FEATURES
RS-232 and RS-422 on One Chip
Single +5 V Supply
0.1 mF Capacitors
Short Circuit Protection
Excellent Noise Immunity
Low Power BiCMOS Technology
High Speed, Low Skew RS-422 Operation
–408C to +858C Operations
APPLICATIONS
DTE-DCE Interface
Packet Switching
Local Area Networks
Data Concentration
Data Multiplexers
Integrated Services Digital Network (ISDN)
GENERAL DESCRIPTION
The AD7306 line driver/receiver is a 5 V monolithic product
which provides an interface between TTL signal levels and dual
standard EIA RS-232/RS-422 signal levels. The part contains
two RS-232 drivers, one RS-422 driver, one RS-232 receiver,
and one receiver path which can be configured either as RS-232
or as RS-422.
An internal charge pump voltage converter facilitates operation
from a single +5 V power supply. The internal charge pump
generates ±10 V levels allowing RS-232 output levels to be developed without the need for external bipolar power supplies.
A highly efficient charge pump design allows operation using
non polarized, miniature 0.1 µF capacitors. This gives a consid-
erable saving in printed circuit board space over conventional
products which can use up to 10 µF capacitors. The charge
pump output voltages may also be used to power external circuitry which requires dual supplies.
RS-232/RS-422 Transceiver
AD7306
FUNCTIONAL BLOCK DIAGRAM
The RS-232 channels are suitable for communications rates up
to 100 kHz and the RS-422 channels are suitable for high speed
communications up to 5 MHz. The RS-422 transmitter complementary outputs are closely matched and feature low timing
skew between the complementary outputs. This is often an essential requirement to meet tight system timing specifications.
All inputs feature ESD protection, all driver outputs feature
high source and sink current capability and are internally protected against short circuits on the outputs. An epitaxial layer is
used to guard against latch-up.
The part is available in a 24-lead SOIC and 24-pin plastic DIP
package.
REV. B
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700Fax: 617/326-8703
AD7306–SPECIFICA TIONS
(VCC = +5 V 6 5%, C1 = C2 = C3 = C4 = 0.1 mF. All specifications T
T
unless otherwise noted.)
MAX
MIN
to
ParameterMinTypMaxUnitsTest Conditions/Comments
RS-232 DRIVER
TTL Input Logic Low, V
TTL Input Logic High, V
INL
INH
2.0V
Input Logic Current0.1±10µAV
0.8V
= 0 V to V
IN
CC
RS-232 High Level Output Voltage5.07.3VRL = 3 kΩ
RS-232 Low Level Output Voltage–5.0–6.5VR
Output Short Circuit Current±5±12mAV
Slew Rate82030V/µsC
4V/µsC
Output Resistance (Powered Down)30010MΩVCC = 0 V, V
= 3 kΩ
L
= 0 V, TA = 0°C to +70°C
OUT
= 50 pF, RL = 3 kΩ
L
= 2500 pF, RL = 3 kΩ
L
OUT
= ±3 V
RS-232 RECEIVER
Input Voltage Range–15+15V
RS-232 Input Threshold Low0.81.3V
RS-232 Input Threshold High1.72.4V
RS-232 Input Hysteresis0.10.41.0V
RS-232 Input Resistance357kΩ
TTL Output Voltage Low, V
TTL Output Voltage High, V
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Lead Temperature (Soldering, 10 secs) . . . . . . . . . . . +300°C
*Stresses above those listed under “Absolute Maximum Ratings” may cause
permanent damage to the device. This is a stress rating only and functional
operation of the device at these or any other conditions above those listed in the
operational sections of this specification is not implied. Exposure to absolute
maximum ratings for extended periods of time may affect device reliability.
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the AD7306 features proprietary ESD protection circuitry, permanent damage may
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.
AD7306JR0°C to +70°C24-Lead SOICR-24
AD7306JN0°C to +70°C24-Pin DIPN-24
AD7306AR–40°C to +85°C24-Lead SOICR-24
AD7306AN–40°C to +85°C24-Pin DIPN-24
–3–
AD7306
PIN FUNCTION DESCRIPTION
SOICDIP
PinPinMnemonicFunction
119V+Internally Generated Positive Supply (+9 V nominal). A 0.1 µF capacitor must be connected
between this pin and GND.
2, 320, 22C1+, C1–External Capacitor 1 Terminals. A 0.1 µF capacitor must be connected between these pins.
423 R2
524 T1
61 T2
72 V
83 R1
94 R1
105T3
116T3
IN
OUT
OUT
CC
(B)RS-422 Receiver R1, Differential Input B.
IN
/R1IN (A)Receiver R1 Input. May be configured to accept either single ended RS-232 levels or
IN
(B)RS-422 Transmitter (Driver) T3, Differential Output B.
OUT
(A)RS-232 Transmitter (Driver) T3, Differential Output A.
OUT
12, 1316, 21NCNo Connect Pins.
14, 187, 11GNDGround Pin. Must be connected to 0 V.
158232/
169T3
1710R1
1912T2
2013T1
2114R2
422 SELSelect Input. This input configures Receiver R1 to accept either RS-232 or RS-422 signal lev-
IN
OUT
IN
IN
OUT
22, 2315, 17C2+, C2–External Capacitor 2 Terminals. A 0.1 µF capacitor must be connected between these pins.
2418V–Internally Generated Negative Supply (–9 V nominal). A 0.1 µF capacitor must be connected
RS-232 Receiver R2 Input. This input accepts RS-232 input voltages.
Figure 2. RS-422 Driver. Propagation Delay Test Circuit
T3 (B)
OUT
OUT
V
OD
RL
DIFF
T3
IN
T3
T3 (A)
Figure 3. RS-422 Driver. Voltage Measurement Test
Circuit
REV. B
Figure 6. RS-232/RS-422 Receiver Enable Timing
–5–
AD7306
GENERAL DESCRIPTION
The AD7306 drivers/receivers provide an interface which is
compatible with RS-232/RS-422 standard interfaces. As both
standards are widely accepted it is often necessary to provide an
interface which is compatible with both. The AD7306 is ideally
suited to this type of application as both standards may be met
using a single package. This part contains two RS-232 drivers,
one RS-422 driver, one RS-232 receiver, and one receiver path
which can be configured as either RS-232 or RS-422. This receiver is configured using the 232/
422 SEL pin.
This part also contains an internal charge pump voltage converter which facilitates operation using a single +5 V power
supply.
Charge Pump DC-DC Voltage Generator
The charge pump voltage generator uses a switched capacitor
technique to develop ±10 V levels from an input +5 V supply. A
highly efficient charge pump design coupled with a high frequency internal oscillator permit operation using four 0.1 µF
capacitors.
+10V
OUTPUT
–10V
OUTPUT
+5V
INPUT
SUPPLY
V
CC
C1+
0.1µF
±10V
POWER SUPPLY
GENERATOR
C1–C2+C2–
C1
C2
0.1µF
V+
V–
C3
0.1µF
C4
0.1µF
Figure 7. Charge Pump Voltage Generator
Capacitors C1 and C2 act as charge storage capacitors while C3
and C4 provide output smoothing. For correct operation all four
capacitors must be included. Either polarized or nonpolarized
capacitors may be used for C1–C4. If a polarized type is used,
then the correct polarity should be observed. This may be ignored with nonpolarized type capacitors.
The charge pump output voltages, V+ and V–, are used internally to power the RS-232 transmitters. This permits RS-232
output levels to be developed on the RS-232 transmitter outputs. The charge pump output voltages may also be used to
power external circuitry if the current requirements are small.
Please refer to the Typical Performance Characteristics.
The generator rise time after power up is 200 µs typical. This
time is necessary to completely charge the storage capacitors in
the charge pump. Therefore, RS-232 data transmission should
not be initiated until this time has elapsed after switch on. This
will ensure that valid data is always transmitted.
RS-232 Drivers
The RS-232 drivers in the AD7306 meet the EIA RS-232
specifications. The drivers are inverting level shifters which
convert TTL/CMOS levels into RS-232 output levels. The input switching threshold is typically 1.3 V. With a typical
RS-232 load, the output levels are ± 7.5 V. Under worst case
load conditions, the drivers are guaranteed to provide ±5 V
which meets the minimum RS-232 requirement. The output
slew rate is internally limited to <30 V/µs without the need for
an external slew limiting capacitor. Short circuit protection is
also provided which prevents damage in the event of output
fault conditions. Active current limiting is used which limits the
output short circuit current to less than 12 mA in the event of
an output fault. This type of current limiting does not degrade
the output voltage swing under normal loading conditions as
would be the case with conventional passive limiting.
The powered-down output impedance is typically 10 MΩ. This
is considerably larger than the 300 Ω minimum value required
by the RS-232 specification. It provides additional protection
under fault conditions where another powered-up transmitter
output is inadvertently shorted to the powered-down device.
RS-232 Receivers
The receivers are inverting level shifters which accept RS-232
input levels (±3 V to ±15 V) and translates them into 5 V
TTL/CMOS levels. The input switching thresholds are 0.8 V
minimum and 2.4 V maximum which are well within the
RS-232 requirement of ±3 V. Internal 5 kΩ pull-down resistors
to GND are provided on the receiver inputs. This ensures that
an unconnected input will be interpreted as a low level giving a
Logic “1” on the TTL/CMOS output. Excellent noise immunity is achieved by the use of hysteresis and internal filtering
circuitry. The filter rejects noise glitches of up to 0.5 µs in
duration.
RS-422 Driver
The RS-422 driver on the AD7306 accepts a TTL/CMOS input and translates it into a differential RS-422 level signal. The
input switching threshold is typically 1.3 V. The unloaded output differential voltage is typically ± 5 V (see Typical Performance Characteristics). Short circuit protection is provided on
the output which limits the current to less than 150 mA.
RS-422 Receiver
The RS-422 receiver on the AD7306 accepts a differential input signal and translates it into a TTL/CMOS output level.
The input resistance on both differential inputs is 5 kΩ typical.
With the receiver inputs unconnected (floating), internal biasing ensures that the receiver output is a Logic “1.”
Excellent noise immunity and high transmission speed is
achieved using the differential configuration.
–6–
REV. B
T ypical Performance Characteristics–AD7306
10
0
10
6
2
2
4
0
8
864
RS-232 TRANSMITTER OUTPUT CURRENT – mA
RS-232 TRANSMITTER OUTPUT VOLTAGE – ±V
–V CURRENT
E
+V CURRENT
E
6
0
60
3
1
10
2
0
5
4
50403020
DIFFERENTIAL O/P CURRENT – mA
DIFFERENTIAL O/P VOLTAGE – V
V = 5.25V
CC
V = 5.0V
CC
V = 4.75V
CC
10
90
100
0%
10ns
5
1V1V
A32 4 V
10
V+
VOLTAGE OUTPUT ± – V
8
6
4
2
0
5
0
V-
V = 5V
CC
T + 25°C
OUTPUT CURRENT ± – mA
Figure 8. V+ and V– Voltage vs. Current
25
+V
20
15
10
SLEW RATE –V/µs
E
–V
E
30
25201510
Figure 11. RS-232 Driver Output Voltage vs. Current
5
0
0
LOAD CAPACITANCE – pF
200015001000500
2500
Figure 9. RS-232 Driver Slew Rate vs. Load Capacitance
A4 -0 370 V
100
90
10
0%
1µs5V5V
Figure 10. RS-232 Driver; RL = 5 kΩ, CL = 50 pF
Figure 12. RS-422 Driver Output Current vs. Output Voltage
Figure 13. RS-422 Driver; R
= 100 Ω, CL1 = CL2 = 100 pF
LDIFF
REV. B
–7–
AD7306
Single-Ended Data Transmission
Single-ended interfaces are used for low speed, short distance
communications such as from a computer terminal to a printer.
A single line is used to carry the signal. Various standards have
been developed to standardize the communication link, the most
popular of these being the RS-232. The RS-232 standard was
introduced in 1962 by the EIA and has been widely used
throughout the industry. The standard has been revised several
times, and the current revision is known as EIA-232E. The
RS-232 standard is suitable for single-ended data transmission
at relatively slow data rates over short distances. A typical
RS-232 interface is shown in Figure 14.
DATA
IN
TX
RS-232 CHANNEL
RX
DATA
OUT
Figure 14. Single-Ended RS-232 Interface
Table I. Comparison of RS-232 and RS-422 Interface Standards
SpecificationEIA-232ERS-422
Transmission TypeSingle-EndedDifferential
Maximum Data Rate20 kB/s10 MB/s
Maximum Cable LengthLoad Dependent4000 ft.
Minimum Driver Output Voltage±5 V±1.5 V
Slew Rate30 V/µs max
Receiver Input Resistance3 kΩ to 7 kΩ4 kΩ min
Receiver Input Sensitivity±3 V±200 mV
Receiver Input Voltage Range±15 V±7 V
No. of Drivers per Line11
No. of Receivers per Line110
Differential Data Transmission
When transmitting at high data rates, over long distances and
through noisy environments, single-ended data transmission is
often inadequate. In this type of application, differential data
transmission offers superior performance. Differential transmission uses two signal lines to transmit data. It rejects ground
shifts and is insensitive to noise signals which appear as common mode voltages on the transmission lines. To accommodate
faster data communication, the differential RS-422 standard was
developed. Therefore, it can be used to reliably transmit data at
higher speeds and over longer distances than single-ended transmission. A typical RS-422 interface is shown in Figure 15.
DATA
IN
TX
RS-422 CHANNEL
RX
DATA
OUT
Figure 15. Differential RS-422 Interface
C1624a–2–8/94
0.6141 (15.60)
0.5985 (15.20)
2413
PIN 1
0.0118 (0.30)
0.0040 (0.10)
0.0500
(1.27)
BSC
24-Lead SOIC (R-24)
0.2992 (7.60)
0.2914 (7.40)
0.4193 (10.65)
0.3937 (10.00)
0.0125 (0.32)
0.0091 (0.23)
0.0192 (0.49)
0.0138 (0.35)
121
0.1043 (2.65)
0.0926 (2.35)
SEATING
PLANE
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
SEATING
0.0291 (0.74)
0.0098 (0.25)
0.0500 (1.27)
8°
0°
0.0157 (0.40)
x 45°
PLANE
0.016 (0.41)
NOTES
1.
2.
–8–
24-Lead Pin Plastic DIP (N-24)
1.228 (31.19)
1.226 (31.14)
0.02 (0.5)
LEAD NO. 1 IDENTIFIED BY DOT OR NOTCH.
PLASTIC LEADS WILL BE EITHER SOLDER DIPPED OR TIN LEAD PLATED
IN ACCORDANCE WITH MIL-M-385 10 REQUIREMENTS.
0.11 (2.79)
0.09 (2.28)
0.07(1.78)
0.05 (1.27)
0.260 ± 0.001
(6.61 ± 0.03)
0.130 (3.30)
0.128 (3.25)
0° - 15°
0.32 (8.128)
0.30 (7.62)
0.011 (0.28)
0.009 (0.23)
REV. B
PRINTED IN U.S.A.
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