19-1144; Rev 1; 10/02
+3.0V to +5.5V, 1µA, up to 250kbps, True
RS-232 Transceiver with AutoShutdown Plus
_______________General Description
The MAX3238 true RS-232 transceiver achieves a
1µA supply current with Maxim’s revolutionary
AutoShutdown Plus™ feature. When the device does
not sense a valid signal transition on either the receiver
or transmitter inputs within 30sec, the on-board power
supply and drivers shut down. This occurs if the RS-232
cable is disconnected or if the transmitters of the con-
nected peripheral are inactive. The system turns on
again when a valid transition is applied to any RS-232
receiver or transmitter input, saving power without
changes to the existing BIOS or operating system.
The MAX3238 5-driver/3-receiver complete serial port is
a 3V-powered EIA/TIA-232 and V.28/V.24 communica-
tions interface intended for notebook or subnotebook
computer applications. A proprietary, high-efficiency,
dual charge-pump power supply and a low-dropout
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 popu-
lar software for communicating with personal comput-
ers. The MAX3238 requires only 0.1µF capacitors in
3.3V operation. It is ideal for 3.3V-only systems, mixed
3.3V and 5.0V systems, or 5V-only systems that require
true RS-232 performance.
Receiver R1 has an extra, always-active output (in addi-
tion to its standard output), which allows external
devices, such as a modem, to be monitored without for-
ward biasing the protection diodes in circuitry that may
have V
CC
completely removed.
The MAX3238 is available in a space-saving SSOP
package.
____________________________Features
o
1µA Supply Current Achieved with
AutoShutdown Plus
o
Guaranteed Data Rate: 250kbps
o
1µA Low-Power Shutdown
o
Receivers Active in AutoShutdown Plus Mode
o
Flow-Through Pinout
o
Meets EIA/TIA-232 Specifications Down to 3.0V
o
Guaranteed 6V/µs Slew Rate
MAX3238
______________Ordering Information
PART
MAX3238CAI
MAX3238EAI
TEMP RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
28 SSOP
28 SSOP
__________________Pin Configuration
TOP VIEW
C2+
GND
C2-
V-
T1OUT
T2OUT
T3OUT
R1IN
R2IN
1
2
3
4
5
6
7
8
9
28 C1+
27 V+
26 V
CC
25 C1-
24 T1IN
________________________Applications
Notebook, Subnotebook, and Palmtop
Computers
High-Speed Modems
Battery-Powered Equipment
Hand-Held Equipment
Peripherals
Printers
MAX3238
23 T2IN
22 T3IN
21 R1OUT
20 R2OUT
19 T4IN
18 R3OUT
17 T5IN
16 R1OUTB
15 INVALID
T4OUT 10
R3IN 11
Typical Operating Circuit appears at end of data sheet.
T5OUT 12
FORCEON 13
FORCEOFF 14
AutoShutdown Plus is a trademark of Maxim Integrated Products.
*P
SSOP
1
________________________________________________________________
Maxim Integrated Products
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, 1µA, up to 250kbps, True
RS-232 Transceiver with AutoShutdown Plus
MAX3238
ABSOLUTE MAXIMUM RATINGS
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)
SSOP (derate 9.52mW/°C above +70°C) ....................762mW
Operating Temperature Ranges
MAX3238CAI ......................................................0°C to +70°C
MAX3238EAI....................................................-40°C to +85°C
Storage Temperature Range ............................-65°C to +160°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.
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
(V
CC
= +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 T
A
= +25°C.)
PARAMETER
DC CHARACTERISTICS
Supply Current, AutoShutdown Plus
V
CC
= 3.3V or 5.0V, T
A
= +25°C, receivers idle,
transmitters idle, FORCEON = GND,
FORCEOFF
= V
CC
FORCEOFF
= GND, T
A
= +25°C
FORCEON =
FORCEOFF
= V
CC
, no load
1.0
10
µA
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Current, Shutdown
Supply Current, AutoShutdown Plus
Disabled
Input Logic Threshold Low
Input Logic Threshold High
Input Leakage Current
Output Leakage Current
Output Voltage Low
Output Voltage High
RECEIVER INPUTS
Input Voltage Range
Input Threshold Low
Input Threshold High
Input Hysteresis
Input Resistance
1.0
10
µA
mA
0.5
2.0
LOGIC INPUTS AND RECEIVER OUTPUTS
T_IN, FORCEON,
FORCEOFF
V
CC
= 3.3V
V
CC
= 5.0V
T_IN, FORCEON,
FORCEOFF
Receivers disabled
I
OUT
= 1.6mA
I
OUT
= -1.0mA
V
CC
-
0.6
-25
V
CC
= 3.3V
V
CC
= 5.0V
V
CC
= 3.3V
V
CC
= 5.0V
T
A
= +25°C
3
0.6
0.8
1.2
1.5
1.5
1.8
0.3
5
7
2.4
2.4
V
CC
-
0.1
25
2.0
2.4
±0.01
±0.05
±1.0
±10
0.4
0.8
V
V
µA
µA
V
V
V
V
V
V
kΩ
2
_______________________________________________________________________________________
+3.0V to +5.5V, 1µA, up to 250kbps, True
RS-232 Transceiver with AutoShutdown Plus
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +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 T
A
= +25°C.)
PARAMETER
AutoShutdown
(FORCEON = GND,
FORCEOFF
= V
CC
)
Receiver Input Threshold to
INVALID
Output High
Receiver Input Threshold to
INVALID
Output Low
INVALID
Output Voltage Low
INVALID
Output Voltage High
Receiver Positive or Negative
Threshold to
INVALID
High (t
INVH
)
Receiver Positive or Negative
Threshold to
INVALID
Low (t
INVL
)
Receiver or Transmitter Edge to
Transmitters Enabled (t
WU
)
Receiver or Transmitter Edge to
Shutdown (t
AUTOSHDN
)
TRANSMITTER OUTPUTS
Output Voltage Swing
Output Resistance
Output Short-Circuit Current
Output Leakage Current
TIMING CHARACTERISTICS
Maximum Data Rate
Receiver Propagation Delay
Receiver Output Enable Time
Receiver Output Disable Time
Transmitter Skew
Receiver Skew
R
L
= 3kΩ, C
L
= 1000pF, one transmitter switching
R_IN to R_OUT,
C
L
= 150pF
Normal operation
Normal operation
| t
PHL
- t
PLH
|
| t
PHL
- t
PLH
|
V
CC
= 3.3V,
T
A
= +25°C,
R
L
= 3Ω to 7kΩ,
measured from +3V to
-3V or -3V to +3V
C
L
= 150pF to 1000pF
C
L
= 150pF to 2500pF
6
t
PHL
t
PLH
250
0.15
0.15
200
200
100
50
30
V/µs
4
30
kbps
µs
ns
ns
ns
ns
All transmitter outputs loaded with 3kΩ to ground
V
CC
= V+ = V- = GND, T
OUT
= 2V
V
CC
≤
3.6V
V
CC
> 3.6V
V
OUT
= ±12V, V
CC
= 0V to 5.5V,
transmitters disabled
±5.0
300
±5.4
10M
±35
±40
±60
±100
±25
V
Ω
mA
µA
Positive threshold
Figure 7a
Negative threshold
Figure 4a
I
OUT
= 1.6mA
I
OUT
= -1.0mA
V
CC
= 5V, Figure 4b
V
CC
= 5V, Figure 4b
V
CC
= 5V, Figure 4b (Note 2)
Figure 4b (Note 2)
15
V
CC -
0.6
0.1
50
25
30
60
-2.7
-0.3
0.3
0.4
V
V
V
µs
µs
µs
sec
2.7
V
CONDITIONS
MIN
TYP
MAX
UNITS
MAX3238
Transition-Region Slew Rate
Note 2:
A transmitter/receiver edge is defined as a transition through the transmitter/receiver input logic thresholds.
_______________________________________________________________________________________
3
+3.0V to +5.5V, 1µA, up to 250kbps, True
RS-232 Transceiver with AutoShutdown Plus
MAX3238
__________________________________________Typical Operating Characteristics
(V
CC
= +3.3V, 250kbps data rate, 0.1µF capacitors, all transmitters loaded with 3kΩ, T
A
= +25°C, unless otherwise noted.)
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCE
MAX3238 TOC-01
SLEW RATE
vs. LOAD CAPACITANCE
–SLEW
+SLEW
MAX3238-02
SUPPLY CURRENT vs. LOAD CAPACITANCE
WHEN TRANSMITTING DATA
MAX3238 TOC-03
7.5
TRANSMITTER OUTPUT VOLTAGE (V)
5.0
2.5
0
-2.5
-5.0
-7.5
0
1000
2000
V
OUT
+
14
12
SLEW RATE (V/µs)
10
8
6
4
1 TRANSMITTER 250kbps
4 TRANSMITTERS 15.6kbps
LOADED 3kΩ
+
C
L
70
60
SUPPLY CURRENT (mA)
50
40
30
20
10
0
20kbps
120kbps
250kbps
FOR DATA RATES UP TO 250kbps
1 TRANSMITTER 250kbps
4 TRANSMITTERS 15.6kbps
LOADED 3kΩ
+
C
L
V
OUT
–
2
0
3000
4000
5000
0
LOAD CAPACITANCE (pF)
2000
4000
1000
3000
LOAD CAPACITANCE (pF)
5000
0
2000
4000
1000
3000
LOAD CAPACITANCE (pF)
5000
______________________________________________________________Pin Description
PIN
NAME
C2+
GND
C2-
V-
T_OUT
R_IN
FORCEON
FUNCTION
Positive Terminal of Inverting Charge-Pump Capacitor
Ground
Negative Terminal of Inverting Charge-Pump Capacitor
-5.5V Generated by the Charge Pump
RS-232 Transmitter Outputs (T1OUT–T5OUT)
RS-232 Receiver Inputs (R1IN–R3IN)
Force-Off Input. Drive high to override AutoShutdown Plus, keeping transmitters and
receivers on (FORCEOFF must be high) (Table 1).
Force-Off Input. Drive low to shut down transmitters, receivers (except R1OUTB), and on-
board supply. This overrides AutoShutdown Plus and FORCEON (Table 1).
Output of the Valid Signal Detector. A logic “1” indicates if a valid RS-232 level is present
on receiver inputs.
Noninverting Complementary Receiver Output. Always active.
TTL/CMOS Transmitter Inputs (T5IN–T1IN)
TTL/CMOS Receiver Outputs (R3OUT–R1OUT)
Negative Terminal of Voltage-Doubler Charge-Pump Capacitor
+3.0V to +5.5V Supply Voltage
+5.5V Generated by the Charge Pump
Positive Terminal of Voltage-Doubler Charge-Pump Capacitor
1
2
3
4
5, 6, 7, 10, 12
8, 9, 11
13
14
FORCEOFF
INVALID
R1OUTB
T_IN
R_OUT
C1-
V
CC
V+
C1+
15
16
17, 19, 22, 23, 24
18, 20, 21
25
26
27
28
4
_______________________________________________________________________________________
+3.0V to +5.5V, 1µA, up to 250kbps, True
RS-232 Transceiver with AutoShutdown Plus
MAX3238
Table 1. Output Control Truth Table
FORCEON
FORCEOFF
AUTOSHUTDOWN
PLUS*
X
OPERATION
STATUS
Shutdown
(Forced Off)
Normal Operation
(Forced On)
Normal
Operation
(AutoShutdown
Plus)
Shutdown
(AutoShutdown
Plus)
T_OUT
R_OUT
R1OUTB
X
0
High-Z
High-Z
Active
1
1
X
Active
Active
Active
0
1
<30sec*
Active
Active
Active
0
1
>30sec*
High-Z
Active
Active
X
= Don’t Care
*Time
since last receiver or transmitter input transition.
_______________Detailed Description
Dual Charge-Pump Voltage Converter
The MAX3238’s internal power supply consists of a reg-
ulated dual charge pump that provides output voltages
of +5.5V (doubling charge pump) and -5.5V (inverting
charge pump), regardless of the input voltage (V
CC
)
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.
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 30sec, the
transmitters are disabled and the outputs go into a
high-impedance state, but the receivers remain active.
When the power is off, the MAX3238 permits the out-
puts to be driven up to ±12V.
The transmitter inputs do not have pull-up resistors.
Connect unused inputs to GND or V
CC
.
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 MAX3238 also features 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 moni-
tored without forward biasing other devices connected
to the receiver outputs. This is ideal for systems where
V
CC
is set to 0V in shutdown to accommodate peripher-
als, such as UARTs (Figure 2).
RS-232 Transmitters
The transmitters are inverting level translators that con-
vert CMOS-logic levels to 5.0V EIA/TIA-232 levels. The
MAX3238 transmitters 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 par-
alleled to drive multiple receivers. Figure 1 shows a
complete system connection.
LapLink is a trademark of Traveling Software.
_______________________________________________________________________________________
5
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