19-1561; Rev 3; 6/10
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
The MAX3387E 3V powered TIA/EIA-232 and V.28/V.24
is a communications interface with low power requirements, high data-rate capabilities, and enhanced electrostatic discharge (ESD) protection. The MAX3387E
has three receivers and three transmitters. All RS-232
inputs and outputs are protected to ±15kV using the
IEC 1000-4-2 Air-Gap Discharge method, ±8kV using
the IEC 1000-4-2 Contact Discharge method, and
±15kV using the Human Body Model.
A proprietary low-dropout transmitter output stage
enables true RS-232 performance from a +3.0V to
+5.5V supply with a dual charge pump. The charge
pump requires only four small 0.1µF capacitors for
operation from a +3.3V supply. The MAX3387E is capable of running at data rates up to 250kbps while maintaining RS-232 compliant output levels.
The MAX3387E has a unique VL pin that allows interoperation in mixed-logic voltage systems. Both input and
output logic levels are pin programmable through the
VL pin. The MAX3387E is available in a space-saving
TSSOP package.
Applications
Features
♦ VL Pin for Compatibility with Mixed-Voltage
Systems
♦ ±15kV ESD Protection on Rx Inputs and Tx Outputs
♦ Low 300µA Supply Current
♦ Guaranteed 250kbps Data Rate
♦ 1µA AutoShutdown Plus™ with Receivers Active
♦ Meets TIA/EIA-232 Specifications Down to 3.0V
Ordering Information
PART
TEMP. RANGE
MAX3387ECUG+
0°C to +70°C
24 TSSOP
MAX3387EEUG+
-40°C to +85°C
24 TSSOP
PIN-PACKAGE
+Denotes a lead(Pb)-free/RoHS-compliant package.
Typical Operating Circuit
+3.3V
CBYPASS
Subnotebook/Palmtop Computers
PDAs and PDA Cradles
C1
0.1μF
Cell Phone Data Cables
Battery-Powered Equipment
Hand-Held Equipment
C2
0.1μF
23
24
FORCEOFF
1 C1+
3
4
5
15
VCC
VL
V+
2
C3
0.1μF
C1-
MAX3387E
C2+
V-
6
C2-
7 T1IN
T1OUT 21
8 T2IN
T2OUT 20
10 T3IN
T3OUT 19
C4
0.1μF
Peripherals
TTL/CMOS
INPUTS
RS-232
OUTPUTS
VL
R1IN 18
14 R1OUT
VL
TTL/CMOS
OUTPUTS
13 R2OUT
5k
R2IN 17
RS-232
INPUTS
5k
VL
12
9
R3OUT
R3IN 16
5k
INVALID
FORCEON
11
GND
22
AutoShutdown Plus is a trademark of Maxim Integrated
Products, Inc.
_______________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
MAX3387E
General Description
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
ABSOLUTE MAXIMUM RATINGS
VCC to GND ..............................................................-0.3V to +6V
VL to GND...................................................-0.3V to (VCC + 0.3V)
V+ to GND ................................................................-0.3V to +7V
V- to GND .................................................................+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........................................................-0.3V to (VL + 0.3V)
Short-Circuit Duration T_OUT to GND........................Continuous
Continuous Power Dissipation (TA = +70°C)
24-Pin TSSOP (derate 12.2mW/°C above +70°C) ........976mW
Operating Temperature Ranges
MAX3387ECUG ...................................................0°C to +70°C
MAX3387EEUG ................................................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
Note 1: V+ and V- can have maximum magnitudes of 7V, but their absolute difference cannot 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.
DC ELECTRICAL CHARACTERISTICS
(VCC = VL = +3.0V to +5.5V; C1–C4 = 0.1µF, tested at +3.3V ±10%; C1 = 0.047µF, C2–C4 = 0.33µF, tested at +5.0V ±10%;
TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = VL = +3.3V, TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DC CHARACTERISTICS (VCC = +3.3V or +5V, TA = +25°C)
Supply Current, AutoShutdown
Plus
All R_IN idle, FORCEON = GND,
FORCEOFF = VCC, all T_IN idle
1.0
10
µA
Supply Current
FORCEOFF = FORCEON = VCC, no load
0.3
1
mA
LOGIC INPUTS
Input Logic Threshold Low
Input Logic Threshold High
T_IN, FORCEON,
FORCEOFF
T_IN, FORCEON,
FORCEOFF
VL = +3.3V or +5.0V
0.8
VL = +2.5V
0.6
VL = +5.0V
2.4
VL = +3.3V
2.0
VL = +2.5V
1.4
VL = +1.8V
V
0.9
Transmitter Input Hysteresis
Input Leakage Current
V
0.5
T_IN, FORCEON, FORCEOFF
±0.01
V
±1
µA
0.4
V
RECEIVER OUTPUTS
Output Voltage Low
Output Voltage High
IOUT = 1.6mA
VL 0.6
IOUT = -1mA
VL 0.1
V
RECEIVER INPUTS
Input Voltage Range
-25
Input Threshold Low
TA = +25°C
Input Threshold High
TA = +25°C
2
+25
VL = +5.0V
0.8
1.5
VL = +3.3V
0.6
1.2
V
VL = +5.0V
1.8
2.4
VL = +3.3V
1.5
2.4
_______________________________________________________________________________________
V
V
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
(VCC = VL = +3.0V to +5.5V; C1–C4 = 0.1µF, tested at +3.3V ±10%; C1 = 0.047µF, C2–C4 = 0.33µF, tested at +5.0V ±10%;
TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = VL = +3.3V, TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
Input Hysteresis
TYP
MAX
UNITS
7
kΩ
0.5
Input Resistance
TA = +25°C
3
5
V
TRANSMITTER OUTPUTS
Output Voltage Swing
All transmitter outputs loaded with 3kΩ to
ground
±5
±5.4
V
Output Resistance
VCC = V+ = V- = 0V, transmitter output = ±2V
300
10M
Ω
Output Short-Circuit Current
VT_OUT = 0V
±60
mA
Output Leakage Current
VT_OUT = ±12V, transmitters disabled;
VCC = 0V or +3.0V to +5.5V
±25
µA
ESD PROTECTION
R_IN, T_OUT
ESD Protection
Human Body Model
±15
IEC 1000-4-2 Air-Gap Discharge method
±15
IEC 1000-4-2 Contact Discharge method
±8
kV
AutoShutdown Plus (FORCEON = GND, FORCEOFF = VCC)
Receiver Input Threshold to
INVALID Output High
Figure 3a
Receiver Input Threshold to
INVALID Output Low
Figure 3a
INVALID Output Voltage Low
IOUT = -1.6mA
INVALID Output Voltage High
IOUT = -1.0mA
Positive threshold
Negative threshold
2.7
-2.7
-0.3
V
0.3
V
0.4
V
VL - 0.6
V
Receiver Positive or Negative
Threshold to INVALID High
tINVH
VCC = +5V, Figure 3b
1
µs
Receiver Positive or Negative
Threshold to INVALID Low
tINVL
VCC = +5V, Figure 3b
30
µs
Receiver or Transmitter Edge to
Transmitters Enabled
tWU
VCC = +5V, Figure 3b
100
µs
Receiver or Transmitter Edge to
tAUTOSHDN VCC = +5V, Figure 3b
Transmitters Shutdown
15
30
60
s
_______________________________________________________________________________________
3
MAX3387E
DC ELECTRICAL CHARACTERISTICS (continued)
TIMING CHARACTERISTICS
(VCC = VL = +3V to +5.5V; C1–C4 = 0.1µF, tested at +3.3V ±10%; C1 = 0.047µF, C2–C4 = 0.33µF, tested at +5.0V ±10%; TA = TMIN
to TMAX, unless otherwise noted. Typical values are at VCC = VL = +3.3V, TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
RL = 3kΩ, CL = 1000pF,
one transmitter switching
Maximum Data Rate
tPHL
Receiver Propagation Delay
Transmitter Skew
⏐VT_OUT⏐ > +3.7V
t
t
⏐ PHL PLH⏐ (Note 2)
Receiver Skew
⏐tPHL - tPLH⏐
VCC = +3.3V,
TA = +25°C,
RL = 3kΩ to 7kΩ,
measured from +3V
to -3V or -3V to +3V
Transition-Region Slew
Rate
TYP
MAX
250
UNITS
kbps
0.15
Receiver input to receiver output,
CL = 150pF
tPLH
Time to Exit Shutdown
µs
0.15
100
µs
100
ns
50
ns
CL = 150pF to
1000pF
6
30
CL = 150pF to
2500pF
4
30
V/µs
Note 2: Transmitter skew is measured at the transmitter zero crosspoints.
Typical Operating Characteristics
(VCC = VL = +3.3V, TA = +25°C, unless otherwise noted.)
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCE
SLEW RATE vs. LOAD CAPACITANCE
5.0
DATA RATE = 250kbps
LOAD = 3kΩ IN PARALLEL WITH CL
14
12
SLEW RATE (V/µs)
2.5
MAX3387E-02
16
MAX3387E-01
7.5
OUTPUT VOLTAGE (V)
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
0
-2.5
SLEW RATE 10
SLEW RATE +
8
6
4
-5.0
2
-7.5
0
0
1000
2000
3000
4000
LOAD CAPACITANCE (pF)
4
5000
0
1000
2000
3000
4000
5000
LOAD CAPACITANCE (pF)
_______________________________________________________________________________________
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
TRANSMITTER OUTPUT VOLTAGE
vs. DATA RATE
SUPPLY CURRENT (mA)
0
LOAD = 3kΩ,
ONE TRANSMITTER
SWITCHING AT DATA
RATE, OTHER
TRANSMITTERS
250kbps
AT 1/8 DATA RATE
50
LOAD = 3kΩ, 1000pF
ONE TRANSMITTER
SWITCHING AT DATA
RATE, OTHER
TRANSMITTERS
AT 1/8 DATA RATE
2.5
-2.5
-5.0
MAX3387E-04
5.0
OUTPUT VOLTAGE (V)
SUPPLY CURRENT vs. LOAD CAPACITANCE
60
MAX3387E-03
7.5
40
120kbps
30
20
20kbps
10
-7.5
0
0
50
100
150
200
250
0
1000
DATA RATE (kbps)
2000
3000
4000
5000
LOAD CAPACITANCE (pF)
Pin Configuration
TOP VIEW
+
C1+ 1
24 FORCEOFF
V+ 2
23 VCC
C1- 3
22 GND
C2+ 4
C2- 5
21 T1OUT
MAX3387E
V- 6
20 T2OUT
19 T3OUT
T1IN 7
18 R1IN
T2IN 8
17 R2IN
INVALID 9
16 R3IN
T3IN 10
15 VL
FORCEON 11
14 R1OUT
R3OUT 12
13 R2OUT
TSSOP
_______________________________________________________________________________________
5
MAX3387E
Typical Operating Characteristics (continued)
(VCC = VL = +3.3V, TA = +25°C, unless otherwise noted.)
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
MAX3387E
Pin Description
6
PIN
NAME
FUNCTION
1
C1+
2
V+
+5.5V Supply Generated by the Charge Pump
3
C1-
Negative Terminal of the Voltage-Doubler Charge-Pump Capacitor
4
C2+
Positive Terminal of the Inverting Charge-Pump Capacitor
5
C2-
Negative Terminal of the Inverting Charge-Pump Capacitor
Positive Terminal of the Voltage-Doubler Charge-Pump Capacitor
6
V-
7
T1IN
-5.5V Generated by the Charge Pump
8
T2IN
9
INVALID
10
T3IN
11
FORCEON
12
R3OUT
13
R2OUT
14
R1OUT
15
VL
16
R3IN
17
R2IN
18
R1IN
19
T3OUT
20
T2OUT
21
T1OUT
22
GND
Ground
23
VCC
+3.0V to +5.5V Supply Voltage
24
FORCEOFF
TTL/CMOS Transmitter Inputs
Output of the Valid Signal Detector. INVALID is high if a valid RS-232 signal is present on
the receiver inputs.
TTL/CMOS Transmitter Inputs
Force-On Input. Drive FORCEON high to override automatic circuitry keeping transmitters
on (FORCEOFF must be high) (Table 1).
TTL/CMOS Receiver Outputs. Swing between 0V and VL.
Logic-Level Supply. All CMOS inputs and outputs are referenced to this supply.
RS-232 Receiver Inputs
RS-232 Transmitter Outputs
Force-Off Input. Drive FORCEOFF low to shut down transmitters and on-board power supply. This overrides all automatic circuitry and FORCEON (Table 1).
_______________________________________________________________________________________
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
Dual Charge-Pump
Voltage Converter
The MAX3387E’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), regardless of the input voltage (VCC) over a +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 transmitters are inverting level translators that convert CMOS-logic levels to 5.0V EIA/TIA-232 levels.
The MAX3387E 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 paralleled to drive multiple receivers or mice. Figure 1
shows a complete system connection.
These RS-232 output stages are turned off (high impedance) when the device is in shutdown mode. When the
power is off, the MAX3387E permits the outputs to be
driven up to ±12V.
The transmitter inputs do not have pull-up resistors.
Connect unused inputs to GND or VL.
RS-232 Receivers
The receivers convert RS-232 signals to CMOS-logic
output levels. The MAX3387E’s receivers are always
active, even when the device is in shutdown.
The MAX3387E features an INVALID output that indicates when no signal is present on any RS-232 receiver
inputs. INVALID is independent of other control logic
functions; it indicates the receiver input conditions only
(Figures 2 and 3).
+0.3V
R_IN
-0.3V
POWERMANAGEMENT
UNIT OR
KEYBOARD
CONTROLLER
30μs
COUNTER
R
INVALID
FORCEON
FORCEOFF
TRANSMITTERS ARE DISABLED, REDUCING SUPPLY CURRENT TO 1μA IF
ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR AT LEAST 30μs.
INVALID
I/O CHIP
POWER SUPPLY
VL
VCC
Figure 2a. INVALID Function Diagram, INVALID = Low
MAX3387E
+2.7V
I/O
CHIP
WITH
UART
R_IN
RS-232
-2.7V
30μs
COUNTER
R
INVALID
CPU
TRANSMITTERS ARE ENABLED IF:
ANY RECEIVER INPUT IS GREATER THAN +2.7V OR LESS THAN -2.7V;
ANY RECEIVER INPUT HAS BEEN BETWEEN +0.3V AND -0.3V FOR LESS THAN 30μs.
Figure 2b. INVALID Function Diagram, INVALID = High
Figure 1. Interface Under Control of PMU
Laplink is a registered trademark of Laplink Software, Inc.
_______________________________________________________________________________________
7
MAX3387E
Detailed Description
T_IN
R_IN
EDGE
DETECT
TRANSMITTERS ENABLED, INVALID HIGH
FORCEOFF
S
30s
TIMER
EDGE
DETECT
+2.7V
AUTOSHDN
R
FORCEON
RECEIVER INPUT LEVELS
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
INDETERMINATE
+0.3V
0V
AutoShutdown, TRANSMITTERS DISABLED,
1μA SUPPLY CURRENT, INVALID LOW
-0.3V
INDETERMINATE
-2.7V
TRANSMITTERS ENABLED, INVALID HIGH
Figure 2c. AutoShutdown Plus Logic
Figure 3a. Receiver Thresholds for INVALID
FORCEOFF
POWERDOWN
FORCEON
AUTOSHDN
POWERDOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE
OPERATIONAL STATUS OF THE TRANSMITTERS AND THE POWER SUPPLIES.
Figure 2d. Power-Down Logic
AutoShutdown Plus Mode
The MAX3387E achieves a1µA 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 and transmitter input for 30sec, the onboard 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 if the UART driving the transmitter
inputs is inactive. 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.
Figure 3a shows valid and invalid RS-232 receiver voltage levels. INVALID indicates the receiver input’s condition, and is independent of FORCEON and
8
FORCEOFF states. Figure 2 and Table 1 summarize the
MAX3387E’s operating modes. FORCEON and FORCEOFF 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.
By connecting FORCEON to INVALID, the MAX3387E
shuts down when no valid receiver level and no receiver or
transmitter edge is detected for 30sec, and wakes up
when a valid receiver level or receiver or transmitter
edge is detected.
By connecting FORCEON and FORCEOFF to INVALID,
the MAX3387E shuts down when no valid receiver level
is detected.
A mouse or other 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 the other system to realize that the MAX3387E
is awake. If the other system outputs valid RS-232 signal transitions within that time, the RS-232 ports on both
systems remain enabled.
VL Logic Supply Input
Unlike other RS-232 interface devices where the receiver outputs swing between 0V and VCC, the MAX3387E
features a separate logic supply input (VL) that sets
VOH for the receiver outputs and sets thresholds for the
receiver inputs. This feature allows a great deal of flexibility in interfacing to many different types of systems
with different logic levels. Connect this input to the host
logic supply (1.8V ≤ VL ≤ VCC). Also, see the Typical
PDA/Cell-Phone Application section.
_______________________________________________________________________________________
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
MAX3387E
RECEIVER
INPUTS
INVALID
} REGION
TRANSMITTER
INPUTS
TRANSMITTER
OUTPUTS
INVALID
OUTPUT
VCC
tINVL
tINVH
0
tAUTOSHDN
tAUTOSHDN
tWU
tWU
V+
VCC
0
V-
Figure 3b. AutoShutdown Plus/INVALID Timing Diagram
±15kV ESD Protection
POWERMANAGEMENT
UNIT
MASTER SHDN LINE
0.1μF
1M
FORCEOFF FORCEON
MAX3387E
Figure 4. AutoShutdown with Initial Turn-On to Wake Up a
System
Software-Controlled Shutdown
If direct software control is desired, INVALID can be
used to indicate a DTR or ring indicator signal. Connect
FORCEOFF and FORCEON together to bypass
AutoShutdown so the line acts like a SHDN input.
As with all Maxim devices, ESD-protection structures
are incorporated on all pins to protect against electrostatic discharges (ESDs) encountered during handling
and assembly. The MAX3387E driver outputs and
receiver inputs have extra protection against static
electricity. Maxim has 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 event, Maxim’s “E” version devices
keep working without latchup, whereas competing RS232 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 method
_______________________________________________________________________________________
9
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
Table 1. Output Control Truth Table
FORCEON
FORCEOFF
VALID
RECEIVER
LEVEL
RECEIVER OR
TRANSMITTER
EDGE WITHIN
30
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
OPERATION STATUS
X = Don’t care
RC
1M
CHARGE-CURRENT
LIMIT RESISTOR
HIGHVOLTAGE
DC
SOURCE
Cs
100pF
RD
1500Ω
IP 100%
90%
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
Ir
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
AMPERES
DEVICE
UNDER
TEST
36.8%
10%
0
0
Figure 5a. Human Body ESD Test Model
tRL
TIME
tDL
CURRENT WAVEFORM
Figure 5b. Human Body Current Waveform
ESD Test Conditions
Human Body Model
ESD performance depends on a variety of conditions.
Contact Maxim for a reliability report that documents
test setup, methodology, and results.
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.
10
______________________________________________________________________________________
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
HIGHVOLTAGE
DC
SOURCE
Cs
150pF
I
100%
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
90%
DEVICE
UNDER
TEST
I PEAK
CHARGE-CURRENT
LIMIT RESISTOR
RD
330Ω
MAX3387E
RC
50M to 100M
10%
Figure 6a. IEC 1000-4-2 ESD Test Model
IEC 1000-4-2
The IEC 1000-4-2 standard covers ESD testing and
performance of finished equipment; it does not specifically refer to ICs. The MAX3387E helps 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 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. 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
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-
t R = 0.7ns to 1ns
t
30ns
60ns
Figure 6b. IEC 1000-4-2 ESD Generator Current Waveform
Table 2. Minimum Required Capacitor
Values
VCC
(V)
C1
(µF)
C2, C3, C4
(µF)
3.0 to 3.6
0.1
0.1
4.5 to 5.5
0.047
0.33
3.0 to 5.5
0.22
1
tors for 3.3V operation. For other supply voltages, see
Table 2 for required capacitor values. Do not use values smaller than those listed in Table 2. 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, and C4 to
maintain the proper ratios (C1 to the other capacitors).
When using the minimum required capacitor values,
make sure the capacitor value does not degrade
excessively with temperature. If in doubt, use capacitors with a larger nominal value. The capacitor’s equivalent series resistance (ESR), which usually rises at low
temperatures, influences the amount of ripple on V+
and V-.
______________________________________________________________________________________
11
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
Power-Supply Decoupling
Operation Down to 2.7V
In most circumstances, a 0.1µF bypass capacitor is adequate. In applications that are sensitive to power-supply
noise, decouple VCC to ground with a capacitor of the
same value as charge-pump capacitor C1. Connect
bypass capacitors as close to the IC as possible.
Transmitter outputs will meet TIA/EIA-562 levels of
±3.7V with supply voltages as low as +2.7V.
5V/div
T2
2V/div
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). 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 V- exceeds approximately 3V.
High Data Rates
T1
VCC = 3.3V
C1–C4 = 0.1μF
50μs/div
Figure 7. Transmitter Outputs when Exiting Shutdown
The MAX3387E maintains 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 1000pF.
Interconnection with
3V and 5V Logic
VCC
0.1μF
VCC
C1+
C1
C1-
V+
C3
MAX3387E
C2+
The MAX3387E can directly interface with various 5V
logic families, including ACT and HCT CMOS. The logic
voltage power-supply pin (VL) sets the output voltage
level of the receivers and the input thresholds of the
transmitters.
VC4
C2
C2-
5V/div
T1IN
T_ OUT
T_ IN
R_ IN
R_ OUT
5V/div
T1OUT
5k
FORCEOFF
VCC
FORCEON
1000pF
5V/div
R1OUT
GND
VCC = 3.3V
2μs/div
Figure 8. Loopback Test Circuit
12
Figure 9. Loopback Test Results at 120kbps
______________________________________________________________________________________
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
5V/div
T1OUT
5V/div
5V/div
R1OUT
VCC = 3.3V
2μs/div
Figure 10. Loopback Test Results at 250kbps
Typical PDA/Cell-Phone Application
The MAX3387E is designed with PDA applications in
mind. Two transmitters and two receivers handle standard full-duplex communication protocol, while an extra
transmitter allows a ring indicator signal to alert the
UART on the PC. Without the ring indicator transmitter,
solutions for these applications would require softwareintensive polling of the cradle inputs.
The ring indicate (RI) signal is generated when a PDA,
phone, or other “cradled” device is plugged into its cradle.
This generates a logic-low signal to the RI transmitter
input, creating +6V at the ring indicate pin. The PC’s
UART RI input is the only pin that can generate an interrupt from signals arriving through the RS-232 port. The
interrupt routine for this UART will then service the RS232 full-duplex communication between the PDA and
the PC.
Chip Information
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns,
go to www.maxim-ic.com/packages. Note that a “+”, “#”, or
“-” in the package code indicates RoHS status only. Package
drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
24 TSSOP
U24+1
21-0066
______________________________________________________________________________________
13
MAX3387E
T1IN
As cell phone design becomes more like that of PDAs,
cell phones will require similar docking ability and communication protocol. Cell phones operate on a single
lithium-ion (Li+) battery and work with a power-supply
voltage of +2.7V to +4V. The baseband logic coming
from the phone connector can be as low as 1.8V at the
transceivers. To prevent forward biasing of a device
internal to the cell phone, the MAX3387E comes with a
logic power-supply pin (VL) that limits the logic levels
presented to the phone. The receiver outputs will sink
to zero for low outputs, but will not exceed VL for logic
highs. The input logic levels for the transmitters are also
altered, scaled by the magnitude of the VL input. The
device will work with V L as low as 1.8V before the
charge-pump noise will begin to cause the transmitter
outputs to oscillate. This is useful with cell phones and
other power-efficient devices with core logic voltage
levels that go as low as 1.8V.
MAX3387E
3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
Revision History
REVISION
NUMBER
REVISION
DATE
3
6/10
DESCRIPTION
PAGES
CHANGED
Added Note 2 to the Electrical Characteristics table
4
Changed the Chip Information section to say “PROCESS: BiCMOS”
13
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
© 2010 Maxim Integrated Products
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