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Table of Contents

Application Note

XR34350 and SP339E/B to THVD4431 System Rollover
Guide

Vikas Kumar Thawani and Chih-Wei Hsu
ABSTRACTThis application note outlines the necessary and potential steps for replacing the Maxlinear's XR34350 andSP339E/B multiprotocol (RS-232, RS-422, RS-485) transceivers with TI’s THVD4431.

Table of Contents
1 Introduction.............................................................................................................................................................................2
2 Key Feature Highlights of THVD4431 Over XR34350 and SP339E/B................................................................................. 2
2.1 Regulated Output Voltage for RS-232................................................................................................................................2
2.2 Full Path Diagnostic Loopback...........................................................................................................................................3
2.3 Operating Ambient Temperature Range............................................................................................................................ 5
2.4 Integrated Switchable Termination Resistor on Both Driver (R1/R2) and Receiver (R3/R4) Bus Pins.............................. 5
2.5 1.65V to 5.5V Supply for Logic Data and Control Signals..................................................................................................5
3 Potential Design Changes......................................................................................................................................................6
3.1 Pin 9 (VIO).......................................................................................................................................................................... 6
3.2 Pin 13 (MODE2).................................................................................................................................................................6
3.3 Pin 17 (TERM_TX) and Pin 18 (TERM_RX)...................................................................................................................... 6
3.4 Pin 19 (SHDN)....................................................................................................................................................................7
3.5 Pin 36 (NC).........................................................................................................................................................................7
4 Pinout Mapping.......................................................................................................................................................................8
5 Summary................................................................................................................................................................................. 9
6 References.............................................................................................................................................................................. 9

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Introduction

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1 Introduction
While the Maxlinear XR34350 and SP339E/B multiprotocol transceivers have many similarities to TI’s
THVD4431, the THVD4431 multiprotocol transceiver offers several advanced features and more integrationthat enable diverse applications and improved system performance. This system rollover document outlines how
to replace the Maxlinear XR34350 and SP339E/B multiprotocol transceivers with TI’s THVD4431 by comparing
the differences in feature set and pinout.

2 Key Feature Highlights of THVD4431 Over XR34350 and SP339E/B
While TI’s THVD4431 is pin-to-pin compatible with the XR34350 and SP339E/B multiprotocol transceivers, theTHVD4431 offers several advanced features in such a manner that new designs can develop a printed circuitboard (PCB) that is common to both THVD4431 and XR34350/SP339. This section provides an overview of theunique features offered by THVD4431.

2.1 Regulated Output Voltage for RS-232
THVD4431 has an integrated high-efficiency and low-noise charge pump to generate large output voltages for
RS-232 signaling. Charge pump consists of a voltage doubler and an inverter to regulate the voltage. Voltage
is regulated to nominal ± 5.5V for a 3.3V VCC or to ±9.5V for a 5V VCC operation. The internal charge pumpis controlled in a way that the output voltage stays regulated for varying load capacitance or varying data rate.
Load capacitance emulates the capacitance offered by the cable between the driver and receiver RS-232 nodes.
Also different applications can have different data rates, as such having regulated output voltage at any data rate
is beneficial.
The Maxlinear XR34350 multiprotocol transceiver is not capable of regulating the RS-232 output voltage withvarying load capacitance and data rate and as a result, output voltage drop can be observed when load
capacitance and/or data rate increases.
A comparison of output voltage for RS-232 between TI’s THVD4431 and Maxlinear’s XR34350 is shown in
Figure 2-1 and Figure 2-2. Figure 2-1 shows output voltage v.s. data rate and Figure 2-2 shows output voltage
v.s. load capacitance. The high output voltage for RS-232 signaling of the THVD4431 multiprotocol transceiver
enables high signal-to-noise ratio (SNR) which is beneficial for noisy industrial environments.

10

RS-232 Output voltage (V)

9
8
7
6
5
XR34350
THVD4431

4
3
2
1
0
0

50

100

150
200
Data rate (kbps)

250

300

Figure 2-1. THVD4431 RS-232 Output Voltage vs Data Rate

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Key Feature Highlights of THVD4431 Over XR34350 and SP339E/B

10

RS-232 Output Voltage (V)

9
8
7
6
5
XR34350
THVD4431

4
3
2
1
0
0

500

1000
1500
2000
Load capacitance (pF)

2500

3000

Figure 2-2. THVD4431 RS-232 Output Voltage vs Load Capacitance

2.2 Full Path Diagnostic Loopback
THVD4431 provides full path diagnostic loopback modes for both RS-232 and RS-485. These modes internallyshort the bus outputs to the bus inputs (shown in Figure 2-3 and Figure 2-4). So, if the digital logic data is
toggled by MCU, data is translated to bus (as analog bus signals) and is reflected back on logic buffer output.
This enables MCU to detect bus side shorts (due to shorted connector or cable) by comparing logic input andlogic output.
While the Maxlinear XR34350 and SP339E/B multiprotocol transceivers also provide diagnostic loopback for
RS-232, the transceivers provide logic loopback by connecting logic driver inputs to logic receiver outputs
bypassing the analog driver and receiver circuitry. The analog/bus pins are internally disconnected in this mode.
As a result, XR34350/SP339 devices are unable to detect bus side faults. Additionally, these devices do nothave RS-485 loopback mode.
Clearly, for safety critical applications, THVD4431 offers enhanced functionality through diagnostic loopback
modes eliminating any external circuitry in place to detect cable/connector shorts.

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Key Feature Highlights of THVD4431 Over XR34350 and SP339E/B

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L1

V+

C2+

VCC

C1+

NC

C1–

C2–

V–

VCC

R1

MODE2, MODE1,MODE0: X00 (RS232 Loopback Mode)

40

39

38

37

36

35

34

33

32

31

1

RX

30

R2

29

GND

5 kΩ
L2

2

RX
5 kΩ

L3

L4

L5

3

TX

28

R3

4

TX

27

R4

5

RX

26

GND

25

R5

5 kΩ
L6

6

TX

L7

7

RX

24

R6

5 kΩ
23

GND

9

22

R7

10

21

R8

L8

8

VIO

GND

RX

18

19
SHDN

20
VCC

17

TERM_RX16

TERM_TX

RS232 Loopback Mode
L4 reflects on R4 and R1 and L1 (red)L3 reflects on R3 and R2 and L2 (blue)
L6 reflects on R5, R6,R7, R8, L5, L7, L8 (green)

15

NC

14

MODE1

DIR

13

MODE0

12

SLR

11

MODE2

5 kΩ

Figure 2-3. THVD4431 in RS-232 Loopback Mode

L1

V+

C2+

VCC

C1+

NC

C1–

C2–

V–

VCC

R1

MODE2, MODE1,MODE0: 111 (RS485 Loopback Mode)

40

39

38

37

36

35

34

33

32

31

1

30

R2

29

GND

28

R3

T1
L2

2

L3

3

L4

4

27

R4

L5

5

26

GND

L6

6

25

R5

L7

7

24

R6

L8

8

23

GND

VIO

9

22

R7

GND

10

21

R8

11

12

13

14

15

16

17

18

19

20

SLR

DIR

MODE2

MODE0

MODE1

NC

TERM_TX

TERM_RX

SHDN

VCC

R1

Figure 2-4. THVD4431 in RS-485 Loopback Mode

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Key Feature Highlights of THVD4431 Over XR34350 and SP339E/B

2.3 Operating Ambient Temperature Range
THVD4431 makes sure that the electrical specifications in extended industrial temperature range (ambient) of-40°C to 125°C. Maxlinear XR34350/SP339 only makes sure performance in limited temperature range of -40°C
to 85°C. Extended temperature range allows system designers to shrink overall system casing size or eliminate
any air-cooling vents, allowing for larger power dissipation inside closer to the PCB as now the device is able tooperate at much higher ambient temperatures.

2.4 Integrated Switchable Termination Resistor on Both Driver (R1/R2) and Receiver (R3/R4)
Bus Pins
THVD4431 has two termination resistors of nominal 120Ω, one across R1/R2 and another across R3/R4 bus
pins in RS-485 mode. Both termination resistors are enabled or disabled using TERM_TX and TERM_RX control
pins as described in Table 7-2 of the THVD4431 data sheet. Both the termination resistors can be enabled or
disabled independent of the state of driver or receiver. Termination is OFF in RS-232 loopback, RS-232 3T5R,
RS-485 loopback, unpowered and thermal shutdown modes.
While the Maxlinear XR34350 and SP339E/B multiprotocol transceivers also provide 120Ω termination resistor
across R3/R4, the transceivers do not offer one across R1/R2 bus pins. Therefore, THVD4431 is more flexible
in RS-485 full duplex applications where it can be used at middle nodes or end nodes without the need ofadditional discrete termination resistor as well as control circuit, which helps save significant PCB area. An
example RS-485 full duplex configuration with THVD4431 is shown in Figure 2-5.
VIO

VIO

MODE1 = MODE0

R1

MODE1 = MODE0
R3
120 
R
R4

R4

R1

R2
L3

D

120 

DIR
THVD4431

L2

R

THVD4431

120 

120 

R3
R3
MODE1 =MODE0
VIO

TERM_TX TERM_RX
VIO
VIO
Commander

R4 R1
120 

120

THVD4431

R
D
L2

D

L2

DIR
L3

R2
TERM_RXTERM_TX
R2
VIO
VIO
TERM_RX
Responder
GND
TERM_TXGND

DIR L3
Responder

Figure 2-5. THVD4431 in Full Duplex RS-485 Network

2.5 1.65V to 5.5V Supply for Logic Data and Control Signals
THVD4431 provides a separate logic supply pin (pin 9), different than the main bus supply VCC. VIO allows users
to interface THVD4431 with microcontrollers (MCU) operating at low voltage supply level such as 1.8V or 2.5V.
Even for the applications which want to run RS-232 or RS-485 bus side circuitry at 5V, a 3.3V MCU interface isstill possible with THVD4431. This application use case is not enabled by Maxlinear XR34350 or SP339E/B.
To enable this feature, connect the desired logic supply voltage to pin 9 and add a 100nF bypass capacitor close
to pin 9, as shown in Figure 2-6. If this feature is not needed, simply connect pin 9 to the same voltage rail asother VCC pins and keep the same bypass capacitor (100nF). Voltage within recommended operating conditionis needed on pin 9VIO for THVD4431 to function properly, this pin cannot be left floating.

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5Potential Design Changes

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100 nF
100 nF3 V to 5.5 V

100 nF

1 uF

V+

C2+

VCC

C1+

NC

C1–

C2–

V–

VCC

R1

3 V to 5.5 V

40

39

38

37

36

35

34

33

32

31

L1

1

30

R2

L2

2

29

GND

L3

3

28

R3

L4

4

27

R4

L5

5

26

GND
R5

THVD4431

1.65 V
to
5.5 V

L6

6

25

L7

7

24

R6

L8

8

23

GND

VIO

9

22

R7

GND 1021

R8

Bus Side Connector

To and From MCU GPIO

100 nF

12

13

14

15

16

17

18

19

DIR

MODE2

MODE0

MODE1

NC

TERM_TX

TERM_RX

SHDN

VIO

20
VCC

11
SLR

100 nF3 V to 5.5 V

From MCU GPIO

Figure 2-6. THVD4431 Application Schematic

3 Potential Design Changes
This section highlights few potential changes that system designers need to take into consideration whenswitching a design from Maxlinear’s XR34350/SP339E/B to TI’s THVD4431.

3.1 Pin 9 (VIO)
Connect this pin to VCC if low I/O voltage support is not needed, this way THVD4431 fits exactly same design
as XR34350/SP339E/B. Otherwise, connect this pin to the desired MCU I/O voltage (example, 1.8V, 2.5V, 3.3V),
while keeping bus supply voltage VCC to 3.3V or 5V. Please note, a bypass capacitor of 100nF close to pin 9 isneeded for THVD4431.

3.2 Pin 13 (MODE2)
Pin 13 is NC (No Connect) for the Maxlinear XR34350 and SP339E/B multiprotocol transceiver. For TI’s
THVD4431, this pin enables/disables the RS485 diagnostic loopback feature (for details, please refer to
THVD4431 data sheet Section 7.4). Pull this pin to VIO if RS-485 loopback feature is needed in combination
with MODE0, MODE1 also pulled high. Leave this pin as NC if same design as Maxlinear is needed.

3.3 Pin 17 (TERM_TX) and Pin 18 (TERM_RX)
As described earlier in this document, TI’s THVD4431 provides 2 on-chip 120Ω termination resistors: one acrossthe R1/R2 terminals (controlled by pin17 TERM_TX and is used in both RS-485 half duplex and full duplex
modes), the other across the R3/R4 terminals (controlled by pin18 TERM_RX and is used in RS-485 full duplexmode).
Refer to Table 3-1 for a way to configure these pins the same as the XR34350 and SP339E/B devices.

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Potential Design Changes

Table 3-1. Pin 17 and Pin 18 Configuration for THVD4431 to Match XR34350 Functionality
Pin 17 TERM_TX

Pin 18 TERM_RX

RS-485 half duplex

Pull up to VIO to enable termination across
R1/R2 or pull-down to GND to disable

NC

RS-485 full duplex

NC

Pull up to VIO to enable termination across
R3/R4 or pull-down to GND to disable

3.4 Pin 19 (SHDN)
Pin 19 is SHDN(shutdown) for TI’s THVD4431 and is EN (enable) for Maxlinear’s XR34350 and SP339E/B.
These pins are identical in functionality – pull Pin 19 to VIO to enable device operation and pull-down to groundto disable device operation. For both devices, asserting this function disables all blocks and the current drawn
from the device is just the leakage current.

3.5 Pin 36 (NC)Pin 36 of TI’s THVD4431 is not internally connected. Pin 36 can be grounded without issue. Also, this pin iscompatible with Maxlinear’s XR34350 and SP339E/B.

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Pinout Mapping

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4 Pinout Mapping
Table 4-1. Pinout Mapping of THVD4431 vs XR34350
THVD4431 Pin Number

XR34350 and SP339E/B pin Description
numberPower and Ground Pins

VCC

20,32,38

9,20,32,38

3 to 5.5V supply voltage

VIO

9

N/A

V-

33

33 (VSS)

C2-

34

34

Negative terminal of charge pump capacitor-2

C1-

35

35

Negative terminal of charge pump capacitor-1

C1+

37

37

Positive terminal of charge pump capacitor-1

C2+

39

39

Positive terminal of charge pump capacitor-2

V+

40

40 (VDD)

GND

10,23,26,29

10,23,26,29,36

1.65V to 5.5V logic supply voltage
Negative charge pump rail

Positive charge pump rail
GroundLogic data pins
L1

1

1

Logic output (RS-232)

L2

2

2

Logic output

L3

3

3

(RS-232/RS-485)
Logic input(RS-232/RS-485)
L4

4

4

Logic input (RS-232)

L5 (L6 for the Maxlinear devices)55Logic output (RS-232)

L6 (L7 for the Maxlinear devices)66Logic input (RS-232)

L7 (L8 for the Maxlinear devices)77Logic output (RS-232)

L8 (L9 for the Maxlinear devices)88Logic output (RS-232)

R1

31

31

RS-232 receiver input or RS-485 bus pin (Z or B)

R2

30

30

RS-232 receiver input or RS-485 bus pin (Y or A)

R3

28

28

RS-232 driver output or RS-485 non-inverting receiver input
(A)

R4

27

27

RS-232 driver output or RS-485 inverting receiver input (B)R5 (R6 for the Maxlinear devices)25

25

RS-232 receiver input

R6 (R7 for the Maxlinear devices)24

24

RS-232 driver output

R7 (R8 for the Maxlinear devices)22

22

RS-232 receiver input

R8 (R9 for the Maxlinear devices)21

21

RS-232 receiver input

Bus pins

Logic control pins

8

SLR (SLEW for Maxlinear devices)11

11

Slew rate control, internal pull-down resistor. SLR=H
enables slow speed

DIR

12

12

RS-485 TX/RX enable/disable. Internal pull-down resistor

MODE2

13

N/A

MODE control pins, Integrated weak pull-down resistor

MODE0

14

14

MODE1

15

15

NC

16, 36

13,16, 18

TERM_TX (TERM for Maxlinear
devices)1717120Ω Termination enable/disable across R1/R2 terminals.
Internal pull down resistor

TERM_RX18

N/A120Ω Termination enable/disable across R3/R4 terminals.
Internal pull down resistor

SHDN (EN for Maxlinear devices)19

19

Device enable/disable

Not connected internally. Can be connected to supply,
ground or left open on PCB

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Summary

5 Summary
By following the guidelines addressed in this application note, a system designer can co-layout a PCB common
to TI's THVD4431 and Maxlinear's XR34350/SP339E/B. Alternatively, the report provides instructions on how to
upgrade a system from Maxlinear's XR34350/SP339E/B to TI's THVD4431.

6 References•

Texas Instruments, THVD4431 Multiprotocol (RS-232, RS-422, RS485) Transceiver with Integrated 120-Ω
Switchable Termination Resistor and IEC-ESD Protection, data sheet.

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