Device-to-Device Propagation
Delay Matching

Same power supply, maximum temperature

25 ns

TA = -40°C to +125°C 18.5

TA = -40°C to +125°C 18.5

t

DSKEW

400

400

difference between devices = +30°C (Note 5)

100

100

MAX3293/MAX3294/MAX3295

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

RS-422 Transmitters

_______________________________________________________________________________________ 5

Y

Z

V

OD

R

R

V

OC

Figure 1. Driver DC Test Load

Figure 2. Driver Timing Test Circuit

Figure 3. Driver Propagation Delays

Figure 4. Enable/Disable Timing Test Load

OUTPUT NORMALLY LOW

OUTPUT NORMALLY HIGH

3V

0V

Y, Z

V

OL

Y, Z

0V

1.5V

1.5V

V

OL

+ 0.25V

V

OH

- 0.25V

2.3V

2.3V

t

ZL(SHDN)

, t

ZL

t

LZ

t

ZH(SHDN)

, t

ZH

t

HZ

DE

Figure 5. Driver Enable and Disable Times

Test Circuits and Timing Diagrams

3V

DE

Y

DI

Z

V

S1

OUTPUT

R

L

UNDER TEST

C

L

S2

C

R

V

DIFF

ID

L

C

L

CC

3V

DI

1.5V

0V

Z

V

O

Y

1/2 V

O

V

O

0V

V

DIFF

10%

-V

O

t

R

f = 1MHz, tR ≤ 3ns, tF ≤ 3ns

t

PLH

V

= V (Y) - V (Z)

DIFF

90%

t

= | t

SKEW

PLH

- t

t

PHL

PHL

1.5V

1/2 V

O

90%

t

F

|

10%

0

10

20

30

40

MAX3293-95 toc09

TEMPERATURE (°C)

PROPAGATION DELAY (ns)

-40 20 50 80-10 110

DRIVER PROPAGATION DELAY

vs. TEMPERATURE

t

PHL

t

PLH

R

DIFF

= 54Ω

C

L

= 50pF

0

1

2

3

4

OUTPUT SKEW vs. TEMPERATURE

MAX3293-95 toc08

TEMPERATURE (°C)

OUTPUT SKEW (ns)

-40 20 50 80-10 110

DRIVER OUTPUT CURRENT

vs. DRIVER OUTPUT HIGH VOLTAGE

MAX3293-95 toc07

2V/div

OUTPUT HIGH VOLTAGE

OUTPUT CURRENT

(20mA/div)

0mA

-7V 5V

120mA

0

10

30

20

40

50

OUTPUT CURRENT

vs. DIFFERENTIAL OUTPUT VOLTAGE

MAX3293-95 toc04

DIFFERENTIAL OUTPUT VOLTAGE (V)

OUTPUT CURRENT (mA)

1.75 2.752.25 2.502.00 3.00 3.25 3.50

1.0

2.0

2.5

3.0

3.5

MAX3293-95 toc05

TEMPERATURE (°C)

DIFFERENTIAL OUTPUT VOLTAGE (V)

-40 20 50 80-10 110

DRIVER DIFFERENTIAL OUTPUT VOLTAGE

vs. TEMPERATURE

R

DIFF

= 54Ω

R

DIFF

= 100Ω

1.5

DRIVER OUTPUT CURRENT

vs. DRIVER OUTPUT LOW VOLTAGE

MAX3293-95 toc06

2V/div

OUTPUT LOW VOLTAGE

OUTPUT CURRENT

(20mA/div)

0mA

0V 12V

120mA

0

5

10

20

15

25

MAX3295

SUPPLY CURRENT vs. DATA RATE

MAX3293-95 toc01

DATA RATE (Mbps)

SUPPLY CURRENT (mA)

01051520

DE = V

CC

NO LOAD

TA = +85°C

TA = +125°C

TA = +25°C

TA = -40°C

0

0.5

1.0

1.5

2.0

SUPPLY CURRENT vs. TEMPERATURE

MAX3293-95 toc02

TEMPERATURE (°C)

SUPPLY CURRENT (mA)

-40 20 50 80-10 110

DE = V

CC

NO LOAD
NO SWITCHING

0

1.6

1.2

0.8

0.4

2.0

MAX3293-95 toc03

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

-40 20 50 80-10 110

SHUTDOWN SUPPLY CURRENT

vs. TEMPERATURE

DE = GND

MAX3293/MAX3294/MAX3295

20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters

6 _______________________________________________________________________________________

Typical Operating Characteristics

(VCC= +3.3V, TA = +25°C, unless otherwise noted.)

DRIVER PROPAGATION DELAY

MAX3293-95 toc10

20ns/div
Y, Z: 1V/div
DI: 2V/div

DI

0V

0V

Y, Z

Typical Operating Characteristics (continued)

(VCC= +3.3V, TA = +25°C, unless otherwise noted.)

MAX3293/MAX3294/MAX3295

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

RS-422 Transmitters

_______________________________________________________________________________________ 7

ENABLE RESPONSE TIME

MAX3293-95 toc11

40ns/div

DE

0V

0V

Y-Z

Y, Z, DE: 2V/div

UNLOADED DRIVER OUTPUT

WAVEFORM (f

IN

= 16Mbps)

MAX3293-95 toc12

20ns/div

Y, Z: 1V/div

0V

Y, Z

LOADED DRIVER OUTPUT WAVEFORM

(f

IN

= 16Mbps)

MAX3293-95 toc13

20ns/div

Y, Z: 500mV/div

0V

Y, Z

EYE DIAGRAM (f

IN

= 20Mbps)

MAX3293-95 toc14

10ns/div

Y, Z: 500mV/div

0V

Y, Z

Pin Description

PIN NAME FUNCTION

1DI

Driver Input. A logic low on DI forces the noninverting output (Y) low and the inverting output (Z)
high. A logic high on DI forces the noninverting output (Y) high and the inverting output (Z) low.

2VCCPositive Supply. VCC = +3.3V ±5%. Bypass VCC to GND with a 0.1µF capacitor.

3DE

Driver Output Enable. Force DE high to enable driver. Pull DE low to disable the driver. Hot-swap

input, see the Hot-Swap Capability section.
4ZInverting RS-485/RS-422 Output
5 GND Ground

6YNoninverting RS-485/RS-422 Output

MAX3293/MAX3294/MAX3295

20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters

8 _______________________________________________________________________________________

Detailed Description

The MAX3293/MAX3294/MAX3295 are low-power
transmitters for RS-485/RS-422 communication. The
MAX3295 operates at data rates up to 20Mbps, the
MAX3294 up to 2.5Mbps (slew-rate limited), and the
MAX3293 up to 250kbps (slew-rate limited). These
devices are enabled using an active-high driver enable
(DE) input. When disabled, outputs enter a high-imped­ance state, and the supply current reduces to 1µA.

The MAX3293/MAX3294/MAX3295 have a hot-swap
input structure that prevents disturbance on the differ­ential signal lines when a circuit board is plugged into
a “hot” backplane (see the Hot-Swap Capability sec­tion). Drivers are also short-circuit current limited and
are protected against excessive power dissipation by
thermal-shutdown circuitry.

Driver

The driver accepts a single-ended, logic-level input
(DI) and translates it to a differential RS-485/RS-422
level output (Y and Z). Driving DE high enables the dri­ver, while pulling DE low places the driver outputs
(Y and Z) into a high-impedance state (see Table 1).

Low-Power Shutdown

Force DE low to disable the MAX3293/MAX3294/
MAX3295. In shutdown mode, the device consumes a
maximum of 10µA of supply current.

Hot-Swap Capability

Hot-Swap Input

When circuit boards are inserted into a “hot” or pow­ered backplane, disturbances to the enable can lead to
data errors. Upon initial circuit board insertion, the
processor undergoes its power-up sequence. During
this period, the output drivers are high impedance and
are unable to drive the DE input of the MAX3293/
MAX3294/MAX3295 to a defined logic level. Leakage
currents up to 10µA from the high-impedance output
could cause DE to drift to an incorrect logic state.
Additionally, parasitic circuit board capacitance could

cause coupling of VCCor GND to DE. These factors
could improperly enable the driver.

The MAX3293/MAX3294/MAX3295 eliminate all above
issues with hot-swap circuitry. When VCCrises, an
internal pulldown circuit holds DE low for approximately
10µs. After the initial power-up sequence, the pulldown
circuit becomes transparent, resetting the hot-swap tol­erable input.

Table 1. MAX3293/MAX3294/
MAX3295 (RS-485/RS-422) Transmitting
Function Table

X = Don’t care.

INPUTS OUTPUTS

DE DI Y Z

0XShutdown Shutdown
1001
1110

Figure 6. Simplified Structure of the Driver Enable Input (DE)

Figure 7. Differential Power-Up Glitch (0.1V/µs)

DIFFERENTIAL POWER-UP GLITCH

(0.1V/µs)

4µs/div

2V/div

V

CC

Y

Z

Y-Z

0V
10mV/div

AC-COUPLED

10mV/div
AC-COUPLED

20mV/div

EN

V

TIMER

CC

10µs

TIMER

5.6kΩ

100µA

M1 M2

2mA

DE

(HOT SWAP)

MAX3293/MAX3294/MAX3295

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

RS-422 Transmitters

_______________________________________________________________________________________ 9

Hot-Swap Input Circuitry

The MAX3293/MAX3294/MAX3295 enable input fea­tures hot-swap capability. At the input, there are two
NMOS devices, M1 and M2 (Figure 6). When V

CC

ramps from zero, an internal 10µs timer turns on M2
and sets the SR latch, which also turns on M1.
Transistors M2, a 2mA current sink, and M1, a 100µA
current sink, pull DE to GND through a 5.6kΩ resistor.
M2 is designed to pull DE to the disabled state against
an external parasitic capacitance up to 100pF that may
drive DE high. After 10µs, the timer deactivates M2
while M1 remains on, holding DE low against three­state leakages that can drive DE high. M1 remains on
until an external source overcomes the required input
current. At this time, the SR latch resets and M1 turns

off. When M1 turns off, DE reverts to a standard, high­impedance CMOS input. Whenever VCCdrops below
1V, the hot-swap input is reset.

Hot-Swap Line Transient

During a hot-swap event when the driver is connected to
the line and is powered up, the driver must not cause the
differential signal to drop below 200mV. Figures 7, 8, and
9 show the results of the MAX3295 during power-up for
three different VCCramp rates (0.1V/µs, 1V/µs, and
10V/µs). The photos show the VCCramp, the single­ended signal on each side of the 100Ω termination, as
well as the differential signal across the termination.

ESD Protection

Human Body Model

Figure 10 shows the Human Body Model, and Figure 11
shows the current waveform it generates when dis­charged into low impedance. This model consists of a
100pF capacitor charged to the ESD voltage of interest,
which is then discharged into the device through a

1.5kΩ resistor.

Figure 8. Differential Power-Up Glitch (1V/µs)

Figure 9. Differential Power-Up Glitch (10V/µs) Figure 11. Current Waveform

DIFFERENTIAL POWER-UP GLITCH

(10V/µs)

200ns/div

2V/div

V

CC

Y

Z

Y-Z

0V

50mV/div
AC-COUPLED

50mV/div
AC-COUPLED

100mV/div

Figure 10. Human Body ESD Test

CHARGE-CURRENT-

LIMIT RESISTOR

DISCHARGE

RESISTANCE

STORAGE

CAPACITOR

C

s

100pF

R

C

1MΩ

R

D

1.5kΩ

HIGH-

VOLTAGE

DC

SOURCE

DEVICE
UNDER

TEST

DIFFERENTIAL POWER-UP GLITCH

(1V/µs)

V

CC

Y

Z

2V/div

0V
100mV/div

AC-COUPLED

100mV/div
AC-COUPLED

Y-Z

1µs/div

200mV/div

IP 100%

90%

AMPERES

36.8%

10%

0V

0V

I

r

PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)

TIME

t

RL

t

DL

CURRENT WAVEFORM

Reduced EMI and Reflections

(MAX3293/MAX3294)

The MAX3293/MAX3294 are slew-rate limited, minimiz­ing EMI and reducing reflections caused by improperly
terminated cables. Figure 12 shows Fourier analysis of
the MAX3295 transmitting a 125kHz signal. High-fre­quency harmonics with large amplitudes are evident.
Figure 13 shows the same information, but for the slew­rate-limited MAX3293, transmitting the same signal.
The high-frequency harmonics have much lower ampli­tudes, 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-shut­down circuit, forces the driver outputs into a high-imped­ance state if the die temperature exceeds +160°C.

MAX3293/MAX3294/MAX3295

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

TRANSISTOR COUNT: 263
PROCESS: BiCMOS

DRIVER OUTPUT WAVEFORM AND

FFT PLOT OF MAX3295

10dB/div

MAX3293/MAX3294/MAX3295

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

RS-422 Transmitters

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 11

© 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages

.)

6LSOT.EPS

F

1

1

21-0058

PACKAGE OUTLINE, SOT-23, 6L