MAXIM MAX14840E, MAX14841E Technical data

19-5131; Rev 0; 2/10

40Mbps, +3.3V, RS-485 Half-Duplex

Transceivers

General Description

The MAX14840E/MAX14841E are +3.3V ESD-protected
transceivers intended for half-duplex RS-485 communi­cation up to 40Mbps. These transceivers are optimized
for high speeds over extended cable runs while maximiz­ing tolerance to noise.

The MAX14840E features symmetrical fail-safe and larg­er receiver hysteresis, providing improved noise rejec­tion and improved recovered signals in high-speed and
long cable applications. The MAX14841E has true fail­safe receiver inputs guaranteeing a logic-high receiver
output when inputs are shorted or open.

The MAX14840E/MAX14841E transceivers draw 1.5mA
(typ) supply current when unloaded or when fully loaded
with the drivers disabled. Hot-swap capability eliminates
undesired transitions on the bus during power-up or hot
insertion.

The MAX14840E/MAX14841E are available in 8-pin SO
and small, 8-pin (3mm x 3mm) TDFN-EP packages. Both
devices operate over the -40NC to +125NC automotive
temperature range.

Applications

Motion Controllers

Fieldbus Networks

Industrial Control Systems

Backplane Buses

HVAC Networks

Ordering Information/Selector Guide

Features

S Half-Duplex RS-485 Transceivers

S +3.3V Supply Voltage

S 40Mbps Maximum Data Rate

S Large (170mV) Receiver Hysteresis on

MAX14840E

S Symmetrical Fail-Safe Receiver Input on

MAX14840E

S Fail-Safe Receiver Input (MAX14841E)

S Hot-Swap Capability

S Short-Circuit Protected Outputs

S Thermal Self-Protection

S Low 10µA (max) Shutdown Current

S Extended ESD Protection for RS-485 I/O Pins

±35kV Human Body Model (HBM)
±20kV Air-Gap Discharge per IEC 61000-4-2
±12kV Contact Discharge per IEC 61000-4-2

S Automotive -40°C to +125°C Operating

Temperature Range

S Available in Industry-Standard 8-Pin SO or

Space-Saving, 8-Pin TDFN-EP (3mm x 3mm)
Packages

MAX14840E/MAX14841E

PART FAIL SAFE TEMP RANGE PIN-PACKAGE

MAX14840EASA+ Symmetrical

MAX14840EATA+ Symmetrical

MAX14841EASA+ True

MAX14841EATA+ True

+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.

_______________________________________________________________ Maxim Integrated Products 1

-40NC to +125NC

-40NC to +125NC

-40NC to +125NC

-40NC to +125NC

8 SO

8 TDFN-EP*

8 SO

8 TDFN-EP*

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.

40Mbps, +3.3V, RS-485 Half-Duplex
Transceivers

ABSOLUTE MAXIMUM RATINGS

(Voltages referenced to GND.)

VCC ..................................................................... -0.3V to +6.0V

RE, RO .................................................. -0.3V to +(V

DE, DI .................................................................. -0.3V to +6.0V

A, B .................................................................... -8.0V to +13.0V

Short-Circuit Duration (RO, A, B) to GND ............... Continuous

Continuous Power Dissipation (TA = +70NC)

8-Pin SO (derate 7.6mW/NC above +70NC) ............... 606mW

8-Pin TDFN (derate 24.4mW/NC above +70NC) ....... 1951mW

Junction-to-Case Thermal Resistance (BJC) (Note 1)

8-Pin SO .......................................................................38NC/W

8-Pin TDFN ....................................................................8NC/W

Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-

layer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.

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.

CC

+ 0.3V)

DC ELECTRICAL CHARACTERISTICS

(VCC = +3.0V to +3.6V, TA = -40NC to +125NC, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25NC.) (Notes 2, 3)

MAX14840E/MAX14841E

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

POWER SUPPLY

Supply Voltage V

Supply Current I

Shutdown Supply Current I

DRIVER

Differential Driver Output V

Change in Magnitude of
Differential Output Voltage

Driver Common-Mode Output
Voltage

Change in Common-Mode
Voltage

Single-Ended Driver Output High V
Single-Ended Driver Output Low V

Driver Short-Circuit Output
Current

RECEIVER

Input Current (A and B) I

Differential Input Capacitance C

DV

V

DV

|I

OSD

CC

CC

SH

OD

OD

OC

OC

OH

OL

A,B

A,B

DE = RE = VCC, or
DE = RE = GND, or
DE = VCC, RE = GND,
DI = VCC or GND, no load

DE = GND and RE = V

RL = 54I, Figure 1

RL = 54I, Figure 1 (Note 4)

RL = 54I, Figure 1

RL = 54I, Figure 1 (Note 4)

A/B output, I
A/B output, I
0V P V

|

-7V P V

DE = GND,
VCC = GND or +3.6V

Between A and B, DE = GND, f = 2MHz 12 pF

P +12V, output low

OUT

P VCC, output high

OUT

Junction-to-Ambient Thermal Resistance (BJA) (Note 1)

8-Pin SO ....................................................................132NC/W

8-Pin TDFN ..................................................................41NC/W

Operating Temperature Range ...................... -40NC to +125NC

Junction Temperature .................................................. +150NC

Storage Temperature Range ......................... -65NC to +150NC

Lead Temperature (soldering, 10s) ...............................+300NC

Soldering Temperature (reflow) ......................................+260NC

3.0 3.6 V

1.5 4 mA

CC

1.5 V

-0.2 0 +0.2 V

VCC/2 3 V

-0.2 0.2 V

= -20mA 2.2 V

OUT

= 20mA 0.8 V

OUT

250

VIN = +12V 1000
VIN = -7V -800

10

250

FA

mA

FA

2 ______________________________________________________________________________________

40Mbps, +3.3V, RS-485 Half-Duplex

Transceivers

DC ELECTRICAL CHARACTERISTICS (continued)

(VCC = +3.0V to +3.6V, TA = -40NC to +125NC, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25NC.) (Notes 2, 3)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Receiver Differential Threshold
Voltage (MAX14840E Only)

Receiver Input Hysteresis
(MAX14840E Only)

Receiver Differential Threshold
Voltage (MAX14841E Only)

Receiver Input Hysteresis
(MAX14841E Only)

LOGIC INTERFACE

Input High Voltage V

Input Low Voltage V
Input Hysteresis V
Input Current I

Input Impedance on First
Transition

Output High Voltage V

Output Low Voltage V

Three-State Output Current at
Receiver

Receiver Output Short-Circuit
Current

PROTECTION

Thermal Shutdown Threshold T
Thermal Shutdown Hysteresis T

ESD Protection: A, B to GND

ESD Protection: All Other Pins HBM

V
V

V

DV

I

OZR

I

OSR

THF

THR

TH

HYS

IN

OH

OL

TS

TSH

-7V P VCM P 12V, V

-7V P VCM P 12V, V

VCM = 0V 20 170 mV

-7V P VCM P 12V

VCM = 0V 10 mV

TH

DE, DI 2.0 5.5

IH

RE

DE, DI, RE

IL

DE, DI, RE
DE, DI, RE

DE, RE

RE = GND, IO = -1mA, VA - VB > 200mV

RE = GND, IO = 1mA, VA - VB < -200mV

RE = VCC, 0V P VO P V

0V P VRO P V

IEC 61000-4-2 Air Gap Discharge

HBM

CC

OD

OD

falling
rising

CC

-200 -10 mV
10 200 mV

-200 -105 -10 mV

2.0

0.8 V

50 mV

-1 +1

1 10

VCC -

1.5

0.4 V

-1 +1

-95 +95 mA

160

15

Q20
Q12
Q35

Q2

V

FA

kI

V

FA

NC
NC

kVIEC 61000-4-2 Contact Discharge

kV

MAX14840E/MAX14841E

SWITCHING CHARACTERISTICS

(VCC = +3.0V to +3.6V, TA = -40NC to +125NC, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25NC.) (Notes 2, 3)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

DRIVER

Propagation Delay

Differential Driver Output Skew
|t

- t

DPHL

|

_______________________________________________________________________________________ 3

DPLH

Driver Differential Output Rise or
Fall Time

t

DPLH

t

DPHL

t

DSKEW

tHL, t

RL = 54I, CL = 50pF, Figures 2 and 3
(Note 5)

RL = 54I, CL = 50pF, Figures 2 and 3
(Notes 5, 8)

RL = 54I, CL = 50pF, Figures 2 and 3

LH

(Notes 5, 8)

5 12 20
5 12 20

7.5 ns

ns

2 ns

40Mbps, +3.3V, RS-485 Half-Duplex
Transceivers

SWITCHING CHARACTERISTICS (continued)

(VCC = +3.0V to +3.6V, TA = -40NC to +125NC, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25NC.) (Notes 2, 3)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Maximum Data Rate DR

Driver Enable to Output High t

Driver Enable to Output Low t

Driver Disable Time from Low t

Driver Disable Time from High t

Driver Enable from Shutdown to
Output Low

Driver Enable from Shutdown to
Output High

Time to Shutdown t

RECEIVER

Propagation Delay

MAX14840E/MAX14841E

Receiver Output Skew t
Maximum Data Rate DR
Receiver Enable to Output High t
Receiver Enable to Output Low t
Receiver Disable Time from Low t
Receiver Disable Time from High t

Receiver Enable from Shutdown
to Output Low

Receiver Enable from Shutdown
to Output High

Time to Shutdown t

Note 2: All devices are 100% production tested at TA = +25NC. Specifications for all temperature limits are guaranteed by design.
Note 3: 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 4: DV OD and DVOC are the changes in VOD and VOC, respectively, when the DI input changes state.
Note 5: Capacitive load includes test probe and fixture capacitance.
Note 6: The timing parameter refers to the driver or receiver enable delay when the device has exited the initial hot-swap protect

state and is in normal operating mode.

Note 7: Shutdown is enabled by driving RE high and DE low. The device is guaranteed to have entered shutdown after t

elapsed.

Note 8: Parameter is guaranteed by characterization and not production tested.

MAX

DZH

DZL

DLZ

DHZ

t

DZL(SHDN)

t

DZH(SHDN)

SHDN

t

RPLH

t

RPHL

RSKEW

MAX

RZH

RZL

RLZ

RHZ

t

RZL(SHDN)

t

RZH(SHDN)

SHDN

RL = 110I, CL = 50pF, Figures 4 and 5
(Notes 5, 6)

RL = 110I, CL = 50pF, Figures 4 and 5
(Notes 5, 6)

RL = 110I, CL = 50pF, Figures 4 and 5
(Notes 5, 6)

RL = 110I, CL = 50pF, Figures 4 and 5
(Notes 5, 6)

RL = 110I, CL = 50pF, Figures 4 and 5
(Notes 5, 6)

RL = 110I, CL = 50pF, Figures 4 and 5
(Notes 5, 6)

(Note 7) 50 800 ns

CL = 15pF, Figures 6 and 7 (Note 5)

CL = 15pF, Figures 6 and 7 (Notes 5, 8) 2 ns

RL = 1kI, CL = 15pF, Figure 8 (Notes 5, 6)
RL = 1kI, CL = 15pF, Figure 8 (Notes 5, 6)
RL = 1kI, CL = 15pF, Figure 8 (Notes 5, 6)
RL = 1kI, CL = 15pF, Figure 8 (Notes 5, 6)

RL = 1kI, CL = 15pF, Figure 8 (Notes 5, 6)

RL = 1kI, CL = 15pF, Figure 8 (Notes 5, 6)

(Note 7) 50 800 ns

40 Mbps

30 ns

30 ns

30 ns

30 ns

4

4

25
25

40 Mbps

20 ns
20 ns
20 ns
20 ns

4

4

SHDN

Fs

Fs

ns

Fs

Fs

has

4 ______________________________________________________________________________________

40Mbps, +3.3V, RS-485 Half-Duplex

Transceivers

Test and Timing Diagrams

MAX14840E/MAX14841E

A

R

L

2

V

OD

R

L

V

OC

2

B

V

CC

DE

DI

A

B

V

OD

Figure 1. Driver DC Test Load Figure 2. Driver Timing Test Circuit

t

LH

f = 1MHz, tLH = 3ns, t

90%

V

CC

1.5V 1.5V

0

t

DPLH

B

A

V

V

O

V

0

OD

-V

O

OD

10%

= 3ns

HL

VOD = [VA - VB]

90%

t

DPHL

t

HL

10%

R

L

C

L

Figure 3. Driver Propagation Delays

A

GND OR V

GENERATOR

DI

CC

D

DE

50I

S1

C

50pF

L

B

Figure 4. Driver Enable and Disable Times (t

_______________________________________________________________________________________ 5

DZH

t

DSKEW = tDPLH

OUT

R

110I

L =

, t

)

DHZ

DE

OUT

- t



DPHL

V

CC

t

DZH

, t

DZH(SHDN)

1.5V

1.5V

0.25V

t

DHZ

0

V

OH

0

40Mbps, +3.3V, RS-485 Half-Duplex
Transceivers

Test and Timing Diagrams (continued)

V

CC

R

110I

L =

OUT

0 OR V

A

DI

CC

D

DE

S1

B

V

OUT

DE

CC

GENERATOR

t

DZL

V

OL

, t

DZL(SHDN)

50I

1.5V

MAX14840E/MAX14841E

Figure 5. Driver Enable and Disable Times (t

Figure 6. Receiver Propagation Delay Test Circuit

ATE

DLZ

, t

DZL

)

V

ID

V

CC

1.5V

t

DLZ

A

B

0

0.25V

RECEIVER

R

OUTPUT

t

RPHL

V

CC

2

f = 1MHz, tLH P 3ns, t

t

RSKEW = tRPHL

A

B

V

OH

RO

V

OL

P 3ns

HL

t

RPLH

V

CC

2

- t



RPLH

Figure 7. Receiver Propagation Delays

6 ______________________________________________________________________________________

1V

-1V

40Mbps, +3.3V, RS-485 Half-Duplex

Transceivers

Test and Timing Diagrams (continued)

MAX14840E/MAX14841E

+1.5V

-1.5V

RE

t

RZH, tRZH(SHDN)

RO

RE

RO

1.5V 1.5V

t

RHZ

0.25V

S3

V

R

ID

RE

GENERATOR

50I

V

CC

S1 OPEN
S2 CLOSED
S3 = +1.5V

0 0

V

OH

V

CC

2

0

V

CC

S1 OPEN
S2 CLOSED
S3 = +1.5V

0

V

OH

R

1kI

RO

C

L

15pF

S1

S2

RE

RO

RE

t

RZL

V

CC

, t

RZL(SHDN)

t

RLZ

V

CC

S1 CLOSED

1.5V1.5V

S2 OPEN
S3 = -1.5V

V

CC

V

CC

2

V

OL

V

CC

S1 CLOSED
S2 OPEN
S3 = -1.5V

0

V

CC

Figure 8. Receiver Enable and Disable Times

_______________________________________________________________________________________ 7

0

RO

0.25V

V

OL

40Mbps, +3.3V, RS-485 Half-Duplex
Transceivers

Typical Operating Characteristics

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

NO-LOAD SUPPLY CURRENT

vs. TEMPERATURE

4

3

2

SUPPLY CURRENT (mA)

1

RE = GND AND DE = VCC,
OR RE = VCC AND DE = V

0

TEMPERATURE (°C)

MAX14840E toc01

SUPPLY CURRENT (µA)

CC

11085603510-15-40 125

RECEIVER OUTPUT HIGH VOLTAGE

vs. OUTPUT CURRENT

(V)
V

5

4

3

RO

2

MAX14840E toc04

(V)

RO

V

MAX14840E/MAX14841E

SHUTDOWN SUPPLY CURRENT

vs. TEMPERATURE

4

3

2

1

0

-40 125

RECEIVER OUTPUT LOW VOLTAGE

vs. OUTPUT CURRENT

5

4

3

2

TEMPERATURE (°C)

RE = V

CC

DE = GND

11085603510-15

MAX14840E toc02

SUPPLY CURRENT (mA)

MAX14840E toc05

(V)
V

SUPPLY CURRENT vs. DATA RATE

100

80

60

40

20

0

0 40

54I LOAD

NO LOAD

DATA RATE (Mbps)

DIFFERENTIAL DRIVER OUTPUT
VOLTAGE vs. OUTPUT CURRENT

5

4

3

OD

2

MAX14840E toc03

302010

MAX14840E toc06

1

0

0 25

IRO (mA)

DIFFERENTIAL DRIVER OUTPUT VOLTAGE

vs. TEMPERATURE

4

3

2

1

DIFFERENTIAL DRIVER OUTPUT VOLTAGE (V)

0

-40 125

TEMPERATURE (°C)

2015105

RL = 54I

11085603510-15

1

0

100

80

MAX14840E toc07

60

40

OUTPUT CURRENT (mA)

20

0

0 27

IRO (mA)

2421181512963

DRIVER OUTPUT CURRENT

vs. OUTPUT HIGH VOLTAGE

-7 5
OUTPUT HIGH VOLTAGE (V)

31-1-3-5

MAX14840E toc08

1

0

0 80

DRIVER OUTPUT CURRENT
vs. OUTPUT LOW VOLTAGE

140

120

100

80

60

OUTPUT CURRENT (mA)

40

20

0

0 12

OUTPUT LOW VOLTAGE (V)

8 ______________________________________________________________________________________

604020

IOD (mA)

MAX14840E toc09

108642

40Mbps, +3.3V, RS-485 Half-Duplex

Transceivers

Typical Operating Characteristics (continued)

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

MAX14840E/MAX14841E

DRIVER PROPAGATION DELAY

vs. TEMPERATURE

25

20

15

10

5

DRIVER PROPAGATION DELAY (ns)

0

TEMPERATURE (°C)

4

3

2

1

DRIVER OUTPUT TRANSITION SKEW (ns)

0

DIFFERENTIAL DRIVER SKEW (t

2.0

11085603510-15-40 125

MAX14840E toc10

1.5

1.0

DRIVER OUTPUT SKEW (ns)

0.5

0

t

DPLH

t

DPHL

RL = 54I, CL = 50pF

DRIVER OUTPUT TRANSITION SKEW

(t

) vs. TEMPERATURE

DSKEW

RL = 54I, CL = 50pF

11085603510-15-40 125

TEMPERATURE (°C)

vs. TEMPERATURE

RL = 54I, CL = 50pF

TEMPERATURE (°C)

MAX14840E toc13

RECEIVER PROPAGATION DELAY (ns)

DSKEW

11085603510-15-40 125

)

MAX14840E toc11

DRIVER OUTPUT RISE AND FALL TIME

10

8

6

TIME (ns)

4

2

0

RECEIVER PROPAGATION DELAY

vs. TEMPERATURE

25

20

15

10

5

0

t

RPLH

t

RPHL

TEMPERATURE (°C)

vs. TEMPERATURE

RL = 54I, CL = 50pF

MAX14840E toc12

RISE TIME

FALL TIME

11085603510-15-40 125

TEMPERATURE (°C)

MAX14840E toc14

CL = 50pF

11085603510-15-40 125

DRIVER/RECEIVER

PROPAGATION DELAY

10ns/div

MAX14840E toc15

DI
5V/div

A/B
2V/div

CAPACITANCE (pF)

RO
5V/div

RECEIVER INPUT CAPACITANCE

vs. FREQUENCY

70

60

50

40

30

20

10

0

100 100,000

FREQUENCY (kHz)

10,0001000

MAX14840E toc16

_______________________________________________________________________________________ 9

40Mbps, +3.3V, RS-485 Half-Duplex
Transceivers

Pin Configurations

TOP VIEW

*CONNECT EXPOSED PAD (EP) TO GND.

MAX14840E/MAX14841E

Pin Descriptions

V

CC

8 6 5

+

1 3 4

RO

A GND

B

7

MAX14840E
MAX14841E

2

DE DIRE

TDFN

*EP

RO

1

2

MAX14840E
MAX14841E

3

DE

4

SO

V

8

CC

BRE

7

A

6

GNDDI

5

PIN NAME FUNCTION

1 RO Receiver Output. See the Function Table.

Active-Low Receiver-Output Enable. Drive RE low to enable RO. RO is high impedance when RE is high.

2

RE

Drive RE high and DE low to enter low-power shutdown mode. RE is a hot-swap input (see the Hot-Swap
Capability section for details).

Driver-Output Enable. Drive DE high to enable driver outputs. These outputs are high impedance when

3 DE

DE is low. Drive RE high and DE low to enter low-power shutdown mode. DE is a hot-swap input (see the
Hot-Swap Capability section for details).

4 DI

Driver Input. With DE high, a low on DI forces the A output low and the B output high. Similarly, a high on
DI forces the A output high and the B output low.

5 GND Ground
6 A Noninverting Receiver Input and Noninverting Driver Output
7 B Inverting Receiver Input and Inverting Driver Output
8 V

Positive Supply Voltage Input. Bypass VCC with a 0.1FF ceramic capacitor to GND.

CC

— EP Exposed Pad (TDFN Only). Connect EP to GND.

10 _____________________________________________________________________________________

40Mbps, +3.3V, RS-485 Half-Duplex

Transceivers

Function Table

TRANSMITTING

INPUTS OUTPUTS

RE

X 1 1 0 1
X 1 0 1 0
0 0 X High Impedance High Impedance
1 0 X Shutdown (see note)

RE

0 X
0 X
0 X Open/Shorted Previous State
1 1 X High Impedance
1 0 X Shutdown (see note)

RE

0 X
0 X
0 X Open/Shorted 1
1 1 X High Impedance
1 0 X Shutdown (see note)

X = Don’t care.
Note: Shutdown mode, driver, and receiver outputs are in high impedance.

DE DI B A

RECEIVING (MAX14840E)

INPUTS OUTPUTS

DE A-B RO

R 200mV

P -200mV

RECEIVING (MAX14841E)

INPUTS OUTPUTS

DE A-B RO

R -10mV

P -200mV

1
0

1
0

MAX14840E/MAX14841E

Functional Diagram

V

CC

MAX14840E
MAX14841E

RO

RE

DE

DI

______________________________________________________________________________________ 11

R

B

SHUTDOWN

A

D

GND

40Mbps, +3.3V, RS-485 Half-Duplex
Transceivers

Detailed Description

The MAX14840E/MAX14841E are +3.3V ESD-protected
RS-485 transceivers intended for high-speed, half-duplex
communications. A hot-swap capability eliminates false
transitions on the bus during power-up or hot insertion.

The MAX14840E features symmetrical fail-safe and larg­er receiver hysteresis, providing improved noise rejec­tion and improved recovered signals in high-speed and
long cable applications. The MAX14841E has true fail­safe receiver inputs guaranteeing a logic-high receiver
output when inputs are shorted or open. All devices have
a 1-unit load receiver input impedance, allowing up to 32
transceivers on the bus.

The MAX14840E/MAX14841E transceivers draw 1.5mA
(typ) supply current when unloaded or when fully loaded
with the drivers disabled.

Symmetrical Fail Safe (MAX14840E)

At high data rates and with long cable lengths, the signal
at the end of the cable is attenuated and distorted due to
the lowpass characteristic of the transmission line. Under

MAX14840E/MAX14841E

these conditions, fail-safe RS-485 receivers, which have
offset threshold voltages, produce recovered signals
with uneven mark-space ratios. The MAX14840E has
symmetrical receiver thresholds, as shown in Figure 9.
This produces near even mark-space ratios at the
receiver’s output (RO). The MAX14840E also has higher
receiver hysteresis than the MAX14841E and most other
RS-485 transceivers. This results in higher receiver noise
tolerance.

Symmetrical fail safe means that the receiver’s output
(RO) remains at the same logic state that it was before
the differential input voltage VOD went to 0V. Under

normal conditions, where UART signaling is used, this
means that the state on the line prior to all drivers being
disabled is a logic-high (i.e., a UART STOP bit).

True Fail Safe (MAX14841E)

The MAX14841E guarantees a logic-high receiver output
when the receiver inputs are shorted or open or when
they are connected to a terminated transmission line
with all drivers disabled. This is the case if the receiver
input threshold is between -10mV and -200mV. RO is
logic-high if the differential receiver input voltage VOD is
greater than or equal to -10mV.

Hot-Swap Capability

Hot-Swap Inputs

When circuit boards are inserted into a hot or powered
backplane, disturbances to the enable inputs and differ­ential receiver inputs can lead to data errors. Upon initial
circuit board insertion, the processor undergoes its pow er­up sequence. During this period, the processor out put
drivers are high impedance and are unable to drive
the DE and RE inputs of the MAX14840E/MAX14841E
to a defined logic level. Leakage currents up to 10FA
from the high-impedance output of a controller could
cause DE and RE to drift to an incorrect logic state.
Additionally, parasitic circuit board capacitance could
cause coupling of VCC or GND to DE and RE. These
factors could improperly enable the driver or receiver.
However, the MAX14840E/MAX14841E have hot-swap
inputs that avoid these potential problems.

When VCC rises, an internal pulldown circuit holds DE
low and RE high. After the initial power-up sequence,
the pulldown circuit becomes transparent, resetting the
hot-swap-tolerable inputs.

RO

V

-200mV +200mV

Figure 9. Symmetrical Hysteresis

12 _____________________________________________________________________________________

V

THF

-10mV +10mV

V

THP

V

THP

OD

40Mbps, +3.3V, RS-485 Half-Duplex

How-Swap Input Circuitry

The MAX14840E/MAX14841E DE and RE enable inputs
feature hot-swap capability. At the input, there are two
nMOS devices, M1 and M2 (Figure 10). When VCC
ramps from 0V, an internal 15Fs timer turns on M2 and
sets the SR latch that also turns on M1. Transistors M2
(a 1mA cur rent sink) and M1 (a 100FA current sink) pull
DE to GND through a 5.6kI resistor. M2 is designed to
pull DE to the disabled state against an external parasitic
capaci tance up to 100pF that can drive DE high. After
15µs, the timer deactivates M2 while M1 remains on,
holding DE low against three-state 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, high-impedance CMOS input.
Whenever VCC drops below 1V, the hot-swap input is
reset.

For RE, there is a complementary circuit employing two
pMOS devices pulling RE to VCC.

Transceivers

MAX14840E/MAX14841E

±35kV ESD Protection

ESD protection structures are incorporated on all pins
to protect against electrostatic discharges encountered
during handling and assembly. The driver outputs and
receiver inputs of the MAX14840E family of devices have
extra protection against static electricity. The ESD struc­tures withstand high ESD in all states: normal operation,
shutdown, and powered down. After an ESD event, the
MAX14840E/MAX14841E keep working without latchup
or damage.

ESD protection can be tested in various ways. The trans­mitter outputs and receiver inputs of the MAX14840E/
MAX14841E are characterized for protection to the fol­lowing limits:

• Q35kV HBM

• Q20kV using the Air Gap Discharge method specified

in IEC 61000-4-2

• Q12kV using the Contact Discharge method specified
in IEC 61000-4-2

V

CC

15Fs

TIMER

TIMER

DE

Figure 10. Simplified Structure of the Driver Enable Pin (DE)

5.6kI

100FA

1mA

DRIVER
ENABLE
(HOT SWAP)

M2M1

______________________________________________________________________________________ 13

40Mbps, +3.3V, RS-485 Half-Duplex
Transceivers

ESD Test Conditions

ESD performance depends on a variety of conditions.
Contact Maxim for a reliability report that documents test
setup, test methodology, and test results.

Human Body Model

Figure 11 shows the HBM, and Figure 12 shows the
current waveform it generates when discharged into a
low-impedance state. This model consists of a 100pF
capacitor charged to the ESD voltage of interest, which
is then discharged into the test device through a 1.5kI
resistor.

IEC 61000-4-2

The IEC 61000-4-2 standard covers ESD testing and
performance of finished equipment. However, it does not
specifically refer to integrated circuits. The MAX14840E/
MAX14841E family of devices helps you design equip­ment to meet IEC 61000-4-2, without the need for addi­tional ESD protection components.

MAX14840E/MAX14841E

HIGH-

VOLTAGE

DC

SOURCE

R

C

1MI

CHARGE CURRENT

LIMIT RESISTOR

C

100pF

S

R

D

1.5kI

DISCHARGE

RESISTANCE

STORAGE
CAPACITOR

DEVICE

UNDER

TEST

The major difference between tests done using the HBM
and IEC 61000-4-2 is higher peak current in IEC 61000-4-2
because series resistance is lower in the IEC 61000-4-2
model. Hence, the ESD withstand voltage measured to
IEC 61000-4-2 is generally lower than that measured
using the HBM.

Figure 13 shows the IEC 61000-4-2 model, and
Figure 14 shows the current waveform for IEC 61000-4-2
ESD Contact Discharge test.

Applications Information

High-Speed Operation

The MAX14840E and MAX14841E are high-performance
RS-485 transceivers supporting data rates up to 40Mbps.

Driver Output Protection

Two mechanisms prevent excessive output current
and power dissipation caused by faults or by bus
contention. Current limit on the output stage provides

HIGH-

VOLTAGE

DC

SOURCE

R

C

50MΩ TO 100MΩ

CHARGE CURRENT

LIMIT RESISTOR

C

150pF

s

RD

Ω

330

DISCHARGE

RESISTANCE

STORAGE
CAPACITOR

DEVICE
UNDER

TEST

Figure 11. Human Body ESD Test Model

IP 100%

AMPERES

90%

36.8%

10%

0

0

t

RL

TIME

CURRENT WAVEFORM

PEAK-TO-PEAK RINGING

I

R

(NOT DRAWN TO SCALE)

t

DL

Figure 12. Human Body current Waveform

Figure 13. IEC 61000-4-2 ESD Test Model

I

100%

90%

PEAK

I

10%

tR = 0.7ns TO 1ns

30ns

60ns

Figure 14. IEC 61000-4-2 ESD Generator Current Waveform

14 _____________________________________________________________________________________

t

40Mbps, +3.3V, RS-485 Half-Duplex

Transceivers

MAX14840E/MAX14841E

120

Ω 120Ω

DI

D

DE

B

B B

AAA

B

D

A

DE

DI

RO

RE

Figure 15. Typical Half-Duplex RS-485 Network

R

MAX14840E
MAX14841E

R

D

DI RO DE

DE

immediate protection against short circuits over the
whole common-mode voltage range (see the Typical
Operating Characteristics). Additionally, a thermal shut­down circuit forces the driver outputs into a high-imped­ance state if the die temperature exceeds +160NC (typ).

Low-Power Shutdown Mode

Low-power shutdown mode is initiated by bringing RE
high and DE low. In shutdown, the devices draw less
than 10FA of supply current.

RE and DE can be driven simultaneously; the parts are
guaranteed not to enter shutdown if RE is high and DE is
low for less than 50ns. If the inputs are in this state for at
least 800ns, the parts are guaranteed to enter shutdown.

R

R

D

DI

RO

RERE

RO
RE

Chip Information

PROCESS: BiCMOS

Package Information

For the latest package outline information and land patterns,
go to www.maxim-ic.com/packages. Note that a “+”, “#”, 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 DOCUMENT NO.

8 SO S8+4

8 TDFN-EP T833+2

21-0041
21-0137

Typical Applications

The MAX14840E/MAX14841E transceivers are designed
for bidirectional data communications on multipoint bus
transmission lines. Figure 15 shows a typical network
application circuit. To minimize reflections, terminate the
line at both ends with its characteristic impedance and
keep stub lengths off the main line as short as possible.

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 15

©

2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.