MAXIM MAX221EUE

19-1520; Rev 0; 8/99
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
The MAX221 is a +5V-powered, single transmit/receive
RS-232 and V.28 communications interface with automatic shutdown/wake-up features and high data rate
capabilities.
The MAX221 achieves a low 1µA supply current with
Maxim’s revolutionary AutoShutdown™ feature.
AutoShutdown saves power without changes to the
existing BIOS or operating system by entering lowpower shutdown mode when the RS-232 cable is disconnected, or when the transmitter of the connected
peripheral is off. The MAX221 wakes up and drives the
INVALID pin high when an active RS-232 cable is connected, signaling the host that a peripheral is connected to the communications port.
The MAX221 is available in a 16-pin SSOP package as
well as a 16-pin TSSOP that uses 50% less board space
than a 16-pin SO. For an equivalent RS-232 transceiver
with enhanced ±15kV ESD protection, refer to the
MAX221E data sheet.
Features
♦ Single RS-232 Transceiver in a Small 16-Pin
TSSOP Package
♦ 1µA Supply Current
♦ AutoShutdown Saves Power Without
Changes to BIOS
♦ Guaranteed 250kbps Data Rate
Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
MAX221CUE
0°C to +70°C
16 TSSOP
MAX221CAE
MAX221EUE
MAX221EAE
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
16 SSOP
16 TSSOP
16 SSOP
Applications
Maintenance/Diagnostic Ports
Industrial Systems
Telecommunications
Typical Operating Circuit
Set-Top Boxes
+5V
Pin Configuration
CBYPASS
C1
0.1µF
TOP VIEW
2 C1+
4 C15
16 FORCEOFF
EN 1
15 VCC
C1+ 2
14 GND
V+ 3
C1- 4
MAX221
C2
0.1µF
15
0.1µF
6
VCC
3
C3
0.1µF
V+
MAX221
C2+
V-
7
C4
0.1µF
C2-
11 TIN
TOUT 13
13 TOUT
C2+ 5
12 FORCEON
C2- 6
11 TIN
9 ROUT
RIN 8
5k
10 INVALID
V- 7
9
RIN 8
ROUT
TSSOP/SSOP
1
12
EN
FORCEON
INVALID
GND
FORCEOFF
10
16
TO POWERMANAGEMENT
UNIT
VCC
14
CAPACITORS MAY BE POLARIZED OR UNPOLARIZED.
AutoShutdown is a trademark of Maxim Integrated Products.
________________________________________________________________ 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.
MAX221
General Description
MAX221
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
ABSOLUTE MAXIMUM RATINGS
VCC ..........................................................................-0.3V to +6V
V+ ...............................................................(VCC - 0.3V) to +14V
V- ...........................................................................-14V to +0.3V
Input Voltages
TIN ..........................................................-0.3V to (V+ + 0.3V)
RIN .................................................................................±30V
FORCEON, FORCEOFF, EN.................-0.3V to (VCC + 0.3V)
Output Voltages
TOUT ..............................................(V- - 0.3V) to (V+ + 0.3V)
ROUT, INVALID ....................................-0.3V to (VCC + 0.3V)
Short-Circuit Duration, TOUT .....................................Continuous
Continuous Power Dissipation (TA = +70°C)
TSSOP (derated 6.7mW/°C above +70°C) ................533mW
SSOP (derated 7.1mW/°C above +70°C) ..................571mW
Operating Temperature Range
MAX221C_ _ .....................................................0°C to +70°C
MAX221E_ _ ..................................................-40°C to +85°C
Maximum Junction Temperature ................................... +150°C
Storage Temperature Range ........................... -65°C to +150°C
Lead Temperature (soldering, 10sec) ............................ +300°C
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 = +5V ±10%, C1–C4 = 0.1µF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DC CHARACTERISTICS
VCC Supply Current
Shutdown Supply Current
AutoShutdown Supply Current
ICC
No load, TA = +25°C
5
10
mA
ISHDN
TA = +25°C, Figure 1
1
10
µA
1
10
µA
IAS
LOGIC INPUTS
Input Leakage Current
IIN
TIN = 0 to VCC
±1
µA
Input Threshold Low
VIL
TIN; EN, FORCEOFF, FORCEON
0.8
V
Input Threshold High
VIH
TIN, EN, FORCEOFF
Output Voltage Low
VOL
ROUT; ISINK = 3.2mA
Output Voltage High
VOH
ROUT; ISOURCE = 1.0mA
2.4
3.5
EN = VCC, 0 ≤ ROUT ≤ VCC
Output Leakage Current
V
0.4
V
V
±0.05
±10
µA
AUTOSHUTDOWN
Receiver Input Threshold,
Transmitter Enabled
Figure 3
Receiver Input Threshold,
Transmitter Disabled
ICC = 1µA, Figure 3
INVALID Output Voltage Low
ISINK = 1.6mA
INVALID Output Voltage High
ISOURCE = 1.0mA
Receiver Threshold to
Transmitter Enabled
2.7
Positive threshold
Negative threshold
-2.7
-0.3
VCC - 0.6
V
0.3
V
0.4
V
V
tWU
Figure 3
250
µs
Receiver Positive or Negative
Threshold to INVALID High
tINVH
Figure 3
1
µs
Receiver Positive or Negative
Threshold to INVALID Low
tINVL
Figure 3
30
µs
2
_______________________________________________________________________________________
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
(VCC = +5V ±10%, C1–C4 = 0.1µF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
25
V
2.4
V
7
kΩ
RECEIVER INPUT
Input Voltage Range
-25
Input Threshold Low
TA = +25°C, VCC = 5V
Input Threshold High
TA = +25°C, VCC = 5V
Input Hysteresis
VCC = 5V, no hysteresis in shutdown
Input Resistance
TA = +25°C, VCC = 5V
0.8
1.2
1.7
V
0.5
3
5
±9
V
TRANSMITTER OUTPUT
Output Voltage Swing
Driver loaded with 3kΩ to ground
±5
Output Resistance
VCC = V+ = V- = 0, VOUT = ±2V
300
Output Short-Circuit Current
V
Ω
±10
±60
mA
MAX
UNITS
TIMING CHARACTERISTICS
(VCC = +5V ±10%, C1–C4 = 0.1µF, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
RL = 3kΩ to 7kΩ, CL = 50pF to 1000pF,
VCC = 4.5V
Maximum Data Rate
MIN
TYP
250
kbps
CL = 150pF
0.15
µs
Receiver Output Enable Time
Normal operation
300
ns
Receiver Output Disable Time
Normal operation
200
ns
(Note 1)
200
ns
50
ns
Receiver Propagation Delay
Transmitter Skew
tPHL, tPLH
| tPHL - tPLH |
| tPHL - tPLH |
Receiver Skew
Transition-Region Slew Rate
TA = +25°C, VCC = 5V, RL = 3kΩ to 7kΩ,
CL = 500pF to 1000pF, measured from
-3V to +3V or +3V to -3V
3
6
30
V/µs
Note 1: Transmitter skew is measured at the transmitter zero crosspoints.
_______________________________________________________________________________________
3
MAX221
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(VCC = +5V, 250kbps data rate, 0.1µF capacitors, transmitter loaded with 3kΩ and CL, TA = +25°C, unless otherwise noted.)
SLEW RATE vs.
LOAD CAPACITANCE
8
40
120kbps
250kbps
2
0
250kbps
-2
-4
20kbps
-6
40
SUPPLY CURRENT (mA)
20kbps
4
SLEW RATE (V/µs)
6
50
MAX221-02
50
MAX221-01
10
OPERATING SUPPLY
CURRENT vs. LOAD CAPACITANCE
MAX221-03
TRANSMITTER OUTPUT
VOLTAGE vs. LOAD CAPACITANCE
TRANSMITTER OUTPUT VOLTAGE (V)
MAX221
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
+SLEW
30
-SLEW
20
120kbps
250kbps
30
20
10
10
0
0
-8
120kbps
-10
0
1000
2000
3000
4000
5000
0
1000
2000
3000
4000
5000
0
LOAD CAPACITANCE (pF)
LOAD CAPACITANCE (pF)
1000
2000
20kbps
3000
4000
5000
LOAD CAPACITANCE (pF)
Pin Description
4
PIN
NAME
FUNCTION
1
EN
2
C1+
3
V+
Positive Voltage Generated by the Charge Pump
4
C1-
Negative Terminal of the Voltage Doubler Charge-Pump Capacitor
5
C2+
Positive Terminal of the Inverting Charge-Pump Capacitor
6
C2-
Negative Terminal of the Inverting Charge-Pump Capacitor
7
V-
8
RIN
9
ROUT
10
INVALID
11
TIN
12
FORCEON
13
TOUT
RS-232 Transmitter Output
14
GND
Ground
15
VCC
+4.5V to +5.5V Supply Voltage
16
FORCEOFF
Receiver Enable Control. Drive low for normal operation. Drive high to force the receiver output
(ROUT) into a high-impedance state.
Positive Terminal of the Voltage Doubler Charge-Pump Capacitor
Negative Voltage Generated by the Charge Pump
RS-232 Receiver Input
TTL/CMOS Receiver Output
Output of the Invalid Signal Detector. INVALID is pulled low if no valid RS-232 level is present on
the receiver input.
TTL/CMOS Transmitter Input
Drive high to override automatic circuitry, keeping transmitter and charge pump on.
FORCEOFF must be high (Table 1).
Force-Off Input, active low. Drive low to shut down transmitter, receiver, and on-board charge
pump. This overrides all automatic circuitry and FORCEON (Table 1).
_______________________________________________________________________________________
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
CBYPASS
C1
0.1µF
ISHDN
2 C1+
4 C15
C2
0.1µF
15
0.1µF
6
C3
0.1µF
VCC
3
V+
MAX221
C2+
V-
7
C4
0.1µF
C2-
11 TIN
TOUT 13
3k
RIN 8
9 ROUT
5k
1
12
EN
FORCEON
INVALID
GND
FORCEOFF
10
TO POWERMANAGEMENT
UNIT
16
14
Figure 1. Shutdown Current Test Circuit
_______________Detailed Description
Dual Charge-Pump Voltage Converter
The MAX221’s internal power supply consists of a dual
charge pump that provides a positive output voltage
(doubling charge pump) and a negative voltage (inverting charge pump) from a single +5V supply. The
charge pumps operate in continuous mode. Each
charge pump requires a flying capacitor (C1, C2) and a
reservoir capacitor (C3, C4) to generate the V+ and Vsupplies.
RS-232 Transmitter
The transmitter is an inverting level translator that converts CMOS-logic levels to 5.0V EIA/TIA-232 levels. It
guarantees a 250kbps data rate with worst-case loads
of 3kΩ in parallel with 1000pF.
When FORCEOFF is driven to ground, or when the
AutoShutdown circuitry senses invalid voltage levels on
the receiver input, the transmitter is disabled and the output is forced into a high-impedance state. The transmitter
input does not have a pull-up resistor.
RS-232 Receiver
The MAX221’s receiver converts RS-232 signals to
CMOS-logic output levels. The receiver has an inverting
three-state output and can be active or inactive. In shutdown (FORCEOFF = low) or in AutoShutdown, the
receiver is active (Table 1). Drive EN high to place the
receiver in a high-impedance state. The receiver is high
impedance when the MAX221 is in shutdown (FORCEOFF = low).
The MAX221’s INVALID output is pulled low when no
valid RS-232 signal level is detected on the receiver
input. INVALID is functional in any mode (Figures 2
and 3).
AutoShutdown
The MAX221 achieves 1µA supply current with Maxim’s
AutoShutdown feature, which operates when FORCEON
is low and FORCEOFF is high. When the device senses
no valid signal levels on the receiver input for 30µs, the
on-board charge pump and driver are shut off, reducing
supply current to 1µA. This occurs if the RS-232 cable is
disconnected or the connected peripheral transmitter is
turned off. The MAX221 turns on again when a valid
level is applied to the RS-232 receiver input. As a result,
the system saves power without changes to the existing
BIOS or operating system.
Table 1 and Figure 2c summarize the MAX221 operating modes. FORCEON and FORCEOFF override
AutoShutdown. When neither control is asserted, the
device selects between these states automatically,
based on the receiver input level. Figures 2a, 2b, and
3a depict valid and invalid RS-232 receiver levels.
Figure 3 shows the input levels and timing diagram for
AutoShutdown operation.
A device or another system with AutoShutdown connected to the MAX221 may need time to wake up.
Figure 4 shows a circuit that forces the transmitter on
for 100ms, allowing enough time for the other system to
realize that the MAX221 is awake. If the other system
transmits valid RS-232 signals within that time, the RS232 ports on both systems remain enabled.
When shut down, the device’s charge pumps are off,
V+ is pulled to VCC, V- is pulled to ground, and the
transmitter output is high impedance. The time required
to exit shutdown is typically 100µs (Figure 3b).
Software-Controlled Shutdown
For direct software control, use INVALID to indicate a
DTR or Ring Indicator signal. Connect FORCEOFF and
FORCEON together to disable AutoShutdown so the
line acts like a SHDN input.
_______________________________________________________________________________________
5
MAX221
+5V
MAX221
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
Table 1. Output Control Truth Table
OPERATION
STATUS
Shutdown
(Forced Off)
Normal Operation
(Forced On)
Normal Operation
(AutoShutdown)
Shutdown
(AutoShutdown)
FORCEON
FORCEOFF
EN
VALID
RECEIVER
LEVEL
TOUT
ROUT
X
0
0
X
High-Z
Active
X
0
1
X
High-Z
High-Z
1
1
0
X
Active
Active
1
1
1
X
Active
High-Z
0
1
0
Yes
Active
Active
0
1
1
Yes
Active
High-Z
0
1
0
No
High-Z
Active
0
1
1
No
High-Z
High-Z
X = Don’t care
FORCEOFF
+0.3V
RIN
-0.3V
30µs
COUNTER
R
TO MAX221
POWER SUPPLY
AND TRANSMITTER
POWER DOWN
FORCEON
INVALID
INVALID
INVALID IS AN INTERNALLY GENERATED SIGNAL USED BY
THE AUTOSHUTDOWN LOGIC AND APPEARS AS AN OUTPUT.
* TRANSMITTER IS DISABLED, REDUCING SUPPLY CURRENT TO 1µA IF
RECEIVER INPUT IS BETWEEN +0.3V AND -0.3V FOR AT LEAST 30µs.
Figure 2a. Entering 1µA Supply Mode via AutoShutdown
POWER DOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE
OPERATIONAL STATUS OF THE TRANSMITTER AND POWER SUPPLIES.
Figure 2c. AutoShutdown Logic
Table 2. INVALID Truth Table
+2.7V
RIN
-2.7V
30µs
COUNTER
R
TO MAX221
POWER SUPPLY
INVALID
RS-232 SIGNAL PRESENT
AT RECEIVER INPUT
INVALID OUTPUT
Yes
High
No
Low
* TRANSMITTER IS ENABLED IF:
RECEIVER INPUT IS GREATER THAN +2.7V OR LESS THAN -2.7V;
RECEIVER INPUT HAS BEEN BETWEEN +0.3V AND -0.3V FOR LESS THAN 30µs.
Figure 2b. Transmitter Enabled Using AutoShutdown
6
_______________________________________________________________________________________
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
Using INVALID
INVALID indicates when an RS-232 signal is present at
the receiver input, and therefore when the port is in use.
INVALID can be used in alternative shutdown control
schemes where it relieves the processor from constantly
polling the port for activity.
RECEIVER INPUT LEVEL
TRANSMITTER ENABLED, INVALID HIGH
+2.7V
INDETERMINATE
+0.3V
0
AUTOSHUTDOWN, TRANSMITTER DISABLED,
1µA SUPPLY CURRENT, INVALID LOW
Capacitor Selection
-0.3V
INDETERMINATE
-2.7V
TRANSMITTER ENABLED, INVALID HIGH
a)
RECEIVER
INPUT
VOLTAGE
(V)
INVALID
REGION
VCC
INVALID
OUTPUT
(V)
0
When using the minimum 0.1µF capacitors, make sure
the capacitance does not degrade excessively with
temperature. If in doubt, use capacitors with a larger
nominal value. The capacitor’s equivalent series resistance (ESR) usually rises at low temperatures and influences the amount of ripple on V+ and V-.
tINVL
tINVH
tWU
V+
VCC
0
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 the
charge-pump capacitor C1. Connect bypass capacitors as close to the IC as possible.
Transmitter Output when
Exiting Shutdown
b)
Figure 3. AutoShutdown Trip Levels
POWERMANAGEMENT
UNIT
The capacitor type used for C1–C4 is not critical for
proper operation; either polarized or nonpolarized
capacitors are acceptable. If polarized capacitors are
used, connect polarity as shown in the Typical Operating
Circuit. The charge pump requires 0.1µF capacitors.
Increasing the capacitor values (e.g., by a factor of 2)
reduces ripple on the transmitter output and slightly
reduces power consumption. C2, C3, and C4 can be
increased without changing C1’s value. However, do not
increase C1’s value without also increasing the values of
C2, C3, and C4 to maintain the proper ratios (C1 to the
other capacitors).
MASTER SHDN LINE
0.1µF
1MΩ
Figure 5 shows the transmitter output when exiting shutdown mode. The transmitter is loaded with 3kΩ in parallel with 2500pF. The transmitter output displays no
ringing or undesirable transients as the MAX221 comes
out of shutdown. Note that the transmitter is enabled only
when the magnitude of V- exceeds approximately 3V.
High Data Rates
FORCEOFF FORCEON
MAX221
The MAX221 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 the loopback test result at 120kbps,
and Figure 8 shows the same test at 250kbps.
Figure 4. AutoShutdown with Initial Turn-On to Wake Up a
Mouse or Another System
_______________________________________________________________________________________
7
MAX221
Applications Information
MAX221
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
5V/div
TIN = GND
5V/div
FORCEON =
FORCEOFF
5V/div
TIN
TOUT
5V/div
TOUT
5V/div
ROUT
TIN = VCC
2µs/div
50µs/div
Figure 5. Transmitter Output Exiting Shutdown or
Powering Up
Figure 7. Loopback Test Result at 120kbps
+5V
0.1µF
5V/div
TIN
5V/div
TOUT
5V/div
ROUT
C3
C1+
VCC
V+
C1
C1C2+
MAX221
VC4
C2
C2TOUT
TIN
RIN
ROUT
0V
EN
2µs/div
Figure 8. Loopback Test Result at 250kbps
5k
1000pF
VCC
FORCEOFF
FORCEON
GND
INVALID
___________________Chip Information
TRANSISTOR COUNT: 157
Figure 6. Loopback Test Circuit
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.
8 _____________________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.