MAX3238E [MAXIM]
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 【15kV ESD-Protected I/O and Logic Pins; + 3.0V至+ 5.5V ， 10nA的， 250kbps的RS - 232收发器，具有± 15kV ESD保护， I / O和逻辑引脚
| 型号： | MAX3238E |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | +3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 【15kV ESD-Protected I/O and Logic Pins |
| 文件： | 总14页 (文件大小：236K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1632; Rev 1; 6/01
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with 15kV ESD-ꢀrotected I/O and Logic ꢀins
General Description
Features
The MAX3238E/MAX3248E transceivers use Maxim’s
revolutionary AutoShutdown Plus™ feature to achieve
10nA supply current. These devices shut down the on-
board power supply and drivers when they do not sense
a valid signal transition on either the receiver or transmit-
ter inputs. This occurs if the RS-232 cable is disconnect-
ed or if the transmitters of the connected peripheral are
turned off. The devices turn on again when a valid transi-
tion 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.
ꢀ 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
All RS-232 inputs and outputs, as well as the logic I/O
pins, have enhanced ESD protection to 1ꢀ5k. The addi-
tional ESD protection on the logic I/O pins ma5es the
MAX3238E/MAX3248E ideal for cell phone data cable
applications because it eliminates the need for costly
ꢀ Low-Level Logic Thresholds (MAX3248E)
ꢀ RS-232-Compatible Outputs to 2.7V
™
external TransZorb or protection schemes.
The MAX3238E/MAX3248E contain five drivers and three
receivers and are 3k-powered EIA/TIA-232 and k.28/k.24
communication interfaces intended for cell phones, data
cables, and modem applications. A proprietary, high-effi-
ciency, dual charge-pump power supply and a low-
dropout transmitter combine to deliver true RS-232
performance from a single +3.0k to +ꢀ.ꢀk supply. A
guaranteed data rate of 2ꢀ05bps provides compatibility
with popular software for communicating with personal
computers.
Ordering Information
PART
TEMP. RANGE
0°C to +70°C
-40°C to +8ꢀ°C
0°C to +70°C
-40°C to +8ꢀ°C
PIN-PACKAGE
MAX3238ECAI
MAX3238EEAI
MAX3248ECAI
MAX3248EEAI
28 SSOP
28 SSOP
28 SSOP
28 SSOP
Typical Operating Circuit appears at end of data sheet.
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 0.6k to 1.2k, which are ideal for 1.8k sys-
tems.
The transmitter inputs, FORCEON, and FORCEOFF have
a 4005Ω active positive feedbac5 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 +3.0k to +ꢀ.ꢀk.
___________________ꢀin Configuration
TOP VIEW
C2+
GND
C2-
V-
28
27
26
25
24
23
22
1
2
C1+
V+
V
CC
3
C1-
4
T1IN
T2IN
T3IN
T1OUT
T2OUT
5
MAX3238E
MAX3248E
6
T3OUT
R1IN
7
Applications
21 R1OUT
8
Cellular Data Cables
Modems
Battery-Powered Equipment
Peripherals
Data Cradles
Printers
9
20
R2IN
R2OUT
19
10
11
12
13
14
T4IN
18 R3OUT
T5IN
T4OUT
R3IN
17
T5OUT
FORCEON
FORCEOFF
AutoShutdown Plus is a trademark of Maxim Integrated Products.
16 R1OUTB
TransZorb is a trademark of General Semiconductor Industries, Inc.
†
15
Covered by U.S. Patent numbers 4,636,930; 4,679,134;
INVALID
4,777,577; 4,797,899; 4,809,152; 4,897,774; 4,999,761; and other
patents pending.
SSOP
________________________________________________________________ Maxim Integrated Products
1
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.
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with 15kV ESD-ꢀrotected I/O and Logic ꢀins
ABSOLUTE MAXIMUM RATINGS
k
CC
...........................................................................-0.3k to +6k
Short-Circuit Duration
k+ (Note 1%...............................................................-0.3k to +7k
k- (Note 1% ................................................................+0.3k to -7k
k+ + |k-| (Note 1%.................................................................+13k
Input koltages
T_IN, FORCEOFF, FORCEON..............................-0.3k to +6k
R_IN ................................................................................. 2ꢀk
Output koltages
T_OUT (one at a time%............................................Continuous
Continuous Power Dissipation (T = +70°C%
A
28-Pin SSOP (derate 9.ꢀ2mW/°C above +70°C% .........762mW
Operating Temperature Ranges
MAX3238ECAI/MAX3248ECAI ...........................0°C to +70°C
MAX3238EEAI/MAX3248EEAI.........................-40°C to +8ꢀ°C
Storage Temperature Range ............................-6ꢀ°C to +1ꢀ0°C
Lead Temperature (soldering, 10s% ................................+300°C
T_OUT........................................................................... 13.2k
R_OUT, INVALID ....................................-0.3k to (k
+ 0.3k%
CC
Note 1: k+ and k- can have a maximum magnitude of +7k, but their absolute difference can not exceed +13k.
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.
ELECTRICAL CHARACTERISTICS
(k
= +3.0k to +ꢀ.ꢀk, C1–C4 = 0.1µF (tested at 3.3k ꢀꢁ%, C1–C4 = 0.22µF (tested at 3.3k 10ꢁ%, C1 = 0.047µF, and
CC
C2–C4 = 0.33µF (tested at ꢀ.0k 10ꢁ%, T = T
to T
, unless otherwise noted. Typical values are at T = +2ꢀ°C.%
MAX A
A
MIN
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
DC CHARACTERISTICS (k
= +3.3k or +ꢀ.0k, T = +2ꢀ°C%
A
CC
Receivers idle, T_IN = k
or GND, FORCEON =
CC
0.7ꢀ
6
µA
GND, FORCEOFF = k
CC
Supply Current, AutoShutdown Plus
Supply Current, Shutdown
R_IN = FORCEON = GND, FORCEOFF = k
CC,
10
10
300
300
2.0
nA
nA
T_IN = k
or GND
CC
FORCEOFF = GND, R_IN = GND, T_IN = k or GND
CC
Supply Current, AutoShutdown Plus
Disabled
0.ꢀ
mA
FORCEON = FORCEOFF = k , no load
CC
LOGIC INPUTS AND RECEIVER OUTPUTS
T_IN (active%
0.8
0.8
1.20
1.00
FORCEON, FORCEOFF, and T_IN
wa5e-up threshold; k
= 3.3k
MAX3238E
CC
FORCEON, FORCEOFF, and T_IN
0.8
0.6
0.6
1.4ꢀ
0.7
wa5e-up threshold; k
= ꢀ.0k
CC
Input Logic Threshold Low
k
T_IN (active%
FORCEON, FORCEOFF, and T_IN
wa5e-up threshold; k = 3.3k
0.8ꢀ
MAX3248E
MAX3238E
MAX3248E
CC
FORCEON, FORCEOFF, and T_IN
0.6
1.0
wa5e-up threshold; k
= ꢀ.0k
CC
T_IN (active%
1.60
1.30
2.0
2.0
FORCEON, FORCEOFF, and T_IN
wa5e-up threshold; k = 3.3k
CC
FORCEON, FORCEOFF, and T_IN
2.10
1.10
0.9ꢀ
2.4
1.2
1.2
wa5e-up threshold; k
= ꢀ.0k
CC
Input Logic Threshold High
k
T_IN (active%
FORCEON, FORCEOFF, and T_IN
wa5e-up threshold; k = 3.3k
CC
FORCEON, FORCEOFF, and T_IN
wa5e-up threshold; k = ꢀ.0k
1.1ꢀ
1.6
CC
2
_______________________________________________________________________________________
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with 15kV ESD-ꢀrotected I/O and Logic ꢀins
ELECTRICAL CHARACTERISTICS (continued)
(k
= +3.0k to +ꢀ.ꢀk, C1–C4 = 0.1µF (tested at 3.3k ꢀꢁ%, C1–C4 = 0.22µF (tested at 3.3k 10ꢁ%, C1 = 0.047µF, and
CC
C2–C4 = 0.33µF (tested at ꢀ.0k 10ꢁ%, T = T
to T
, unless otherwise noted. Typical values are at T = +2ꢀ°C.%
MAX A
A
MIN
PARAMETER
CONDITIONS
MIN
TYP
9
MAX
18
UNITS
µA
Input Lea5age Current
Output Lea5age Current
Output koltage Low
T_IN, FORCEON, FORCEOFF (Note 2%
Receivers disabled
0.0ꢀ
10
µA
I
= 1.0mA
0.4
k
OUT
k
0.6
-
k
0.1
-
CC
CC
Output koltage High
I
= -1.0mA
k
OUT
RECEIVER INPUTS
Input koltage Range
-2ꢀ
0.6
0.8
2ꢀ
k
k
k
k
k
k
= 3.3k
= ꢀ.0k
= 3.3k
= ꢀ.0k
1.0
1.4
1.ꢀ
2.0
0.6
ꢀ
CC
CC
CC
CC
Input Threshold Low
Input Threshold High
2.4
2.4
k
Input Hysteresis
Input Resistance
k
T
A
= +2ꢀ°C
3
7
5Ω
AutoShutdown (FORCEON = GND, FORCEOFF = k
%
CC
Positive threshold
Negative threshold
2.7
Receiver Input Threshold to
Figure 4a
k
INVALID Output High
-2.7
-0.3
Receiver Input Threshold to
Figure 4a
0.3
0.4
k
k
k
INVALID Output Low
I
= 1.0mA
INVALID Output koltage Low
OUT
OUT
k
CC -
0.6
I
= -1.0mA
INVALID Output koltage High
Receiver Positive or Negative
k
k
k
= ꢀk, Figure 4b
= ꢀk, Figure 4b
0.3
60
µs
µs
CC
Threshold to INVALID High (t
%
INkH
Receiver Positive or Negative
Threshold to INVALID Low (t
CC
CC
%
INkL
Receiver or Transmitter Edge to
Transmitters Enabled (t
= ꢀk, Figure 4b (Note 3%
2ꢀ
30
µs
s
%
WU
Receiver or Transmitter Edge to
Shutdown (t
Figure 4b
1ꢀ
60
%
AUTOSHDN
TRANSMITTER OUTPUTS
Output koltage Swing
Output Resistance
All transmitter outputs loaded with 35Ω to ground
ꢀ.0
ꢀ.4
ꢀ05
3ꢀ
k
k
CC
k
CC
k
CC
= 0, T
=
2k
300
Ω
OUT
≤ 3.6k
60
Output Short-Circuit Current
mA
> 3.6k
40
100
ESD PROTECTION
IEC 1000-4-2 Air-Gap Discharge Method
IEC 1000-4-2 Contact Discharge Method
Human Body Model
1ꢀ
8
ESD Protection (R_IN, T_IN, R_OUT,
T_OUT, FORCEON, FORCEOFF,
INVALID, R_OUTB%
5k
1ꢀ
_______________________________________________________________________________________
3
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with 15kV ESD-ꢀrotected I/O and Logic ꢀins
ELECTRICAL CHARACTERISTICS (continued)
(k
= +3.0k to +ꢀ.ꢀk, C1–C4 = 0.1µF (tested at 3.3k ꢀꢁ%, C1–C4 = 0.22µF (tested at 3.3k 10ꢁ%, C1 = 0.047µF, and
CC
C2–C4 = 0.33µF (tested at ꢀ.0k 10ꢁ%, T = T
to T
, unless otherwise noted. Typical values are at T = +2ꢀ°C.%
MAX A
A
MIN
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
TIMING CHARACTERISTICS
Maximum Data Rate
R = 35Ω, C = 1000pF, one transmitter switching
2ꢀ0
5bps
µs
L
L
t
0.1ꢀ
0.1ꢀ
2.6
2.4
ꢀ0
PHL
PLH
R_IN to R_OUT,
C = 1ꢀ0pF
L
Receiver Propagation Delay
t
Receiver Output Enable Time
Receiver Output Disable Time
Transmitter S5ew
Normal operation
Normal operation
µs
µs
ns
ns
| t
| t
- t
|
|
PHL PLH
Receiver S5ew
- t
ꢀ0
PHL PLH
k
= 3.3k,
= +2ꢀ°C,
CC
C = 1ꢀ0pF to 1000pF
6
4
30
30
L
T
A
Transition-Region Slew Rate
R = 35Ω to 75Ω,
measured from +3k to
-3k or -3k to +3k
k/µs
L
C = 1ꢀ0pF to 2ꢀ00pF
L
Note 2: The transmitter inputs have an active positive feedbac5 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
wa5e-up thresholds.
__________________________________________Typical Operating Characteristics
(k
= +3.3k, 2ꢀ05bps data rate, 0.1µF capacitors, all transmitters loaded with 35Ω, T = +2ꢀ°C, unless otherwise noted.%
A
CC
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCE
SUPPLY CURRENT vs. LOAD CAPACITANCE
WHEN TRANSMITTING DATA
SLEW RATE vs. LOAD CAPACITANCE
6
50
40
30
20
10
0
12
10
8
5
4
V
+
250kbps
120kbps
OUT
SR-
3
2
FOR DATA RATES UP TO 250kbps
1 TRANSMITTER 250kbps
1
SR+
4 TRANSMITTERS 15.6kbps
ALL TRANSMITTERS LOADED
0
6
20kbps
-1
-2
-3
-4
-5
-6
WITH 3kΩ + C
L
1 TRANSMITTER 20kbps, 120 kbps, 250kbps
4 TRANSMITTERS 15.6kbps
4
1 TRANSMITTER 250kbps
4 TRANSMITTERS 15.6kbps
ALL TRANSMITTERS LOADED
ALL TRANSMITTERS LOADED
2
WITH 3kΩ + C
L
V
OUT-
WITH 3kΩ + C
L
0
0
500 1000 1500 2000 2500 3000
LOAD CAPACITANCE (pF)
0
500 1000 1500 2000 2500 3000
LOAD CAPACITANCE (pF)
0
500 1000 1500 2000 2500 3000
LOAD CAPACITANCE (pF)
4
_______________________________________________________________________________________
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with 15kV ESD-ꢀrotected I/O and Logic ꢀins
Typical Operating Characteristics (continued)
(k
= +3.3k, 2ꢀ05bps data rate, 0.1µF capacitors, all transmitters loaded with 35Ω, T = +2ꢀ°C, unless otherwise noted.%
A
CC
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
TRANSMITTER OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
50
40
30
20
10
0
6
5
V
+
OUT
4
3
2
1 TRANSMITTER 250kbps
4 TRANSMITTERS 15.6kbps
ALL TRANSMITTERS LOADED
WITH 3kΩ +1000pF
1
0
-1
-2
-3
-4
-5
-6
1 TRANSMITTER 250kbps
4 TRANSMITTERS 15.6kbps
ALL TRANSMITTERS LOADED
WITH 3kΩ +1000pF
V
OUT-
2.0
2.5
3.0
3.5
4.0
4.5
5.0
2.0
2.5
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
______________________________________________________________ꢀin Description
PIN
NAME
FUNCTION
C2+
GND
C2-
Positive Terminal of Inverting Charge-Pump Capacitor
Ground
1
2
3
4
Negative Terminal of Inverting Charge-Pump Capacitor
-ꢀ.ꢀk Generated by the Charge Pump
RS-232 Transmitter Outputs (T1OUT–TꢀOUT%
RS-232 Receiver Inputs (R1IN–R3IN%
k-
ꢀ, 6, 7, 10, 12
8, 9, 11
T_OUT
R_IN
Force-On Input. Drive high to override AutoShutdown Plus, 5eeping transmitters and
receivers on (FORCEOFF must be high% (Table 1%. This pin has an active positive feedbac5
resistor. Once driven to a valid logic level, the pin retains that level if left unconnected until
power is cycled.
13
14
FORCEON
Force-Off Input. Drive low to shut down transmitters, receivers (except R1OUTB%, and on-
board supply. This overrides AutoShutdown Plus and FORCEON (Table 1%. This pin has an
active positive feedbac5 resistor. Once driven to a valid logic level, the pin retains that
level if left unconnected until power is cycled.
FORCEOFF
Output of the kalid Signal Detector. A logic 1 indicates if a valid RS-232 level is present on
receiver inputs.
1ꢀ
16
INVALID
R1OUTB
Noninverting Complementary Receiver Output. Always active.
TTL/CMOS Transmitter Inputs (TꢀIN–T1IN%. This pin has an active positive feedbac5 resis-
tor. Once driven to a valid logic level, the pin retains that level if left unconnected until
power is cycled.
17, 19, 22, 23, 24
T_IN
18, 20, 21
R_OUT
C1-
TTL/CMOS Receiver Outputs (R3OUT–R1OUT%
Negative Terminal of koltage-Doubler Charge-Pump Capacitor
+3.0k to +ꢀ.ꢀk Supply koltage
2ꢀ
26
27
28
k
CC
k+
+ꢀ.ꢀk Generated by the Charge Pump
C1+
Positive Terminal of koltage-Doubler Charge-Pump Capacitor
_______________________________________________________________________________________
5
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with 15kV ESD-ꢀrotected I/O and Logic ꢀins
Table 1. Output Control Truth Table
AutoShutdown
Plus
OPERATION
STATUS
FORCEON
T_OUT
R_OUT
R1OUTB
FORCEOFF
Shutdown
(Forced Off%
X
1
0
1
X
X
High-Z
Active
High-Z
Active
Active
Active
Normal Operation
(Forced On%
Normal
Operation
(AutoShutdown
Plus%
0
1
1
<30s*
>30s*
Active
High-Z
Active
Active
Active
Active
Shutdown
(AutoShutdown
Plus%
0
X = Don’t care
*Time since last receiver or transmitter input transition.
When FORCEOFF is driven to ground, the transmitters
and receivers are disabled and the outputs go high
impedance, except for R1OUTB. When the Auto-
Shutdown 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 per-
mit the outputs to be driven up to 12k.
_______________Detailed Description
Dual Charge-ꢀump Voltage Converter
The MAX3238E/MAX3248Es’ internal power supply
consists of a regulated dual charge pump that provides
output voltages of +ꢀ.ꢀk (doubling charge pump% and
-ꢀ.ꢀk (inverting charge pump%, regardless of the input
voltage (k % over the 3.0k to ꢀ.ꢀk range. The charge
CC
pumps operate in a discontinuous mode: if the output
voltages are less than ꢀ.ꢀk, the charge pumps are
enabled; if the output voltages exceed ꢀ.ꢀk, the charge
pumps are disabled. Each charge pump requires a fly-
ing capacitor (C1, C2% and a reservoir capacitor (C3,
C4% to generate the k+ and k- supplies.
The transmitter inputs, FORCEON and FORCEOFF,
have a 4005Ω active positive-feedbac5 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 Transmitters
The MAX3248E transmitters are inverting level translators
that convert a logic low of 0.6k and logic high of 1.2k to
ꢀ.0k EIA/TIA-232 levels. The MAX3238E transmitters are
inverting level translators that convert CMOS-logic levels
to ꢀ.0k EIA/TIA-232 levels. The MAX3238E/MAX3248E
transmitters both guarantee a 2ꢀ05bps data rate with
worst-case loads of 35Ω in parallel with 1000pF, provid-
ing compatibility with PC-to-PC communication software
(such as LapLin5™%. Transmitters can be paralleled to
drive multiple receivers. Figure 1 shows a complete sys-
tem connection.
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 sys-
tems where k
is set to 0 in shutdown to accommo-
CC
date peripherals, such as UARTs (Figure 2%.
LapLink is a trademark of Traveling Software.
6
_______________________________________________________________________________________
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with 15kV ESD-ꢀrotected I/O and Logic ꢀins
V
CC
POWER
MANAGEMENT
UNIT OR
KEYBOARD
CONTROLLER
FORCEOFF
FORCEON
INVALID
PROTECTION
DIODE
PREVIOUS
RS-232
MAX3238E/
MAX3248E
V
CC
I
Rx
Tx
T1
5kΩ
UART
T2
T3
GND
SHDN = GND
I/O
T4
CHIP
WITH
UART
CPU
RS-232
T5
R1
R2
a) OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM ACTIVE
RECEIVER OUTPUT IN SHUTDOWN.
V
CC
TO
µP
LOGIC
TRANSITION
DETECTOR
R3
MAX3238E
MAX3248E
I
PROTECTION
DIODE
Figure 1. Interface Under Control of PMU
R1OUTB
V
CC
AutoShutdown ꢀlus 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 on-
board power supply and drivers are shut off, reducing
supply current to 1µA. If the receiver inputs are in the
invalid range (-0.3k < R_IN < +0.3k% and the transmit-
R1IN
Rx
R1OUT
THREE-STATED
UART
5kΩ
T1OUT
T1IN
Tx
GND
FORCEOFF = GND
ter inputs are at GND or k , supply current is further
CC
reduced to 10nA. This occurs if the RS-232 cable is
disconnected or if the connected peripheral transmit-
ters 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 sys-
tem. 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%.
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.
Figure 2. MAX3238E/MAX3248E detect RS-232 activity when
the UART and interface are shut down.
_______________________________________________________________________________________
7
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with 15kV ESD-ꢀrotected I/O and Logic ꢀins
Table 2. INVALID Truth Table
+0.3V
RS-232 SIGNAL PRESENT AT
INVALID OUTPUT
ANY RECEIVER INPUT
R_IN
-0.3V
60µs
TIMER
R
INVALID
Yes
No
H
L
INVALID ASSERTED IF ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR
AT LEAST 60µs.
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 low-
power 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.
Figure 3a. INVALID Functional Diagram, INVALID Low
+2.7V
R_IN
When shut down, the devices’ charge pumps turn off,
60µs
TIMER
R
k+ decays to k
k- decays to ground, and the trans-
CC,
INVALID
mitter outputs are disabled (high impedance%. The time
required to recover from shutdown is typically 2ꢀµs
(Figure 4b%.
-2.7V
INVALID DEASSERTED IF ANY RECEIVER INPUT HAS BEEN BETWEEN +2.7V AND -2.7V
FOR LESS THAN 60µs.
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 li5e a SHDN input.
Figure 3b. INVALID Functional Diagram, INVALID High
EDGE
T_IN
ESD ꢀrotection
As with all Maxim devices, ESD protection structures
are incorporated to protect against electrostatic dis-
charges (ESDs% encountered during handling and
assembly. The MAX3238E/MAX3248E RS-232 transmit-
ters and receivers, as well as the I/O have extra protec-
tion against static electricity found in normal operation.
Maxim’s engineers developed state-of-the-art struc-
tures to protect these pins against ESD of 1ꢀ5k with-
out damage. After an ESD event, the MAX3238E/
MAX3248E 5eep wor5ing without latchup.
FORCEOFF
DETECT
S
30s TIMER
R
AUTOSHDN
EDGE
DETECT
R_IN
FORCEON
Figure 3c. AutoShutdown Plus Logic
ESD protection can be tested in various ways. The pins
are characterized for protection to 1ꢀ5k and 85k
(see Electrical Characteristics%.
FORCEOFF
POWERDOWN*
ESD Test Conditions
Contact Maxim for a reliability report that documents
test setup, methodology, and results.
FORCEON
AUTOSHDN
Human Body Model
Figure ꢀa shows the Human Body Model, and Figure
ꢀb shows the current waveform it generates when dis-
charged into a low impedance. This model consists of
a 100pF capacitor charged to the ESD voltage of inter-
* POWER DOWN IS ONLY AN INTERNAL SIGNAL.
IT CONTROLS THE OPERATIONAL STATUS OF
THE TRANSMITTERS AND THE POWER SUPPLIES.
Figure 3d. Power-Down Logic
8
_______________________________________________________________________________________
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with 15kV ESD-ꢀrotected I/O and Logic ꢀins
help you design equipment that meets Level 4 (the high-
est level% of IEC 1000-4-2, without additional ESD pro-
tection components.
INVALID HIGH
+2.7V
The major difference between tests done using the
INDETERMINATE
Human Body Model and IEC 1000-4-2 is higher pea5
current in IEC 1000-4-2. Because series resistance is
+0.3V
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 85k IEC 1000-4-2 Level 4 ESD Contact Discharge
test.
0V
INVALID LOW
INDETERMINATE
INVALID HIGH
-0.3V
-2.7V
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.
Figure 4a. Receiver Positive/Negative Thresholds for INVALID
Machine Model
The Machine Model for ESD testing uses a 200pF stor-
age capacitor and zero-discharge resistance. Its objec-
tive is to mimic the stress caused by contact that
occurs with handling and assembly during manufactur-
ing. Of course, all pins (not just RS-232 inputs and out-
puts% require this protection during manufacturing.
est, which is then discharged into the test device
through a 1.ꢀ5Ω resistor.
IEC 1000-4-2
The IEC 1000-4-2 standard covers ESD testing and per-
formance of finished equipment; it does not specifically
refer to integrated circuits. The MAX3238E/MAX3248E
INVALID
REGION
*
**
RECEIVER
INPUTS
VOLTAGE
TRANSMITTER
INPUTS
VOLTAGE
TRANSMITTER
OUTPUTS
VOLTAGE
V
INVALID
OUTPUT
CC
0
t
AUTOSHDN
I
t
AUTOSHDN
NVL
t
t
WU
WU
V+
V
CC
0
V-
*ALL RECEIVERS/TRANSMITTERS INACTIVE
**ANY ONE RECEIVER/TRANSMITTER BECOMES ACTIVE
FORCEON = GND, FORCEOFF = V
CC
Figure 4b. AutoShutdown Plus and INVALID Timing Diagram
_______________________________________________________________________________________
9
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with 15kV ESD-ꢀrotected I/O and Logic ꢀins
R
1MΩ
R 1500Ω
D
C
I 100%
P
90%
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
I
r
DISCHARGE
RESISTANCE
CHARGE-CURRENT
LIMIT RESISTOR
AMPERES
HIGH-
VOLTAGE
DC
DEVICE
UNDER
TEST
C
STORAGE
CAPACITOR
s
36.8%
100pF
SOURCE
10%
0
TIME
0
t
RL
t
DL
CURRENT WAVEFORM
Figure 5a. Human Body ESD Test Model
Figure 5b. Human Body Model Current Waveform
R
50MΩ to 100MΩ
R 330Ω
D
C
I
100%
90%
DISCHARGE
RESISTANCE
CHARGE-CURRENT
LIMIT RESISTOR
HIGH-
VOLTAGE
DC
DEVICE
UNDER
TEST
C
STORAGE
CAPACITOR
s
150pF
SOURCE
10%
30ns
t
tr = 0.7ns to 1ns
60ns
Figure 6a. IEC 1000-4-2 ESD Test Model
Figure 6b. IEC 1000-4-2 ESD Generator Current Waveform
Therefore, the Machine Model is less relevant to the I/O
ports than the Human Body Model and IEC 1000-4-2.
ꢀower-Supply Decoupling
In most applications, decouple k
to ground with a
CC
0.1µF capacitor. Further increasing this capacitor value
reduces power-supply ripple and enhances noise mar-
gin. Connect the bypass capacitor as close to the IC as
possible.
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 capaci-
tors for 3.3k operation. For other supply voltages, see
Table 3 for required capacitor values. Do not use val-
ues 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,
Table 3. Required Minimum Capacitance
Values
V
CC
C1, C
C2, C3, C4
(µF)
BYPASS
(V)
(µF)
0.22
0.1
3.0 to 3.6
3.1ꢀ to 3.6
4.ꢀ to ꢀ.ꢀ
3.0 to ꢀ.ꢀ
0.22
0.1
0.33
1
0.047
0.22
and C
to maintain the proper ratios (C1 to the
BYPASS
other capacitors%.
10 ______________________________________________________________________________________
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with 15kV ESD-ꢀrotected I/O and Logic ꢀins
FORCEON =
FORCEOFF
+5V
0
5V/div
T1IN
T1OUT
R1OUT
T2OUT
+5V
0
2V/div
-5V
+5V
0
T1OUT
4µs/div
= 3.3V, C1–C4 = 0.1µF, R
2µs/div
= 3.3V, C1–C4 = 0.1µF, C
V
= 1000pF
LOAD
V
= 3kΩ, C
= 2500pF
LOAD
CC
CC
LOAD
Figure 7. Transmitter Outputs when Recovering from Shutdown
or Powering Up
Figure 9. Loopback Test Result at 120kbps
V
CC
+5V
0
T1IN
V
CC
C1+
V+
V-
C3*
C4
+5V
0
C1
C1-
C2+
T1OUT
MAX3238E
MAX3248E
-5V
C2
C2-
+5V
0
R1OUT
T_ OUT
T_ IN
2µs/div
V
= 3.3V, C1–C4 = 0.1µF, C
= 1000pF
LOAD
CC
R_ IN
R_ OUT
Figure 10. Loopback Test Result at 250kbps
5kΩ
FORCEON
FORCEOFF
1000pF
puts are shown going to opposite RS-232 levels (one
transmitter input is high, the other is low%. Each trans-
mitter is loaded with 35Ω in parallel with 2ꢀ00pF. 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 k-
exceeds approximately 3k.
V
CC
GND
*C3 CAN BE RETURNED TO V OR GND.
CC
Figure 8. Loopback Test Circuit
High Data Rates
The MAX3238E/MAX3248E maintain the RS-232 ꢀ.0k
minimum transmitter output voltage even at high data
rates. Figure 8 shows a transmitter loopbac5 test cir-
cuit. Figure 9 shows a loopbac5 test result at 1205bps,
Transmitter Outputs when
Recovering from Shutdown
Figure 7 shows two transmitter outputs when recovering
from shutdown mode. As they become active, the out-
______________________________________________________________________________________ 11
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with 15kV ESD-ꢀrotected I/O and Logic ꢀins
28
25
27
1
3
C1+
C1-
C2+
C2-
V-
+
C1
C2
0.1µF
0.1µF
MAX3238E
MAX3248E
4
V+
C4
0.1µF
C3
0.1µF
15kV ESD
PROTECTION
15kV ESD
PROTECTION
26
V
CC
TVS
C5
0.1µF
DCD
DSR
RD
24 T1IN
T1OUT
T2OUT
T3OUT
5
1
23 T2IN
6
7
6
7
8
9
22 T3IN
2
3
RTS
19 T4IN
T4OUT 10
T5OUT 12
SUB-
MINIATURE
CONNECTOR
TD
CTS
DTR
RI
17 T5IN
21 R1OUT
20 R2OUT
18 R3OUT
16 R1OUTB
R1IN
R2IN
8
9
4
5
R3IN 11
FORCEON
FORCEOFF
INVALID
13
14
15
GND
2
Figure 11. Data Cable Application Example
12 ______________________________________________________________________________________
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with 15kV ESD-ꢀrotected I/O and Logic ꢀins
and Figure 10 shows the same test at 2ꢀ05bps. For
Typical Operating Circuit
Figure 9, all transmitters were driven simultaneously at
+3.3V
1205bps into RS-232 loads in parallel with 1000pF. For
Figure 10, a single transmitter was driven at 2ꢀ05bps,
and all transmitters were loaded with an RS-232 receiv-
er in parallel with 1000pF.
1µF
26
CC
Data Cable Applications
V
28 C1+
25 C1-
V+ 27
The MAX3238E/MAX3248Es’ 1ꢀ5k ESD protection on
both the RS-232 I/Os as well as the logic I/Os ma5es
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.
0.1µF*
0.1µF
0.1µF
0.1µF
MAX3238E
MAX3248E
1
3
C2+
C2-
V-
4
Previous data cable approaches suffered from com-
plexity 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.
24 T1IN
T1OUT
T2OUT
T3OUT
5
6
7
T1
T2
T3
T4
T5
23 T2IN
The MAX3238E/MAX3248Es’ five-transmitter and three-
receiver configuration is optimized for a data communi-
cation equipment (DCE% application, allowing full hard-
ware handsha5ing. The 9-pin RS-232 connector is
configured for direct attachment to a PC’s serial port.
22 T3IN
LOGIC
INPUTS
RS-232
OUTPUTS
19 T4IN
T4OUT 10
T5OUT 12
17 T5IN
R1OUTB is also connected to the subminiature con-
nector. 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%.
14 FORCEOFF
AutoShutdown Plus
13
INVALID 15
FORCEON
16 R1OUTB
21 R1OUT
___________________Chip Information
R1IN
8
9
R1
R2
R3
TRANSISTOR COUNT: 2110
5kΩ
LOGIC
OUTPUTS
20 R2OUT
18 R3OUT
R2IN
RS-232
INPUTS
5kΩ
R3IN 11
5kΩ
GND
2
*C3 MAY BE RETURNED TO EITHER V OR GND.
CC
______________________________________________________________________________________ 13
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with 15kV ESD-ꢀrotected I/O and Logic ꢀins
________________________________________________________ꢀackage 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 ꢀroducts, 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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