19-1437; Rev 1; 10/99
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
____________________________Features
♦ ESD Protection for RS-232 I/O Pins
±15kV—Human Body Model
±8kV—IEC 1000-4-2, Contact Discharge
±15kV—IEC 1000-4-2, Air-Gap Discharge
♦ Latchup Free
♦ 300µA Supply Current
♦ 1µA Low-Power Shutdown with Receivers Active
♦ 250kbps Guaranteed Data Rate
♦ 250µs Time to Exit Shutdown with 3kΩ Load on V+
♦ 6V/µs Guaranteed Slew Rate
♦ Meets EIA/TIA-232 Specifications Down to 3.0V
Ordering Information
PART
TEMP. RANGE
MAX3385ECAP
0°C to +70°C
20 SSOP
MAX3385ECWN
0°C to +70°C
18 SO
MAX3385EEAP
PIN-PACKAGE
-40°C to +85°C
20 SSOP
Typical Operating Circuit
+3.3V
________________________Applications
Hand-Held Equipment
Peripherals
Printers
Battery-Powered
Equipment
CBYPASS
C1
0.1µF
C1+
VCC
V+
C1-
MAX3385E
Pin Configurations
C2
0.1µF
C2+
V-
C2-
N.C. 1
20 SHDN
C1+ 2
19 VCC
V+ 3
18 GND
RS-232
OUTPUTS
TTL/CMOS
INPUTS
T2IN
T2OUT
17 T1OUT
C1- 4
C2- 6
C4
0.1µF
T1OUT
T1IN
TOP VIEW
C2+ 5
C3*
0.1µF
MAX3385E
R1OUT
R1IN
16 R1IN
15 R1OUT
V- 7
14 T1IN
T2OUT 8
13 T2IN
R2IN 9
12 R2OUT
N.C. 10
11 N.C.
TTL/CMOS
OUTPUTS
5k
R2OUT
5k
GND
SSOP
Pin Configurations continued at end of data sheet.
RS-232
INPUTS
R2IN
SHDN
* C3 CAN BE RETURNED TO EITHER VCC OR GROUND.
NOTE: SEE TABLE 2 FOR CAPACITOR SELECTION
†Cg.
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
MAX3385E †
________________General Description
The MAX3385E is a 3V-powered EIA/TIA-232 and
V.28/V.24 communications interface with low power
requirements, high data-rate capabilities, and enhanced electrostatic discharge (ESD) protection. All
transmitter outputs and receiver inputs are protected to
±15kV using IEC 1000-4-2 Air-Gap Discharge, ±8kV
using IEC 1000-4-2 Contact Discharge, and ±15kV
using the Human Body Model.
The transceiver has a proprietary low-dropout transmitter output stage, delivering 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. Each device is
guaranteed to run at data rates of 250kbps while maintaining RS-232 output levels.
The MAX3385E has two receivers and two drivers. It
features a 1µA shutdown mode that reduces power consumption and extends battery life in portable systems.
Its receivers can remain active in shutdown mode,
allowing external devices such as modems to be monitored using only 1µA supply current.
The MAX3385E is available in a space-saving SSOP
package in either the commercial (0°C to +70°C) or
extended-industrial (-40°C to +85°C) temperature range.
MAX3385E
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
ABSOLUTE MAXIMUM RATINGS
VCC to GND ..............................................................-0.3V to +6V
V+ to GND (Note 1) ..................................................-0.3V to +7V
V- to GND (Note 1) ...................................................+0.3V to -7V
V+ + |V-| (Note 1) .................................................................+13V
Input Voltages
T_IN, SHDN to GND ..............................................-0.3V to +6V
R_IN to GND .....................................................................±25V
Output Voltages
T_OUT to GND...............................................................±13.2V
R_OUT .....................................................-0.3V to (VCC + 0.3V)
Short-Circuit Duration, T_OUT to GND.......................Continuous
Continuous Power Dissipation (TA = +70°C)
20-Pin SSOP (derate 8.00mW/°C above +70°C) ..........640mW
18-Pin SO (derate 9.52mW/°C above +70°C)...............762mW
Operating Temperature Ranges
MAX3385ECAP ....................................................0°C to +70°C
MAX3385ECWN ...................................................0°C to +70°C
MAX3385EEAP .................................................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10sec) .............................+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.
ELECTRICAL CHARACTERISTICS
(VCC = +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 TA = +25°C.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
0.3
1
mA
1
10
µA
0.8
V
DC CHARACTERISTICS (VCC = +3.3V or +5V, TA = +25°C)
Supply Current
SHDN = VCC, no load
Shutdown Supply Current
SHDN = GND
LOGIC INPUTS
Input Logic Threshold Low
Input Logic Threshold High
T_IN, SHDN
T_IN, SHDN
VCC = 3.3V
2.0
VCC = 5.0V
2.4
Transmitter Input Hysteresis
V
0.5
V
T_IN, SHDN
±0.01
±1
µA
Output Leakage Current
R_OUT, receivers disabled
±0.05
±10
µA
Output Voltage Low
IOUT = 1.6mA
0.4
V
Input Leakage Current
RECEIVER OUTPUTS
Output Voltage High
VCC 0.6
IOUT = -1.0mA
VCC 0.1
V
RECEIVER INPUTS
Input Voltage Range
-25
Input Threshold Low
TA = +25°C
Input Threshold High
TA = +25°C
0.6
1.2
VCC = 5.0V
0.8
1.5
1.5
2.4
VCC = 5.0V
1.8
2.4
2
0.5
TA = +25°C
3
5
_______________________________________________________________________________________
V
V
VCC = 3.3V
Input Hysteresis
Input Resistance
+25
VCC = 3.3V
V
V
7
kΩ
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
(VCC = +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 TA = +25°C.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
TRANSMITTER OUTPUTS
Output Voltage Swing
All transmitter outputs loaded with 3kΩ to ground
±5
±5.4
V
Output Resistance
VCC = V+ = V- = 0, transmitter output = ±2V
300
10M
Ω
Output Short-Circuit Current
Output Leakage Current
VCC = 0 or 3V to 5.5V, VOUT = ±12V, transmitters disabled
±60
mA
±25
µA
ESD PROTECTION
R_IN, T_OUT
Human Body Model
±15
IEC1000-4-2 Air Discharge
±15
IEC1000-4-2 Contact Discharge
±8
kV
TIMING CHARACTERISTICS
(VCC = +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 TA = +25°C.)
PARAMETER
SYMBOL
RL = 3kΩ, CL = 1000pF,
one transmitter switching
Maximum Data Rate
Receiver Propagation Delay
tPHL
tPLH
Time to Exit Shutdown
Transmitter Skew
tPHL - tPLH
Receiver Skew
tPHL - tPLH
Transition-Region Slew Rate
CONDITIONS
MIN
TYP
MAX
250
UNITS
kbps
Receiver input to receiver output,
CL = 150pF
0.15
VOUT ≥ +3.7V, RLOAD at V+ = 3kΩ
250
µs
(Note 2)
100
ns
50
ns
VCC = 3.3V,
TA = +25°C,
RL = 3kΩ to 7kΩ,
measured from +3V
to -3V or -3V to +3V
µs
0.15
CL = 150pF to
1000pF
6
30
CL = 150pF to
2500pF
4
30
V/µs
Note 2: Transmitter skew is measured at the transmitter zero cross points.
_______________________________________________________________________________________
3
MAX3385E
ELECTRICAL CHARACTERISTICS (continued)
__________________________________________Typical Operating Characteristics
(VCC = +3.3V, 250kbps data rate, 0.1µF capacitors, all transmitters loaded with 3kΩ and CL, TA = +25°C, unless otherwise noted.)
14
-SLEW
12
SLEW RATE (V/µs)
T1 TRANSMITTING AT 250kbps
T2 TRANSMITTING AT 15.6kbps
2
1
0
-1
-2
-3
-4
-5
-6
16
10
+SLEW
8
6
4
VOUT-
45
MAX3885E-02
VOUT+
2000
3000
4000
5000
120kbps
25
20
20kbps
15
0
0
LOAD CAPACITANCE (pF)
250kbps
30
5
FOR DATA RATES UP TO 250kbps
1000
35
10
2
0
0
T1 TRANSMITTING AT 250kbps
T2 TRANSMITTING AT 15.6kbps
40
SUPPLY CURRENT (mA)
5
4
3
MAX3385E-01
6
OPERATING SUPPLY CURRENT
vs. LOAD CAPACITANCE
SLEW RATE vs. LOAD CAPACITANCE
MAX3885E-03
TRANSMITTER OUTPUT VOLTAGE
vs. LOAD CAPACITANCE
TRANSMITTER OUTPUT VOLTAGE (V)
MAX3385E
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
1000
2000
3000
4000
5000
0
LOAD CAPACITANCE (pF)
1000
2000
3000
4000
5000
LOAD CAPACITANCE (pF)
______________________________________________________________ Pin Description
PIN
4
PIN
NAME
FUNCTION
SO
SSOP
1
1, 10, 11
N.C.
No Connection. Not internally connected.
2
2
C1+
Positive terminal of the voltage-doubler charge-pump capacitor.
3
3
V+
+5.5V generated by the charge pump.
4
4
C1-
Negative terminal of the voltage-doubler charge-pump capacitor.
5
5
C2+
Positive terminal of inverting charge-pump capacitor.
6
6
C2-
Negative terminal of inverting charge-pump capacitor.
7
7
V-
8, 15
8, 17
T_OUT
9, 14
9, 16
R_IN
10, 13
12, 15
R_OUT
TTL/CMOS Receiver Outputs
11, 12
13, 14
T_IN
TTL/CMOS Transmitter Inputs
16
18
GND
Ground
17
19
VCC
+3.0V to +5.5V Supply Voltage
18
20
SHDN
-5.5V generated by the charge pump.
RS-232 Transmitter Outputs
RS-232 Receiver Inputs
Active-Low Shutdown-Control Input. Drive low to shut down transmitters and charge
_______________________________________________________________________________________
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
VCC
0.1µF
C1+
0.1µF
VCC
C1+
V+
C1
C3
C1C2+
3k
VCC
C2+
3k
C3
C1-
V-
MAX3385E
V-
C2
C4
C4
C2-
C2T_ OUT
T_ IN
T_ OUT
T_ IN
R_ IN
R_ OUT
R_ IN
R_ OUT
5k
SHDN
V+
C1
MAX3385E
C2
VCC
MAX3385E
VCC
5k
3k
GND
2500pF
VCC
SHDN
MINIMUM SLEW-RATE TEST CIRCUIT
GND
150pF
7k
MAXIMUM SLEW-RATE TEST CIRCUIT
Figure 1. Slew-Rate Test Circuits
_______________Detailed Description
Dual Charge-Pump Voltage Converter
The MAX3385E’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), over the 3.0V to 5.5V VCC
range. The charge pump operates in discontinuous
mode; if the output voltages are less than 5.5V, the
charge pump is enabled, and if the output voltages
exceed 5.5V, the charge pump is disabled. Each
charge pump requires a flying capacitor (C1, C2) and a
reservoir capacitor (C3, C4) to generate the V+ and Vsupplies (Figure 1).
RS-232 Transmitters
The transmitters are inverting level translators that convert CMOS-logic levels to ±5.0V EIA/TIA-232 levels.
The MAX3385E 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.
Laplink is a trademark of Traveling Software.
The MAX3385E’s transmitters are disabled and the outputs are forced into a high-impedance state when the
device is in shutdown (SHDN = GND). The MAX3385E
permits the outputs to be driven up to ±12V in shutdown.
The transmitter inputs do not have pull-up resistors.
Connect unused inputs to GND or VCC.
RS-232 Receivers
The receivers convert RS-232 signals to CMOS-logic
output levels (Table 1).
Shutdown Mode
Supply current falls to less than 1µA in shutdown mode
(SHDN = low). When shut down, the device’s charge
pumps are shut off, V+ is pulled down to VCC, V- is
pulled to ground, and the transmitter outputs are disabled (high impedance). The time required to exit shut-
Table 1. Shutdown Truth Table
SHDN
T_OUT
R_OUT
0
High-Z
Active
1
Active
Active
_______________________________________________________________________________________
5
MAX3385E
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
5V/div
0
SHDN
T2OUT
2V/div
0
T1OUT
VCC = 3.3V
C1–C4 = 0.1µF
40µs/div
Figure 2. Transmitter Outputs Exiting Shutdown or
Powering Up
down is typically 100µs, as shown in Figure 2. Connect
SHDN to VCC if the shutdown mode is not used.
±15kV ESD Protection
As with all Maxim devices, ESD-protection structures
are incorporated on all pins to protect against electrostatic discharges encountered during handling and
assembly. The driver outputs and receiver inputs of the
MAX3385E have extra protection against static electricity. Maxim’s engineers have 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” versions 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 method.
ESD Test Conditions
ESD performance depends on a variety of conditions.
Contact Maxim for a reliability report that documents
test setup, test methodology, and test results.
Human Body Model
Figure 3a shows the Human Body Model, and Figure
3b shows the current waveform it generates when dis6
charged 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.
IEC 1000-4-2
The IEC 1000-4-2 standard covers ESD testing and performance of finished equipment; it does not specifically
refer to integrated circuits. The MAX3385E 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 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.
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. Of course, 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 capacitors for 3.3V operation. For other supply voltages, refer
to Table 2 for required capacitor values. Do not use val-
Table 2. Required Minimum Capacitance
Values
VCC
(V)
C1, CBYPASS
(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
0.1
0.47
_______________________________________________________________________________________
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
RD
1500Ω
CHARGE-CURRENT
LIMIT RESISTOR
HIGHVOLTAGE
DC
SOURCE
MAX3385E
RC
1M
Cs
100pF
IP 100%
90%
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
DEVICE
UNDER
TEST
Ir
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
AMPERES
36.8%
10%
0
0
Figure 3a. Human Body ESD Test Model
TIME
tRL
tDL
CURRENT WAVEFORM
Figure 3b. Human Body Model Current Waveform
I
100%
CHARGE-CURRENT
LIMIT RESISTOR
HIGHVOLTAGE
DC
SOURCE
Cs
150pF
90%
RD
330Ω
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
I PEAK
RC
50M to 100M
DEVICE
UNDER
TEST
10%
t r = 0.7ns to 1ns
t
30ns
60ns
Figure 4a. IEC 1000-4-2 ESD Test Model
Figure 4b. IEC 10000-4-2 ESD Generator Current Waveform
ues 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, C4,
and CBYPASS to maintain the proper ratios (C1 to
the other capacitors).
In most circumstances, a 0.1µF VCC bypass capacitor
is adequate. In applications that are sensitive to powersupply noise, use a capacitor of the same value as
charge-pump capacitor C1. Connect bypass capacitors as close to the IC as possible.
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-.
Power-Supply Decoupling
Operation Down to 2.7V
Transmitter outputs will meet EIA/TIA-562 levels of
±3.7V with supply voltages as low as 2.7V.
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 lev-
_______________________________________________________________________________________
7
MAX3385E
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
els (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.
Figure 8 shows the same test at 250kbps. For Figure 7,
all transmitters were driven simultaneously at 120kbps
into RS-232 loads in parallel with 1000pF. For Figure 8,
a single transmitter was driven at 250kbps, and all
transmitters were loaded with an RS-232 receiver in
parallel with 1000pF.
High Data Rates
Interconnection with 3V and 5V Logic
The MAX3385E maintains the RS-232 ±5.0V minimum
transmitter output voltage even at high data rates.
Figure 6 shows a transmitter loopback test circuit.
Figure 7 shows a loopback test result at 120kbps, and
The MAX3385E can directly interface with various 5V
logic families, including ACT and HCT CMOS. See
Table 3 for more information on possible combinations
of interconnections.
VCC
0.1µF
5V/div
T1IN
VCC
C1+
V+
C3
C1
C1C2+
5V/div
MAX3385E
T1OUT
VC4
C2
C2-
R1OUT
T_ OUT
T_ IN
5V/div
VCC = 3.3V
C1–C4 = 0.1µF
2µs/div
R_ IN
R_ OUT
Figure 7. MAX3385E Loopback Test Result at 120kbps
5k
VCC
SHDN
1000pF
GND
T1IN
5V/div
T1OUT
5V/div
Figure 6. Loopback Test Circuit
R1OUT
5V/div
VCC = 3.3V
C1–C4 = 0.1µF
2µs/div
Figure 8. MAX3385E Loopback Test Result at 250kbps
8
_______________________________________________________________________________________
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
TOP VIEW
SYSTEM
POWER-SUPPLY
VOLTAGE
(V)
VCC SUPPLY
VOLTAGE
(V)
3.3
3.3
5
5
Pin Configurations (continued)
COMPATIBILITY
Compatible with all
CMOS families
5
Compatible with all TTL
and CMOS families
3.3
Compatible with ACT
and HCT CMOS, and
with AC, HC, or
CD4000 CMOS
N.C. 1
18 SHDN
C1+ 2
17 VCC
V+ 3
16 GND
15 T1OUT
C1- 4
C2+ 5
MAX3385E
14 R1IN
13 R1OUT
C2- 6
V- 7
12 T1IN
T2OUT 8
11 T2IN
10 R2OUT
R2IN 9
SO
___________________Chip Information
TRANSISTOR COUNT: 1129
_______________________________________________________________________________________
9
MAX3385E
Table 3. Logic-Family Compatibility with
Various Supply Voltages
________________________________________________________Package Information
SSOP.EPS
MAX3385E
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
10
______________________________________________________________________________________
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
SOICW.EPS
______________________________________________________________________________________
11
MAX3385E
Package Information (continued)
MAX3385E
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
NOTES
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.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 1999 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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