19-1437; Rev 1; 10/99
±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 en-
hanced 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 transmit-
ter 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 capac-
itors for operation from a +3.3V supply. Each device is
guaranteed to run at data rates of 250kbps while main-
taining RS-232 output levels.
The MAX3385E has two receivers and two drivers. It
features a 1µA shutdown mode that reduces power con-
sumption and extends battery life in portable systems.
Its receivers can remain active in shutdown mode,
allowing external devices such as modems to be moni-
tored 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 3kΩ Load on V+
o
6V/µs Guaranteed Slew Rate
o
Meets EIA/TIA-232 Specifications Down to 3.0V
MAX3385E
†
Ordering Information
PART
MAX3385ECAP
MAX3385ECWN
MAX3385EEAP
TEMP. RANGE
0°C to +70°C
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
20 SSOP
18 SO
20 SSOP
Typical Operating Circuit
+3.3V
C
BYPASS
C1
0.1µF
C1+
C1-
________________________Applications
Hand-Held Equipment
Peripherals
Printers
Battery-Powered
Equipment
V
CC
V+
C3
*
0.1µF
C4
0.1µF
MAX3385E
Pin Configurations
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 V
CC
18 GND
17 T1OUT
C2
0.1µF
C2+
C2-
T1IN
V-
T1OUT
RS-232
OUTPUTS
TTL/CMOS
INPUTS
T2IN
T2OUT
MAX3385E
R1OUT
R1IN
5k
RS-232
INPUTS
16 R1IN
15 R1OUT
14 T1IN
13 T2IN
12 R2OUT
GND
TTL/CMOS
OUTPUTS
R2OUT
R2IN
5k
SHDN
11 N.C.
SSOP
Pin Configurations continued at end of data sheet.
†
Cg.
*
C3 CAN BE RETURNED TO EITHER V
CC
OR GROUND.
NOTE: SEE TABLE 2 FOR CAPACITOR SELECTION
________________________________________________________________
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
V
CC
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 (V
CC
+ 0.3V)
Short-Circuit Duration, T_OUT to GND.......................Continuous
Continuous Power Dissipation (T
A
= +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
(V
CC
= +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%; T
A
= T
MIN
to T
MAX
,
unless otherwise noted. Typical values are at T
A
= +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
T
A
= +25°C
3
T
A
= +25°C
T
A
= +25°C
V
CC
= 3.3V
V
CC
= 5.0V
V
CC
= 3.3V
V
CC
= 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
kΩ
R_OUT, receivers disabled
I
OUT
= 1.6mA
I
OUT
= -1.0mA
V
CC
-
0.6
V
CC
-
0.1
±0.05
±10
0.4
µA
V
V
T_IN,
SHDN
T_IN,
SHDN
T_IN,
SHDN
V
CC
= 3.3V
V
CC
= 5.0V
2.0
2.4
0.5
±0.01
±1
0.8
V
V
V
µA
SHDN
= V
CC
, no load
SHDN
= GND
CONDITIONS
MIN
TYP
0.3
1
MAX
1
10
UNITS
mA
µA
DC CHARACTERISTICS
(V
CC
= +3.3V or +5V, T
A
= +25°C)
_______________________________________________________________________________________
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +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%; T
A
= T
MIN
to T
MAX
,
unless otherwise noted. Typical values are at T
A
= +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
V
CC
= 0 or 3V to 5.5V, V
OUT
= ±12V, transmitters disabled
All transmitter outputs loaded with 3kΩ to ground
V
CC
= V+ = V- = 0, transmitter output = ±2V
±5
300
±5.4
10M
±60
±25
V
Ω
mA
µA
CONDITIONS
MIN
TYP
MAX
UNITS
MAX3385E
TIMING CHARACTERISTICS
(V
CC
= +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%; T
A
= T
MIN
to T
MAX
,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Maximum Data Rate
Receiver Propagation Delay
Time to Exit Shutdown
Transmitter Skew
Receiver Skew
t
PHL
- t
PLH
t
PHL
- t
PLH
V
CC
= 3.3V,
T
A
= +25°C,
R
L
= 3kΩ to 7kΩ,
measured from +3V
to -3V or -3V to +3V
C
L
= 150pF to
1000pF
C
L
= 150pF to
2500pF
6
4
t
PHL
t
PLH
SYMBOL
CONDITIONS
R
L
= 3kΩ, C
L
= 1000pF,
one transmitter switching
Receiver input to receiver output,
C
L
= 150pF
V
OUT
≥
+3.7V, R
LOAD
at V+ = 3kΩ
(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.
_______________________________________________________________________________________
3
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
MAX3385E
__________________________________________Typical Operating Characteristics
(V
CC
= +3.3V, 250kbps data rate, 0.1µF capacitors, all transmitters loaded with 3kΩ and C
L
, T
A
= +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
1000
2000
3000
V
OUT+
T1 TRANSMITTING AT 250kbps
T2 TRANSMITTING AT 15.6kbps
16
14
12
SLEW RATE (V/µs)
10
8
6
4
+SLEW
-SLEW
45
V
OUT-
2
FOR DATA RATES UP TO 250kbps
0
5
0
4000
5000
0
1000
2000
3000
4000
5000
4000
5000
0
1000
2000
3000
LOAD CAPACITANCE (pF)
LOAD CAPACITANCE (pF)
LOAD CAPACITANCE (pF)
______________________________________________________________ Pin Description
PIN
SO
1
2
3
4
5
6
7
8, 15
9, 14
10, 13
11, 12
16
17
18
PIN
SSOP
1, 10, 11
2
3
4
5
6
7
8, 17
9, 16
12, 15
13, 14
18
19
20
NAME
N.C.
C1+
V+
C1-
C2+
C2-
V-
T_OUT
R_IN
R_OUT
T_IN
GND
V
CC
SHDN
FUNCTION
No Connection. Not internally connected.
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
4
_______________________________________________________________________________________
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
MAX3385E
V
CC
0.1µF
V
CC
V
CC
0.1µF
V
CC
C1+
C1
C1-
C2+
C2
C2-
T_ IN
V+
C3
3k
C1
C1+
C1-
C2+
C4
C2
C2-
T_ IN
V+
C3
3k
MAX3385E
V-
MAX3385E
V-
C4
T_ OUT
T_ OUT
R_ OUT
R_ IN
R_ OUT
R_ IN
5k
V
CC
SHDN
GND
3k
2500pF
V
CC
SHDN
GND
5k
7k
150pF
MINIMUM SLEW-RATE TEST CIRCUIT
Figure 1. Slew-Rate Test Circuits
MAXIMUM SLEW-RATE TEST CIRCUIT
_______________Detailed Description
Dual Charge-Pump Voltage Converter
The MAX3385E’s internal power supply consists of a
regulated dual charge pump that provides output volt-
ages of +5.5V (doubling charge pump) and -5.5V
(inverting charge pump), 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 V-
supplies (Figure 1).
The MAX3385E’s transmitters are disabled and the out-
puts 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 shut-
down.
The transmitter inputs do not have pull-up resistors.
Connect unused inputs to GND or V
CC
.
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 dis-
abled (high impedance). The time required to exit shut-
RS-232 Transmitters
The transmitters are inverting level translators that con-
vert 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 paral-
leled 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
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