Datasheet MAX3238E, MAX3248E Datasheet (MAXIM)

________________________________________________________________ Maxim Integrated Products 1

General Description

The MAX3238E/MAX3248E transceivers use Maxim’s
revolutionary AutoShutdown Plus™ feature to achieve
10nA supply current. These devices shut down the on­board power supply and drivers when they do not sense
a valid signal transition on either the receiver or transmit­ter inputs. This occurs if the RS-232 cable is disconnect­ed or if the transmitters of the connected peripheral are
turned off. The devices turn on again when a valid transi­tion is applied to any RS-232 receiver or transmitter input.
AutoShutdown Plus automatically achieves this power
savings through its on-board circuitry, as no changes are
required to the existing BIOS or operating system.

All RS-232 inputs and outputs, as well as the logic I/O
pins, have enhanced ESD protection to ±15kV. The addi­tional ESD protection on the logic I/O pins makes the
MAX3238E/MAX3248E ideal for cell phone data cable
applications because it eliminates the need for costly
external TransZorb™or protection schemes.

The MAX3238E/MAX3248E contain five drivers and three
receivers and are 3V-powered EIA/TIA-232 and V.28/V.24
communication interfaces intended for cell phones, data
cables, and modem applications. A proprietary, high-effi­ciency, dual charge-pump power supply and a low­dropout transmitter combine to deliver true RS-232
performance from a single +3.0V to +5.5V supply. A
guaranteed data rate of 250kbps provides compatibility
with popular software for communicating with personal
computers.

The MAX3238E and the MAX3248E differ only in their
input logic thresholds. The MAX3238E has standard logic
thresholds, while the MAX3248E has low-level logic
thresholds of 0.6V to 1.2V, which are ideal for 1.8V sys­tems.

The transmitter inputs, FORCEON, and FORCEOFF have
a 400kΩ active positive feedback resistor. Once driven to
a valid logic level, they will retain this level if the driving
signal is removed or goes high impedance. Unused
transmitter and logic inputs may be left unconnected. The
MAX3238E/MAX3248E can operate with supply voltages
ranging from +3.0V to +5.5V.

Applications

Features

♦ Enhanced ESD Protection on RS-232 I/O Pins and

All Logic Pins

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

♦ Guaranteed Data Rate: 250kbps

♦ 10nA Low-Power Shutdown with Receivers Active

♦ Schmitt Triggers on All Inputs

♦ Flow-Through Pinout

♦ Meets EIA/TIA-232 Specifications Down to 3.0V

♦ Guaranteed 6V/µs Slew Rate

♦ Low-Level Logic Thresholds (MAX3248E)

♦ RS-232-Compatible Outputs to 2.7V

MAX3238E/MAX3248E

†

+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers

with ±15kV ESD-Protected I/O and Logic Pins

28

27

26

25

24

23

22

21

20

19

18

17

16

15

1

2

3

4

5

6

7

8

9

10

11

12

13

14

C1+

V+

V

CC

C1-

T1IN

T2IN

INVALID

T3IN

R1OUT

R2OUT

T4IN

R3OUT

T5IN

R1OUTB

FORCEOFF

FORCEON

T5OUT

R3IN

T4OUT

R2IN

R1IN

T3OUT

T2OUT

T1OUT

V-

C2-

GND

C2+

SSOP

TOP VIEW

MAX3238E
MAX3248E

___________________Pin Configuration

19-1632; Rev 1; 6/01

Ordering Information

AutoShutdown Plus is a trademark of Maxim Integrated Products.

TransZorb is a trademark of General Semiconductor Industries, Inc.

†

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; and other
patents pending.

Cellular Data Cables
Modems
Battery-Powered Equipment

Peripherals
Data Cradles
Printers

Typical Operating Circuit appears at end of data sheet.

28 SSOP

28 SSOP

28 SSOP

28 SSOP

PIN-PACKAGETEMP. RANGE

0°C to +70°C

-40°C to +85°C

0°C to +70°C

-40°C to +85°CMAX3248EEAI

MAX3248ECAI

MAX3238EEAI

MAX3238ECAI

PART

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.

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.

MAX3238E/MAX3248E

+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= +3.0V to +5.5V, C1–C4 = 0.1µF (tested at 3.3V ±5%), C1–C4 = 0.22µF (tested at 3.3V ±10%), C1 = 0.047µF, and
C2–C4 = 0.33µF (tested at 5.0V ±10%), T

A

= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

V

CC

...........................................................................-0.3V to +6V

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

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

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

Input Voltages

T_IN, FORCEOFF, FORCEON ..............................-0.3V to +6V

R_IN .................................................................................±25V

Output Voltages

T_OUT...........................................................................±13.2V

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

CC

+ 0.3V)

Short-Circuit Duration

T_OUT (one at a time) ............................................Continuous

Continuous Power Dissipation (T

A

= +70°C)

28-Pin SSOP (derate 9.52mW/°C above +70°C) .........762mW

Operating Temperature Ranges

MAX3238ECAI/MAX3248ECAI ...........................0°C to +70°C

MAX3238EEAI/MAX3248EEAI .........................-40°C to +85°C

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

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

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

1.10 1.2

1.15 1.6

0.95 1.2

MAX3248E

FORCEON, FORCEOFF, and T_IN
wake-up threshold; V

CC

= 5.0V

FORCEON, FORCEOFF, and T_IN
wake-up threshold; V

CC

= 3.3V

T_IN (active)

FORCEON, FORCEOFF, and T_IN
wake-up threshold; V

CC

= 5.0V

FORCEON, FORCEOFF, and T_IN
wake-up threshold; V

CC

= 3.3V

T_IN (active)

FORCEON, FORCEOFF, and T_IN
wake-up threshold; V

CC

= 5.0V

FORCEON, FORCEOFF, and T_IN
wake-up threshold; V

CC

= 3.3V

T_IN (active)

FORCEON, FORCEOFF, and T_IN
wake-up threshold; V

CC

= 5.0V

FORCEON, FORCEOFF, and T_IN
wake-up threshold; V

CC

= 3.3V

T_IN (active)

PARAMETER MIN TYP MAX UNITS

Input Logic Threshold Low

0.8 1.20

V

Supply Current, AutoShutdown Plus
Disabled

0.5 2.0 mA

Supply Current, AutoShutdown Plus

Input Logic Threshold High

1.60 2.0

0.75 6 µA

V

10 300

2.10 2.4

1.30 2.0

MAX3238E

0.6 0.7

0.8 1.45

0.6 1.0

0.6 0.85

0.8 1.00

MAX3248E

Supply Current, Shutdown 10 300 nA

CONDITIONS

FORCEOFF = GND, R_IN = GND, T_IN = VCCor GND

MAX3238E

FORCEON = FORCEOFF = VCC, no load

Receivers idle, T_IN = VCCor GND, FORCEON =
GND, FORCEOFF = V

CC

R_IN = FORCEON = GND, FORCEOFF = V

CC,

T_IN = VCCor GND

nA

DC CHARACTERISTICS (VCC= +3.3V or +5.0V, TA= +25°C)

LOGIC INPUTS AND RECEIVER OUTPUTS

MAX3238E/MAX3248E

+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers

with ±15kV ESD-Protected I/O and Logic Pins

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VCC= +3.0V to +5.5V, C1–C4 = 0.1µF (tested at 3.3V ±5%), C1–C4 = 0.22µF (tested at 3.3V ±10%), C1 = 0.047µF, and
C2–C4 = 0.33µF (tested at 5.0V ±10%), T

A

= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

Figure 4a

Figure 4a

Figure 4b

VCC= 5V, Figure 4b (Note 3)

VCC= 5V, Figure 4b

I

OUT

= 1.0mA

I

OUT

= -1.0mA

VCC= 5V, Figure 4b

V-0.3 0.3

Receiver Input Threshold to
INVALID Output Low

V

2.7

Receiver Input Threshold to
INVALID Output High

s15 30 60

Receiver or Transmitter Edge to
Shutdown (t

AUTOSHDN

)

µs25

Receiver or Transmitter Edge to
Transmitters Enabled (tWU)

µs60

Receiver Positive or Negative
Threshold to INVALID Low (t

INVL

)

V0.4

INVALID Output Voltage Low

V

V

CC -

0.6

INVALID Output Voltage High

µs0.3

Receiver Positive or Negative
Threshold to INVALID High (t

INVH

)

Positive threshold

Negative threshold -2.7

V-25 25

I

OUT

= -1.0mA

I

OUT

= 1.0mA

Input Voltage Range

VCC= 3.3V

Receivers disabled

T_IN, FORCEON, FORCEOFF (Note 2)

0.6 1.0

CONDITIONS

VCC= 5.0V

V

0.8 1.4

Input Threshold Low

VCC= 3.3V 1.5 2.4

VCC= 5.0V

V

2.0 2.4

Input Threshold High

V0.6Input Hysteresis

TA= +25°C kΩ357Input Resistance

V

V

CC

-V

CC

-

0.6 0.1

Output Voltage High

V0.4Output Voltage Low

µA±0.05 ±10Output Leakage Current

µA918Input Leakage Current

UNITSMIN TYP MAXPARAMETER

All transmitter outputs loaded with 3kΩ to ground V±5.0 ±5.4Output Voltage Swing

VCC= 0, T

OUT

= ±2V Ω300 50kOutput Resistance

VCC≤ 3.6V ±35 ±60

VCC> 3.6V

mA

±40 ±100

Output Short-Circuit Current

IEC 1000-4-2 Air-Gap Discharge Method ±15

IEC 1000-4-2 Contact Discharge Method ±8

Human Body Model

kV

±15

ESD Protection (R_IN, T_IN, R_OUT,
T_OUT, FORCEON, FORCEOFF,
INVALID, R_OUTB)

RECEIVER INPUTS

AutoShutdown (FORCEON = GND, FORCEOFF = VCC)

TRANSMITTER OUTPUTS

ESD PROTECTION

-6

-2

-4

2

0

4

6

-5

-3

1

-1

3

5

0 1000 1500500 2000 2500 3000

TRANSMITTER OUTPUT VOLTAGE

vs. LOAD CAPACITANCE

MAX3238E toc01

LOAD CAPACITANCE (pF)

TRANSMITTER OUTPUT VOLTAGE (V)

V

OUT-

V

OUT

+

FOR DATA RATES UP TO 250kbps
1 TRANSMITTER 250kbps
4 TRANSMITTERS 15.6kbps
ALL TRANSMITTERS LOADED
WITH 3kΩ + C

L

0

4

2

8

6

10

12

0 1000 1500500 2000 2500 3000

SLEW RATE vs. LOAD CAPACITANCE

MAX3238E toc02

LOAD CAPACITANCE (pF)

SLEW RATE (V/µs)

SR+

SR-

1 TRANSMITTER 250kbps
4 TRANSMITTERS 15.6kbps
ALL TRANSMITTERS LOADED
WITH 3kΩ + C

L

50

20

10

0

0 1000500 2000 3000

SUPPLY CURRENT vs. LOAD CAPACITANCE

WHEN TRANSMITTING DATA

30

MAX3238 TOC-03

SUPPLY CURRENT (mA)

LOAD CAPACITANCE (pF)

1500 2500

40

250kbps

20kbps

120kbps

1 TRANSMITTER 20kbps, 120 kbps, 250kbps
4 TRANSMITTERS 15.6kbps
ALL TRANSMITTERS LOADED
WITH 3kΩ + C

L

__________________________________________Typical Operating Characteristics

(VCC= +3.3V, 250kbps data rate, 0.1µF capacitors, all transmitters loaded with 3kΩ, TA= +25°C, unless otherwise noted.)

MAX3238E/MAX3248E

+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(VCC= +3.0V to +5.5V, C1–C4 = 0.1µF (tested at 3.3V ±5%), C1–C4 = 0.22µF (tested at 3.3V ±10%), C1 = 0.047µF, and
C2–C4 = 0.33µF (tested at 5.0V ±10%), T

A

= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

Note 2: The transmitter inputs have an active positive feedback resistor. The input current goes to zero when the inputs are at the

supply rails.

Note 3: During AutoShutdown only, a transmitter/receiver edge is defined as a transition through the transmitter/receiver input logic

wake-up thresholds.

CONDITIONS UNITSMIN TYP MAXPARAMETER

| t

PHL

- t

PLH

|

430

t

PHL

R_IN to R_OUT,
CL= 150pF

t

PLH

CL= 150pF to 1000pF

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

CL= 150pF to 2500pF

0.15

VCC= 3.3V,
T

A

= +25°C,
RL= 3kΩ to 7kΩ,
measured from +3V to

-3V or -3V to +3V

Normal operation

Normal operation

| t

PHL

- t

PLH

|

µs

0.15

Receiver Propagation Delay

kbps250Maximum Data Rate

V/µs

630

Transition-Region Slew Rate

µs2.6Receiver Output Enable Time

µs2.4Receiver Output Disable Time

ns50

ns50Receiver Skew

Transmitter Skew

TIMING CHARACTERISTICS

MAX3238E/MAX3248E

+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers

with ±15kV ESD-Protected I/O and Logic Pins

_______________________________________________________________________________________ 5

Typical Operating Characteristics (continued)

(VCC= +3.3V, 250kbps data rate, 0.1µF capacitors, all transmitters loaded with 3kΩ, TA= +25°C, unless otherwise noted.)

______________________________________________________________Pin Description

Output of the Valid Signal Detector. A logic 1 indicates if a valid RS-232 level is present on
receiver inputs.

INVALID

15

Noninverting Complementary Receiver Output. Always active.R1OUTB16

TTL/CMOS Transmitter Inputs (T5IN–T1IN). This pin has an active positive feedback resis­tor. Once driven to a valid logic level, the pin retains that level if left unconnected until
power is cycled.

T_IN17, 19, 22, 23, 24

TTL/CMOS Receiver Outputs (R3OUT–R1OUT)R_OUT18, 20, 21

Negative Terminal of Voltage-Doubler Charge-Pump CapacitorC1-25

RS-232 Transmitter Outputs (T1OUT–T5OUT)T_OUT5, 6, 7, 10, 12

RS-232 Receiver Inputs (R1IN–R3IN)R_IN8, 9, 11

Force-On Input. Drive high to override AutoShutdown Plus, keeping transmitters and
receivers on (FORCEOFF must be high) (Table 1). This pin has an active positive feedback
resistor. Once driven to a valid logic level, the pin retains that level if left unconnected until
power is cycled.

FORCEON13

Force-Off Input. Drive low to shut down transmitters, receivers (except R1OUTB), and on­board supply. This overrides AutoShutdown Plus and FORCEON (Table 1). This pin has an
active positive feedback resistor. Once driven to a valid logic level, the pin retains that
level if left unconnected until power is cycled.

FORCEOFF

14

-5.5V Generated by the Charge PumpV-4

Negative Terminal of Inverting Charge-Pump CapacitorC2-3

PIN

GroundGND2

Positive Terminal of Inverting Charge-Pump CapacitorC2+

1

FUNCTIONNAME

26 V

CC

+3.0V to +5.5V Supply Voltage

27 V+ +5.5V Generated by the Charge Pump

28 C1+ Positive Terminal of Voltage-Doubler Charge-Pump Capacitor

TRANSMITTER OUTPUT VOLTAGE

vs. SUPPLY VOLTAGE

6
5
4
3
2

1 TRANSMITTER 250kbps

1

4 TRANSMITTERS 15.6kbps

0

ALL TRANSMITTERS LOADED

-1

WITH 3kΩ +1000pF

-2

-3

-4

TRANSMITTER OUTPUT VOLTAGE (V)

-5

-6

2.0 3.0 3.52.5 4.0 4.5 5.0
SUPPLY VOLTAGE (V)

V

+

OUT

V

MAX3238E toc04

OUT-

50

40

30

20

SUPPLY CURRENT (mA)

10

0

2.0 3.0 3.52.5 4.0 4.5 5.0

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

1 TRANSMITTER 250kbps
4 TRANSMITTERS 15.6kbps
ALL TRANSMITTERS LOADED
WITH 3kΩ +1000pF

SUPPLY VOLTAGE (V)

MAX3238E toc05

MAX3238E/MAX3248E

+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins

6 _______________________________________________________________________________________

_______________Detailed Description

Dual Charge-Pump Voltage Converter

The MAX3238E/MAX3248Es’ 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), regardless of the input
voltage (VCC) over the 3.0V to 5.5V range. The charge
pumps operate in a discontinuous mode: if the output
voltages are less than 5.5V, the charge pumps are
enabled; if the output voltages exceed 5.5V, the charge
pumps are disabled. Each charge pump requires a fly­ing capacitor (C1, C2) and a reservoir capacitor (C3,
C4) to generate the V+ and V- supplies.

RS-232 Transmitters

The MAX3248E transmitters are inverting level translators
that convert a logic low of 0.6V and logic high of 1.2V to

5.0V EIA/TIA-232 levels. The MAX3238E transmitters are
inverting level translators that convert CMOS-logic levels
to 5.0V EIA/TIA-232 levels. The MAX3238E/MAX3248E
transmitters both guarantee a 250kbps data rate with
worst-case 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.

LapLink is a trademark of Traveling Software.

When FORCEOFF is driven to ground, the transmitters
and receivers are disabled and the outputs go high
impedance, except for R1OUTB. When the Auto­Shutdown Plus circuitry senses that all receiver and
transmitter inputs are inactive for more than 30s, the
transmitters are disabled and the outputs go into a
high-impedance state, but the receivers remain active.
When the power is off, the MAX3238E/MAX3248E per­mit the outputs to be driven up to ±12V.

The transmitter inputs, FORCEON and FORCEOFF,
have a 400kΩ active positive-feedback resistor. Once
driven to a valid logic level, they will retain this level if
the driving signal is removed or goes high-impedance.
Unused transmitter inputs may be left unconnected.

RS-232 Receivers

The receivers convert RS-232 signals to CMOS-logic
output levels. All receivers have inverting three-state
outputs and are inactive in shutdown (FORCEOFF)
(Table 1). The MAX3238E/MAX3248E also feature an
extra, always-active noninverting output, R1OUTB. This
extra output monitors receiver activity while the other
receivers are high impedance, allowing Ring Indicator
to be monitored without forward biasing other devices
connected to the receiver outputs. This is ideal for sys­tems where V

CC

is set to 0 in shutdown to accommo-

date peripherals, such as UARTs (Figure 2).

Table 1. Output Control Truth Table

FORCEON

FORCEOFF

AutoShutdown

Plus

OPERATION

STATUS

T_OUT R_OUT R1OUTB

X 0 X

Shutdown
(Forced Off)

High-Z High-Z Active

1 1 X

Normal Operation
(Forced On)

Active Active Active

0 1 <30s*

Normal
Operation
(AutoShutdown
Plus)

Active Active Active

0 1 >30s*

Shutdown
(AutoShutdown
Plus)

High-Z Active Active

X = Don’t care
*Time since last receiver or transmitter input transition.

MAX3238E/MAX3248E

+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers

with ±15kV ESD-Protected I/O and Logic Pins

_______________________________________________________________________________________ 7

AutoShutdown Plus Mode

A 10nA supply current is achieved with Maxim’s
AutoShutdown Plus feature, which operates when
FORCEOFF is low and FORCEON is high. When the
MAX3238E/MAX3248E sense no valid signal transitions
on all receiver and transmitter inputs for 30s, the on­board power supply and drivers are shut off, reducing
supply current to 1µA. If the receiver inputs are in the
invalid range (-0.3V < R_IN < +0.3V) and the transmit­ter inputs are at GND or VCC, supply current is further
reduced to 10nA. This occurs if the RS-232 cable is
disconnected or if the connected peripheral transmit­ters are turned off. The system turns on again when a
valid transition is 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. The INVALID output is high when the receivers are
active. Since INVALID indicates the receiver inputs’
condition, it can be used in any mode (Figure 3).

Figure 1. Interface Under Control of PMU

Figure 2. MAX3238E/MAX3248E detect RS-232 activity when
the UART and interface are shut down.

POWER

MANAGEMENT

UNIT OR

KEYBOARD

CONTROLLER

CPU

FORCEOFF

FORCEON

INVALID

I/O
CHIP
WITH
UART

MAX3238E/

MAX3248E

T1

T2

T3

T4

T5

R1

R2

R3

RS-232

V

CC

PROTECTION
DIODE

V

CC

SHDN = GND

I

V

CC

Rx

UART

Tx

GND

a) OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM ACTIVE
RECEIVER OUTPUT IN SHUTDOWN.

TO

LOGIC

µP

TRANSITION

DETECTOR

PREVIOUS

RS-232

5kΩ

I

PROTECTION
DIODE

V

CC

Rx

UART

Tx

GND

b) NEW MAX3238E/MAX3248E: IN SHUTDOWN, R1OUTB IS USED TO MONITOR
EXTERNAL DEVICES AND R1OUT IS THREE STATED, ELIMINATING A CURRENT
PATH THROUGH THE UART'S PROTECTION DIODE.

R1OUTB

R1OUT

THREE-STATED

T1IN

FORCEOFF = GND

MAX3238E
MAX3248E

R1IN

5kΩ

T1OUT

MAX3238E/MAX3248E

+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins

8 _______________________________________________________________________________________

Tables 1 and 2 and Figure 3 summarize the MAX3238E/
MAX2348Es’ operating modes. FORCEON and FORCE-
OFF override the automatic circuitry and force the
transceiver into its normal operating state or into its low­power standby state. When neither control is asserted,
the IC enters AutoShutdown Plus mode and selects
between these states automatically, based on the last
receiver or transmitter input edge received.

When shut down, the devices’ charge pumps turn off,
V+ decays to V

CC,

V- decays to ground, and the trans­mitter outputs are disabled (high impedance). The time
required to recover from shutdown is typically 25µs
(Figure 4b).

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 feature so the line acts like a SHDN input.

ESD Protection

As with all Maxim devices, ESD protection structures
are incorporated to protect against electrostatic dis­charges (ESDs) encountered during handling and
assembly. The MAX3238E/MAX3248E RS-232 transmit­ters and receivers, as well as the I/O have extra protec­tion against static electricity found in normal operation.
Maxim’s engineers developed state-of-the-art struc­tures to protect these pins against ESD of ±15kV with­out damage. After an ESD event, the MAX3238E/
MAX3248E keep working without latchup.

ESD protection can be tested in various ways. The pins
are characterized for protection to ±15kV and ±8kV
(see Electrical Characteristics).

ESD Test Conditions

Contact Maxim for a reliability report that documents
test setup, methodology, and 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 inter-

Table 2. INVALID Truth Table

Figure 3a.

INVALID

Functional Diagram,

INVALID

Low

Figure 3b.

INVALID

Functional Diagram,

INVALID

High

Figure 3c. AutoShutdown Plus Logic

Figure 3d. Power-Down Logic

L

No

HYes

INVALID OUTPUT

RS-232 SIGNAL PRESENT AT

ANY RECEIVER INPUT

+0.3V

R_IN

-0.3V

INVALID ASSERTED IF ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR
AT LEAST 60µs.

+2.7V

R_IN

-2.7V

INVALID DEASSERTED IF ANY RECEIVER INPUT HAS BEEN BETWEEN +2.7V AND -2.7V
FOR LESS THAN 60µs.

T_IN

R_IN

FORCEOFF

FORCEON

AUTOSHDN

EDGE

DETECT

EDGE

DETECT

FORCEON

60µs

TIMER

R

60µs

TIMER

R

FORCEOFF

S

30s TIMER

R

INVALID

INVALID

AUTOSHDN

POWERDOWN*

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

MAX3238E/MAX3248E

+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers

with ±15kV ESD-Protected I/O and Logic Pins

_______________________________________________________________________________________ 9

est, 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 MAX3238E/MAX3248E

help you design equipment that meets Level 4 (the high­est level) of IEC 1000-4-2, without 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 ESD test model (Figure 6a),
the ESD withstand voltage measured to this standard is
generally lower than that measured using the Human
Body Model. 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 testing uses a 200pF stor­age capacitor and zero-discharge resistance. Its objec­tive is to mimic the stress caused by contact that
occurs with handling and assembly during manufactur­ing. Of course, all pins (not just RS-232 inputs and out­puts) require this protection during manufacturing.

Figure 4a. Receiver Positive/Negative Thresholds for

INVALID

Figure 4b. AutoShutdown Plus and

INVALID

Timing Diagram

INVALID HIGH

+2.7V

INDETERMINATE

+0.3V

0V

-0.3V

RECEIVER INPUT LEVELS

-2.7V

INVALID LOW

INDETERMINATE

INVALID HIGH

INVALID

REGION

RECEIVER

INPUTS

VOLTAGE

***

TRANSMITTER

INPUTS

VOLTAGE

TRANSMITTER

OUTPUTS

VOLTAGE

V

INVALID

OUTPUT

*ALL RECEIVERS/TRANSMITTERS INACTIVE
**ANY ONE RECEIVER/TRANSMITTER BECOMES ACTIVE FORCEON = GND, FORCEOFF = V

CC

0

I

NVL

V+

V

CC

0

V-

t

AUTOSHDN

t

t

WU

AUTOSHDN

t

WU

CC

MAX3238E/MAX3248E

10 ______________________________________________________________________________________

Therefore, the Machine Model is less relevant to the I/O
ports than the Human Body Model and IEC 1000-4-2.

Applications Information

Capacitor Selection

The capacitor type used for C1–C4 is not critical for
proper operation; polarized or nonpolarized capacitors
can be used. The charge pump requires 0.1µF capaci­tors for 3.3V operation. For other supply voltages, see
Table 3 for required capacitor values. Do not use val­ues smaller than those listed in Table 3. Increasing the
capacitor values (e.g., by a factor of 2) reduces ripple
on the transmitter outputs and slightly reduces power
consumption. C2, C3, and C4 can be increased without
changing C1’s value. However, do not increase C1

without also increasing the values of C2, C3, C4,
and C

BYPASS

to maintain the proper ratios (C1 to the

other capacitors).

Power-Supply Decoupling

In most applications, decouple VCCto ground with a

0.1µF capacitor. Further increasing this capacitor value
reduces power-supply ripple and enhances noise mar­gin. Connect the bypass capacitor as close to the IC as
possible.

Figure 5a. Human Body ESD Test Model

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

Figure 5b. Human Body Model Current Waveform

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

+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins

V

CC

(V)

C2, C3, C4

(µF)

3.0 to 3.6 0.22

C1, C

BYPASS

(µF)

0.22

4.5 to 5.5 0.33

3.0 to 5.5 1

0.047

0.22

Table 3. Required Minimum Capacitance
Values

3.15 to 3.6 0.10.1

1MΩ RD 1500Ω

R

C

PEAK-TO-PEAK RINGING

I

r

(NOT DRAWN TO SCALE)

HIGH-

VOLTAGE

DC

SOURCE

CHARGE-CURRENT

LIMIT RESISTOR

C

s

100pF

DISCHARGE

RESISTANCE

STORAGE
CAPACITOR

DEVICE
UNDER

TEST

AMPERES

IP 100%

90%

36.8%

10%

0

0

t

RL

TIME

t

DL

CURRENT WAVEFORM

50MΩ to 100MΩ RD 330Ω

R

C

CHARGE-CURRENT

LIMIT RESISTOR

HIGH-

VOLTAGE

DC

SOURCE

C

150pF

DISCHARGE

RESISTANCE

STORAGE

s

CAPACITOR

DEVICE
UNDER

TEST

I

100%

90%

PEAK

I

10%

tr = 0.7ns to 1ns

30ns

60ns

t

MAX3238E/MAX3248E

______________________________________________________________________________________ 11

Transmitter Outputs when

Recovering from Shutdown

Figure 7 shows two transmitter outputs when recovering
from shutdown mode. As they become active, the out-

puts are shown going to opposite RS-232 levels (one
transmitter input is high, the other is low). Each trans­mitter is loaded with 3kΩ in parallel with 2500pF. 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 V­exceeds approximately 3V.

High Data Rates

The MAX3238E/MAX3248E 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,

Figure 10. Loopback Test Result at 250kbps

Figure 9. Loopback Test Result at 120kbps

Figure 7. Transmitter Outputs when Recovering from Shutdown
or Powering Up

Figure 8. Loopback Test Circuit

+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers

with ±15kV ESD-Protected I/O and Logic Pins

5V/div

FORCEON =
FORCEOFF

T2OUT

T1IN

+5V

0

+5V

2V/div

T1OUT

4µs/div

VCC = 3.3V, C1–C4 = 0.1µF, R

LOAD

= 3kΩ, C

LOAD

= 2500pF

V

CC

V

CC

MAX3238E
MAX3248E

V+

C3*

V-

C4

T_ OUT

C1

C2

C1+

C1-

C2+

C2-

T_ IN

T1OUT

R1OUT

2µs/div

VCC = 3.3V, C1–C4 = 0.1µF, C

LOAD

= 1000pF

T1IN

T1OUT

R1OUT

0

-5V

+5V

0

+5V

0

+5V

0

-5V

+5V

0

5kΩ

R_ IN

1000pF

R_ OUT

FORCEON

V

CC

*C3 CAN BE RETURNED TO VCC OR GND.

FORCEOFF

GND

2µs/div

VCC = 3.3V, C1–C4 = 0.1µF, C

LOAD

= 1000pF

MAX3238E/MAX3248E

Figure 11. Data Cable Application Example

12 ______________________________________________________________________________________

+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins

28 1

C1+

+

C1

0.1µF

0.1µF

TVS

SUB-

MINIATURE

CONNECTOR

0.1µF

25

C1-

27

C3

C5

V+

±15kV ESD

26

24

23

22

19

17

PROTECTION

V

CC

T1IN T1OUT

T2IN T2OUT

T3IN T3OUT

T4IN T4OUT

T5IN

R1OUT21

R2OUT20

R3OUT18

MAX3238E
MAX3248E

±15kV ESD

PROTECTION

C2+

C2-

T5OUT

R2IN 9

R3IN 11

C2

3

0.1µF

4

V-

C4

0.1µF

5

6

7

10

12

8R1IN

DCD

DSR

RTS

CTS

DTR

1

6

RD

TD

RI

2

7

3

8

4

9

R1OUTB16

FORCEON

13

FORCEOFF

14

15

INVALID

CONTROL

GND

2

5

MAX3238E/MAX3248E

+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers

with ±15kV ESD-Protected I/O and Logic Pins

______________________________________________________________________________________ 13

Typical Operating Circuit

___________________Chip Information

TRANSISTOR COUNT: 2110

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 1000pF.

Data Cable Applications

The MAX3238E/MAX3248Es’ ±15kV ESD protection on
both the RS-232 I/Os as well as the logic I/Os makes
them ideal candidates for data cable applications. A
data cable is both an electrical connection and a level
translator, allowing ultra-miniaturization of cell phones
and other small portable devices.

Previous data cable approaches suffered from com­plexity due to the required protection circuits on both
the logic side of the cable as well as on the RS-232
connections. The example shown in Figure 10 shows
the ease of using the MAX3238E/MAX3248E in data
cable applications.

The MAX3238E/MAX3248Es’ five-transmitter and three­receiver configuration is optimized for a data communi­cation equipment (DCE) application, allowing full hard­ware handshaking. The 9-pin RS-232 connector is
configured for direct attachment to a PC’s serial port.

R1OUTB is also connected to the subminiature con­nector. This allows the remote system to shut down
until the PC asserts the ready to send (RTS) signal.
R1OUTB stays active when the MAX3238E/MAX3248E
is shut down (FORCEOFF = GND).

0.1µF

0.1µF

LOGIC

INPUTS

+3.3V

1µF

26

V

C1+

28

25

C1-

1

C2+ V-

3

C2-

24

T1IN T1OUT

23

T2IN T2OUT

22

T3IN T3OUT

19

T4IN T4OUT

T5IN

17

14

FORCEOFF

13

FORCEON

R1OUTB16

CC

MAX3238E
MAX3248E

T1

T2

T3

T4

T5

AutoShutdown Plus

INVALID

27

V+

4

5

6

7

10

12T5OUT

15

0.1µF*

0.1µF

RS-232
OUTPUTS

R1OUT 8R1IN21

LOGIC

OUTPUTS

R2OUT 9R2IN20

R3OUT 11

*C3 MAY BE RETURNED TO EITHER V

R1

5kΩ

R2

5kΩ

R3

GND

2

OR GND.

CC

R3IN18

5kΩ

RS-232
INPUTS

MAX3238E/MAX3248E

+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins

________________________________________________________Package Information

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.

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

© 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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