MAXIM MAX221 User Manual

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General Description

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.

Applications

Maintenance/Diagnostic Ports
Industrial Systems
Telecommunications
Set-Top Boxes

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

MAX221

+5V, 1µA, Single RS-232 Transceiver

with AutoShutdown

________________________________________________________________

Maxim Integrated Products

1

Typical Operating Circuit

19-1520; Rev 0; 8/99

PART

MAX221CUE
MAX221CAE
MAX221EUE -40°C to +85°C

0°C to +70°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

16 TSSOP
16 SSOP
16 TSSOP

AutoShutdown is a trademark of Maxim Integrated Products.

Pin Configuration

Ordering Information

MAX221EAE -40°C to +85°C 16 SSOP

TOP VIEW

1

EN FORCEOFF

C1+

2

V+

3

MAX221

4

C1-

C2+

5

C2-

6

V-

7

RIN

8

TSSOP/SSOP

16

15

14

13

12

11

10

9

V

CC

GND

TOUT

FORCEON

TIN

INVALID

ROUT

+5V

C

BYPASS

0.1µF

C1

0.1µF

C2

0.1µF

11

12

2

4

5

6

1

C1+

C1-

C2+

C2-

TIN

ROUT9

EN

FORCEON

15

V

CC

MAX221

GND

14

V+

V-

TOUT 13

RIN 8

5k

INVALID

FORCEOFF

3

7

10

16

C3

0.1µF

C4

0.1µF

TO POWER­MANAGEMENT
UNIT

V

CC

CAPACITORS MAY BE POLARIZED OR UNPOLARIZED.

MAX221

+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(V

CC

= +5V ±10%, C1–C4 = 0.1µF, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°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.

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 (V

CC

+ 0.3V)

Output Voltages

TOUT ..............................................(V- - 0.3V) to (V+ + 0.3V)

ROUT, INVALID....................................-0.3V to (V

CC

+ 0.3V)

Short-Circuit Duration, TOUT .....................................Continuous

Continuous Power Dissipation (T

A

= +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

Figure 3

Figure 3

No load, TA= +25°C

Figure 3

I

SOURCE

= 1.0mA

I

SINK

= 1.6mA

CONDITIONS

ICC= 1µA, Figure 3

ROUT; I

SINK

= 3.2mA

Figure 3

TIN; EN, FORCEOFF, FORCEON

TA= +25°C, Figure 1

EN = VCC, 0 ≤ ROUT ≤ V

CC

TIN = 0 to V

CC

ROUT; I

SOURCE

= 1.0mA

µs30t

INVL

Receiver Positive or Negative
Threshold to INVALID Low

µs1t

INVH

Receiver Positive or Negative
Threshold to INVALID High

µs250t

WU

Receiver Threshold to
Transmitter Enabled

VVCC- 0.6

INVALID Output Voltage High

V0.4

INVALID Output Voltage Low

V

-0.3 0.3

Receiver Input Threshold,
Transmitter Disabled

-2.7

Positive threshold

V

2.7

Receiver Input Threshold,
Transmitter Enabled

µA

±0.05 ±10

Negative threshold

Output Leakage Current

V

3.5

V

OH

Output Voltage High

mA

510

I

CC

VCCSupply Current

UNITSMIN TYP MAXSYMBOLPARAMETER

V

0.4

V

OL

Output Voltage Low

V

0.8

V

IL

Input Threshold Low

µA

110

I

SHDN

Shutdown Supply Current

µA

110

I

AS

AutoShutdown Supply Current

µA

±1

I

IN

Input Leakage Current

TIN, EN, FORCEOFF

V

2.4

V

IH

Input Threshold High

DC CHARACTERISTICS

LOGIC INPUTS

AUTOSHUTDOWN

MAX221

+5V, 1µA, Single RS-232 Transceiver

with AutoShutdown

_______________________________________________________________________________________ 3

TIMING CHARACTERISTICS

(VCC= +5V ±10%, C1–C4 = 0.1µF, TA = T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

ELECTRICAL CHARACTERISTICS (continued)

(V

CC

= +5V ±10%, C1–C4 = 0.1µF, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at TA= +25°C.)

CONDITIONS UNITSMIN TYP MAXSYMBOLPARAMETER

V

CC

= V+ = V- = 0, V

OUT

= ±2V

Driver loaded with 3kΩ to ground

TA= +25°C, V

CC

= 5V

VCC= 5V, no hysteresis in shutdown

TA= +25°C, VCC= 5V

TA= +25°C, VCC= 5V

mA±10 ±60Output Short-Circuit Current

Ω300Output Resistance

V±5 ±9Output Voltage Swing

kΩ357Input Resistance

V0.5Input Hysteresis

V1.7 2.4Input Threshold High

V0.8 1.2Input Threshold Low

V-25 25Input Voltage Range

RL= 3kΩ to 7kΩ, CL= 50pF to 1000pF,
VCC= 4.5V

CONDITIONS

kbps

250

Maximum Data Rate

UNITSMIN TYP MAXSYMBOLPARAMETER

TA= +25°C, VCC= 5V, RL= 3kΩ to 7kΩ,
CL= 500pF to 1000pF, measured from

-3V to +3V or +3V to -3V

(Note 1)

Normal operation

Normal operation

CL= 150pF

V/µs

3630

Transition-Region Slew Rate

ns

50

|

t

PHL

- t

PLH|

Receiver Skew

ns

200

|

t

PHL

- t

PLH|

Transmitter Skew

ns

200

Receiver Output Disable Time

ns

300

Receiver Output Enable Time

µs

0.15

t

PHL,tPLH

Receiver Propagation Delay

Note 1: Transmitter skew is measured at the transmitter zero crosspoints.

RECEIVER INPUT

TRANSMITTER OUTPUT

MAX221

+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown

4 _______________________________________________________________________________________

Typical Operating Characteristics

(VCC= +5V, 250kbps data rate, 0.1µF capacitors, transmitter loaded with 3kΩ and CL, TA= +25°C, unless otherwise noted.)

-10

-6

-8

-2

-4

2

0

4

8

6

10

0

1000

2000

3000

4000

5000

TRANSMITTER OUTPUT

VOLTAGE vs. LOAD CAPACITANCE

MAX221-01

LOAD CAPACITANCE (pF)

TRANSMITTER OUTPUT VOLTAGE (V)

250kbps

250kbps

120kbps

20kbps

20kbps

120kbps

0

10

20

30

40

50

0

1000

2000

3000

4000

5000

SLEW RATE vs.

LOAD CAPACITANCE

MAX221-02

LOAD CAPACITANCE (pF)

SLEW RATE (V/µs)

+SLEW

-SLEW

0

10

20

30

40

50

0

1000

2000

3000

4000

5000

OPERATING SUPPLY

CURRENT vs. LOAD CAPACITANCE

MAX221-03

LOAD CAPACITANCE (pF)

SUPPLY CURRENT (mA)

250kbps

20kbps

120kbps

FUNCTIONPIN NAME

1

EN

Receiver Enable Control. Drive low for normal operation. Drive high to force the receiver output
(ROUT) into a high-impedance state.

2 C1+ Positive Terminal of the Voltage Doubler Charge-Pump Capacitor

3 V+ Positive Voltage Generated by the Charge Pump

7 V- Negative Voltage Generated by the Charge Pump

6 C2- Negative Terminal of the Inverting Charge-Pump Capacitor

5 C2+ Positive Terminal of the Inverting Charge-Pump Capacitor

4 C1- Negative Terminal of the Voltage Doubler Charge-Pump Capacitor

12 FORCEON

Drive high to override automatic circuitry, keeping transmitter and charge pump on.
FORCEOFF must be high (Table 1).

11 TIN TTL/CMOS Transmitter Input

10

INVALID

Output of the Invalid Signal Detector. INVALID is pulled low if no valid RS-232 level is present on
the receiver input.

9 ROUT TTL/CMOS Receiver Output

8 RIN RS-232 Receiver Input

Pin Description

16

FORCEOFF

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).

15 V

CC

+4.5V to +5.5V Supply Voltage

14 GND Ground

13 TOUT RS-232 Transmitter Output

MAX221

+5V, 1µA, Single RS-232 Transceiver

with AutoShutdown

_______________________________________________________________________________________ 5

_______________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 (FORCE-
OFF = 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 V

CC

, 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.

Figure 1. Shutdown Current Test Circuit

I

SHDN

+5V

0.1µF

C2

0.1µF

C1

0.1µF

6

11

12

2

4

5

1

C1+

C1-

C2+

C2-

TIN

ROUT9

EN

FORCEON

C

BYPASS

15

V

CC

MAX221

GND

FORCEOFF

14

TOUT 13

5k

INVALID

V+

V-

RIN 8

3

7

10

16

C3

0.1µF

C4

0.1µF

3k

TO POWER­MANAGEMENT
UNIT

MAX221

+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown

6 _______________________________________________________________________________________

Table 1. Output Control Truth Table

1 No

Shutdown
(AutoShutdown)

High-Z1 High-Z0

1

1

1

OPERATION

STATUS

X0

VALID

RECEIVER

LEVEL

EN

X

Shutdown
(Forced Off)

X

Normal Operation
(Forced On)

X0

Yes

Normal Operation
(AutoShutdown)

No

Yes0

0

High-Z

Active

Active

High-Z

TOUT

Active

High-Z

Active

0

FORCEOFF

1

0

1

1

1

1

High-Z

High-Z

Active

Active

ROUT

High-Z

Active

Active

X

FORCEON

1

X

1

0

0

0

X = Don’t care

RS-232 SIGNAL PRESENT

AT RECEIVER INPUT

INVALID OUTPUT

Yes High

No Low

Table 2. INVALID Truth Table

Figure 2b. Transmitter Enabled Using AutoShutdown

Figure 2a. Entering 1µA Supply Mode via AutoShutdown

Figure 2c. AutoShutdown Logic

+0.3V

TO MAX221

RIN

-0.3V

* TRANSMITTER IS DISABLED, REDUCING SUPPLY CURRENT TO 1µA IF
RECEIVER INPUT IS BETWEEN +0.3V AND -0.3V FOR AT LEAST 30µs.

30µs

COUNTER

R

POWER SUPPLY
AND TRANSMITTER

INVALID

+2.7V

RIN

-2.7V

* 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.

30µs

COUNTER

R

TO MAX221
POWER SUPPLY

INVALID

FORCEOFF

FORCEON

INVALID

INVALID IS AN INTERNALLY GENERATED SIGNAL USED BY
THE AUTOSHUTDOWN LOGIC AND APPEARS AS AN OUTPUT.

POWER DOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE
OPERATIONAL STATUS OF THE TRANSMITTER AND POWER SUPPLIES.

POWER DOWN

Applications Information

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.

Capacitor Selection

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).

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-.

Power-Supply Decoupling

In most circumstances, a 0.1µF VCCbypass 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

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

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.

MAX221

+5V, 1µA, Single RS-232 Transceiver

with AutoShutdown

_______________________________________________________________________________________ 7

Figure 4. AutoShutdown with Initial Turn-On to Wake Up a
Mouse or Another System

b)

a)

Figure 3. AutoShutdown Trip Levels

+2.7V

+0.3V

0

-0.3V

RECEIVER INPUT LEVEL

-2.7V

RECEIVER

INPUT

VOLTAGE

(V)

V

CC

INVALID

OUTPUT

(V)

0

V+

V

CC

0

V-

TRANSMITTER ENABLED, INVALID HIGH

INDETERMINATE

AUTOSHUTDOWN, TRANSMITTER DISABLED,

1µA SUPPLY CURRENT, INVALID LOW

INDETERMINATE

TRANSMITTER ENABLED, INVALID HIGH

t

INVL

t

INVH

INVALID
REGION

t

WU

POWER-

MANAGEMENT

UNIT

MASTER SHDN LINE

0.1µF1MΩ

FORCEOFF

FORCEON

MAX221

MAX221

+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown

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.

TRANSISTOR COUNT: 157

___________________Chip Information

Figure 7. Loopback Test Result at 120kbps

Figure 8. Loopback Test Result at 250kbps

Figure 6. Loopback Test Circuit

Figure 5. Transmitter Output Exiting Shutdown or
Powering Up

5V/div

TIN = GND

5V/div

TIN = V

50µs/div

+5V

0.1µF

V

CC

MAX221

TOUT

C1

C2

C1+

C1-

C2+

C2-

TIN

FORCEON =
FORCEOFF

TOUT

CC

5V/div

5V/div

5V/div

2µs/div

TIN

TOUT

ROUT

C3

5V/div

V+

5V/div

V-

C4

5V/div

TIN

TOUT

ROUT

5k

INVALID

RIN

1000pF

2µs/div

ROUT

0V

V

CC

EN

FORCEOFF
FORCEON

GND