Datasheet MAX3235EEWP, MAX3235ECPP, MAX3233EEWP, MAX3233EEPP, MAX3233ECWP Datasheet (Maxim)

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________________General Description

The MAX3233E/MAX3235E are EIA/TIA-232 and V.28/V.24
communications interfaces with automatic shutdown/
wake-up features, high data-rate capabilities, and
enhanced electrostatic discharge (ESD) protection. All
transmitter outputs and receiver inputs are protected to
±15kV using IEC 1000-4-2 Air-Gap Discharge, to ±8kV
using IEC 1000-4-2 Contact Discharge, and to ±15kV
using the Human Body Model. The MAX3233E operates
from a +3.3V supply; the MAX3235E operates from +5.0V.

All devices achieve a 1µA supply current using Maxim’s
revolutionary AutoShutdown Plus™ feature. These
devices automatically enter a low-power shutdown
mode when the following two conditions occur: either
the RS-232 cable is disconnected or the transmitters of
the connected peripherals are inactive, and the UART
driving the transmitter inputs is inactive for more than
30 seconds. They turn on again when they sense a
valid transition at any transmitter or receiver input.
AutoShutdown Plus saves power without changes to
the existing BIOS or operating system.

The MAX3233E/MAX3235E have internal dual charge
pumps requiring no external capacitors. Both trans­ceivers have a proprietary low-dropout transmitter out­put stage that enables true RS-232 performance from a
+3.0V to +3.6V supply for the MAX3233E or a +4.5V to
+5.5V supply for the MAX3235E. These devices are
guaranteed to operate up to 250kbps. Both are avail­able in space-saving 20-pin wide SO or plastic DIP
packages.

________________________Applications

Subnotebook and Palmtop Computers
Cellular Phones
Battery-Powered Equipment
Hand-Held Equipment
Peripherals
Embedded Systems

____________________________Features

♦ ESD Protection for RS-232 I/O Pins

±15kV—Human Body Model
±8kV—IEC 1000-4-2, Contact Discharge
±15kV—IEC 1000-4-2, Air-Gap Discharge

♦ Latchup Free
♦ 1µA Supply Current
♦ AutoShutdown Plus—1997 EDN Magazine

Innovation of the Year

♦ Single-Supply Operation

+3.0V to +3.6V (MAX3233E)
+4.5V to +5.5V (MAX3235E)

♦ 250kbps Guaranteed Data Rate
♦ 6V/µs Guaranteed Slew Rate
♦ Meets EIA/TIA-232 Specifications Down to 3.0V

(MAX3233E)

♦ Internal Charge-Pump Capacitors

MAX3233E

†

/MAX3235E

†

±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual

RS-232 Transceivers with Internal Capacitors

________________________________________________________________

Maxim Integrated Products

1

19-1473; Rev 0; 4/99

PART

MAX3233ECWP

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

20 SO

AutoShutdown Plus is a trademark of Maxim Integrated Products.

_______________Ordering Information

Ordering Information continued at end of data sheet.

MAX3233E
MAX3235E

12

13

14

15

16

17

18

4

1

R2OUT R2IN

T2OUT

GND

V-

C2-

C2+

C1-

C1+

V+

V+

INVALID

T2IN

T1IN

FORCEON

R1OUT

T1OUT

R1IN

V

CC

FORCEOFF

2

9

10

5

6

7

8

3

19

20

11

CHARGE

PUMP

SO/DIP

Pin Configuration/

Functional Diagram

Typical Operating Circuit appears at end of data sheet.

MAX3233ECPP 0°C to +70°C 20 Plastic DIP

MAX3233EEPP -40°C to +85°C 20 Plastic DIP

MAX3233EEWP -40°C to +85°C 20 SO

†

Covered by U.S. Patent numbers 4,636,930; 4,679,134; 4,777,577;
4,797,899; 4,809,152; 4,897,774; 4,999,761; 5,649,210; and other
patents pending.

MAX3233E/MAX3235E

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= +3.0V to +3.6V for MAX3233E, VCC= +4.5V to +5.5V for MAX3235E; TA= T

MIN

to T

MAX

; unless otherwise noted. Typical val-

ues are at T

A

= +25°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.

VCCto GND (MAX3233E).........................................-0.3V to +4V

V

CC

to GND (MAX3235E).........................................-0.3V to +6V

V+ to GND (Note 1)..................................................-0.3V to +7V

V- to GND (Note 1)...................................................+0.3V to -7V

V+ +

|V-| (Note 1).................................................................+13V

Input Voltages

T_IN, FORCEON,

FORCEOFF to GND....................-0.3V to +6V

R_IN to GND...................................................................±25V

Output Voltages

T_OUT to GND.............................................................±13.2V

R_OUT, INVALID to GND......................-0.3V to (V

CC

+ 0.3V)

Short-Circuit Duration

T_OUT to GND......................................................Continuous

Continuous Power Dissipation (T

A

= +70°C)

Wide SO (derate 10mW/°C above +70°C)..................800mW

Plastic DIP (derate 11.11mW/°C above +70°C) .........889mW

Operating Temperature Ranges

MAX323_EC_P...................................................0°C to +70°C

MAX323_EE_P................................................-40°C to +85°C

Storage Temperature Range.............................-65°C to +150°C

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

Note 1: V+ and V- can have maximum magnitudes of 7V, but their absolute difference cannot exceed 13V.

FORCEON = GND, FORCEOFF = VCC,
all R_IN idle, all T_IN idle

TA= +25°C

CONDITIONS

kΩ357Input Resistance

V0.5Input Hysteresis

1.8 2.4

V

1.5 2.4

Input Threshold High

0.8 1.3

V

0.6 1.0

Input Threshold Low

V-25 +25Input Voltage Range

V

VCC- 0.6 VCC- 0.1

Output Voltage High

V0.4Output Voltage Low

µA110Supply Current, Shutdown

µA110

Supply Current,
AutoShutdown Plus

µA±0.01 ±1

Transmitter Input Hysteresis V0.5

V

2.4

Input Logic Threshold High

mA0.3 1

Supply Current,
AutoShutdown Plus Disabled

V0.8Input Logic Threshold Low

2

UNITSMIN TYP MAXSYMBOLPARAMETER

FORCEOFF = GND

TA= +25°C

T_IN, FORCEON, FORCEOFF

FORCEON = FORCEOFF = VCC, no load

T_IN, FORCEON, FORCEOFF

I

OUT

= -1.0mA

I

OUT

= 1.6mA

Input Leakage Current

DC CHARACTERISTICS (VCC= 3.3V for MAX3233E, VCC= 5.0V for MAX3235E, TA= +25°C.)

LOGIC INPUTS AND RECEIVER OUTPUTS

RECEIVER INPUTS

TA= +25°C

VCC= 5.0V, MAX3235E

VCC= 3.3V, MAX3233E

VCC= 5.0V, MAX3235E

VCC= 3.3V, MAX3233E

±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual
RS-232 Transceivers with Internal Capacitors

T_IN, FORCEON,

FORCEOFF

VCC= 5.0V, MAX3235E

VCC= 3.3V, MAX3233E

MAX3233E/MAX3235E

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VCC= +3.0V to +3.6V for MAX3233E, VCC= +4.5V to +5.5V for MAX3235E; TA= T

MIN

to T

MAX

; unless otherwise noted. Typical val-

ues are at T

A

= +25°C.)

CONDITIONS

Ω300 10MOutput Resistance

V±5 ±5.4Output Voltage Swing

UNITSMIN TYP MAXSYMBOLPARAMETER

Figure 3a

sec15 30 60t

AUTOSHDN

Receiver or Transmitter Edge to
Transmitters Shut Down

µs100t

WU

Receiver or Transmitter Edge to
Transmitters Enabled

µs1t

INVH

Receiver Positive or Negative
Threshold to INVALID High

V

V

CC

- 0.6

INVALID, Output Voltage High

V0.4

INVALID Output Voltage Low

V-0.3 0.3

Receiver Input Threshold to
INVALID Output Low

-2.7

V

2.7

Receiver Input Threshold to
INVALID Output High

±15

±8R_IN, T_OUT kV

±15

µA

±25

Output Leakage Current

±60 mAOutput Short-Circuit Current

VCC= V+ = V- = 0, transmitter outputs = ±2V

All transmitter outputs loaded with 3kΩ to
ground

Figure 3b (Note 2)

Figure 3b (Note 2)

Figure 3b

I

OUT

= -1.0mA

I

OUT

= -1.6mA

Figure 3a

Human Body Model

V

OUT

= ± 12V
transmitters
disabled

IEC1000-4-2 Contact Discharge

IEC1000-4-2 Air Discharge

VCC= 0 or +4.5V to

5.5V (MAX3235E)

VCC= 0 or +3.0V to

3.6V (MAX3233E)

±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual

RS-232 Transceivers with Internal Capacitors

±25

MAX3233E
MAX3235E 50

µs

70

t

INVL

Receiver Positive or Negative
Threshold to INVALID Low

Figure 3b

TRANSMITTER OUTPUTS

ESD PROTECTION

AutoShutdown PLUS (FORCEON = GND, FORCEOFF = VCC)

Positive threshold
Negative threshold

ns

MAX3233E/MAX3235E

4 _______________________________________________________________________________________

TIMING CHARACTERISTICS (continued)

(VCC= +3.0V to +3.6V for MAX3233E, VCC= +4.5V to +5.5V for MAX3235E; TA= T

MIN

to T

MAX

; unless otherwise noted. Typical val-

ues are at T

A

= +25°C.)

Note 2: A transmitter/receiver edge is defined as a transition through the transmitter/receiver input logic thresholds.
Note 3: Transmitter skew is measured at the transmitter zero cross points.

CL= 150pF
to 2500pF

CL= 150pF
to 1000pF

R_IN to R_OUT,
CL= 150pF

RL= 3kΩ, CL= 1000pF,
one transmitter switching

VCC= 3.3V (MAX3233E),
VCC= 5.0V (MAX3235E),
TA= +25°C,
RL= 3kΩ to 7kΩ,

measured from +3V to -3V
or -3V to +3V

Normal operation
Normal operation
(Note 3)

CONDITIONS

100

ns

70

t

PHL

kbps250Maximum Data Rate

Receiver Propagation Delay

V/µs

430

630

Transition-Region Slew Rate

ns200Receiver Output Enable Time
ns200Receiver Output Disable Time
ns150



t

PHL

- t

PLH



Transmitter Skew

ns

180



t

PHL

- t

PLH 

Receiver Skew

UNITSMIN TYP MAXSYMBOLPARAMETER

__________________________________________Typical Operating Characteristics

(VCC= +3.3V for MAX3233E, VCC= +5.0V for MAX3235E; 250kbps data rate; all transmitters loaded with 3kΩ and CL; TA= +25°C;
unless otherwise noted.)

±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual
RS-232 Transceivers with Internal Capacitors

150

250

t

PLH

MAX3233E
MAX3235E
MAX3233E
MAX3235E

50MAX3235E

MAX3233E

TRANSMITTER OUTPUT VOLTAGE vs.

LOAD CAPACITANCE

10.0

7.5

5.0

2.5
0

-2.5

-5.0

TRANSMITTER OUTPUT VOLTAGE (V)

-7.5

-10.0
0 1000 2000 3000 4000 5000

LOAD CAPACITANCE (pF)

+

V

OUT

-

V

OUT

MAX3233E/35Etoc01

SUPPLY CURRENT (mA)

OPERATING SUPPLY CURRENT

vs. LOAD CAPACITANCE

45

TRANSMITTER 1 AT DATA RATE

40

TRANSMITTER 2 AT 1/16 DATA RATE
35
30
25
20
15
10

5
0

0 20001000 3000 4000 5000

250kbps

120kbps

20kbps

LOAD CAPACITANCE (pF)

MAX3233E/35E toc02

SLEW RATE (V/µs)

SLEW RATE vs.

LOAD CAPACITANCE

16
14
12
10

8
6
4
2
0

0 1000 2000 3000 4000 5000

LOAD CAPACITANCE (pF)

SLEW RATE -

SLEW RATE +

MAX3233E/35Etoc01

MAX3233E/MAX3235E

_______________________________________________________________________________________

5

______________________________________________________________Pin Description

TTL/CMOS Receiver Outputs

FUNCTIONPIN NAME

1

3

7

8

9

10

11, 12

14
15

R2OUT

16
17
18

Invalid Signal Detector Output, active low. A logic high indicates that a valid RS-232
level is present on a receiver.

T2N

TTL/CMOS Transmitter Outputs

2

INVALID

5

T1OUT

RS-232 Transmitter Outputs

FORCEON

Force-On Input, active high. Drive high to override AutoShutdown Plus, keeping
transmitters and receivers active (FORCEOFF must be high) (Table 1).

13

R1IN

RS-232 Receiver Outputs

C1+

Positive terminal of the internal voltage-doubling charge-pump capacitor. Leave
unconnected or connect to an external 0.1µF capacitor. See

Charge Pump

Section.

V

CC

Supply Voltage (MAX3233E = +3.3V, MAX3235E = +5.0V)

FORCEOFF

Force-Off Input, active low. Drive low to shut down transmitters, receivers, and charge
pump. This overrides AutoShutdown Plus and FORCEON (Table 1).

V+ +5.5V generated by the charge pump. Do not connect.

C1-

Negative terminal of the internal voltage-doubling charge-pump capacitor. Leave
unconnected or connect to an external 0.1µF capacitor. See

Charge Pump

Section.

C2+ Positive terminal of the internal inverting charge-pump capacitor. Do not connect.

C2- Negative terminal of the internal inverting charge-pump capacitor. Do not connect.

V- -5.5V generated by the charge pump. Do not connect.

GND Ground

±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual

RS-232 Transceivers with Internal Capacitors

6 R1OUT

4 T1IN

19 T2OUT

20 R2IN

_______________Detailed Description

Dual Charge-Pump Voltage Converter

The MAX3233E/MAX3235E’s internal power supply
consists of a regulated dual charge pump that provides
output voltages of +5.5V (doubling charge pump) and

-5.5V (inverting charge pump), with no external capaci­tors. The charge pump operates in discontinuous
mode: if the output voltages are less than 5.5V, the
charge pump is enabled; if the output voltages exceed

5.5V, the charge pump is disabled.

RS-232 Transmitters

The transmitters are inverting level translators that
convert CMOS-logic levels to 5.0V EIA/TIA-232 levels.
The devices guarantee a 250kbps data rate with worst­case loads of 3kΩ in parallel with 1000pF, providing
compatibility with PC-to-PC communication software
(such as LapLink™). Transmitters can be paralleled to
drive multiple receivers. Figure 1 shows a complete
system connection.

When FORCEOFF is driven to ground or when the Auto­Shutdown Plus circuitry senses that all receiver and
transmitter inputs are inactive for more than 30sec, the
transmitters are disabled and the outputs go into a high­impedance state. When powered off or shut down, the
outputs can be driven to ±12V. The transmitter inputs
do not have pull-up resistors. Connect unused inputs to
GND or VCC.

RS-232 Receivers

The receivers convert RS-232 signals to CMOS-logic
output levels. They feature inverting outputs that always
remain active (Table 1).

The MAX3233E/MAX3235E feature an INVALID output
that is enabled low when no valid RS-232 voltage levels
have been detected on all receiver inputs. Because
INVALID indicates the receiver input’s condition, it is
independent of FORCEON and FORCEOFF states
(Figures 2 and 3).

AutoShutdown Plus Mode

The devices achieve a 1µA supply current with Maxim’s
AutoShutdown Plus feature, which operates when
FORCEOFF is high and a FORCEON is low. When these
devices do not sense a valid signal transition on any
receiver or transmitter input for 30sec, the on-board
charge pumps are shut down, reducing supply current
to 1µA. This occurs if the RS-232 cable is disconnected,
or if the connected peripheral transmitters are turned off
and the UART driving the transmitter inputs is inactive.
The system turns on again when a valid transition is

MAX3233E/MAX3235E

±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual
RS-232 Transceivers with Internal Capacitors

6 _______________________________________________________________________________________

MAX3233E
MAX3235E

I/O
CHIP
WITH
UART

CPU

RS-232

POWER-

MANAGEMENT

UNIT OR

KEYBOARD

CONTROLLER

FORCEOFF
FORCEON

INVALID

Figure 1. Interface Under Control of PMU

LapLink is a trademark of Traveling Software.

+0.3V

-0.3V

INVALID

R_IN

INVALID ASSERTED IF ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR
AT LEAST 80µs.

80µs

TIMER

R

Figure 2a. INVALID Functional Diagram, INVALID Low

Figure 2b. INVALID Functional Diagram, INVALID High

+2.7V

R_IN

-2.7V

INVALID DEASSERTED IF ANY RECEIVER INPUT HAS BEEN ABOVE +2.7V OR BELOW

-2.7V FOR 1µs.

80µs

TIMER

R

INVALID

MAX3233E/MAX3235E

±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual

RS-232 Transceivers with Internal Capacitors

_______________________________________________________________________________________ 7

applied to any RS-232 receiver or transmitter input. As a
result, the system saves power without changes to the
existing BIOS or operating system.

Figures 2a and 2b depict invalid and valid RS-232
receiver voltage levels. INVALID indicates the receiver
input’s condition, and is independent of FORCEON and
FORCEOFF states. Figure 2 and Tables 1 and 2 sum­marize the operating modes. FORCEON and FORCE-

OFF override AutoShutdown Plus circuitry. When nei­ther control is asserted, the IC selects between these
states automatically based on the last receiver or trans­mitter input edge received.

When shut down, the device’s charge pumps turn off,
V+ is pulled to V

CC

, V- is pulled to ground, and the
transmitter outputs are high impedance. The time
required to exit shutdown is typically 100µs (Figure 7).

Table 1. Output Control Truth Table

X = Don’t care

*

INVALID connected to FORCEON

**

INVALID connected to FORCEON and FORCEOFF

OPERATION STATUS FORCEON

FORCEOFF

VALID

RECEIVER

LEVEL

Rx or Tx EDGE

WITHIN 30sec

T_OUT R_OUT

Shutdown (Forced Off) X 0 X X High-Z Active

Normal Operation (Forced On) 1 1 X X Active Active

Normal Operation
(AutoShutdown Plus)

0 1 X Yes Active Active

Shutdown
(AutoShutdown Plus)

0 1 X No High-Z Active

Normal Operation

INVALID*

1 Yes X Active Active

Normal Operation

INVALID*

1 X Yes Active Active

Shutdown

INVALID*

1 No No High-Z Active

Normal Operation
(AutoShutdown)

INVALID* INVALID**

Yes X Active Active

Shutdown (AutoShutdown)

INVALID* INVALID**

No X High-Z Active

Figure 2c. AutoShutdown Plus Logic

POWERDOWN*

AUTOSHDN

FORCEOFF

FORCEON

POWERDOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE OPERATIONAL
STATUS OF THE TRANSMITTERS AND THE POWER SUPPLIES.

*

Figure 2d. Power-Down Logic

EDGE

T_IN

DETECT

EDGE

R_IN

DETECT

FORCEON

*AUTOSHDN IS ONLY AN INTERNAL SIGNAL.

FORCEOFF

S

30sec

TIMER

R

AUTOSHDN*

By connecting FORCEON to INVALID, the device shuts
down when no valid receiver level and no receiver or
transmitter edge is detected for 30sec. It wakes up
when a valid receiver level or receiver or transmitter
edge is detected.

By connecting FORCEON and FORCEOFF to INVALID,
the device shuts down when no valid receiver level is
detected and wakes up when a valid receiver level is
detected.

A system with AutoShutdown Plus may need time to
wake up. Figure 4 shows a circuit that forces the
transmitters on for 100ms, allowing enough time
for another system to realize that the MAX3233E/

MAX3235E is awake. If another system outputs valid
RS-232 signal transitions within that time, the RS-232
ports on both systems remain enabled.

Software-Controlled Shutdown

If direct software control is desired, use INVALID to
indicate DTR or Ring Indicator signal. Tie FORCEOFF
and FORCEON together to bypass the AutoShutdown
Plus so the line acts like a SHDN input.

±15kV ESD Protection

As with all Maxim devices, ESD-protection structures are
incorporated on all pins to protect against electrostatic
discharges encountered during handling and assembly.
The driver outputs and receiver inputs have extra pro­tection against static electricity. Maxim’s engineers have
developed state-of-the-art structures to protect these
pins against ESD of ±15kV without damage. The ESD
structures withstand high ESD in all states: normal
operation, shutdown, and powered down. After an ESD

MAX3233E /MAX3235E

±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual
RS-232 Transceivers with Internal Capacitors

8 _______________________________________________________________________________________

Table 2. INVALID Truth Table

LowNo

HighYes

INVALID OUTPUT

RS-232 SIGNAL

PRESENT AT ANY

RECEIVER INPUT

Figure 3a. Receiver Positive/Negative Thresholds for INVALID

V

CC

0

V+

V-

V

CC

0

INVALID
OUTPUT

TRANSMITTER

INPUTS

RECEIVER

INPUTS

}

INVALID
REGION

TRANSMITTER

OUTPUTS

t

AUTOSHDN

t

WU

t

WU

t

INVL

t

INVH

t

AUTOSHDN

Figure 3b. AutoShutdown Plus, INVALID, and READY Timing Diagram

INVALID HIGH

+2.7

INDETERMINATE

+0.3

0

-0.3

RECEIVER INPUT LEVELS (V)

-2.7

INVALID LOW

INDETERMINATE

INVALID HIGH

MAX3233E/MAX3235E

±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual

RS-232 Transceivers with Internal Capacitors

_______________________________________________________________________________________ 9

event, Maxim’s E versions keep working without
latchup, whereas competing RS-232 products can
latch and must be powered down to remove latchup.

ESD protection can be tested in various ways; the
transmitter outputs and receiver inputs of this product
family are characterized for protection to the following
limits:

1) ±15kV using the Human Body Model

2) ±8kV using the Contact Discharge method specified
in IEC 1000-4-2

3) ±15kV using IEC 1000-4-2’s Air-Gap Discharge
method

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 5a shows the Human Body Model and Figure 5b
shows the current waveform it generates when dis­charged into a low impedance. This model consists of
a 100pF capacitor charged to the ESD voltage of inter­est, which is then discharged into the test device
through a 1.5kΩ resistor.

IEC 1000-4-2

The IEC 1000-4-2 standard covers ESD testing and per­formance of finished equipment; it does not specifically
refer to integrated circuits. The MAX3233E/MAX3235E
help you design equipment that meets Level 4 (the high­est level) of IEC 1000-4-2, without the need for additional
ESD-protection components.

The major difference between tests done using the
Human Body Model and IEC 1000-4-2 is higher peak cur­rent in IEC 1000-4-2, because series resistance is lower
in the IEC 1000-4-2 model. Hence, the ESD withstand
voltage measured to IEC 1000-4-2 is generally lower than

FORCEON

MASTER SHDN LINE

0.1µF 1M

FORCEOFF

MAX3233E
MAX3235E

POWER-

MANAGEMENT

UNIT

Figure 4. AutoShutdown Plus Initial Turn-On to Wake Up
Another System

IP 100%

90%

36.8%

t

RL

TIME

t

DL

CURRENT WAVEFORM

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

I

r

10%

0

0

AMPERES

Figure 5b. Human Body Current Waveform

CHARGE-CURRENT

LIMIT RESISTOR

DISCHARGE

RESISTANCE

STORAGE
CAPACITOR

C

s

100pF

R

C

1M RD 1500Ω

HIGH-

VOLTAGE

DC

SOURCE

DEVICE
UNDER

TEST

Figure 5a. Human Body ESD Test Model

Figure 6a. IEC 1000-4-2 ESD Test Model

CHARGE CURRENT

LIMIT RESISTOR

DISCHARGE

RESISTANCE

STORAGE
CAPACITOR

C

s

150pF

R

C

50M to 100M RD 330Ω

HIGH-

VOLTAGE

DC

SOURCE

DEVICE
UNDER

TEST

that measured using the Human Body Model. Figure 6a
shows the IEC 1000-4-2 model, and Figure 6b shows the
current waveform for the ±8kV, IEC 1000-4-2, Level 4,
ESD contact-discharge test.

The air-gap test involves approaching the device with a
charged probe. The contact-discharge method connects
the probe to the device before the probe is energized.

Machine Model

The Machine Model for ESD tests all pins using a
200pF storage capacitor and zero discharge resis­tance. Its objective is to emulate the stress caused by
contact that occurs with handling and assembly during

manufacturing. Of course, all pins require this protec­tion during manufacturing, not just RS-232 inputs and
outputs. Therefore, after PC board assembly, the
Machine Model is less relevant to I/O ports.

__________Applications Information

Charge Pumps

The MAX3233E/MAX3235E do not require external
capacitors to operate their internal charge pumps.

The MAX3235E can be operated down to 3.0V by par­alleling the internal C1 capacitor with an external 0.1µF.
When using an external capacitor across the C1 termi­nals, check to confirm that the total supply voltage
measured from V+ to V- does not exceed the absolute
maximum voltage of 13V. With the external 0.1µF
capacitor added, the MAX3235E should not be used
with a supply greater than +3.9V.

Power-Supply Decoupling

In most applications, a 0.1µF VCCbypass capacitor is
adequate. Connect bypass capacitors as close to the
IC as possible.

Transmitter Outputs

when Exiting Shutdown

Figure 7 shows two transmitter outputs when exiting
shutdown mode. As they become active, the two trans­mitter outputs are shown going to opposite RS-232
levels (one transmitter input is high, the other is low).

MAX3233E/MAX3235E

±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual
RS-232 Transceivers with Internal Capacitors

10 ______________________________________________________________________________________

tr = 0.7ns to 1ns

30ns

60ns

t

100%

90%

10%

I

PEAK

I

Figure 6b. IEC 1000-4-2 ESD Generator Current Waveform

10µs/div

T1OUT

T2OUT

5V/div

0

2V/div

0

10V/div

0

VCC = 3.3V

FORCEON = FORCEOFF

Figure 7. Transmitter Outputs when Exiting Shutdown or
Powering Up

MAX3233E
MAX3235E

5k

R_ IN

R_ OUT

FORCEON

V

CC

C

BYPASS

V

CC

FORCEOFF

T_ OUT

T_ IN

GND

V

CC

1000pF

Figure 8. Loopback Test Circuit

MAX3233E/MAX3235E

±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual

RS-232 Transceivers with Internal Capacitors

______________________________________________________________________________________ 11

Each transmitter is loaded with 3kΩ in parallel with
1000pF. The transmitter outputs display no ringing or
undesirable transients as they come out of shutdown.
Note that the transmitters are enabled only when the
magnitude of V- exceeds approximately -3V.

High Data Rates

The MAX3233E/MAX3235E maintain the RS-232 ±5.0V
minimum transmitter output voltage even at high data
rates. Figure 8 shows a transmitter loopback test cir­cuit. Figure 9 shows a loopback test result at 120kbps,
and Figure 10 shows the same test at 250kbps. For

Figure 9, all transmitters were driven simultaneously at
120kbps into RS-232 loads in parallel with 1000pF. For
Figure 10, a single transmitter was driven at 250kbps,
and all transmitters were loaded with an RS-232 receiv­er in parallel with 250pF.

Interconnection with 3V and 5V Logic

The MAX3233E/MAX3235E can directly interface with
various 5V logic families, including ACT and HCT
CMOS. See Table 3 for more information on possible
combinations of interconnections.

Figure 9. Loopback Test Result at 120kbps

2µs/div

T1IN

T1OUT

R1OUT

5V/div

5V/div

5V/div

VCC = 3.3V (MAX3233E), VCC = 5.0V (MAX3235E)

Figure 10. Loopback Test Result at 250kbps

2µs/div

T1IN

T1OUT

R1OUT

5V/div

5V/div

5V/div

VCC = 3.3V (MAX3233E), VCC = 5.0V (MAX3235E)

COMPATIBILITY

Compatible with all CMOS families
Compatible with ACT and HCT CMOS, and

with AC, HC, or CD4000 CMOS
Compatible with all TTL and CMOS families

DEVICE

V

CC

SUPPLY VOLTAGE

(V)

MAX3233E 3.3

MAX3233E 3.3

LOGIC POWER-SUPPLY

VOLTAGE

(V)

3.3

5

MAX3235E 53.3/5

Table 3. Logic Family Compatibility with Various Supply Voltages

MAX3233E/MAX3235E

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.

12

____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

___________________Chip Information

TRANSISTOR COUNT: 1129

Typical Operating Circuit Ordering Information (continued)

C

BYPASS

MAX3233E
MAX3235E

R2OUT1

R1OUT6

FORCEON

INVALID

FORCEOFF

2
10
5

R2IN

20

GND

18

RS-232
OUTPUTS

TTL/CMOS

INPUTS

T2IN

3

T1IN

4

C2-

16

C2+

15

C1-

14

C1+

13

R1IN

8

T2OUT

19

T1OUT 7

V-

17

V+

11, 12

V

CC

V

CC

0.1µF

9

V

CC

RS-232
INPUTS

TTL/CMOS

OUTPUTS

5k

5k

AUTOSHUTDOWN

PLUS

PART TEMP. RANGE PIN-PACKAGE

MAX3235ECWP

MAX3235ECPP 0°C to +70°C

0°C to +70°C 20 SO

20 Plastic DIP
MAX3235EEWP -40°C to +85°C 20 SO
MAX3235EEPP -40°C to +85°C 20 Plastic DIP

±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual
RS-232 Transceivers with Internal Capacitors