MAXIM MAX3294AUT-T

19-2770; Rev 1; 2/03
20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters
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
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)
Ordering Information
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
PART
Clock Distribution
Selector Guide
Telecom Equipment
Automotive
MAXIMUM
DATA RATE
(Mbps)
SLEW-RATE
LIMITED
TOP
MARK
MAX3293AUT-T
0.25
Yes
ABNI
MAX3294AUT-T
2.5
Yes
ABNJ
MAX3295AUT-T
20
No
ABNK
PART
Security Equipment
Point-of-Sale Equipment
Industrial Control
Pin Configuration
Typical Operating Circuit
120Ω
TOP VIEW
DI 1
VCC 2
6
MAX3293
MAX3294
MAX3295
DE 3
Y
5
GND
4
Z
DI
Z
D
Y
R
RO
DE
MAX3293
MAX3294
MAX3295
MAX3280E
MAX3281E
MAX3283E
MAX3284E
SOT23-6
________________________________________________________________ Maxim Integrated Products
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.
1
MAX3293/MAX3294/MAX3295
General Description
MAX3293/MAX3294/MAX3295
20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters
ABSOLUTE MAXIMUM RATINGS
(All voltages referenced to GND, unless otherwise noted.)
Supply Voltage (VCC).............................................................+6V
DE, DI .......................................................................-0.3V to +6V
Y, Z .........................................................................-7V to +12.5V
Maximum Continuous Power Dissipation (TA = +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
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.
ELECTRICAL CHARACTERISTICS
(VCC = +3.3V ±5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25°C.) (Notes 1, 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
3.135
3.300
3.465
V
5
mA
10
µA
POWER SUPPLY
Supply Voltage
Supply Current in Normal
Operation
Supply Current in Shutdown Mode
VCC
IQ
ISHDN
No load, DI = VCC or GND, DE = VCC
No load, DE = GND
1
DRIVER
Differential Driver Output
Change in Magnitude of
Differential Output Voltage
Driver Common-Mode Output
Voltage
Change in Magnitude of CommonMode Voltage
VOD
∆VOD
VOC
∆VOC
Figure 1, DE = VCC,
DI = GND or VCC
R = 50Ω (RS-422),
TA ≤ +85°C
2.0
VCC
R = 27Ω (RS-485),
TA ≤ +85°C
1.5
VCC
V
Figure 1, R = 27Ω or 50Ω,
DE = VCC (Note 3)
Figure 1, R = 27Ω or 50Ω,
DE = VCC, DI = VCC or GND
-1
Figure 1, R = 27Ω or 50Ω (Note 3)
0.2
V
+3
V
0.2
V
DRIVER LOGIC
Input High Voltage
VIH
DE, DI
Input Low Voltage
VIL
DE, DI
Input Current
IIN
DE, DI
IO
Y, Z
DE = GND,
VCC = GND or
+3.3V
Output Leakage
Driver Short-Circuit Foldback
Output Current
IOSFD
Driver Short-Circuit
Output Current
IOSD
2.0
V
0.8
V
-2
+2
µA
VIN = +12V
-20
+20
VIN = -7V
-20
+20
µA
(VCC - 1V) ≤ VOUT ≤ +12V, output high
+25
-7V ≤ VOUT ≤ 1V, output high
0 ≤ VOUT ≤ +12V, output low
-25
-250
-7V ≤ VOUT ≤ VCC, output high
+250
mA
mA
Thermal-Shutdown Threshold
TTS
160
°C
Thermal-Shutdown Hysteresis
TTSH
40
°C
±9
kV
ESD Protection
2
Y, Z
Human Body Model
_______________________________________________________________________________________
20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters
(VCC = +3.3V ±5%, TA = +25°C, unless otherwise noted. Typical values are at VCC = +3.3V.)
PARAMETER
Driver Propagation Delay
Driver Differential Output Rise
or Fall Time
Driver Output Skew
Differential Driver Output Skew
SYMBOL
tPLH
tPHL
tR
tF
CONDITIONS
MIN
TYP
MAX
Figures 2, 3; RDIFF = 54Ω,
CL = 50pF
400
1300
400
1300
Figures 2, 3; RDIFF = 54Ω,
CL = 50pF
400
1200
400
1200
tSKEW
Figures 2, 3; RDIFF = 54Ω, CL = 50pF,
tSKEW = | tPLH - tPHL | (Note 5)
-400
+400
tDSKEW
Figures 2, 3; RDIFF = 54Ω, CL = 50pF
-100
+100
Figures 2, 3; RDIFF = 54Ω, CL = 50pF
250
Maximum Data Rate
UNITS
ns
ns
ns
ns
kbps
Driver Enable to Output High
tZH
Figures 4, 5; S2 closed, RL = 500Ω,
CL = 100pF
2000
ns
Driver Enable to Output Low
tZL
Figures 4, 5; S1 closed, RL = 500Ω,
CL = 100pF
2000
ns
Driver Disable Time from Low
tLZ
Figures 4, 5; S1 closed, RL = 500Ω,
CL = 100pF
1000
ns
Driver Disable Time from High
tHZ
Figures 4, 5; S2 closed, RL = 500Ω,
CL = 100pF
1000
ns
Same power supply, maximum temperature
difference between devices = +30°C (Note 5)
900
ns
MAX
UNITS
Device-to-Device Propagation
Delay Matching
SWITCHING CHARACTERISTICS (MAX3294)
(VCC = +3.3V ±5%, TA = +25°C, unless otherwise noted. Typical values are at VCC = +3.3V.)
PARAMETER
Driver Propagation Delay
Driver Differential Output Rise
or Fall Time
Driver Output Skew
Differential Driver Output Skew
SYMBOL
tPLH
tPHL
tR
tF
CONDITIONS
MIN
24
70
24
70
Figures 2, 3; RDIFF = 54Ω,
CL = 50pF
10
70
10
70
-40
+40
+6
tSKEW
Figures 2, 3; RDIFF = 54Ω, CL = 50pF,
tSKEW = | tPLH - tPHL | (Note 5)
tDSKEW
Figures 2, 3; RDIFF = 54Ω, CL = 50pF
-6
Figures 2, 3; RDIFF = 54Ω, CL = 50pF
2.5
Maximum Data Rate
TYP
Figures 2, 3; RDIFF = 54Ω,
CL = 50pF
ns
ns
ns
ns
Mbps
Driver Enable to Output High
tZH
Figures 4, 5; S2 closed, RL = 500Ω,
CL = 100pF
400
ns
Driver Enable to Output Low
tZL
Figures 4, 5; S1 closed, RL = 500Ω,
CL = 100pF
400
ns
Driver Disable Time from Low
tLZ
Figures 4, 5; S1 closed, RL = 500Ω,
CL = 100pF
100
ns
Driver Disable Time from High
tHZ
Figures 4, 5; S2 closed, RL = 500Ω,
CL = 100pF
100
ns
Same power supply, maximum temperature
difference between devices = +30°C (Note 5)
46
ns
Device-to-Device Propagation
Delay Matching
_______________________________________________________________________________________
3
MAX3293/MAX3294/MAX3295
SWITCHING CHARACTERISTICS (MAX3293)
MAX3293/MAX3294/MAX3295
20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters
SWITCHING CHARACTERISTICS (MAX3295)
(VCC = +3.3V ±5%, TA = +25°C, unless otherwise noted. Typical values are at VCC = +3.3V.)
PARAMETER
Driver Propagation Delay
Driver Differential Output Rise
or Fall Time
SYMBOL
tPLH
tPHL
tR
tF
Driver Output Skew
Differential Driver Output Skew
CONDITIONS
MIN
TYP
25
Figures 2, 3; RDIFF = 54Ω, CL = 50pF
25
TA = -40°C to +125°C
Figures 2, 3;
RDIFF = 54Ω,
CL = 50pF
MAX
UNITS
ns
18.5
TA < +85°C
15
TA = -40°C to +125°C
18.5
TA < +85°C
ns
15
tSKEW
Figures 2, 3; RDIFF = 54Ω, CL = 50pF,
tSKEW = | tPLH - tPHL |
5
ns
tDSKEW
Figures 2, 3; RDIFF = 54Ω, CL = 50pF
5
ns
Maximum Data Rate
Figures 2, 3; RDIFF = 54Ω, CL = 50pF,
TA ≤ +85°C
20
Figures 2, 3; RDIFF = 54Ω, CL = 50pF
16
Mbps
Driver Enable to Output High
tZH
Figures 4, 5; S2 closed, RL = 500Ω,
CL = 100pF
400
ns
Driver Enable to Output Low
tZL
Figures 4, 5; S1 closed, RL = 500Ω,
CL = 100pF
400
ns
Driver Disable Time from Low
tLZ
Figures 4, 5; S1 closed, RL = 500Ω,
CL = 100pF
100
ns
Driver Disable Time from High
tHZ
Figures 4, 5; S2 closed, RL = 500Ω,
CL = 100pF
100
ns
Same power supply, maximum temperature
difference between devices = +30°C (Note 5)
25
ns
Device-to-Device Propagation
Delay Matching
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: ∆VOD and ∆VOC are the changes in VOD and 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.
4
_______________________________________________________________________________________
20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters
Y
R
RL
OUTPUT
UNDER TEST
VOD
S1
VCC
CL
R
S2
VOC
Z
Figure 1. Driver DC Test Load
Figure 4. Enable/Disable Timing Test Load
3V
DE
3V
1.5V
1.5V
0V
DE
DI
tZL(SHDN), tZL
CL
Y
VID
RDIFF
Z
tLZ
Y, Z
VOL
CL
2.3V OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
Y, Z
2.3V
VOH - 0.25V
0V
tZH(SHDN), tZH
Figure 2. Driver Timing Test Circuit
tHZ
Figure 5. Driver Enable and Disable Times
f = 1MHz, tR ≤ 3ns, tF ≤ 3ns
3V
DI
VOL + 0.25V
1.5V
0V
1.5V
tPLH
tPHL
1/2 VO
Z
VO
Y
1/2 VO
VO
VDIFF 0V
-VO
VDIFF = V (Y) - V (Z)
90%
90%
10%
10%
tR
tF
tSKEW = | tPLH - tPHL |
Figure 3. Driver Propagation Delays
_______________________________________________________________________________________
5
MAX3293/MAX3294/MAX3295
Test Circuits and Timing Diagrams
Typical Operating Characteristics
(VCC = +3.3V, TA = +25°C, unless otherwise noted.)
TA = +25°C
10
TA = -40°C
1.0
0.5
5
10
15
-10
20
50
80
-40
110
-10
20
50
80
110
DATA RATE (Mbps)
TEMPERATURE (°C)
TEMPERATURE (°C)
OUTPUT CURRENT
vs. DIFFERENTIAL OUTPUT VOLTAGE
DRIVER DIFFERENTIAL OUTPUT VOLTAGE
vs. TEMPERATURE
DRIVER OUTPUT CURRENT
vs. DRIVER OUTPUT LOW VOLTAGE
20
10
0
3.0
120mA
OUTPUT CURRENT
(20mA/div)
30
MAX3293-95 toc05
40
MAX3293-95 toc06
3.5
DIFFERENTIAL OUTPUT VOLTAGE (V)
MAX3293-95 toc04
50
RDIFF = 100Ω
2.5
2.0
RDIFF = 54Ω
1.5
0mA
1.0
2.50 2.75
3.00
3.25
3.50
-40
-10
20
50
80
DRIVER OUTPUT CURRENT
vs. DRIVER OUTPUT HIGH VOLTAGE
OUTPUT SKEW vs. TEMPERATURE
4
120mA
3
OUTPUT SKEW (ns)
12V
2V/div
OUTPUT LOW VOLTAGE
TEMPERATURE (°C)
MAX3293-95 toc07
0V
110
DIFFERENTIAL OUTPUT VOLTAGE (V)
DRIVER PROPAGATION DELAY
vs. TEMPERATURE
2
1
40
MAX3293-95 toc09
2.25
PROPAGATION DELAY (ns)
1.75 2.00
MAX3293-95 toc08
OUTPUT CURRENT (mA)
-40
20
0.8
0
0
0
1.2
0.4
5
0
DE = GND
1.6
SUPPLY CURRENT (µA)
SUPPLY CURRENT (mA)
15
DE = VCC
NO LOAD
NO SWITCHING
1.5
SUPPLY CURRENT (mA)
TA = +85°C
TA = +125°C
2.0
MAX3293-95 toc02
DE = VCC
NO LOAD
20
2.0
MAX3293-95 toc01
25
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
SUPPLY CURRENT vs. TEMPERATURE
MAX3293-95 toc03
MAX3295
SUPPLY CURRENT vs. DATA RATE
OUTPUT CURRENT
(20mA/div)
MAX3293/MAX3294/MAX3295
20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters
RDIFF = 54Ω
CL = 50pF
30
tPHL
20
tPLH
10
0mA
-7V
6
5V
2V/div
OUTPUT HIGH VOLTAGE
0
0
-40
-10
20
50
TEMPERATURE (°C)
80
110
-40
-10
20
50
TEMPERATURE (°C)
_______________________________________________________________________________________
80
110
20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters
DRIVER PROPAGATION DELAY
UNLOADED DRIVER OUTPUT
WAVEFORM (fIN = 16Mbps)
ENABLE RESPONSE TIME
MAX3293-95 toc10
MAX3293-95 toc12
MAX3293-95 toc11
DI
DE
0V
0V
Y, Z
Y-Z
0V
Y, Z
0V
0V
20ns/div
20ns/div
40ns/div
Y, Z: 1V/div
DI: 2V/div
Y, Z: 1V/div
Y, Z, DE: 2V/div
LOADED DRIVER OUTPUT WAVEFORM
(fIN = 16Mbps)
EYE DIAGRAM (fIN = 20Mbps)
MAX3293-95 toc13
MAX3293-95 toc14
Y, Z
Y, Z
0V
0V
20ns/div
Y, Z: 500mV/div
10ns/div
Y, Z: 500mV/div
Pin Description
PIN
NAME
FUNCTION
1
DI
2
VCC
Positive Supply. VCC = +3.3V ±5%. Bypass VCC to GND with a 0.1µF capacitor.
3
DE
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.
4
Z
5
GND
6
Y
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.
Inverting RS-485/RS-422 Output
Ground
Noninverting RS-485/RS-422 Output
_______________________________________________________________________________________
7
MAX3293/MAX3294/MAX3295
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
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.
cause coupling of VCC or GND to DE. These factors
could improperly enable the driver.
The MAX3293/MAX3294/MAX3295 eliminate all above
issues with hot-swap circuitry. When VCC rises, 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.
VCC
10µs
TIMER
Driver
TIMER
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.
5.6kΩ
2mA
100µA
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
DE
(HOT SWAP)
EN
M1
M2
Figure 6. Simplified Structure of the Driver Enable Input (DE)
DIFFERENTIAL POWER-UP GLITCH
(0.1V/µs)
2V/div
VCC
0V
Table 1. MAX3293/MAX3294/
MAX3295 (RS-485/RS-422) Transmitting
Function Table
INPUTS
DE
0
1
1
X = Don’t care.
8
DI
X
0
1
OUTPUTS
Y
Z
Shutdown
Shutdown
0
1
1
0
Y
10mV/div
AC-COUPLED
Z
10mV/div
AC-COUPLED
20mV/div
Y-Z
4µs/div
Figure 7. Differential Power-Up Glitch (0.1V/µs)
_______________________________________________________________________________________
20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters
DIFFERENTIAL POWER-UP GLITCH
(1V/µs)
2V/div
VCC
off. When M1 turns off, DE reverts to a standard, highimpedance CMOS input. Whenever VCC drops 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 V CC ramp rates (0.1V/µs, 1V/µs, and
10V/µs). The photos show the VCC ramp, 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.
0V
100mV/div
AC-COUPLED
Y
RC
1MΩ
100mV/div
AC-COUPLED
Z
RD
1.5kΩ
DISCHARGE
RESISTANCE
CHARGE-CURRENTLIMIT RESISTOR
200mV/div
Y-Z
1µs/div
HIGHVOLTAGE
DC
SOURCE
Cs
100pF
DEVICE
UNDER
TEST
STORAGE
CAPACITOR
Figure 8. Differential Power-Up Glitch (1V/µs)
Figure 10. Human Body ESD Test
DIFFERENTIAL POWER-UP GLITCH
(10V/µs)
2V/div
VCC
0V
Y
50mV/div
AC-COUPLED
Z
50mV/div
AC-COUPLED
Y-Z
Ir
IP 100%
90%
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
AMPERES
36.8%
10%
0V
0V
TIME
100mV/div
tRL
200ns/div
Figure 9. Differential Power-Up Glitch (10V/µs)
tDL
CURRENT WAVEFORM
Figure 11. Current Waveform
_______________________________________________________________________________________
9
MAX3293/MAX3294/MAX3295
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
MAX3293/MAX3294/MAX3295
20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters
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.
Chip Information
TRANSISTOR COUNT: 263
PROCESS: BiCMOS
DRIVER OUTPUT WAVEFORM AND
FFT PLOT OF MAX3295
DRIVER OUTPUT WAVEFORM AND
FFT PLOT OF MAX3293
10dB/div
10dB/div
Figure 12. Driver Output Waveform and FFT Plot of MAX3295
Transmitting a 125kHz Signal
10
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.
Figure 13. Driver Output Waveform and FFT Plot of MAX3293
Transmitting a 125kHz Signal
______________________________________________________________________________________
20Mbps, +3.3V, SOT23 RS-485/
RS-422 Transmitters
6LSOT.EPS
PACKAGE OUTLINE, SOT-23, 6L
21-0058
F
1
1
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.
MAX3293/MAX3294/MAX3295
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.)