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19-1437; Rev 0; 3/99

±15kV ESD-Protected, 3.0V to 5.5V, Low-Power, up to 250kbps, True RS-232 Transceiver
________________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.

____________________________Features
o 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 o Latchup Free o 300µA Supply Current o 1µA Low-Power Shutdown with Receivers Active o 250kbps Guaranteed Data Rate o 250µs Time to Exit Shutdown with 3k Load on V+ o 6V/µs Guaranteed Slew Rate o Meets EIA/TIA-232 Specifications Down to 3.0V

MAX3385E

Ordering Information
PART MAX3385ECAP MAX3385EEAP TEMP. RANGE 0°C to +70°C -40°C to +85°C PIN-PACKAGE 20 SSOP 20 SSOP

Typical Operating Circuit
+3.3V CBYPASS C1 0.1µF 2 C1+ 4 5 C119 VCC V+ 3 C3* 0.1µF 7 C4 0.1µF

________________________Applications
Hand-Held Equipment Peripherals Printers Battery-Powered Equipment

MAX3385E
C2+ C2V-

Pin Configuration
TOP VIEW
N.C. 1 C1+ 2 V+ 3 C1- 4 C2+ 5 C2- 6 V- 7 T2OUT 8 R2IN 9 N.C. 10 20 SHDN 19 VCC 18 GND 17 T1OUT

C2 0.1µF

6

14 T1IN TTL/CMOS INPUTS 13 T2IN

T1OUT 17 RS-232 OUTPUTS T2OUT 8

15 R1OUT TTL/CMOS OUTPUTS 12 R2OUT

R1IN 16 5k R2IN 9 5k GND 18 SHDN 20 RS-232 INPUTS

MAX3385E

16 R1IN 15 R1OUT 14 T1IN 13 T2IN 12 R2OUT 11 N.C.

* C3 CAN BE RETURNED TO EITHER VCC OR GROUND.
SSOP
NOTE: SEE TABLE 2 FOR CAPACITOR SELECTION

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; and other patents pending.

________________________________________________________________ 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.

±15kV ESD-Protected, 3.0V to 5.5V, Low-Power, up to 250kbps, True RS-232 Transceiver MAX3385E
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) SSOP (derate 8.00mW/°C above +70°C) .....................640mW Operating Temperature Ranges MAX3385ECAP ....................................................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, C1­C4 = 0.1µF, tested at 3.3V ±10%; C1 = 0.047µF, C2­C4 = 0.33µF, tested at 5.0V ±10%; TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Supply Current Shutdown Supply Current LOGIC INPUTS Input Logic Threshold Low Input Logic Threshold High Transmitter Input Hysteresis Input Leakage Current RECEIVER OUTPUTS Output Leakage Current Output Voltage Low Output Voltage High RECEIVER INPUTS Input Voltage Range Input Threshold Low Input Threshold High Input Hysteresis Input Resistance 2 TA = +25°C 3 TA = +25°C TA = +25°C VCC = 3.3V VCC = 5.0V VCC = 3.3V VCC = 5.0V -25 0.6 0.8 1.2 1.5 1.5 1.8 0.5 5 7 2.4 2.4 +25 V V V V k R_OUT, receivers disabled IOUT = 1.6mA IOUT = -1.0mA VCC 0.6 VCC 0.1 ±0.05 ±10 0.4 µA V V T_IN, SHDN T_IN, SHDN T_IN, SHDN VCC = 3.3V VCC = 5.0V 2.0 2.4 0.5 ±0.01 ±1 0.8 V V V µA SHDN = VCC, no load SHDN = GND CONDITIONS MIN TYP 0.3 1 MAX 1 10 UNITS mA µA DC CHARACTERISTICS (VCC = +3.3V or +5V, TA = +25°C)

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±15kV ESD-Protected, 3.0V to 5.5V, Low-Power, up to 250kbps, True RS-232 Transceiver
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3V to +5.5V, C1­C4 = 0.1µF, tested at 3.3V ±10%; C1 = 0.047µF, C2­C4 = 0.33µF, tested at 5.0V ±10%; TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER TRANSMITTER OUTPUTS Output Voltage Swing Output Resistance Output Short-Circuit Current Output Leakage Current ESD PROTECTION Human Body Model R_IN, T_OUT IEC1000-4-2 Air Discharge IEC1000-4-2 Contact Discharge ±15 ±15 ±8 kV VCC = 0 or 3V to 5.5V, VOUT = ±12V, transmitters disabled All transmitter outputs loaded with 3k to ground VCC = V+ = V- = 0, transmitter output = ±2V ±5 300 ±5.4 10M ±60 ±25 V mA µA CONDITIONS MIN TYP MAX UNITS

MAX3385E

TIMING CHARACTERISTICS
(VCC = +3V to +5.5V, C1­C4 = 0.1µF, tested at 3.3V ±10%; C1 = 0.047µF, C2­C4 = 0.33µF, tested at 5.0V ±10%; TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Maximum Data Rate Receiver Propagation Delay Time to Exit Shutdown Transmitter Skew Receiver Skew tPHL - tPLH tPHL - tPLH VCC = 3.3V, TA = +25°C, RL = 3k to 7k, measured from +3V to -3V or -3V to +3V CL = 150pF to 1000pF CL = 150pF to 2500pF 6 4 tPHL tPLH SYMBOL CONDITIONS RL = 3k, CL = 1000pF, one transmitter switching Receiver input to receiver output, CL = 150pF VOUT +3.7V, RLOAD at V+ = 3k (Note 2) MIN 250 0.15 0.15 250 100 50 30 V/µs 30 TYP MAX UNITS kbps µs µs ns ns

Transition-Region Slew Rate

Note 2: Transmitter skew is measured at the transmitter zero cross points.

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±15kV ESD-Protected, 3.0V to 5.5V, Low-Power, up to 250kbps, True RS-232 Transceiver MAX3385E
__________________________________________Typical Operating Characteristics
(VCC = +3.3V, 250kbps data rate, 0.1µF capacitors, all transmitters loaded with 3k and CL, TA = +25°C, unless otherwise noted.)

TRANSMITTER OUTPUT VOLTAGE vs. LOAD CAPACITANCE
MAX3385E-01

SLEW RATE vs. LOAD CAPACITANCE
MAX3885E-02

OPERATING SUPPLY CURRENT vs. LOAD CAPACITANCE
40 SUPPLY CURRENT (mA) 35 250kbps 30 25 20 15 10 20kbps 120kbps T1 TRANSMITTING AT 250kbps T2 TRANSMITTING AT 15.6kbps
MAX3885E-03

6 TRANSMITTER OUTPUT VOLTAGE (V) 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 0 VOUT+ T1 TRANSMITTING AT 250kbps T2 TRANSMITTING AT 15.6kbps

16 14 12 SLEW RATE (V/µs) 10 8 6 4 +SLEW -SLEW

45

VOUT-

2 FOR DATA RATES UP TO 250kbps 0

5 0 4000 5000 0 1000 2000 3000 4000 5000

1000

2000

3000

4000

5000

0

1000

2000

3000

LOAD CAPACITANCE (pF)

LOAD CAPACITANCE (pF)

LOAD CAPACITANCE (pF)

______________________________________________________________ Pin Description
PIN 2 3 4 5 6 7 8, 17 9, 16 12, 15 13, 14 18 19 20 1, 10, 11 4 NAME C1+ V+ C1C2+ C2VT_OUT R_IN R_OUT T_IN GND VCC SHDN N.C. FUNCTION Positive terminal of the voltage-doubler charge-pump capacitor. +5.5V generated by the charge pump. Negative terminal of the voltage-doubler charge-pump capacitor. Positive terminal of inverting charge-pump capacitor. Negative terminal of inverting charge-pump capacitor. -5.5V generated by the charge pump. RS-232 Transmitter Outputs RS-232 Receiver Inputs TTL/CMOS Receiver Outputs TTL/CMOS Transmitter Inputs Ground +3.0V to +5.5V Supply Voltage Active-Low Shutdown-Control Input. Drive low to shut down transmitters and charge pump. No Connection. Not internally connected.

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±15kV ESD-Protected, 3.0V to 5.5V, Low-Power, up to 250kbps, True RS-232 Transceiver MAX3385E
VCC 0.1µF VCC VCC 0.1µF VCC

C1+ C1 C1C2+ C2 C2T_ IN

V+ C3 3k C1

C1+ C1C2+ C4 C2 C2T_ IN

V+ C3 3k

MAX3385E
V-

MAX3385E
VC4 T_ OUT

T_ OUT

R_ OUT

R_ IN

R_ OUT

R_ IN

5k VCC SHDN GND 3k 2500pF VCC SHDN GND

5k 7k 150pF

MINIMUM SLEW-RATE TEST CIRCUIT

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 V CC 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).

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 V CC, V- is pulled to ground, and the transmitter outputs are disabled (high impedance). The time required to exit shut-

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 3k in parallel with 1000pF, providing compatibility with PC-to-PC communication software (such as LapLinkTM). Transmitters can be paralleled to drive multiple receivers or mice.
Laplink is a trademark of Traveling Software.

Table 1. Shutdown Truth Table
SHDN 0 1 T_OUT High-Z Active R_OUT Active Active 5

_______________________________________________________________________________________

±15kV ESD-Protected, 3.0V to 5.5V, Low-Power, up to 250kbps, True RS-232 Transceiver MAX3385E
5V/div 0 SHDN T2OUT

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 1.5k resistor.

2V/div 0

VCC = 3.3V C1­C4 = 0.1µF 40µs/div

T1OUT

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.

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.

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 C1­C4 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-

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

Table 2. Required Minimum Capacitance Values
VCC (V) 3.0 to 3.6 4.5 to 5.5 3.0 to 5.5 C1, CBYPASS (µF) 0.1 0.047 0.1 C2, C3, C4 (µF) 0.1 0.33 0.47

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±15kV ESD-Protected, 3.0V to 5.5V, Low-Power, up to 250kbps, True RS-232 Transceiver MAX3385E
RC 1M CHARGE-CURRENT LIMIT RESISTOR HIGHVOLTAGE DC SOURCE RD 1500 DISCHARGE RESISTANCE DEVICE UNDER TEST

IP 100% 90% AMPERES 36.8% 10% 0 0 tRL TIME

Ir

PEAK-TO-PEAK RINGING (NOT DRAWN TO SCALE)

Cs 100pF

STORAGE CAPACITOR

tDL CURRENT WAVEFORM

Figure 3a. Human Body ESD Test Model

Figure 3b. Human Body Model Current Waveform
I 100%

RC 50M to 100M CHARGE-CURRENT LIMIT RESISTOR HIGHVOLTAGE DC SOURCE

RD 330 I PEAK DISCHARGE RESISTANCE DEVICE UNDER TEST

90%

Cs 150pF

STORAGE CAPACITOR

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). 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
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.

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 lev7

_______________________________________________________________________________________

±15kV ESD-Protected, 3.0V to 5.5V, Low-Power, up to 250kbps, True RS-232 Transceiver MAX3385E
els (one transmitter input is high, the other is low). Each transmitter is loaded with 3k 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
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

Interconnection with 3V and 5V Logic
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 T1IN V+ C3 C1C2+ C2 C2R1OUT T_ IN T_ OUT VCC = 3.3V C1­C4 = 0.1µF 2µs/div R_ OUT R_ IN 5V/div 5V/div 5V/div

VCC C1+ C1

MAX3385E

VC4

T1OUT

Figure 7. MAX3385E Loopback Test Result at 120kbps
5k VCC SHDN* 1000pF

GND

Figure 6. Loopback Test Circuit

8

_______________________________________________________________________________________

±15kV ESD-Protected, 3.0V to 5.5V, Low-Power, up to 250kbps, True RS-232 Transceiver MAX3385E MAX3385E
Table 3. Logic-Family Compatibility with Various Supply Voltages
T1IN 5V/div

SYSTEM POWER-SUPPLY VOLTAGE (V) 3.3 5

VCC SUPPLY VOLTAGE (V) 3.3 5

COMPATIBILITY

T1OUT

5V/div

Compatible with all CMOS families Compatible with all TTL and CMOS families Compatible with ACT and HCT CMOS, and with AC, HC, or CD4000 CMOS

R1OUT

5V/div VCC = 3.3V C1­C4 = 0.1µF

5
2µs/div

3.3

Figure 8. MAX3385E Loopback Test Result at 250kbps

___________________Chip Information
TRANSISTOR COUNT: 1129

_______________________________________________________________________________________

9

±15kV ESD-Protected, 3.0V to 5.5V, Low-Power, up to 250kbps, True RS-232 Transceiver MAX3385E
________________________________________________________Package Information
SSOP.EPS

10

______________________________________________________________________________________

±15kV ESD-Protected, 3.0V to 5.5V, Low-Power, up to 250kbps, True RS-232 Transceiver
NOTES

MAX3385E
11

______________________________________________________________________________________

±15kV ESD-Protected, 3.0V to 5.5V, Low-Power, up to 250kbps, True RS-232 Transceiver MAX3385E
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.