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MAX3387-MAX3387ECUG-MAX3387EEUG
3V / 15kV ESD-Protected / AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones
General DescriptionThe MAX3387E 3V powered EIA/TIA-232 and V.28/V.24
is a communications interface with low power require-
ments, high data-rate capabilities, and enhanced elec-
trostatic 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 capa-
ble of running at data rates up to 250kbps while main-
taining RS-232 compliant output levels.
The MAX3387E has a unique VLpin that allows interop-
eration in mixed-logic voltage systems. Both input and
output logic levels are pin programmable through thepin. The MAX3387E is available in a space-saving
TSSOP package.
ApplicationsSubnotebook/Palmtop Computers
PDAs and PDA Cradles
Cell Phone Data Cables
Battery-Powered Equipment
Hand-Held Equipment
Peripherals
FeaturesVLPin for Compatibility with Mixed-Voltage
Systems ±15kV ESD Protection on Rx Inputs and Tx OutputsLow 300μA Supply Current Guaranteed 250kbps Data Rate 1μA AutoShutdown Plus™with Receivers ActiveMeets EIA/TIA-232 Specifications Down to 3.0V
MAX3387E, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phonesypical Operating Circuit19-1561; Rev 1; 10/99
Pin Configuration
Ordering InformationAutoShutdown Plus is a trademark of Maxim Integrated Products.
MAX3387E, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
ABSOLUTE MAXIMUM RATINGS
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=
TMINto TMAX, unless otherwise noted. Typical values are at VCC= VL= +3.3V, TA= +25°C.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Note 1:V+ and V- can have maximum magnitudes of 7V, but their absolute difference cannot exceed 13V.
VCCto GND..............................................................-0.3V to +6Vto 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, FORCEOFFto 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 7.8mW/°C above +70°C)..........625mW
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, 10sec).............................+300°C
MAX3387E, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
DC ELECTRICAL CHARACTERISTICS (continued)(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=
TMINto TMAX, unless otherwise noted. Typical values are at VCC= VL= +3.3V, TA= +25°C.)
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.)
MAX3387E, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
MAX3387E, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell PhonesTRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCE
MAX3387E-01
LOAD CAPACITANCE (pF)
OUTPUT VOLTAGE (V)10002000300040005000
SLEW RATE vs. LOAD CAPACITANCEMAX3387E-02
LOAD CAPACITANCE (pF)
SLEW RATE (V/µs)
TRANSMITTER OUTPUT VOLTAGE
vs. DATA RATE
MAX3387E-03
DATA RATE (kbps)
OUTPUT VOLTAGE (V)10002000300040005000
SUPPLY CURRENT vs. LOAD CAPACITANCEMAX3387E-04
LOAD CAPACITANCE (pF)
SUPPLY CURRENT (mA)
Typical Operating Characteristics(VCC= VL= +3.3V, TA = +25°C, unless otherwise noted.)
MAX3387E, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
Pin Descriptions
MAX3387E, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
Detailed Description
Dual Charge-Pump
Voltage ConverterThe MAX3387E’s internal power supply consists of a
regulated dual charge pump that provides output volt-
ages of +5.5V (doubling charge pump) and -5.5V
(inverting charge pump), regardless of the input volt-
age (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 fly-
ing capacitor (C1, C2) and a reservoir capacitor (C3,
C4) to generate the V+ and V- supplies.
RS-232 TransmittersThe transmitters are inverting level translators that con-
vert CMOS-logic levels to 5.0V EIA/TIA-232 levels.
The MAX3387E transmitters guarantee a 250kbps data
rate with worst-case loads of 3kΩin parallel with
1000pF, providing compatibility with PC-to-PC commu-
nication software (such as LapLink™). Transmitters canparalleled to drive multiple receivers or mice. Figure 1
shows a complete system connection.
These RS-232 output stages are turned off (high imped-
ance) 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 INVALIDoutput that indi-
cates when no signal is present on any RS-232 receiver
inputs. INVALIDis independent of other control logic
functions; it indicates the receiver input conditions only
(Figures 2 and 3).
LapLink is a trademark of Traveling Software.
MAX3387E, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
AutoShutdown Plus ModeThe MAX3387E achieves a1μAsupplycurrentwith
Maxim’s AutoShutdown Plus feature, which operates
when FORCEOFFis 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 on-
board charge pumps are shut down, reducing supply
current to 1μA. This occurs if the RS-232 cable is dis-
connected 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 sys-
tem.
Figures 2a and 2b show valid and invalid RS-232
receiver voltage levels. INVALIDindicates the receiver
input’s condition, and is independent of FORCEON and
FORCEOFFstates. Figure 2 and Table 1 summarize the
MAX3387E’s operating modes. FORCEON and FORCE-
OFFoverride AutoShutdown Plus circuitry. When nei-
ther control is asserted, the IC selects between these
states automatically based on the last receiver or trans-
mitter 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 FORCEOFFto 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 sig-
nal transitions within that time, the RS-232 ports on both
systems remain enabled.
Logic Supply InputUnlike other RS-232 interface devices where the receiv-
er outputs swing between 0 and VCC, the MAX3387E
features a separate logic supply input (VL) that sets
VOHfor the receiver outputs and sets thresholds for the
receiver inputs. This feature allows a great deal of flexi-
bility 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 Applicationsection.
