General Description
The MAX3535E evaluation kit (EV kit) is a fully assem-
bled and tested PCB that contains a 2500VRMS isolated
RS-485/RS-422 transceiver with ESD protection. The EV
kit circuit features a differential driver and one receiver.
The circuit’s receiver is a 1/8 unit load for the RS-485
bus and communicates up to 1000kbps. The MAX3535E
fail-safe circuitry and driver slew-rate features are demon-
strated and easily reconfigured.
Additionally, the EV kit features an H-bridge DC-DC
converter to power the isolated section of the MAX3535E
RS-485/RS-422 circuit. Input power to the circuit is
supplied by a +3V to +5.5VDC source. This circuit uses a
full-wave rectifier on the unregulated output and provides
unregulated voltage to the MAX3535E internal, linear
low-dropout (LDO) regulator. Using an H-bridge design
minimizes input ripple current and radiated noise.
Undervoltage lockout (UVLO) and thermal shutdown
provide for a robust, isolated RS-485/RS-422 transceiver
circuit and power supply. The surface-mount transformer
provides up to 2500VRMS galvanic isolation and the out-
put is powered from a center-tapped, full-wave rectifier
circuit to reduce output voltage ripple.
The isolated H-bridge DC-DC converter operation at
420kHz allows the use of ceramic-only output capaci-
tors and a small transformer.
Features
Designed for 2500VRMS Isolation
1/8 RS-485 Unit Load
1000kbps Full-Duplex RS-485/RS-422
Communication (Configurable for Half Duplex)
+3.0V to +5.5VDC Input Range
Isolated VCC2 Output
Center-Tapped, Full-Wave Rectifier Output
420kHz Switching Frequency
Undervoltage Lockout (UVLO) and Thermal
Shutdown
Low-Cost Integrated-FET H-Bridge Design
Fully Assembled and Tested
Evaluates: MAX3535E
MAX3535E Evaluation Kit
________________________________________________________________
Maxim Integrated Products
1
19-0716; Rev 0; 12/06
Component List
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.
Ordering Information
PART TEMP RANGE IC PACKAGE
MAX3535EEVKIT+ 0°C to +70°C* 28 Wide SO
DESIGNATION QTY DESCRIPTION
C1, C3 2
10µF ±10%, 10V X7R ceramic
capacitors (1206)
Murata GRM31CR71A106K
C2, C4 2
0.1µF ±10%, 25V X7R ceramic
capacitors (0805)
Murata GRM21BR71E104K
D1 1 30V , 200m A S chottky d i od e ( S O T- 23)
C entr al S em i cond uctor C BAT54C
JU1 1 3-pin header
JU2, JU3, JU4 3 2-pin headers
R1, R2 0 Not installed, resistors (0805)
10kΩ ±1% resistor recommended
R3, R4 2 100kΩ ±5% resistors (0805)
T1 1
500µH, 3kVRMS 1CT:1:33CT turns
transformer (6 pin)
HALO Electronics TGMR-340NA5RL
U1 1 MAX3535EEWI+ (28-pin Wide SO)
— 4 Shunts (JU1–JU4)
— 4 Rubber bumpers
— 1 PCB: MAX3535EEVKIT+
+
Denotes a lead-free and RoHS-compliant EV Kit.
*
This limited temperature range applies to the EV kit PCB only.
The MAX3535E IC temperature range is -40°C to +85°C.
Component Suppliers
SUPPLIER PHONE WEBSITE
C entr al
S emi cond uctor 631-435-1110 www.centralsemi.com
HALO Electronics 650-903-3800 w w w.haloel ectr oni cs.com
M urata M fg . C o., Ltd. 770-436-1300 www.murata.com
Note: Indicate that you are using the MAX3535E when contact-
ing these component suppliers.
Evaluates: MAX3535E
MAX3535E Evaluation Kit
2 _______________________________________________________________________________________
Quick Start
Required Equipment
• One 5V, 1A current-limited power supply with built-in
current meter
• One voltmeter
• One logic signal generator
• One oscilloscope
Procedure
The MAX3535E EV kit is fully assembled and tested.
Follow the steps below to verify board operation.
Caution: Do not turn on the power supply until all con-
nections are completed.
1) Connect a voltmeter to the VCC2 and SGND PC
pads.
2) Verify that a shunt is installed across pins 2-3 of
jumper JU1 (receiver enabled).
3) Verify that a shunt is not installed across the pins of
jumper JU2 (fast slew rate).
4) Verify that a shunt is installed across the pins of
jumpers JU3 and JU4 (half duplex).
5) Connect the +5V power supply to the VCC1 pad.
Connect the power supply’s ground to the GND
pad.
6) Turn on the power supply and verify that the volt-
meter at VCC2 reads over +5V.
7) Apply a logic signal to the DI PCB pad and GND.
Using an oscilloscope, verify the signal at the A-B,
RO2, and RO1 output pads.
The +5V supply powering the MAX3535E EV kit must
be current limited at 1A.
Detailed Description
The EV kit features a MAX3535E IC in a 28-pin wide SO
surface-mount package and demonstrates the
MAX3535E 2500VRMS isolated RS-485/RS-422 trans-
ceiver with ESD protection. The circuit’s differential dri-
ver and receiver are configurable for full- or half-duplex
operation and can communicate up to 1000kbps. The
circuit is a 1/8 unit load on the receiver’s bus.
The EV kit features PCB pads to ease interfacing with
logic signals for the driver and receiver signals. On the
nonisolated side, the DI pad is the driver input pad and
the RO1 pad is the receiver-signal output pad. Resistor
R3 pulls the DI pad up to VCC1, and resistor R4 pulls
the DE pad up to VCC1. On the isolated side, the RO2
pad is the receiver output.
The MAX3535E fail-safe circuitry signals are also provid-
ed on the RO1 (receiver output) and RO2 (isolated receiv-
er output) PC pads. Either pad gives a logic-high if A-B is
> -10mV, or if A-B floats or shorts. A logic-low is given if
A-B is < -200mV. Refer to the
Fail Safe
section and
Table
3
in the MAX3535E IC data sheet for additional informa-
tion on the fail-safe circuitry and operation.
The circuit’s input power is typically a +5VDC source,
or is operated from a +3V to +5.5VDC source with a
corresponding reduction in the output voltage on the
isolated side. The EV kit circuit’s DC source must pro-
vide at least 350mA of current, but can also be operat-
ed at lower voltages consistent with the UVLO limit.
The MAX3535E integrates a primary-side controller and
H-bridge drivers. The device contains an on-board
oscillator, protection circuitry, and internal FET drivers
to provide up to 500mW of power to the primary of
transformer T1.
The MAX3535E driver slew rate is reconfigured using
jumper JU2 on the EV kit. The slew rate can be config-
ured for 400kbps (slow) operation to minimize EMI radi-
ation or 1000kbps (fast). See the
Slew-Rate Selection
section for configuring the slew rate.
The circuit’s H-bridge DC-DC converter powers the
MAX3535E isolated section of the circuit. One of the
benefits of the easy-to-use H-bridge DC-DC converter
topology is minimized input ripple current, and radiated
noise by the inherent balanced nature of the design,
with no interruption in the input current. UVLO and ther-
mal shutdown provide for a robust isolated supply.
Thermal-shutdown circuitry provides additional protec-
tion against damage due to overtemperature condi-
tions. The MAX3535E IC’s UVLO provides controlled
turn-on while powering up and during brownouts.
The surface-mount transformer provides up to
2500VRMS galvanic isolation and the output is powered
from a center-tapped, full-wave rectifier circuit to
reduce output voltage ripple. The isolated H-bridge
DC-DC converter operation at 420kHz allows the use of
ceramic-only output capacitors and a small trans-
former. The switching-frequency duty cycle is fixed at
50% to control energy transfer to the isolated output
and to prevent DC current flow in the transformer.
The PCB is designed for 2500V isolation with 300 mils
spacing between the GND and SGND planes. Test
points TP1 (GND) and TP2 (SGND) are provided on the
PCB for probing the respective ground plane, or to con-
nect the GND to SGND planes for nonisolated evalua-
tion of the circuit.
Jumper Selection
The MAX3535E EV kit features several jumpers to
reconfigure the circuit’s receiver/driver enable circuits,
slew-rate control, and full- or half-duplex operation.
Additionally, PCB pads are provided for connecting an
external load to the isolated output at VCC2 and SGND.
Driver and Receiver Enable Selection
The MAX3535E EV kit features a 3-pin jumper (JU1) to
set the MAX3535E driver and receiver output-enable
modes. Table 1 lists the jumper options for the various
modes of operation. Refer to the MAX3535E IC data
sheet for more information on the MAX3535E DE and
RE pin’s driver/receiver modes of operation. See Table 3
for configuring the MAX3535E communication mode.
Slew-Rate Selection
The MAX3535E EV kit features a 2-pin jumper (JU2) to
set the MAX3535E communication slew rate. Table 2
lists jumper options for configuring the slew rate that
will affect the maximum data rate. Refer to the
MAX3535E IC data sheet for more information on the
slew-rate configuration.
Full-/Half-Duplex Communication Configuration
The MAX3535E EV kit features two jumpers that set the
communication mode of operation (full duplex or half
duplex). Jumpers JU3 and JU4 configure the circuit for
the mode (see Table 3 for configuration options). See
Table 2 for reconfiguring the communication slew rate,
which also impacts the maximum communication
speed; see Table 1 for configuring the MAX3535E
receiver and driver modes of operation.
Resistors R1 and R2 Configuration
Pads are provided for pullup and pulldown resistors for
the A-B lines, although the use of these resistors is
purely optional. Pullup and pulldown resistors are used
on the receiver inputs to guarantee a known state in the
event that all nodes on the bus are in receive mode, or
the cable becomes disconnected. The exact value for
these resistors varies with the application. For example,
a cable that is doubly terminated with 120Ωresistors
may use 750Ω, while an unterminated cable may use
10kΩ. These resistors are not required because the
MAX3535E has a fail-safe receiver designed to guaran-
tee a high output in the event a cable disconnects or
shorts between A-B. Use surface-mount 0805 case-size
resistors for R1 and R2.
Evaluating Other Transformer
Configurations/Designs
Evaluating the HALO TGM-350NA Transformer
Use the layout of the MAX3535E EV kit to evaluate other
pin-for-pin transformer replacements for the TGM-340,
provided with the EV kit. For example, the TGM-350,
which has a 1:1 turns ratio and lowers the primary cur-
rent consumption, can be used in place of the default
transformer that has a 3:4 turns ratio. The lower turns
ratio causes the circuit to have a lower output voltage,
while being able to supply slightly more current. This
lower output voltage implies an increase of the lower
bound for the input-supply voltage. When used with the
TGM-350 transformer, the input-supply voltage range is
Evaluates: MAX3535E
MAX3535E Evaluation Kit
_______________________________________________________________________________________ 3
SHUNT
LOCATION DE PIN RE PIN
MAX3535E
DRIVER/
RECEIVER
MODE
1-2
Connected
to RE and R4
pulled up to
VCC1
Connected to
DE and
pulled up to
VCC1 by R4
Driver is enabled,
receiver is
disabled and vice
versa.
2-3*
(default)
Connected
to DE PC
pad and R4
pulled up to
VCC1
Connected to
GND
Receiver is
always on and
driver is enabled
with the DE
signal.
None*
Connected
to DE PC
pad and R4
pulled up to
VCC1
Connected to
RE PC pad
only
Independent
control of driver-
and receiver-
enable states.
Table 1. Driver and Receiver Functions
(JU1)
SHUNT
LOCATION SLO PIN SLEW-RATE
(DATA RATE)
None Not connected Fast (up to 1000kbps)
Installed Connected to
SGND Slow (up to 400kbps)
Table 2. Slew-Rate Functions (JU2)
*
To avoid bus contention, ensure that only one driver has con-
trol of the bus.
JU3 SHUNT
LOCATION
JU4 SHUNT
LOCATION
COMMUNICATION
MODE
Installed Installed Half duplex
None None Full duplex
Table 3. Communication Mode Functions
(JU3 and JU4)
Evaluates: MAX3535E
reduced to +3.6V to +5.5V. Other changes to the trans-
former turns ratio may be possible to suit the exact
needs of the application. Refer to the MAX3535E IC
data sheet for more information. Contact HALO
Electronics to obtain a TGM-350NA transformer.
Smaller Transformer and 2kV Isolation Design
The transformer (T1) is an integral part of the dielectric-
withstand voltage of the EV kit circuit. The MAX3535E
IC is guaranteed to withstand 2500VRMS for one minute
(min). However, the circuit uses an isolated transformer
to transfer power from the primary side to the sec-
ondary side. The withstand voltage of the transformer,
as well as the MAX3535E, must be considered when
designing and testing the EV kit circuit. For example, if
less than 3kV isolation is needed, a smaller 2kV trans-
former can be used to save board area, but the entire
circuit will have only 2kV of isolation.
MAX3535E Evaluation Kit
4 _______________________________________________________________________________________
Figure 1. MAX3535E EV Kit Schematic
T1
D1
VCC2
3
2
1
4
5
6
2
1
3
14
16
32
VCC2
VCC2
ST2ST1
VCC2
C4
0.1µF
C3
10µF
R1
OPEN
A
A
A
Y
R2
OPEN
B
B
A
17
18
R02
SGND
VCC2
VCC2
R02
SLO
15
13
B
Y
12
JU3
B
Z
12
Z
1
1
2
2
JU4
JU2
TP2
SGND
TP1
GND
GND2
GND1
411
C1
10µF
C2
0.1µF
1VCC1
25 DI
DI
26
27
DE
RE
DE
VCC1
VCC1
VCC1
VCC1
GND
VCC1
R3
100kΩ
R4
100kΩ
JU1
1
2
3
28 RO1
RO1
RE
U1
MAX3535E
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 _____________________
5
© 2006 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
Evaluates: MAX3535E
MAX3535E Evaluation Kit
Boblet
Figure 2. MAX3535E EV Kit Component Placement Guide—
Component Side
Figure 3. MAX3535E EV Kit PCB Layout—Component Side
Figure 4. MAX3535E EV Kit PCB Layout—Solder Side
