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19-1632; Rev 0; 1/00
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins
General Description
The MAX3238E/MAX3248E transceivers use Maxim's revolutionary AutoShutdown PlusTM feature to achieve 10nA supply current. These devices shut down the onboard power supply and drivers when they do not sense a valid signal transition on either the receiver or transmitter inputs. This occurs if the RS-232 cable is disconnected or if the transmitters of the connected peripheral are turned off. The devices turn on again when a valid transition is applied to any RS-232 receiver or transmitter input. AutoShutdown Plus automatically achieves this power savings through its on-board circuitry, as no changes are required to the existing BIOS or operating system. All RS-232 inputs and outputs, as well as the logic I/O pins, have enhanced ESD protection to 15kV. The additional ESD protection on the logic I/O pins makes the MAX3238E/MAX3248E ideal for cell phone data cable applications because it eliminates the need for costly external TransZorbTM or protection schemes. The MAX3238E/MAX3248E contain five drivers and three receivers and are 3V-powered EIA/TIA-232 and V.28/V.24 communication interfaces intended for cell phones, data cables, and modem applications. A proprietary, high-efficiency, dual charge-pump power supply and a lowdropout transmitter combine to deliver true RS-232 performance from a single +3.0V to +5.5V supply. A guaranteed data rate of 250kbps provides compatibility with popular software for communicating with personal computers. The MAX3238E and the MAX3248E differ only in their input logic thresholds. The MAX3238E has standard logic thresholds, while the MAX3248E has low-level logic thresholds of 0.6V to 1.2V, which are ideal for 1.8V systems. The transmitter inputs, FORCEON, and FORCEOFF have a 400k active positive feedback resistor. Once driven to a valid logic level, they will retain this level if the driving signal is removed or goes high impedance. Unused transmitter and logic inputs may be left unconnected. The MAX3238E/MAX3248E can operate with supply voltages ranging from +3.0V to +5.5V.
Features
o Enhanced ESD Protection on RS-232 Receiver and All Logic Pins 15kV--Human Body Model 8kV--IEC 1000-4-2 Contact Discharge 15kV--IEC 1000-4-2 Air-Gap Discharge o 15kV ESD Protection on RS-232 Transmitter Outputs (Human Body Model) o Guaranteed Data Rate: 250kbps o 10nA Low-Power Shutdown with Receivers Active o Schmitt Triggers on All Inputs o Flow-Through Pinout o Meets EIA/TIA-232 Specifications Down to 3.0V o Guaranteed 6V/s Slew Rate o Low-Level Logic Thresholds (MAX3248E) o RS-232-Compatible Outputs to 2.7V
MAX3238E/MAX3248E
Ordering Information
PART MAX3238ECAI MAX3238EEAI MAX3248ECAI MAX3248EEAI TEMP. RANGE 0C to +70C -40C to +85C 0C to +70C -40C to +85C PIN-PACKAGE 28 SSOP 28 SSOP 28 SSOP 28 SSOP
Typical Operating Circuit appears at end of data sheet.
___________________Pin Configuration
TOP VIEW
C2+ GND C2VT1OUT T2OUT T3OUT 1 2 3 4 5 6 7 8 9 28 C1+ 27 V+ 26 VCC 25 C124 T1IN
MAX3238E MAX3248E
23 T2IN 22 T3IN 21 R1OUT 20 R2OUT 19 T4IN 18 R3OUT 17 T5IN 16 R1OUTB 15 INVALID
Applications
Cellular Data Cables Modems Battery-Powered Equipment Peripherals Data Cradles Printers
R1IN R2IN
T4OUT 10 R3IN 11 T5OUT 12 FORCEON 13 FORCEOFF 14
AutoShutdown Plus is a trademark of Maxim Integrated Products. TransZorb is a trademark of General Semiconductor Industries, Inc. 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.
Covered
SSOP
________________________________________________________________ Maxim Integrated Products
1
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800. For small orders, phone 1-800-835-8769.
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins MAX3238E/MAX3248E
ABSOLUTE MAXIMUM RATINGS
VCC ...........................................................................-0.3V to +6V V+ (Note 1) ...............................................................-0.3V to +7V V- (Note 1) ................................................................+0.3V to -7V V+ + |V-| (Note 1) .................................................................+13V Input Voltages T_IN, FORCEOFF, FORCEON ..............................-0.3V to +6V R_IN .................................................................................25V Output Voltages T_OUT...........................................................................13.2V R_OUT, INVALID ....................................-0.3V to (VCC + 0.3V) Short-Circuit Duration T_OUT (one at a time) ............................................Continuous Continuous Power Dissipation (TA = +70C) 28-Pin SSOP (derate 9.52mW/C above +70C) .........762mW Operating Temperature Ranges MAX3238ECAI/MAX3248ECAI ...........................0C to +70C MAX3238EEAI/MAX3248EEAI .........................-40C to +85C Storage Temperature Range ............................-65C to +150C Lead Temperature (soldering, 10s) ................................+300C
Note 1: V+ and V- can have a maximum magnitude of +7V, but their absolute difference can not 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 = +3.0V to +5.5V, C1-C4 = 0.1F (tested at 3.3V 5%), C1-C4 = 0.22F (tested at 3.3V 10%), C1 = 0.047F, and C2-C4 = 0.33F (tested at 5.0V 10%), TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER CONDITIONS Receivers idle, T_IN = VCC or GND, FORCEON = GND, FORCEOFF = VCC R_IN = FORCEON = GND, FORCEOFF = VCC, T_IN = VCC or GND FORCEOFF = GND, R_IN = GND, T_IN = VCC or GND FORCEON = FORCEOFF = VCC, no load MIN TYP MAX UNITS DC CHARACTERISTICS (VCC = +3.3V or +5.0V, TA = +25C) 0.75 10 10 0.5 6 300 300 2.0 A nA nA mA
Supply Current, AutoShutdown Plus
Supply Current, Shutdown Supply Current, AutoShutdown Plus Disabled
LOGIC INPUTS AND RECEIVER OUTPUTS T_IN (active) MAX3238E FORCEON, FORCEOFF, and T_IN wake-up threshold; VCC = 3.3V FORCEON, FORCEOFF, and T_IN wake-up threshold; VCC = 5.0V T_IN (active) MAX3248E FORCEON, FORCEOFF, and T_IN wake-up threshold; VCC = 3.3V FORCEON, FORCEOFF, and T_IN wake-up threshold; VCC = 5.0V T_IN (active) MAX3238E FORCEON, FORCEOFF, and T_IN wake-up threshold; VCC = 3.3V FORCEON, FORCEOFF, and T_IN wake-up threshold; VCC = 5.0V T_IN (active) MAX3248E FORCEON, FORCEOFF, and T_IN wake-up threshold; VCC = 3.3V FORCEON, FORCEOFF, and T_IN wake-up threshold; VCC = 5.0V 2 0.8 0.8 0.8 0.6 0.6 0.6 1.20 1.00 1.45 0.7 0.85 1.0 1.60 1.30 2.10 1.10 0.95 1.15 2.0 2.0 2.4 1.2 1.2 1.6 V V
Input Logic Threshold Low
Input Logic Threshold High
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+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +5.5V, C1-C4 = 0.1F (tested at 3.3V 5%), C1-C4 = 0.22F (tested at 3.3V 10%), C1 = 0.047F, and C2-C4 = 0.33F (tested at 5.0V 10%), TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Input Leakage Current Output Leakage Current Output Voltage Low Output Voltage High RECEIVER INPUTS Input Voltage Range Input Threshold Low Input Threshold High Input Hysteresis Input Resistance TA = +25C Positive threshold Negative threshold -2.7 -0.3 0.3 0.4 VCC 0.6 0.3 60 25 15 30 60 3 AutoShutdown (FORCEON = GND, FORCEOFF = VCC) Receiver Input Threshold to INVALID Output High Receiver Input Threshold to INVALID Output Low INVALID Output Voltage Low INVALID Output Voltage High Receiver Positive or Negative Threshold to INVALID High (tINVH) Receiver Positive or Negative Threshold to INVALID Low (tINVL) Receiver or Transmitter Edge to Transmitters Enabled (tWU) Receiver or Transmitter Edge to Shutdown (tAUTOSHDN) TRANSMITTER OUTPUTS Output Voltage Swing Output Resistance Output Short-Circuit Current ESD PROTECTION ESD Protection (R_IN, T_IN, R_OUT, FORCEON, FORCEOFF, INVALID, R_OUTB) ESD Protection (T_OUT) IEC 1000-4-2 Air-Gap Discharge Method IEC 1000-4-2 Contact Discharge Method Human Body Model Human Body Model 15 8 15 15 kV 3 kV All transmitter outputs loaded with 3k to ground VCC = 0, TOUT = 2V VCC 3.6V VCC > 3.6V 5.0 300 5.4 50k 35 40 60 100 V mA Figure 4a Figure 4a IOUT = 1.0mA IOUT = -1.0mA VCC = 5V, Figure 4b VCC = 5V, Figure 4b VCC = 5V, Figure 4b (Note 3) Figure 4b 2.7 V V V V s s s s VCC = 3.3V VCC = 5.0V VCC = 3.3V VCC = 5.0V -25 0.6 0.8 1.0 1.4 1.5 2.0 0.6 5 7 2.4 2.4 25 V V V V k CONDITIONS T_IN, FORCEON, FORCEOFF (Note 2) Receivers disabled IOUT = 1.0mA IOUT = -1.0mA VCC 0.6 VCC 0.1 MIN TYP 9 0.05 MAX 18 10 0.4 UNITS A A V V
MAX3238E/MAX3248E
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+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins MAX3238E/MAX3248E
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +5.5V, C1-C4 = 0.1F (tested at 3.3V 5%), C1-C4 = 0.22F (tested at 3.3V 10%), C1 = 0.047F, and C2-C4 = 0.33F (tested at 5.0V 10%), TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER TIMING CHARACTERISTICS Maximum Data Rate Receiver Propagation Delay Receiver Output Enable Time Receiver Output Disable Time Transmitter Skew Receiver Skew RL = 3k, CL = 1000pF, one transmitter switching R_IN to R_OUT, CL = 150pF Normal operation Normal operation | tPHL - tPLH | | tPHL - tPLH | VCC = 3.3V, TA = +25C, RL = 3k to 7k, measured from +3V to -3V or -3V to +3V CL = 150pF to 1000pF CL = 150pF to 2500pF 6 tPHL tPLH 250 0.15 0.15 2.6 2.4 50 50 30 V/s 4 30 kbps s s s ns ns CONDITIONS MIN TYP MAX UNITS
Transition-Region Slew Rate
Note 2: The transmitter inputs have an active positive feedback resistor. The input current goes to zero when the inputs are at the supply rails. Note 3: During AutoShutdown only, a transmitter/receiver edge is defined as a transition through the transmitter/receiver input logic wake-up thresholds.
__________________________________________Typical Operating Characteristics
(VCC = +3.3V, 250kbps data rate, 0.1F capacitors, all transmitters loaded with 3k, TA = +25C, unless otherwise noted.)
TRANSMITTER OUTPUT VOLTAGE vs. LOAD CAPACITANCE
6 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 0
MAX3238E toc01
SLEW RATE vs. LOAD CAPACITANCE
MAX3238E toc02
SUPPLY CURRENT vs. LOAD CAPACITANCE WHEN TRANSMITTING DATA
250kbps 40 SUPPLY CURRENT (mA) 120kbps
MAX3238 TOC-03
12 10 SLEW RATE (V/s) 8 SR+ 6 4 2 1 TRANSMITTER 250kbps 4 TRANSMITTERS 15.6kbps ALL TRANSMITTERS LOADED WITH 3k + CL 0 500 1000 1500 2000 2500
50
TRANSMITTER OUTPUT VOLTAGE (V)
VOUT+
SR-
FOR DATA RATES UP TO 250kbps 1 TRANSMITTER 250kbps 4 TRANSMITTERS 15.6kbps ALL TRANSMITTERS LOADED WITH 3k + CL
30 20kbps 20 1 TRANSMITTER 20kbps, 120 kbps, 250kbps 4 TRANSMITTERS 15.6kbps ALL TRANSMITTERS LOADED WITH 3k + CL
10
VOUT0 500 1000 1500 2000 2500 3000
0 3000 0 500 LOAD CAPACITANCE (pF) 1000 1500 2000 2500 LOAD CAPACITANCE (pF) 3000
LOAD CAPACITANCE (pF)
4
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+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins MAX3238E/MAX3248E
Typical Operating Characteristics (continued)
(VCC = +3.3V, 250kbps data rate, 0.1F capacitors, all transmitters loaded with 3k, TA = +25C, unless otherwise noted.)
TRANSMITTER OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
6 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 2.0 TRANSMITTER OUTPUT VOLTAGE (V) VOUT+
MAX3238E toc04
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX3238E toc05
50
40 SUPPLY CURRENT (mA)
1 TRANSMITTER 250kbps 4 TRANSMITTERS 15.6kbps ALL TRANSMITTERS LOADED WITH 3k +1000pF
30
20 1 TRANSMITTER 250kbps 4 TRANSMITTERS 15.6kbps ALL TRANSMITTERS LOADED WITH 3k +1000pF 2.0 2.5 3.0 3.5 4.0 4.5 5.0
10 VOUT0 2.5 3.0 3.5 4.0 4.5 5.0 SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
______________________________________________________________Pin Description
PIN NAME C2+ GND C2VT_OUT R_IN FUNCTION Positive Terminal of Inverting Charge-Pump Capacitor Ground Negative Terminal of Inverting Charge-Pump Capacitor -5.5V Generated by the Charge Pump RS-232 Transmitter Outputs (T1OUT-T5OUT) RS-232 Receiver Inputs (R1IN-R3IN) Force-On Input. Drive high to override AutoShutdown Plus, keeping transmitters and receivers on (FORCEOFF must be high) (Table 1). This pin has an active positive feedback resistor. Once driven to a valid logic level, the pin retains that level if left unconnected until power is cycled. Force-Off Input. Drive low to shut down transmitters, receivers (except R1OUTB), and onboard supply. This overrides AutoShutdown Plus and FORCEON (Table 1). This pin has an active positive feedback resistor. Once driven to a valid logic level, the pin retains that level if left unconnected until power is cycled. Output of the Valid Signal Detector. A logic 1 indicates if a valid RS-232 level is present on receiver inputs. Noninverting Complementary Receiver Output. Always active. TTL/CMOS Transmitter Inputs (T5IN-T1IN). This pin has an active positive feedback resistor. Once driven to a valid logic level, the pin retains that level if left unconnected until power is cycled. TTL/CMOS Receiver Outputs (R3OUT-R1OUT) Negative Terminal of Voltage-Doubler Charge-Pump Capacitor +3.0V to +5.5V Supply Voltage +5.5V Generated by the Charge Pump Positive Terminal of Voltage-Doubler Charge-Pump Capacitor 5
1
2 3 4 5, 6, 7, 10, 12 8, 9, 11
13
FORCEON
14
FORCEOFF
15 16 17, 19, 22, 23, 24 18, 20, 21 25 26 27 28
INVALID R1OUTB T_IN R_OUT C1VCC V+ C1+
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+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins MAX3238E/MAX3248E
Table 1. Output Control Truth Table
FORCEON FORCEOFF AutoShutdown Plus X OPERATION STATUS Shutdown (Forced Off) Normal Operation (Forced On) Normal Operation (AutoShutdown Plus) Shutdown (AutoShutdown Plus) T_OUT R_OUT R1OUTB
X
0
High-Z
High-Z
Active
1
1
X
Active
Active
Active
0
1
<30s*
Active
Active
Active
0
1
>30s*
High-Z
Active
Active
X = Don't care *Time since last receiver or transmitter input transition.
_______________Detailed Description
Dual Charge-Pump Voltage Converter
The MAX3238E/MAX3248Es' 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 the 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.
When FORCEOFF is driven to ground, the transmitters and receivers are disabled and the outputs go high impedance, except for R1OUTB. When the AutoShutdown Plus circuitry senses that all receiver and transmitter inputs are inactive for more than 30s, the transmitters are disabled and the outputs go into a high-impedance state, but the receivers remain active. When the power is off, the MAX3238E/MAX3248E permit the outputs to be driven up to 12V. The transmitter inputs, FORCEON and FORCEOFF, have a 400k active positive-feedback resistor. Once driven to a valid logic level, they will retain this level if the driving signal is removed or goes high-impedance. Unused transmitter inputs may be left unconnected.
RS-232 Transmitters
The MAX3248E transmitters are inverting level translators that convert a logic low of 0.6V and logic high of 1.2V to 5.0V EIA/TIA-232 levels. The MAX3238E transmitters are inverting level translators that convert CMOS-logic levels to 5.0V EIA/TIA-232 levels. The MAX3238E/MAX3248E transmitters both 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. Figure 1 shows a complete system connection.
RS-232 Receivers
The receivers convert RS-232 signals to CMOS-logic output levels. All receivers have inverting three-state outputs and are inactive in shutdown (FORCEOFF) (Table 1). The MAX3238E/MAX3248E also feature an extra, always-active noninverting output, R1OUTB. This extra output monitors receiver activity while the other receivers are high impedance, allowing Ring Indicator to be monitored without forward biasing other devices connected to the receiver outputs. This is ideal for systems where VCC is set to 0 in shutdown to accommodate peripherals, such as UARTs (Figure 2).
LapLink is a trademark of Traveling Software. 6 _______________________________________________________________________________________
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins MAX3238E/MAX3248E
POWER MANAGEMENT UNIT OR KEYBOARD CONTROLLER FORCEOFF FORCEON INVALID PROTECTION DIODE VCC
MAX3238E/ MAX3248E
T1
VCC Rx UART I
PREVIOUS RS-232
5k Tx
T2 T3 I/O CHIP WITH UART GND T4 RS-232 T5 a) OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM ACTIVE RECEIVER OUTPUT IN SHUTDOWN. R1 VCC R2 R3 TO P LOGIC TRANSITION DETECTOR SHDN = GND
CPU
I
Figure 1. Interface Under Control of PMU
PROTECTION DIODE VCC Rx UART
MAX3238E MAX3248E
R1OUTB
AutoShutdown Plus Mode
A 10nA supply current is achieved with Maxim's AutoShutdown Plus feature, which operates when FORCEOFF is low and FORCEON is high. When the MAX3238E/MAX3248E sense no valid signal transitions on all receiver and transmitter inputs for 30s, the onboard power supply and drivers are shut off, reducing supply current to 1A. If the receiver inputs are in the invalid range (-0.3V < R_IN < +0.3V) and the transmitter inputs are at GND or VCC, supply current is further reduced to 10nA. This occurs if the RS-232 cable is disconnected or if the connected peripheral transmitters are turned off. 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. The INVALID output is high when the receivers are active. Since INVALID indicates the receiver inputs' condition, it can be used in any mode (Figure 3).
R1OUT THREE-STATED 5k
R1IN
Tx GND
T1IN FORCEOFF = GND
T1OUT
b) NEW MAX3238E/MAX3248E: IN SHUTDOWN, R1OUTB IS USED TO MONITOR EXTERNAL DEVICES AND R1OUT IS THREE STATED, ELIMINATING A CURRENT PATH THROUGH THE UART'S PROTECTION DIODE.
Figure 2. MAX3238E/MAX3248E detect RS-232 activity when the UART and interface are shut down.
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+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins MAX3238E/MAX3248E
Table 2. INVALID Truth Table
RS-232 SIGNAL PRESENT AT ANY RECEIVER INPUT Yes No INVALID OUTPUT H
-0.3V +0.3V
R_IN
60s TIMER R
INVALID
L
INVALID ASSERTED IF ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR AT LEAST 60s.
Tables 1 and 2 and Figure 3 summarize the MAX3238E/ MAX2348Es' operating modes. FORCEON and FORCEOFF override the automatic circuitry and force the transceiver into its normal operating state or into its lowpower standby state. When neither control is asserted, the IC enters AutoShutdown Plus mode and selects between these states automatically, based on the last receiver or transmitter input edge received. When shut down, the devices' charge pumps turn off, V+ decays to VCC, V- decays to ground, and the transmitter outputs are disabled (high impedance). The time required to recover from shutdown is typically 25s (Figure 4b).
Figure 3a. INVALID Functional Diagram, INVALID Low
+2.7V
R_IN
-2.7V
60s TIMER R
INVALID
Software-Controlled Shutdown
If direct software control is desired, use INVALID to indicate DTR or Ring Indicator signal. Tie FORCEOFF and FORCEON together to bypass the AutoShutdown Plus feature so the line acts like a SHDN input.
INVALID DEASSERTED IF ANY RECEIVER INPUT HAS BEEN BETWEEN +2.7V AND -2.7V FOR LESS THAN 60s.
Figure 3b. INVALID Functional Diagram, INVALID High
ESD Protection
As with all Maxim devices, ESD protection structures are incorporated to protect against electrostatic discharges (ESDs) encountered during handling and assembly. The MAX3238E/MAX3248E RS-232 transmitters and receivers, as well as the I/O have extra protection against static electricity found in normal operation. Maxim's engineers developed state-of-the-art structures to protect these pins against ESD of 15kV without damage. After an ESD event, the MAX3238E/ MAX3248E keep working without latchup. ESD protection can be tested in various ways. The pins are characterized for protection to 15kV and 8kV (see Electrical Characteristics). ESD Test Conditions Contact Maxim for a reliability report that documents test setup, methodology, and results. Human Body Model 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 inter8
T_IN
EDGE DETECT
FORCEOFF S
R_IN
EDGE DETECT
30s TIMER R
AUTOSHDN
FORCEON
Figure 3c. AutoShutdown Plus Logic
FORCEOFF
POWERDOWN*
FORCEON AUTOSHDN
* POWER DOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE OPERATIONAL STATUS OF THE TRANSMITTERS AND THE POWER SUPPLIES.
Figure 3d. Power-Down Logic
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+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins
INVALID HIGH +2.7V RECEIVER INPUT LEVELS INDETERMINATE +0.3V 0V -0.3V INDETERMINATE -2.7V INVALID HIGH
INVALID LOW
Figure 4a. Receiver Positive/Negative Thresholds for INVALID
help you design equipment that meets Level 4 (the highest level) of IEC 1000-4-2, without 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 ESD test model (Figure 6a), the ESD withstand voltage measured to this standard is generally lower than that measured using the Human Body Model. 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 testing uses a 200pF storage capacitor and zero-discharge resistance. Its objective is to mimic the stress caused by contact that occurs with handling and assembly during manufacturing. Of course, all pins (not just RS-232 inputs and outputs) require this protection during manufacturing.
MAX3238E/MAX3248E
est, which is then discharged into the test device through a 1.5k 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 MAX3238E/MAX3248E
INVALID REGION RECEIVER INPUTS VOLTAGE TRANSMITTER INPUTS VOLTAGE TRANSMITTER OUTPUTS VOLTAGE INVALID OUTPUT VCC 0 V+ VCC 0 V*ALL RECEIVERS/TRANSMITTERS INACTIVE **ANY ONE RECEIVER/TRANSMITTER BECOMES ACTIVE INVL tAUTOSHDN
*
**
tAUTOSHDN tWU tWU
FORCEON = GND, FORCEOFF = VCC
Figure 4b. AutoShutdown Plus and INVALID Timing Diagram
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+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins MAX3238E/MAX3248E
RC 1M CHARGE-CURRENT LIMIT RESISTOR HIGHVOLTAGE DC SOURCE RD 1500 DISCHARGE RESISTANCE DEVICE UNDER TEST IP 100% 90% AMPERES Cs 100pF STORAGE CAPACITOR 36.8% 10% 0 0 tRL TIME tDL CURRENT WAVEFORM Ir PEAK-TO-PEAK RINGING (NOT DRAWN TO SCALE)
Figure 5a. Human Body ESD Test Model
Figure 5b. Human Body Model Current Waveform
RC 50M to 100M CHARGE-CURRENT LIMIT RESISTOR HIGHVOLTAGE DC SOURCE
RD 330 DISCHARGE RESISTANCE DEVICE UNDER TEST IPEAK
I 100% 90%
Cs 150pF
STORAGE CAPACITOR
10% tr = 0.7ns to 1ns 30ns 60ns t
Figure 6a. IEC 1000-4-2 ESD Test Model
Figure 6b. IEC 1000-4-2 ESD Generator Current Waveform
Therefore, the Machine Model is less relevant to the I/O ports than the Human Body Model and IEC 1000-4-2.
Power-Supply Decoupling
In most applications, decouple VCC to ground with a 0.1F capacitor. Further increasing this capacitor value reduces power-supply ripple and enhances noise margin. Connect the bypass capacitor as close to the IC as possible.
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 0.1F capacitors for 3.3V operation. For other supply voltages, see Table 3 for required capacitor values. Do not use values smaller than those listed in Table 3. 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).
Table 3. Required Minimum Capacitance Values
VCC (V) 3.0 to 3.6 3.15 to 3.6 4.5 to 5.5 3.0 to 5.5 C1, CBYPASS (F) 0.22 0.1 0.047 0.22 C2, C3, C4 (F) 0.22 0.1 0.33 1
10
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+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins MAX3238E/MAX3248E
FORCEON = FORCEOFF
5V/div T2OUT T1IN +5V 0
+5V 2V/div T1OUT 0 -5V
T1OUT
+5V R1OUT 0 2s/div VCC = 3.3V, C1-C4 = 0.1F, CLOAD = 1000pF
4s/div VCC = 3.3V, C1-C4 = 0.1F, RLOAD = 3k, CLOAD = 2500pF
Figure 7. Transmitter Outputs when Recovering from Shutdown or Powering Up
Figure 9. Loopback Test Result at 120kbps
VCC
+5V 0
T1IN
VCC C1+ C1 C1C2+ C2 C2R1OUT
V+ C3*
T1OUT +5V 0 -5V +5V 0
MAX3238E MAX3248E
VC4
T_ IN
T_ OUT
2s/div
R_ OUT
R_ IN 5k
VCC = 3.3V, C1-C4 = 0.1F, CLOAD = 1000pF
Figure 10. Loopback Test Result at 250kbps
FORCEON VCC FORCEOFF 1000pF
GND
*C3 CAN BE RETURNED TO VCC OR GND.
Figure 8. Loopback Test Circuit
puts are shown going to opposite RS-232 levels (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 Vexceeds approximately 3V.
Transmitter Outputs when Recovering from Shutdown
Figure 7 shows two transmitter outputs when recovering from shutdown mode. As they become active, the out-
High Data Rates
The MAX3238E/MAX3248E maintain 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,
11
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+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins MAX3238E/MAX3248E
+ C1 0.1F 28 25 27 C3 0.1F 26 TVS C5 0.1F C1+ C1C2+ C21 3 C2 0.1F
V+
MAX3238E MAX3248E
15kV ESD PROTECTION 15kV ESD PROTECTION
V- 4
C4 0.1F
VCC
24 T1IN 23 T2IN 22 T3IN 19 T4IN SUBMINIATURE CONNECTOR 17 T5IN 21 R1OUT 20 R2OUT 18 R3OUT 16 R1OUTB 13 FORCEON 14 FORCEOFF 15 INVALID CONTROL
T1OUT 5 T2OUT 6 T3OUT 7 T4OUT 10 T5OUT 12 R1IN 8 R2IN 9 R3IN 11
DCD DSR RD RTS TD CTS DTR RI
1 6 2 7 3 8 4 9 5
GND 2
Figure 11. Data Cable Application Example
12
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+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins
Typical Operating Circuit
+3.3V
1F 26 28 C1+ 0.1F 25 C11 C2+ 0.1F 3 C224 T1IN 23 T2IN 22 T3IN 19 T4IN 17 T5IN 14 FORCEOFF AutoShutdown Plus 13 FORCEON 16 R1OUTB INVALID 15 T1OUT 5 T2OUT 6 T3OUT 7 T4OUT 10 T5OUT 12 VCC V+ 27 0.1F*
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.
MAX3238E/MAX3248E
Data Cable Applications
The MAX3238E/MAX3248Es' 15kV ESD protection on both the RS-232 I/Os as well as the logic I/Os makes them ideal candidates for data cable applications. A data cable is both an electrical connection and a level translator, allowing ultra-miniaturization of cell phones and other small portable devices. Previous data cable approaches suffered from complexity due to the required protection circuits on both the logic side of the cable as well as on the RS-232 connections. The example shown in Figure 10 shows the ease of using the MAX3238E/MAX3248E in data cable applications. The MAX3238E/MAX3248Es' five-transmitter and threereceiver configuration is optimized for a data communication equipment (DCE) application, allowing full hardware handshaking. The 9-pin RS-232 connector is configured for direct attachment to a PC's serial port. R1OUTB is also connected to the subminiature connector. This allows the remote system to shut down until the PC asserts the ready to send (RTS) signal. R1OUTB stays active when the MAX3238E/MAX3248E is shut down (FORCEOFF = GND).
MAX3238E MAX3248E
V- 4 0.1F
T1 T2 T3 T4 T5
LOGIC INPUTS
RS-232 OUTPUTS
___________________Chip Information
21 R1OUT R1 R1IN 8
TRANSISTOR COUNT: 2110
5k
LOGIC OUTPUTS 20 R2OUT R2
R2IN 9 5k
RS-232 INPUTS
18 R3OUT
R3
R3IN 11 5k
GND 2
*C3 MAY BE RETURNED TO EITHER VCC OR GND.
______________________________________________________________________________________
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+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins MAX3238E/MAX3248E
________________________________________________________Package Information
SSOP.EPS
14
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+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins MAX3238E/MAX3248E
NOTES
______________________________________________________________________________________
15
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers with 15kV ESD-Protected I/O and Logic Pins MAX3238E/MAX3248E
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.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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