ADM3311EARS-REEL25 [ADI]
15 kV ESD Protected, +2.7 V to +3.6 V Serial Port Transceiver with Green Idle⑩; 15千伏ESD保护， + 2.7V至+ 3.6V串行端口收发器与绿色Idle⑩
| 型号： | ADM3311EARS-REEL25 |
| 厂家： | 
ADI |
| 描述： | 15 kV ESD Protected, +2.7 V to +3.6 V Serial Port Transceiver with Green Idle⑩ |
| 文件： | 总12页 (文件大小：181K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
15 kV ESD Protected, +2.7 V to +3.6 V
™
a
Serial Port Transceiver with Green Idle
ADM3311E*
FEATURES
Green Idle Power Saving Mode
Full RS-232 Compliance
FUNCTIONAL BLOCK DIAGRAM
C1
0.1F
Operates with 3 V Logic
Low EMI
Ultralow Power CMOS: 450 A Operation
Low Power Shutdown: 20 nA
460 kbits/s Data Rate
0.1 F to 1 F Charge Pump Capacitors
Single +2.7 V to +3.6 V Power Supply
One Receiver Active in Shutdown
ESD >15 kV
C4
0.1F
C3
28
27
26
25
24
23
1
2
3
4
5
6
V+
C3+
0.1F
0.1F
GND
C2+
CERAMIC
VOLTAGE
TRIPLER/
INVERTER
+3V TO ؎9V
V
V
C3–
V–
CC
CC
1F
C5
0.1F
C2
0.1F
C2–
EN
ENABLE
INPUT
C1–
SD
SHUTDOWN
INPUT
C1+
Pin Compatible with DS14C335
22
21
20
19
18
17
16
15
APPLICATIONS
Laptop Computers
Notebook Computers
Printers
Peripherals
Modems
7
8
9
T1
IN
T1
T1
OUT
OUT
OUT
EIA/TIA-232
OUTPUTS
CMOS
T2
T2
T3
T2
IN
INPUTS*
T3
T3
IN
10
11
12
13
14
R1
R1
R2
R3
R4
R1
IN
IN
IN
IN
OUT
OUT
R2
R2
EIA/TIA-232
INPUTS**
CMOS
OUTPUTS
R3
R3
R4
OUT
R4
OUT
GENERAL DESCRIPTION
The ADM3311E is a three driver/five receiver product designed
to fully meet the EIA-232 standard while operating with a single
+2.7 V to +3.6 V power supply. The device features an on-board,
charge pump, dc-to-dc converter, eliminating the need for dual
power supplies. This dc-to-dc converter contains a voltage tri-
pler and voltage inverter, which internally generates positive and
negative supplies from the input +3 V power supply. The dc-
to-dc converter operates in Green Idle Mode, whereby the
charge pump oscillator is gated on and off to maintain the out-
put voltage at 7.25 V under varying load conditions. This
minimizes the power consumption and makes these products
ideal for battery powered portable devices.
R5
R5
R5
OUT
IN
ADM3311E
NOTES:
* INTERNAL 400k⍀ PULL-UP RESISTOR ON EACH CMOS INPUT
** INTERNAL 5k⍀ PULL-DOWN RESISTOR ON EACH RS-232 INPUT
A shutdown facility is also provided that reduces the power
consumption to 3 µW. While in shutdown, one receiver remains
active, thereby allowing monitoring of peripheral devices. This
feature allows the device to be shut down until a peripheral device
begins communication. The active receiver can alert the processor,
which can then take the ADM3311E out of the shutdown
mode.
The ADM3311E is suitable for operation in harsh electrical
environments and contains ESD protection up to 15 kV on all
I-O lines.
The ADM3311E is fabricated using CMOS technology for
minimal power consumption. It features a high level of over-
voltage protection and latch-up immunity.
The ADM3311E contains three drivers and five receivers and
is intended for serial port applications on notebook/laptop
computers.
The ADM3311E is packaged in a 28-lead SSOP/TSSOP
package.
*Protected by Patent No. 5,606,491.
Green Idle is a trademark of Analog Devices, Inc.
REV. A
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: 781/329-4700
Fax: 781/326-8703
World Wide Web Site: http://www.analog.com
© Analog Devices, Inc., 2000
(VCC = +2.7 V to +3.6 V, C1–C5 = 0.1 F. All specifications TMIN to TMAX unless
otherwise noted.)
ADM3311E–SPECIFICATIONS
Parameter
Min
Typ
Max
Units
Test Conditions/Comments
Operating Voltage Range
VCC Power Supply Current
+2.7
+3.3
0.45
+3.6
1
V
mA
VCC = 3.0 V to 3.6 V, TA = 0°C to +85°C,
No Load
0.45
4.5
mA
VCC = 2.7 V to 3.6 V, TA = –40°C to +85°C,
No Load
35
1
25
1
0.8
0.4
mA
µA
µA
µA
V
V
V
V
V
µA
V
V
V
V
V
V
kΩ
V
V
RL = 3 kΩ to GND on all TOUTS
Shutdown Supply Current
Input Pull-Up Current
Input Leakage Current, SD, EN
Input Logic Threshold Low, VINL
0.02
10
TIN = GND
TIN, EN, SD
TIN, EN, SD, VCC = 2.7 V
TIN, EN, SD
Input Logic Threshold High, VINH
CMOS Output Voltage Low, VOL
CMOS Output Voltage High, VOH
CMOS Output Leakage Current
Charge Pump Output Voltage, V+
Charge Pump Output Voltage, V–
EIA-232 Input Voltage Range
EIA-232 Input Threshold Low
EIA-232 Input Threshold High
EIA-232 Input Hysteresis
2.0
0.4
5
IOUT = 1.6 mA
VCC – 0.6
IOUT = –200 µA
EN = VCC, 0 V < ROUT < VCC
No Load
0.05
7.25
–7.25
No Load
–25
0.4
+25
2.4
7
1.3
2.0
0.14
5
6.4
5.5
EIA-232 Input Resistance
3
Output Voltage Swing (VCC = 3.0 V)
Output Voltage Swing (VCC = 2.7 V)
Transmitter Output Resistance
RS-232 Output Short Circuit Current
Maximum Data Rate
Receiver Propagation Delay, TPHL, TPLH
Receiver Output Enable Time, tER
Receiver Output Disable Time, tDR
Transmitter Propagation Delay, TPHL, TPLH
Transition Region Slew Rate
5.0
All Transmitter Outputs
Loaded with 3 kΩ to Ground
VCC = 0 V, VOUT = 2 V
300
Ω
15
460
0.3
100
300
500
18
60
mA
kbps
µs
RL = 3 kΩ to 7 kΩ, CL = 50 pF to 1000 pF
CL = 150 pF
ns
ns
ns
V/µs
RL = 3 kΩ, CL = 1000 pF
6
RL = 3 kΩ, CL = 50 pF to 1000 pF,
Measured from +3 V to –3 V or –3 V to +3 V
IEC1000-4-2 Contact Discharge
IEC1000-4-2 Air Discharge
Human Body Model, MIL-STD-883B
IEC1000-4-4
ESD Protection (I-O Pins)
8
15
3.0
4
kV
kV
kV
kV
ESD Protection (All Other Pins)
EFT Protection (I-O Pins)
EMI Immunity
10
V/m
IEC1000-4-3
Specifications subject to change without notice.
Operating Temperature Range
ABSOLUTE MAXIMUM RATINGS*
(TA = +25°C unless otherwise noted)
Industrial (A Version) . . . . . . . . . . . . . . . . –40°C to +85°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . .+300°C
ESD Rating (MIL-STD-883B) (I-O Pins) . . . . . . . . . . 15 kV
ESD Rating (MIL-STD-883B) (Except I-O) . . . . . . . 3.0 kV
ESD Rating (IEC1000-4-2 Contact) (I-O Pins) . . . . . . 8 kV
ESD Rating (IEC1000-4-2 Air) (I-O Pins) . . . . . . . . . 15 kV
EFT Rating (IEC1000-4-4) (I-O Pins) . . . . . . . . . . . . . 4 kV
VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +4 V
V+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (VCC –0.3 V) to +8 V
V– . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +0.3 V to –8 V
Input Voltages
TIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +6 V
RIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 V
Output Voltages
*This is a stress rating only and functional operation of the device at these or any
other conditions above those indicated in the operation sections of this specifica-
tion is not implied. Exposure to absolute maximum rating conditions for extended
periods of time may affect reliability.
TOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ROUT . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to (VCC +0.3 V)
Short Circuit Duration
TOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Continuous
Power Dissipation
15 V
RU-28 TSSOP (Derate 12 mW/°C Above +70°C) . . 900 mW
RS-28 SSOP (Derate 10 mW/°C Above +70°C) . . . . 900 mW
–2–
REV. A
ADM3311E
PIN FUNCTION DESCRIPTIONS
Mnemonic
Function
VCC
Power Supply Input +2.7 V to +3.6 V. Requires capacitor of 1 µF or greater to GND.
V+
V–
GND
C1+, C1–
Internally generated positive supply (+7.25 V nominal) Capacitor C4 is connected between VCC and V+.
Internally generated negative supply (–7.25 V nominal) Capacitor C5 is connected between V– and GND.
Ground Pin. Must be connected to 0 V.
External capacitor 1 is connected between these pins. A 0.1 µF capacitor is recommended, but larger capacitors
up to 1 µF may be used.
C2+, C2–
C3+, C3–
TIN
External capacitor 2 is connected between these pins. A 0.1 µF capacitor is recommended, but larger capacitors
up to 1 µF may be used.
External capacitor 3 is connected between these pins. A 0.1 µF capacitor is recommended, but larger capacitors
up to 1 µF may be used.
Transmitter (Driver) Inputs. These inputs accept TTL/CMOS levels. An internal 400 kΩ pull-up resistor to VCC
is connected on each input.
TOUT
RIN
Transmitter (Driver) Outputs, (typically 6.4 V).
Receiver Inputs. These inputs accept RS-232 signal levels. An internal 5 kΩ pull-down resistor to GND is
connected on each of these inputs.
ROUT
EN
Receiver Outputs. These are TTL/CMOS levels.
Receiver Enable. A high level three-states all the receiver outputs.
SD
Shutdown Control. A high level will disable the charge pump and reduce the quiescent current to 20 nA.
All transmitters and receivers R1–R4 are disabled. Receiver R5 remains active in shutdown.
Table I. Truth Table
Status TOUT1–3 ROUT1–4 ROUT
PIN CONFIGURATION
SD
EN
5
1
2
V+
28
27
26
25
24
23
22
21
C3+
GND
C3–
V–
0
0
Normal
Enabled
Enabled
Enabled
C2+
Operation
3
V
CC
0
1
Receivers Enabled
Disabled Disabled
4
C2–
Disabled
5
C1–
SD
EN
1
1
0
1
Shutdown Disabled Disabled Enabled
Shutdown Disabled Disabled Disabled
6
C1+
ADM3311E
TOP VIEW
(Not to Scale)
7
T1
IN
T1
OUT
8
T2
IN
T2
OUT
9
T3
IN
20 T3
OUT
10
11
12
13
14
19
18
17
16
15
R1
R1
OUT
OUT
OUT
OUT
OUT
IN
IN
IN
IN
R2
R3
R4
R5
R2
R3
R4
R5
IN
ORDERING GUIDE
Temperature
Range
Package
Descriptions
Package
Option
Model
ADM3311EARS-Reel 2.5
ADM3311EARU-Reel 2.5
–40°C to +85°C
–40°C to +85°C
28-Lead Shrink Small Outline (SSOP)
28-Lead Thin Shrink Small Outline (TSSOP)
RS-28
RU-28
REV. A
–3–
–Typical Performance Characteristics
ADM3311E
10
8
90
80
T
HIGH
OUT
EN 55022 CLASS B
CONDUCTED QUASI-PEAK dBV
6
70
60
50
40
30
20
10
4
2
0
–2
–4
–6
–8
T
LOW
OUT
0
500
1000
1500
2000
2500
100k
1M
10M
FREQUENCY – Hz
LOAD CAPACITANCE – pF
Figure 1. EMC Conducted Emissions
Figure 4. Transmitter Output High/Low vs. Load
Capacitance
0.57
0.56
0.55
0.54
0.53
0.52
0.51
0.50
70
60
50
40
30
20
10
0
EN 55022 CLASS B
RADIATED EMISSIONS dBV/m (EUT at 3m)
20
40
60
80
100
120
140
160
180
200
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
3.5
3.6
FREQUENCY – MHz
V
– Volts
CC
Figure 2. EMC Radiated Emissions
Figure 5. Power Supply Current vs. Power Supply Voltage
(Unloaded)
8
7
25
20
15
10
5
6
5
V+
4
3
2
1
0
–1
–2
–3
–4
–5
–6
–7
–8
V–
0
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
3.5
3.6
0
2
4
6
8
10
12
14
16
18
20
V
– Volts
I
– mA
CC
LOAD
Figure 3. Charge Pump V+, V– vs. Load Current
Figure 6. Power Supply Current vs. Power Supply Voltage
(RL = 3 kΩ)
–4–
REV. A
ADM3311E
12
10
8
40
35
30
25
20
6
15
10
5
4
2
0
0
0
50
100
150
200
250
300
0
150
470
1000
1500
2000
2500
LOAD CAPACITANCE – pF
OSCILLATOR FREQUENCY – kHz
Figure 7. Slew Rate vs. Load Capacitance
Figure 10. Load Current vs. Oscillator Frequency
40
Tek Stop 500kS/s
429 Acqs
T
]
[
35
30
25
20
15
10
5
T
T
SD
1
Tx O/P HIGH
2
Ch1 5.00V
Ch2 5.00V
M 100s Ch1
0V
0
0
500
1000
1500
2000
2500
LOAD CAPACITANCE – pF
Figure 11. Transmitter Output (High) Exiting Shutdown
Figure 8. Supply Current vs. Load Capacitance (RL = 3 kΩ)
Tek Stop 500kS/s
247 Acqs
T
30
25
20
15
10
5
[
]
T
T
SD
1
2
Tx O/P LOW
Ch1 5.00V
Ch2 5.00V
M 100s Ch1
0V
0
0
500
1000
1500
2000
2500
LOAD CAPACITANCE – pF
Figure 9. Supply Current vs. Load Capacitance (RL = ∞)
Figure 12. Transmitter Output (Low) Exiting Shutdown
REV. A
–5–
ADM3311E
Tek Stop 500kS/s
244 Acqs
T
Tek Stop 500kS/s
101 Acqs
T
]
[
]
[
T
T
T
T
SD
SD
V+
1
1
2
2
V–
Ch1 5.00V
Ch2 5.00V
M 100s Ch1
0V
Ch1 5.00V
Ch2 5.00V
M 100s Ch1
0V
Figure 13. Charge Pump V– Exiting Shutdown
Figure 14. Charge Pump V+ Exiting Shutdown
GENERAL DESCRIPTION
9 V in practice. This saves power as well as maintaining a
more constant output voltage.
The ADM3311E is a ruggedized RS-232 line driver/receiver
that operates from a single supply of +2.7 V to +3.6 V. Step-up
voltage converters, coupled with level-shifting transmitters and
receivers, allow RS-232 levels to be developed while operating
from a single supply. Features include low power consumption,
Green Idle operation, high transmission rates and compatibility
with the EU directive on electromagnetic compatibility. EM
compatibility includes protection against radiated and conducted
interference including high levels of electrostatic discharge.
The tripler operates in two phases. During the oscillator low
phase, S1 and S2 are closed and C1 charges rapidly to VCC. S3,
S4 and S5 are open. S6 and S7 are closed.
During the oscillator high phase, S1 and S2 are open. S3 and
S4 are closed, so the voltage at the output of S3 is 2 VCC. This
voltage is used to charge C2. In the absence of any discharge
current, C2 will charge up to 2 VCC after a several cycles. Dur-
ing the oscillator high phase, as previously mentioned, S6 and
S7 are closed, so the voltage at the output of S6 will be 3 VCC
This voltage is used to charge C3.
All RS-232 inputs and outputs contain protection against
electrostatic discharges up to 15 kV and electrical fast tran-
sients up to 4 kV.
.
The device is ideally suited for operation in electrically harsh
environments or where RS-232 cables are frequently being
plugged/unplugged, and is immune to high RF field strengths
without special shielding precautions.
S6
S1
S2
S3
S4
V
CC
V+ = 3V
CC
+
+
+
S5
C1
C4
C2
S7
GND
V
CC
V
CC
Emissions are also controlled to within very strict limits. CMOS
technology is used to keep the power dissipation to an absolute
minimum allowing maximum battery life in portable applications.
INTERNAL
OSCILLATOR
Figure 15. Charge Pump Voltage Tripler
CIRCUIT DESCRIPTION
The internal circuitry consists of three main sections. These are:
The voltage inverter is illustrated in Figure 14. During the oscil-
lator high phase S10 and S11 are open, S8 and S9 are closed
and (over several cycles) C2 is charged to +3 VCC from the out-
put of the voltage tripler. During the oscillator low phase, S8
and S9 are open, while S10 and S11 are closed. C3 is connected
across C5, whose positive terminal is grounded and whose nega-
tive terminal is the V– output. Over several cycles C5 charges to
1. A charge pump voltage converter.
2. 3.3 V logic to EIA-232 transmitters.
3. EIA-232 to 3 V logic receivers.
4. Transient protection circuit on all I-O lines.
Charge Pump DC-DC Voltage Converter
–3 VCC
.
The charge pump voltage converter consists of a 180 kHz oscil-
lator and a switching matrix. The converter generates a 9 V
supply from the input +3.0 V level. This is done in two stages
using a switched capacitor technique as illustrated below. First,
the +3.0 V input supply is tripled to +9.0 V using capacitor C4
as the charge storage element. The +9.0 V level is then inverted
to generate –9.0 V using C5 as the storage element.
S8
S9
S10
S11
V+
GND
FROM
VOLTAGE
TRIPLER
+
+
C5
C3
V– = –(V+)
GND
INTERNAL
OSCILLATOR
However, it should be noted that, unlike other charge-pump dc-
dc converters, the charge pump on the ADM3311E does not
run open-loop. The output voltage is regulated to 7.25 V by
the Green Idle circuit (as described later) and will never reach
Figure 16. Charge Pump Voltage Inverter
The V+ and V– supplies may also be used to power external
circuitry if the current requirements are small. Please refer to
Figures 13 and 14 in the Typical Performance section.
–6–
REV. A
ADM3311E
GREEN IDLE
OVERSHOOT
What Is Green Idle?
7.25V
7V
Green Idle is a method of minimizing power consumption under
idle (no transmit) conditions while still maintaining the ability
to instantly transmit data.
V+
OSC
How Does it Work?
LIGHT LOAD
Charge pump type dc-dc converters used in RS-232 line drivers
normally operate open-loop, i.e., the output voltage is not regu-
lated in any way. Under light load conditions the output voltage
is close to twice the supply voltage for a doubler and three times
the supply voltage for a tripler, with very little ripple. As the
load current increases, the output voltage falls and the ripple
voltage increases.
7.25V
V+
7V
OSC
MEDIUM LOAD
7.25V
V+
Even under no-load conditions, the oscillator and charge pump
are operating at a very high frequency with consequent switch-
ing losses and current drain.
7V
OSC
Green Idle works by monitoring the output voltage and main-
taining it at a constant value around 7 V. When the voltage rises
above 7.25 V, the oscillator is turned off. When the supply volt-
age falls below 7.00 V, the oscillator is turned on and a burst of
charging pulses is sent to the reservoir capacitor. When the
oscillator is turned off the power consumption of the charge
pump is virtually zero, so the average current drain under light
load conditions is greatly reduced.
HEAVY LOAD
Figure 18. Operation of Green Idle Under Various Load
Conditions
Green Idle vs. Shutdown
Shutdown mode minimizes power consumption by shutting
down the charge pump altogether. In this condition the switches
in the voltage tripler are configured so that V+ is connected
directly to VCC. V– is zero because there is no charge pump
operation to charge C5. This means there is a delay after com-
ing out shutdown before V+ and V– achieve their normal
operating voltages. Green Idle maintains the transmitter
supply voltages under transmitter idle conditions, so this delay
does not occur.
A block diagram of the Green Idle circuit is shown in Figure 17.
Both V+ and V– are monitored and compared to a reference
voltage derived from an on-chip bandgap device. If either V+ or
V– fall below 7 V, the oscillator will start up until the voltage
rises above 7.25 V.
BANDGAP
Doesn’t It Increase Supply Voltage Ripple?
V+ VOLTAGE
VOLTAGE
COMPARATOR
REFERENCE
The ripple on the output voltage of a charge pump operating
open-loop depends on three factors: the oscillator frequency, the
value of the reservoir capacitor and the load current. The value
of the reservoir capacitor is fixed. Increasing the oscillator fre-
quency will decrease the ripple voltage; decreasing the oscillator
frequency will increase it. Increasing the load current will in-
crease the ripple voltage; decreasing the load current will de-
crease it. The ripple voltage at light loads will naturally be lower
than that for high load currents.
WITH 250mV
HYSTERESIS
START/STOP
V+
CHARGE
PUMP
SHUTDOWN
TRANSCEIVERS
V–
START/STOP
V– VOLTAGE
COMPARATOR
WITH 250mV
HYSTERESIS
Using Green Idle, the ripple voltage is determined by the high
and low thresholds of the Green Idle circuit. These are nomi-
nally 7.00 V and 7.25 V, so the ripple will be 250 mV under
most load conditions. With very light load conditions there may
be some overshoot above 7.25 V, so the ripple will be slightly
greater. Under heavy load conditions where the output never
reaches 7.25 V, the Green Idle circuit will be inoperative and
the ripple voltage will be determined by the load current, the
same as in a normal charge pump.
Figure 17. Block Diagram of Green Idle Circuit
The operation of Green Idle for V+ under various load condi-
tions is illustrated in Figure 18. Under light load conditions, C1
is maintained in a charged condition and only a single oscillator
pulse will be required to charge up C2. Under these conditions
V+ may actually overshoot 7.25 V slightly.
What About Electromagnetic Compatibility?
Under medium load conditions it may take several cycles for C2
to charge up to 7.25 V. The average frequency of the oscillator
will be higher because there are more pulses in each burst and
the bursts of pulses are closer and more frequent.
Because Green Idle does not operate with a constant oscillator
frequency, the frequency and spectrum of the oscillator signal
will vary with load. Any radiated and conducted emissions will
also vary accordingly. Like other Analog Devices RS-232 trans-
ceiver products, the ADM3311E features slew rate limiting and
other techniques to minimize radiated and conducted emissions.
The device is characterized for EMC under all load conditions,
and is well within the requirements of EN55022/CISPR22.
Under high load conditions, the oscillator will be on continu-
ously if the charge pump output cannot reach 7.25 V.
REV. A
–7–
ADM3311E
Transmitter (Driver) Section
HIGH BAUD RATE
The drivers convert 3.3 V logic input levels into EIA-232 output
levels. With VCC = +3.0 V and driving an EIA-232 load, the
output voltage swing is typically 6.4 V.
The ADM3311E features high slew rates permitting data trans-
mission at rates well in excess of the EIA/RS-232E specifications.
RS-232 voltage levels are maintained at data rates up to 460 kbps.
This allows for high speed data links between two terminals or
indeed it is suitable for the new generation ISDN modem stan-
dards which requires data rates of 230 kbps. The slew rate is
internally controlled to less than 30 V/µs in order to minimize
EMI interference.
Unused inputs may be left unconnected, as an internal 400 k⍀
pull-up resistor pulls them high, forcing the outputs into a low
state. The input pull-up resistors typically source 8 A when
grounded, so unused inputs should either be connected to VCC
or left unconnected in order to minimize power consumption.
Receiver Section
LAYOUT AND SUPPLY DECOUPLING
The receivers are inverting level-shifters that accept RS-232
input levels and translate them into 3 V logic output levels.
The inputs have internal 5 kΩ pull-down resistors to ground and
are also protected against overvoltages of up to 30 V. Uncon-
nected inputs are pulled to 0 V by the internal 5 k⍀ pull-down
resistor. This, therefore, results in a Logic 1 output level for
unconnected inputs or for inputs connected to GND.
Because of the high frequencies at which the ADM3311E oscil-
lator operates, particular care should be taken with printed
circuit board layout, with all traces being as short as possible
and C1 to C5 being connected as close to the device as possible.
The use of a ground plane under and around the device is highly
recommended.
When the oscillator starts up during Green Idleoperation, large
current pulses are taken from VCC. For this reason VCC should
be decoupled with a parallel combination of 1 F or greater
tantalum and 0.1 F ceramic capacitor, mounted as close to the
VCC pin as possible.
The receivers have Schmitt trigger inputs with a hysteresis level
of 0.4 V. This ensures error-free reception for both noisy inputs
and for inputs with slow transition times.
ENABLE AND SHUTDOWN
Capacitors C1 to C5 can have values between 0.1 F and 1 F,
larger values will give lower ripple. These capacitors can be
either electrolytic capacitors chosen for low equivalent series
resistance (ESR) or nonpolarized types, but the use of ceramic
types is highly recommended. If polarized electrolytic capacitors
are used, then polarity must be observed (as shown by C1+ for
example).
The enable function is intended to facilitate data bus connec-
tions where it is desirable to three-state the receiver outputs. In
the disabled mode, all receiver outputs are placed in a high
impedance state. The shutdown function is intended to shut the
device down, thereby minimizing the quiescent current. In shut-
down, all transmitters are disabled as are receivers R1 to R4.
Receiver R5 remains enabled in shutdown. Note that disabled
transmitters are not three-stated in shutdown, so it is not per-
mitted to connect multiple (RS-232) driver outputs together.
ESD/EFT TRANSIENT PROTECTION SCHEME
The ADM3311E uses protective clamping structures on all in-
puts and outputs, which clamps the voltage to a safe level and
dissipates the energy present in ESD (Electrostatic) and EFT
(Electrical Fast Transients) discharges. A simplified schematic of
the protection structure is shown below. Each input and output
contains two back-to-back high speed clamping diodes. During
normal operation with maximum RS-232 signal levels, the diodes
have no effect as one or the other is reverse biased, depending on
the polarity of the signal. If, however, the voltage exceeds about
50 V, reverse breakdown occurs and the voltage is clamped
at this level. The diodes are large p-n junctions designed to
handle the instantaneous current surge, which can exceed
several amperes.
The shutdown feature is very useful in battery operated systems
since it reduces the power consumption to 0.06 µW. During
shutdown the charge pump is also disabled. When exiting shut-
down, the charge pump is restarted and it takes approximately
100 µs for it to reach its steady state operating condition.
3V
EN INPUT
0V
tDR
V
OH
V
– 0.1V
OH
RECEIVER
OUTPUT
The transmitter outputs and receiver inputs have a similar pro-
tection structure. The receiver inputs can also dissipate some of
the energy through the internal 5 kΩ resistor to GND as well as
through the protection diodes.
V
+ 0.1V
V
OL
OL
Figure 19. Receiver Disable Timing
The protection structure achieves ESD protection up to 15 kV
and EFT protection up to 4 kV on all RS-232 I-O lines. The
methods used to test the protection scheme are discussed later.
3V
EN INPUT
0V
tER
V
OH
RECEIVER
Rx
3V
INPUT
RECEIVER
OUTPUT
D1
R
0.4V
IN
V
OL
D2
Figure 20. Receiver Enable Timing
Figure 21a. Receiver Input Protection Scheme
REV. A
–8–
ADM3311E
100
90
TRANSMITTER
OUTPUT
Tx
D1
D2
Figure 21b. Transmitter Output Protection Scheme
36.8
10.0
ESD TESTING (IEC1000-4-2)
IEC1000-4-2 (previously 801-2) specifies compliance testing
using two coupling methods, contact discharge and air-gap
discharge. Contact discharge calls for a direct connection to the
unit being tested. Air-gap discharge uses a higher test voltage
but does not make direct contact with the unit under test. With
air discharge, the discharge gun is moved toward the unit under
test, developing an arc across the air gap, hence the term air
discharge. This method is influenced by humidity, temperature,
barometric pressure, distance and rate of closure of the discharge
gun. The contact-discharge method, while less realistic, is more
repeatable and is gaining acceptance in preference to the air-gap
method.
tRL
tDL
TIME t
Figure 23. Human Body Model ESD Current Waveform
100
90
Although very little energy is contained within an ESD pulse,
the extremely fast rise time coupled with high voltages can cause
failures in unprotected semiconductors. Catastrophic destruc-
tion can occur immediately as a result of arcing or heating. Even
if catastrophic failure does not occur immediately, the device
may suffer from parametric degradation, which may result in
degraded performance. The cumulative effects of continuous
exposure can eventually lead to complete failure.
10
0.1 TO 1ns
TIME t
30ns
60ns
Figure 24. IEC1000-4-2 ESD Current Waveform
I-O lines are particularly vulnerable to ESD damage. Simply
touching or plugging in an I-O cable can result in a static dis-
charge that can damage or completely destroy the interface
product connected to the I-O port. Traditional ESD test meth-
ods such as the MIL-STD-883B method 3015.7 do not fully
test a product’s susceptibility to this type of discharge. This test
was intended to test a product’s susceptibility to ESD damage
during handling. Each pin is tested with respect to all other
pins. There are some important differences between the tradi-
tional test and the IEC test:
The ADM3311E is tested using both of the above-mentioned
test methods. All pins are tested with respect to all other pins as
per the MIL-STD-883B specification. In addition, all I-O pins
are tested as per the IEC test specification. The products were
tested under the following conditions:
(a) Power-On—Normal Operation
(b) Power-Off
Four levels of compliance are defined by IEC1000-4-2. The
ADM3311E meets the most stringent compliance level for con-
tact discharge. This means that the products are able to with-
stand contact discharges in excess of 8 kV.
(a) The IEC test is much more stringent in terms of discharge
energy. The peak current injected is over four times greater.
(b) The current rise time is significantly faster in the IEC test.
(c) The IEC test is carried out while power is applied to the device.
Table II. IEC1000-4-2 Compliance Levels
It is possible that the ESD discharge could induce latch-up in the
device under test. This test is therefore more representative of a
real-world I-O discharge where the equipment is operating nor-
mally with power applied. For maximum peace of mind however,
both tests should be performed, thus ensuring maximum protec-
tion both during handling and later, during field service.
Contact Discharge
(kV)
Air Discharge
(kV)
Level
1
2
3
4
2
4
6
8
2
4
8
15
HIGH
VOLTAGE
GENERATOR
R1
R2
Table III. ADM3311E ESD Test Results
DEVICE
UNDER TEST
C1
ESD Test Method
I-O Pins (kV)
Other Pins (kV)
MIL-STD-883B
15
3
ESD TEST METHOD
R2
C1
H. BODY MIL-STD883B
IEC1000-4-2
1.5k⍀
330⍀
100pF
150pF
IEC1000-4-2
Contact
8
Figure 22. ESD Test Standards
REV. A
–9–
ADM3311E
FAST TRANSIENT BURST TESTING (IEC1000-4-4)
IEC1000-4-4 (previously 801-4) covers electrical fast-transient/
burst (EFT) immunity. Electrical fast transients occur as a
result of arcing contacts in switches and relays. The tests simu-
late the interference generated when, for example, a power relay
disconnects an inductive load. A spark is generated due to the
well known back EMF effect. In fact, the spark consists of a
burst of sparks as the relay contacts separate. The voltage appear-
ing on the line, therefore, consists of a burst of extremely fast
transient impulses. A similar effect occurs when switching on
fluorescent lights.
Test results are classified according to the following:
1. Normal performance within specification limits.
2. Temporary degradation or loss of performance, which is self-
recoverable.
3. Temporary degradation or loss of function or performance,
which requires operator intervention or system reset.
4. Degradation or loss of function that is not recoverable due to
damage.
The ADM3311E has been tested under worst case conditions
using unshielded cables and meet Classification 2. Data trans-
mission during the transient condition is corrupted but it may
be resumed immediately following the EFT event without user
intervention.
The fast transient burst test defined in IEC1000-4-4 simulates
this arcing and its waveform is illustrated in Figure 25. It con-
sists of a burst of 2.5 kHz to 5 kHz transients repeating at
300 ms intervals. It is specified for both power and data lines.
C
L
D
R
R
HIGH
VOLTAGE
SOURCE
C
M
V
50⍀
OUTPUT
Z
C
S
C
t
Figure 26. IEC1000-4-4 Fast Transient Generator
300ms
15ms
5ns
V
IEC1000-4-3 RADIATED IMMUNITY
IEC1000-4-3 (previously IEC801-3) describes the measurement
method and defines the levels of immunity to radiated electro-
magnetic fields. It was originally intended to simulate the elec-
tromagnetic fields generated by portable radio transceivers or
any other device that generates continuous wave radiated
electromagnetic energy. Its scope has since been broadened to
include spurious EM energy which can be radiated from fluores-
cent lights, thyristor drives, inductive loads, etc.
50ns
t
0.2/0.4ms
Figure 25. IEC1000-4-4 Fast Transient Waveform
Testing for immunity involves irradiating the device with an EM
field. There are various methods of achieving this including
use of anechoic chamber, stripline cell, TEM cell, GTEM cell. A
stripline cell consists of two parallel plates with an electric field
developed between them. The device under test is placed within
the cell and exposed to the electric field. There are three severity
levels having field strengths ranging from 1 V to 10 V/m. Results
are classified in a similar fashion to those for IEC1000-4-4.
Table IV.
V Peak (kV)
PSU
V Peak (kV)
I-O
Level
1
2
3
4
0.5
1
2
0.25
0.5
1
4
2
1. Normal operation.
2. Temporary degradation or loss of function, which is self-
recoverable when the interfering signal is removed.
A simplified circuit diagram of the actual EFT generator is
illustrated in Figure 26.
3. Temporary degradation or loss of function that requires
operator intervention or system reset when the interfering
signal is removed.
The transients are coupled onto the signal lines using an EFT
coupling clamp. The clamp is 1 m long and it completely sur-
rounds the cable, providing maximum coupling capacitance
(50 pF to 200 pF typ) between the clamp and the cable. High
energy transients are capacitively coupled onto the signal lines.
Fast rise times (5 ns) as specified by the standard result in very
effective coupling. This test is very severe since high voltages are
coupled onto the signal lines. The repetitive transients can often
cause problems where single pulses don’t. Destructive latch-up
may be induced due to the high energy content of the transients.
Note that this stress is applied while the interface products are
powered up and transmitting data. The EFT test applies hun-
dreds of pulses with higher energy than ESD. Worst case tran-
sient current on an I-O line can be as high as 40 A.
4. Degradation or loss of function that is not recoverable due to
damage.
The ADM3311E easily meets Classification 1 at the most strin-
gent (Level 3) requirement. In fact, field strengths up to 30 V/m
showed no performance degradation and error-free data trans-
mission continued even during irradiation.
–10–
REV. A
ADM3311E
Table V. Test Severity Levels (IEC1000-4-3)
Field Strength
1
2
Level
V/m
SWITCHING GLITCHES
1
2
3
1
3
10
Figure 28. Switching Glitches
EMISSIONS/INTERFERENCE
EN55022, CISPR22 defines the permitted limits of radiated
and conducted interference from Information Technology (IT)
equipment. The objective of the standard is to minimize the
level of emissions both conducted and radiated.
90
80
70
60
50
40
30
20
10
EN 55022 CLASS B
For ease of measurement and analysis, conducted emissions are
assumed to predominate below 30 MHz and radiated emissions
are assumed to predominate above 30 MHz.
CONDUCTED QUASI-PEAK dBV
CONDUCTED EMISSIONS
This is a measure of noise that is conducted onto the line power
supply. Switching transients from the charge pump, which are
20 V in magnitude and contain significant energy, can lead to
conducted emissions. Other sources of conducted emissions can
be due to overlap in switch on times in the charge pump voltage
converter. In the voltage tripler shown in Figure 27, if S2 has
not fully turned off before S4 turns on, this results in a transient
current glitch between VCC and GND which results in conducted
emissions. It is therefore important that the switches in the charge
pump guarantee break-before-make switching under all condi-
tions so that instantaneous short circuit conditions do not occur.
100k
1M
10M
FREQUENCY – Hz
Figure 29. Conducted Emissions Plot
RADIATED EMISSIONS
Radiated emissions are measured at frequencies in excess of
30 MHz. RS-232 outputs designed for operation at high baud
rates while driving cables can radiate high frequency EM energy.
The reasons already discussed which cause conducted emissions
can also be responsible for radiated emissions. Fast RS-232 out-
put transitions can radiate interference, especially when lightly
loaded and driving unshielded cables. Charge pump devices are
also prone to radiating noise due to the high frequency oscillator
and high voltages being switched by the charge pump. The move
toward smaller capacitors in order to conserve board space has
resulted in higher frequency oscillators being employed in the
charge pump design. This has resulted in higher levels of emis-
sion, both conducted and radiated.
The ADM3311E has been designed to minimize the switching
transients and ensure break-before-make switching thereby
minimizing conducted emissions. This has resulted in the level
of emissions being well below the limits required by the specifi-
cation. No additional filtering/decoupling other than the recom-
mended 0.1 µF capacitor is required.
Conducted emissions are measured by monitoring the line
power supply. The equipment used consists of a LISN (Line
Impedance Stabilizing Network) which essentially presents a
fixed impedance at RF, and a spectrum analyzer. The spectrum
analyzer scans for emissions up to 30 MHz and a plot for the
ADM3311E is shown in Figure 28.
The RS-232 outputs on the ADM3311E products feature a
controlled slew rate in order to minimize the level of radiated emis-
sions, yet are fast enough to support data rates up to 230 kBaud.
S1
S2
S6
+
S3
V+ = 3V
V
CC
CC
+
+
C2
C1
C4
S7
S5
S4
V
GND
CC
RADIATED NOISE
V
CC
INTERNAL
OSCILLATOR
DUT
Figure 27. Charge Pump Voltage Tripler
TO
RECEIVER
ADJUSTABLE
ANTENNA
TURNTABLE
Figure 30. Radiated Emissions Test Setup
REV. A
–11–
ADM3311E
Figure 31 shows a plot of radiated emissions vs. frequency. This
shows that the levels of emissions are well within specifications
without the need for any additional shielding or filtering compo-
nents. The ADM3311E was operated at maximum baud rates
and configured as in a typical RS-232 interface.
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
28-Lead SSOP (RS-28)
0.407 (10.34)
0.397 (10.08)
Testing for radiated emissions was carried out in a shielded
anechoic chamber.
28
15
14
70
60
1
50
EN55022 CLASS B
RADIATED EMISSIONS dBV/m (EUT at 3m)
0.07 (1.79)
40
0.078 (1.98)
PIN 1
0.066 (1.67)
0.068 (1.73)
30
20
10
0
0.03 (0.762)
0.022 (0.558)
8°
0°
0.0256
(0.65)
BSC
0.015 (0.38)
0.010 (0.25)
0.008 (0.203)
0.002 (0.050)
SEATING
PLANE
0.009 (0.229)
0.005 (0.127)
28-Lead TSSOP (RU-28)
20
40
60
80
100
120
140
160
180
200
FREQUENCY – MHz
0.386 (9.80)
0.378 (9.60)
Figure 31. Radiated Emissions Plot
15
14
28
1
PIN 1
0.006 (0.15)
0.002 (0.05)
0.0433
(1.10)
MAX
0.028 (0.70)
0.020 (0.50)
8°
0°
0.0118 (0.30)
0.0075 (0.19)
0.0256 (0.65)
BSC
SEATING
PLANE
0.0079 (0.20)
0.0035 (0.090)
–12–
REV. A
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