Maxim MAX3388E 2.5v, â±15kv esd-protected rs-232 transceivers for pdas and cell phone Datasheet

19-1845; Rev 1; 9/01
2.5V, ±15kV ESD-Protected RS-232
Transceivers for PDAs and Cell Phones
Features
♦ VL Pin for Compatibility with Mixed-Voltage
Systems
♦ Additional I/O for Hot-Sync Applications
♦ ±15kV ESD Protection on Rx Inputs, Tx Outputs,
LIN, and SWIN
♦ Low 300µA Supply Current
♦ Guaranteed 460kbps Data Rate
♦ 1µA Low-Power Shutdown
♦ Integrated Switch for Powering Remote Circuitry
♦ Flow-Through Pinout
♦ LOUT Active During Shutdown (MAX3389E)
Applications
Subnotebook/Palmtop Computers
PDAs and PDA Cradles
Cell Phone Data Cables
Battery-Powered Equipment
Hand-Held Equipment
Peripherals
Ordering Information
PART
Typical Operating Circuit
+2.5V
24
CBYPASS
1 C1+
C1
0.1µF
3
4
C2
0.1µF
5
14
23
VCC
SHDN
VL
V+
2
MAX3388E
MAX3389E
V-
24 TSSOP
MAX3388EEUG
-40°C to +85°C
24 TSSOP
MAX3389ECUG
0°C to +70°C
24 TSSOP
MAX3389EEUG
-40°C to +85°C
24 TSSOP
Pin Configuration
6
C4
0.1µF
C2-
7 T1IN
TOP VIEW
T1OUT
21
C1+ 1
20
9 T3IN
T3OUT
19
RS-232
I/O
VL
V+ 2
23 VCC
C1- 3
22 GND
C2+ 4
C2- 5
17
T1IN 7
18 R1IN
T2IN 8
17 R2IN
16
T3IN 9
16 LIN
SWIN 15
SWOUT 11
14 VL
R2OUT 12
13 R1OUT
V- 6
VL
12 R2OUT
MAX3388E
MAX3389E
18
5kΩ
20 T2OUT
19 T3OUT
R2IN
10 LOUT
5kΩ
LIN
30kΩ
SHDN
= ±15kV ESD PROTECTION
21 T1OUT
R1IN
13 R1OUT
SWOUT
24 SHDN
T2OUT
8 T2IN
11
PIN-PACKAGE
0°C to +70°C
C3
0.1µF
C1C2+
TEMP. RANGE
MAX3388ECUG
GND
22
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.
LOUT 10
15 SWIN
TSSOP
________________________________________________________________ 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.
1
MAX3388E/MAX3389E
General Description
The MAX3388E/MAX3389E are 2.5V-powered EIA/TIA232 and V.28/V.24 communications interfaces with low
power requirements, high data-rate capabilities, and
enhanced electrostatic discharge (ESD) protection. The
MAX3388E/MAX3389E have two 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.
In addition to the traditional RS-232 I/O, these devices have
dedicated logic-level I/O pins for additional device-todevice handshaking. During shutdown the logic-level I/O
pins are active for the MAX3389E. An internal 62Ω switch is
provided to switch power to external circuitry or modules.
A proprietary low-dropout transmitter output stage
enables RS-232 compatible performance from a +2.35V
to +3.0V supply with a dual charge pump. The charge
pump requires only four small 0.1µF capacitors for operation from a +2.5V supply. The MAX3388E/MAX3389E
are capable of running at data rates up to 460kbps while
maintaining RS-232-compatible output levels.
The MAX3388E/MAX3389E have 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 MAX3388E/MAX3389E are
available in a space-saving TSSOP package.
MAX3388E/MAX3389E
2.5V, ±15kV ESD-Protected RS-232
Transceivers 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, SHDN, LIN to GND.......................................-0.3V to +6V
R_IN to GND .....................................................................±25V
SWIN to GND...........................................-0.3V to (VCC + 0.3V)
Output Voltages
T_OUT to GND...............................................................±13.2V
R_OUT, SWOUT, LOUT to GND ................-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) ........975mW
Operating Temperature Ranges
MAX338_ECUG ...................................................0°C to +70°C
MAX338_EEUG.................................................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°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 = +2.35V to +3.0V, C1–C4 = 0.1µF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = VL = +2.5V,
TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
1
10
µA
0.3
1
mA
0.6
V
DC CHARACTERISTICS (VCC = +2.5V, TA = +25°C)
Shutdown Supply Current
SHDN = GND, all inputs at GND
Supply Current
SHDN = VCC, no load
LOGIC INPUTS (T_IN, SHDN)
Input Logic Low
VL = +2.5V
Input Logic High
VL = +2.5V
1.5
Transmitter Input Hysteresis
V
0.4
Input Leakage Current
V
±0.01
±1
µA
±0.05
±10
µA
0.4
V
RECEIVER OUTPUTS
Output Leakage Current
R_OUT, SHDN = 0
Output Voltage Low
IOUT = 1.6mA
Output Voltage High
IOUT = -1mA
VL 0.6
VL 0.13
V
RECEIVER INPUTS
Input Voltage Range
-25
Input Threshold Low
TA = +25°C, VL = +2.5V
Input Threshold High
TA = +25°C, VL = +2.5V
0.6
1.8
Input Hysteresis
Input Resistance
+25
1.1
V
2.4
V
7
kΩ
0.7
TA = +25°C
3
5
V
V
TRANSMITTER OUTPUTS
Output Voltage Swing
All transmitter outputs loaded with 3kΩ to
ground
±3.7
±4.2
V
Output Resistance
VCC = 0, transmitter output = ±2V
300
10M
Ω
Output Short-Circuit Current
VT_OUT = 0
2
_______________________________________________________________________________________
±60
mA
2.5V, ±15kV ESD-Protected RS-232
Transceivers for PDAs and Cell Phones
(VCC = VL = +2.35V to +3.0V, C1–C4 = 0.1µF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = VL = +2.5V,
TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
VT_OUT = ±12V, transmitters disabled,
VCC = 0 or +2.5V
Output Leakage Current
MAX
UNITS
±25
µA
HANDSHAKING I/O (LIN, LOUT)
Input Voltage Range
0
Input Threshold Low
LIN, VL = +2.5V, TA = +25°C
Input Threshold High
LIN, VL = +2.5V, TA = +25°C
0.6
VCC
1.1
1.7
Input Hysteresis
V
V
2
V
40
kΩ
0.6
V
Input Resistance
TA = +25oC
Output Voltage Low
LOUT, ISINK = 1.6mA
0.4
V
Output Leakage Current
LOUT = VL, LIN = low or float
±10
µA
VCC
V
20
SWITCH (SWIN, SWOUT)
Input Voltage Range
0
On-Resistance
62
SHDN = 0
Off-Leakage Current
100
Ω
±1
µA
Turn-On Time
0.18
µs
Turn-Off Time
0.7
µs
ESD PROTECTION
R_IN, T_OUT, LIN, SWIN
ESD Protection
Human Body Model
±15
IEC 1000-4-2 Air-Gap Discharge method
±15
IEC 1000-4-2 Contact Discharge method
±8
kV
TIMING CHARACTERISTICS
(VCC = VL = +2.35V to +3.0V, C1–C4 = 0.1µF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = VL = +2.5V,
TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
RL = 3kΩ, CL = 1000pF,
one transmitter switching
MIN
TYP
MAX
250
Maximum Data Rate
Receiver Propagation Delay
UNITS
kbps
tPHL - tPLH
RL = 3kΩ, CL = 150pF,
one transmitter switching (Note 2)
tPHL
Receiver input to receiver output,
CL = 150pF
tPLH
460
0.15
µs
0.15
Receiver Output Enable Time
200
ns
Receiver Output Disable Time
200
ns
Time to Exit Shutdown
Transmitter Skew
Receiver Skew
Transition-Region Slew
Rate
VT_OUT > 3.7V
tPHL - tPLH RL = 3kΩ, CL = 1000pF (Note 3)
tPHL - tPLH
VCC = +2.5V, TA = +25°C, CL = 150pF to
RL = 3kΩ to 7kΩ,
1000pF
measured from +3V
CL = 150pF to
to -3V or -3V to +3V,
2500pF
one transmitter switching
6
30
µs
100
ns
50
ns
30
V/µs
4
30
Note 2: Guaranteed by correlation.
Note 3: Transmitter skew is measured at the transmitter zero crosspoint.
_______________________________________________________________________________________
3
MAX3388E/MAX3389E
DC ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(VCC = VL = +2.5V, TA = +25°C, unless otherwise noted.)
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCE
SLEW RATE vs. LOAD CAPACITANCE
MAX3386E toc02
MAX3388E toc01
16
14
2.5
12
SLEW RATE (V/µs)
OUTPUT VOLTAGE (V)
5.0
DATA RATE = 460kbps
LOAD = 3kΩ IN PARALLEL
0
-2.5
SLEW RATE 10
SLEW RATE +
8
6
4
2
-5.0
0
1000
2000
3000
4000
5000
0
2000
3000
4000
LOAD CAPACITANCE (pF)
TRANSMITTER OUTPUT VOLTAGE
vs. DATA RATE
SUPPLY CURRENT
vs. LOAD CAPACITANCE
60
MAX3388E toc03
5.0
LOAD = 3kΩ, 1000pF
ONE TRANSMITTER SWITCHING
AT DATA RATE, OTHER
TRANSMITTERS AT 1/8
DATA RATE
LOAD = 3kΩ
ONE TRANSMITTER SWITCHING
AT DATA RATE, OTHER
TRANSMITTERS AT 1/8
DATA RATE
50
SUPPLY CURRENT (mA)
2.5
0
1000
LOAD CAPACITANCE (pF)
40
5000
MAX3388E toc04
0
OUTPUT VOLTAGE (V)
460kbps
30
240kbps
20
-2.5
20kbps
10
0
-5.0
50 100 150 200 250 300 350 400 450
0
1000
2000
3000
4000
DATA RATE (kbps)
LOAD CAPACITANCE (pF)
LIN TO LOUT tPD
ON-RESISTANCE
vs. SWIN VOLTAGE
LIN
70
5000
MAX3388E toc06
0
MAX3388E toc05
TA = +85°C
65
TA = +25°C
RON (Ω)
MAX3388E/MAX3389E
2.5V, ±15kV ESD-Protected RS-232
Transceivers for PDAs and Cell Phones
1V/div
60
55
TA = -40°C
50
LOUT
RPULLUP = 1kΩ
45
200ns/div
0
0.5
1.0
1.5
2.0
2.5
VSWIN (V)
4
_______________________________________________________________________________________
2.5V, ±15kV ESD-Protected RS-232
Transceivers for PDAs and Cell Phones
PIN
NAME
1
C1+
2
V+
+4.2V 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
6
V-
7, 8, 9
T1IN,
T2IN, T3IN
FUNCTION
Positive Terminal of the Voltage-Doubler Charge-Pump Capacitor
-4.2V Supply Generated by the Charge Pump
CMOS Transmitter Inputs
10
LOUT
11
SWOUT
Switch Output
12, 13
R2OUT,
R1OUT
CMOS Receiver Outputs. Swing between 0 and VL.
14
VL
15
SWIN
Handshaking Output. This output is active during shutdown for the MAX3389E.
Logic-Level Supply. All CMOS inputs and outputs are referred to this supply. VL = +1.8V to +3.0V.
Switch Input.
16
LIN
17, 18
R2IN,
R1IN
Handshaking Input. This input is active during shutdown for the MAX3389E.
19, 20, 21
T3OUT,
T2OUT,
T1OUT
22
GND
Ground
23
VCC
+2.35V to +3V Supply Voltage
24
SHDN
RS-232 Receiver Inputs
RS-232 Transmitter Outputs
Shutdown Input. 0 = shutdown, switch open; 1 = normal operation, switch closed.
_______________________________________________________________________________________
5
MAX3388E/MAX3389E
Pin Description
MAX3388E/MAX3389E
2.5V, ±15kV ESD-Protected RS-232
Transceivers for PDAs and Cell Phones
Table 1. Shutdown Logic Truth Table
SHDN
TRANSMITTER
OUTPUTS
RECEIVER
OUTPUTS
CHARGE
PUMP
SWITCH
L
High-Z
High-Z
Inactive
H
Active
Active
Active
POWERMANAGEMENT
UNIT OR
KEYBOARD
CONTROLLER
LOUT
MAX3389E
Open
MAX3388E
High-Z
Closed
LIN
LIN
LIN
5V/div
SHDN
T1
I/O CHIP
POWER SUPPLY
VL
2V/div
MAX3388E
MAX3389E
T2
VCC = +2.5V
C1–C4 = 0.1µF
CL = 1000pF, RL = 3kΩ
I/O
CHIP
WITH
UART
RS-232
CPU
Figure 2. Transmitter Outputs when Exiting Shutdown
Figure 1. Interface Under Control of PMU
Detailed Description
Dual Charge-Pump
Voltage Converter
The MAX3388E/MAX3389E’s internal power supply
consists of a regulated dual charge pump that provides
output voltages of +4.2V (doubling charge pump) and 4.2V (inverting charge pump), regardless of the input
voltage (VCC) over a +2.5V to +3.0V range. The charge
pumps operate in a discontinuous mode: if the output
voltages are less than 4.2V, the charge pumps are
enabled; if the output voltages exceed 4.2V, the charge
pumps are disabled. Each charge pump requires flying
capacitors (C1, C2) and reservoir capacitors (C3, C4)
to generate the V+ and V- supplies.
RS-232 Transmitters
The transmitters are inverting level translators that convert
CMOS-logic levels to ±3.7V EIA/TIA-232-compatible
levels.
6
10µs/div
The MAX3388E/MAX3389E’s transmitters guarantee a
250kbps data rate with loads of 3kΩ in parallel with
1000pF and 460kbps data rate with loads of 3kΩ in parallel with 150pF. Figure 1 shows a complete system connection.
These RS-232 output stages are turned off (high
impedance) when the devices are in shutdown mode.
When the power is off, the MAX3388E/MAX3389E permit
the outputs to be driven up to ±12V.
The transmitter inputs do not have pullup resistors.
Connect unused inputs to GND or VL.
RS-232 Receivers
The receivers convert RS-232 signals to CMOS-logic
output levels. The MAX3388E/MAX3389E’s receivers
have inverting outputs. The outputs are high impedance in shutdown.
Shutdown Mode
Supply current falls to less than 1µA when the
MAX3388E/MAX3389E are placed in shutdown mode
(SHDN logic low). When shut down, the device’s charge
pumps are turned off, V+ decays to VCC, V- is pulled to
ground, the switch is opened, and the transmitter outputs
are disabled (high impedance). The time required to exit
_______________________________________________________________________________________
2.5V, ±15kV ESD-Protected RS-232
Transceivers for PDAs and Cell Phones
VL Logic Supply Input
Unlike other RS-232 interface devices where the receiver
outputs swing between 0 and V CC, the MAX3388E/
MAX3389E feature a separate logic supply input (VL)
that sets VOH for the receiver outputs and sets thresholds for the transmitter 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.
RC
1MΩ
RD
1500Ω
CHARGE-CURRENT
LIMIT RESISTOR
DISCHARGE
RESISTANCE
HIGHVOLTAGE
DC
SOURCE
Cs
100pF
MAX3388E/MAX3389E
shutdown is typically 30µs, as shown in Figure 2.
Connect SHDN to VCC if the shutdown mode is not used.
In shutdown mode, the receiver outputs are high impedance (Table 1).
DEVICE
UNDER
TEST
STORAGE
CAPACITOR
Figure 3a. Human Body ESD Test Model
±15kV ESD Protection
As with all Maxim devices, ESD-protection structures are
incorporated on all pins to protect against ESDs encountered during handling and assembly. The MAX3388E/
MAX3389E’s driver outputs, receiver inputs, the handshaking input LIN, and the switch terminal SWIN have
extra protection against static electricity. Maxim has
developed state-of-the-art structures to protect these pins
against an 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 RS-232 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 Discharge
method
ESD Test Conditions
ESD performance depends on a variety of conditions.
Contact Maxim for a reliability report that documents
test setup, methodology, and results.
Human Body Model
Figure 3a shows the Human Body Model, and Figure 3b
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.
IP 100%
90%
Ir
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
AMPERES
36.8%
10%
0
0
tRL
TIME
tDL
CURRENT WAVEFORM
Figure 3b. Human Body Current Waveform
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 MAX3388E/MAX3389E helps you
design equipment that meets Level 4 (the highest level)
of IEC 1000-4-2, without the need for additional ESDprotection 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 4a shows the IEC 1000-4-2 model, and
Figure 4b shows the current waveform for the ±8kV IEC
1000-4-2 Level 4 ESD Contact Discharge test.
_______________________________________________________________________________________
7
RC
50MΩ to 100MΩ
RD
330Ω
CHARGE-CURRENT
LIMIT RESISTOR
DISCHARGE
RESISTANCE
HIGHVOLTAGE
DC
SOURCE
Cs
150pF
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.
DEVICE
UNDER
TEST
STORAGE
CAPACITOR
__________Applications Information
Figure 4a. IEC 1000-4-2 ESD Test Model
Capacitor Selection
I
100%
90%
I PEAK
MAX3388E/MAX3389E
2.5V, ±15kV ESD-Protected RS-232
Transceivers for PDAs and Cell Phones
10%
t R = 0.7ns to 1ns
t
30ns
60ns
Power-Supply Decoupling
Figure 4b. IEC 1000-4-2 ESD Generator Current Waveform
Table 2. Minimum Required Capacitor
Values
8
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 2.5V operation (Table 2). 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-.
VCC
(V)
C1–C4
(µF)
2.5 to 3.0
0.1
In most circumstances, a 0.1µF bypass capacitor is
adequate. In applications that are sensitive to powersupply 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 when
Exiting Shutdown
Figure 2 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
1000pF. 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 2.5V.
_______________________________________________________________________________________
2.5V, ±15kV ESD-Protected RS-232
Transceivers for PDAs and Cell Phones
VCC
0.1µF
VCC
C1+
C1
C1-
Power Switch
The MAX3388E/MAX3389E contain an internal switch
for powering external circuitry. This can be used to
power hot-sync circuitry or other low-power circuitry.
The switch on- resistance is typically 62Ω. The SWIN
side of the switch is ESD protected to ±15kV.
MAX3388E/MAX3389E
High Data Rates
The MAX3388E/MAX3389E maintain RS-232-compatible
transmitter output voltages even at high data rates. Figure
5 shows a transmitter loopback test circuit. Figure 6 shows
a loopback test result at 250kbps, and Figure 7 shows the
same test at 460kbps. For Figure 6, all transmitters were
driven simultaneously at 250kbps into RS-232 loads in
parallel with 1000pF. For Figure 7, a single transmitter was
driven at 460kbps, and all transmitters were loaded with
an RS-232 receiver in parallel with 150pF.
V+
C3
MAX3388E
MAX3389E
C2+
VC4
C2
C2-
T_ OUT
T_ IN
Logic-Level I/O
In addition to the traditional RS-232 I/O, the
MAX3388E/MAX3389E have a logic-level transceiver
from the RS-232 connector side to the CMOS-logic
side. The input impedance is typically 30kΩ, and the
output is open drain. The logic level I/O is active during
shutdown for the MAX3389E.
This I/O transceiver is useful for hot syncing or other
dedicated communication capability. The input is ESD
protected to ±15kV.
R_ IN
R_ OUT
5kΩ
VCC
SHDN
CL
GND
Typical PDA/Cell-Phone Application
The MAX3388E/MAX3389E 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 (RI) signal to alert
the UART on the PC. Without the ring indicator transmitter, solutions for these applications would require software-intensive polling of the cradle inputs.
The RI signal is generated when a PDA, cellular phone, or
other “cradled” device is plugged into its cradle. This
generates a logic-low signal to RI transmitter input, creating +3.7V 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 RS-232 full-duplex communication between the PDA and the PC.
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 generate a regulated output voltage of +2.35V to +3V from the phone connector.
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 MAX3388E/MAX3389E come with a logic powersupply pin (VL) that limits the logic levels presented to
Figure 5. Loopback Test Circuit
T1IN
2V/div
T1OUT
5V/div
R1OUT
5V/div
CL = 1000pF
1µs/div
Figure 6. Loopback Test Results at 250kbps
_______________________________________________________________________________________
9
MAX3388E/MAX3389E
2.5V, ±15kV ESD-Protected RS-232
Transceivers for PDAs and Cell Phones
T1IN
2V/div
T1OUT
5V/div
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 devices
will work with VL as low as 1.8V. This is useful with cell
phones and other power-efficient devices with core
logic voltage levels that go as low as 1.8V.
Chip Information
TRANSISTOR COUNT: 1323
R1OUT
5V/div
CL = 150pF
1µs/div
Figure 7. Loopback Test Results at 460kbps
10
______________________________________________________________________________________
2.5V, ±15kV ESD-Protected RS-232
Transceivers for PDAs and Cell Phones
TSSOP.EPS
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________11
© 2001 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
MAX3388E/MAX3389E
Package Information
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