a
15 kV ESD Protected, +2.7 V to +3.6 V
™
Serial Port Transceiver with Green Idle
ADM3311E*
FEATURES
Green Idle
Power Saving Mode
Full RS-232 Compliance
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
Pin Compatible with DS14C335
APPLICATIONS
Laptop Computers
Notebook Computers
Printers
Peripherals
Modems
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 tripler and voltage inverter, which internally generates positive and
negative supplies from the input +3 V power supply. The dcto-dc converter operates in Green Idle Mode, whereby the
charge pump oscillator is gated on and off to maintain the output voltage at ±7.25 V under varying load conditions. This
minimizes the power consumption and makes these products
ideal for battery powered portable devices.
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 contains three drivers and five receivers and
is intended for serial port applications on notebook/laptop
computers.
FUNCTIONAL BLOCK DIAGRAM
C1
0.1F
C4
V
CC
ENABLE
INPUT
0.1F
1
V+
0.1F
CERAMIC
1F
CMOS
INPUTS*
R1
R2
CMOS
OUTPUTS
R3
R4
R5
NOTES:
* INTERNAL 400k⍀ PULL-UP RESISTOR ON EACH CMOS INPUT
** INTERNAL 5k⍀ PULL-DOWN RESISTOR ON EACH RS-232 INPUT
0.1F
T1
T2
T3
OUT
OUT
OUT
OUT
OUT
2
C2+
VOLTAGE
TRIPLER/
3
V
CC
INVERTER
4
C2–
5
EN
6
C1+
7
8
9
10
11
12
13
14
+3V TO ⴞ9V
T1
R1
R2
ADM3311E
C2
IN
IN
IN
C3+
GND
C3–
C1–
SD
T2
T3
R3
R4
R5
C3
28
0.1F
27
26
C5
25
V–
24
23
22
21
20
19
18
17
16
15
0.1F
SHUTDOWN
INPUT
T1
OUT
T2
OUT
T3
OUT
R1
IN
R2
IN
EIA/TIA-232
R3
IN
INPUTS
R4
IN
R5
IN
EIA/TIA-232
OUTPUTS
**
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 fabricated using CMOS technology for
minimal power consumption. It features a high level of overvoltage protection and latch-up immunity.
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 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 2000
ADM3311E–SPECIFICATIONS
(VCC = +2.7 V to +3.6 V, C1–C5 = 0.1 F. All specifications T
otherwise noted.)
MIN
to T
MAX
unless
Parameter Min Typ Max Units Test Conditions/Comments
Operating Voltage Range +2.7 +3.3 +3.6 V
V
Power Supply Current 0.45 1 mA VCC = 3.0 V to 3.6 V, TA = 0°C to +85°C,
CC
No Load
0.45 4.5 mA VCC = 2.7 V to 3.6 V, TA = –40°C to +85°C,
No Load
35 mA RL = 3 kΩ to GND on all T
OUTS
Shutdown Supply Current 0.02 1 µA
Input Pull-Up Current 10 25 µAT
= GND
IN
Input Leakage Current, SD, EN ± 1 µA
Input Logic Threshold Low, V
Input Logic Threshold High, V
CMOS Output Voltage Low, V
CMOS Output Voltage High, V
INL
INH
OL
OH
2.0 V TIN, EN, SD
VCC – 0.6 V I
CMOS Output Leakage Current 0.05 ± 5 µA EN = V
0.8 V TIN, EN, SD
0.4 V T
0.4 V I
EN, SD, VCC = 2.7 V
IN,
= 1.6 mA
OUT
= –200 µA
OUT
, 0 V < R
CC
OUT
< V
CC
Charge Pump Output Voltage, V+ 7.25 V No Load
Charge Pump Output Voltage, V– –7.25 V No Load
EIA-232 Input Voltage Range –25 +25 V
EIA-232 Input Threshold Low 0.4 1.3 V
EIA-232 Input Threshold High 2.0 2.4 V
EIA-232 Input Hysteresis 0.14 V
EIA-232 Input Resistance 357kΩ
Output Voltage Swing (V
Output Voltage Swing (V
Transmitter Output Resistance 300 Ω V
= 3.0 V) ± 5.0 ± 6.4 V All Transmitter Outputs
CC
= 2.7 V) ± 5.5 V Loaded with 3 kΩ to Ground
CC
= 0 V, V
CC
OUT
= ± 2 V
RS-232 Output Short Circuit Current ± 15 ± 60 mA
Maximum Data Rate 460 kbps RL = 3 kΩ to 7 kΩ, CL = 50 pF to 1000 pF
Receiver Propagation Delay, T
Receiver Output Enable Time, t
Receiver Output Disable Time, t
Transmitter Propagation Delay, T
PHL
ER
DR
, T
PHL
PLH
, T
PLH
Transition Region Slew Rate 6 18 V/µsR
0.3 µsC
= 150 pF
L
100 ns
300 ns
500 ns RL = 3 kΩ, CL = 1000 pF
= 3 kΩ, CL = 50 pF to 1000 pF,
L
Measured from +3 V to –3 V or –3 V to +3 V
ESD Protection (I-O Pins) ± 8 kV IEC1000-4-2 Contact Discharge
± 15 kV IEC1000-4-2 Air Discharge
ESD Protection (All Other Pins) ± 3.0 kV Human Body Model, MIL-STD-883B
EFT Protection (I-O Pins) ± 4 kV IEC1000-4-4
EMI Immunity 10 V/m IEC1000-4-3
Specifications subject to change without notice.
ABSOLUTE MAXIMUM RATINGS*
(TA = +25°C unless otherwise noted)
VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +4 V
V+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (V
–0.3 V) to +8 V
CC
V– . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +0.3 V to –8 V
Input Voltages
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +6 V
T
IN
R
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 30 V
IN
Output Voltages
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±15 V
T
OUT
R
. . . . . . . . . . . . . . . . . . . . . . . –0.3 V to (VCC +0.3 V)
OUT
Short Circuit Duration
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Continuous
T
OUT
Power Dissipation
RU-28 TSSOP (Derate 12 mW/°C Above +70°C) . . 900 mW
RS-28 SSOP (Derate 10 mW/°C Above +70°C) . . . . 900 mW
Operating Temperature Range
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
*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 specification is not implied. Exposure to absolute maximum rating conditions for extended
periods of time may affect reliability.
–2–
REV. A
ADM3311E
PIN FUNCTION DESCRIPTIONS
Mnemonic Function
V
CC
V+ Internally generated positive supply (+7.25 V nominal) Capacitor C4 is connected between VCC and V+.
V– Internally generated negative supply (–7.25 V nominal) Capacitor C5 is connected between V– and GND.
GND Ground Pin. Must be connected to 0 V.
C1+, C1– External capacitor 1 is connected between these pins. A 0.1 µF capacitor is recommended, but larger capacitors
C2+, C2– External capacitor 2 is connected between these pins. A 0.1 µF capacitor is recommended, but larger capacitors
C3+, C3– External capacitor 3 is connected between these pins. A 0.1 µF capacitor is recommended, but larger capacitors
T
IN
T
OUT
R
IN
R
OUT
EN 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.
Power Supply Input +2.7 V to +3.6 V. Requires capacitor of 1 µF or greater to GND.
up to 1 µF may be used.
up to 1 µF may be used.
up to 1 µF may be used.
Transmitter (Driver) Inputs. These inputs accept TTL/CMOS levels. An internal 400 kΩ pull-up resistor to V
is connected on each input.
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.
Receiver Outputs. These are TTL/CMOS levels.
All transmitters and receivers R1–R4 are disabled. Receiver R5 remains active in shutdown.
CC
Table I. Truth Table
SD EN Status T
OUT
1–3 R
OUT
1–4 R
OUT
5
0 0 Normal Enabled Enabled Enabled
Operation
0 1 Receivers Enabled Disabled Disabled
Disabled
1 0 Shutdown Disabled Disabled Enabled
1 1 Shutdown Disabled Disabled Disabled
PIN CONFIGURATION
1
V+
2
C2+
3
V
CC
4
C2–
5
EN
6
C1+
ADM3311E
7
T1
T2
T3
R1
OUT
R2
OUT
R3
OUT
R4
OUT
R5
OUT
IN
8
IN
9
IN
10
11
12
13
14
TOP VIEW
(Not to Scale)
28
C3+
27
GND
26
C3–
25
V–
24
C1–
23
SD
22
T1
21
T2
T3
20
19
R1
18
R2
17
R3
16
R4
15
R5
OUT
OUT
OUT
IN
IN
IN
IN
IN
ORDERING GUIDE
Temperature Package Package
Model Range Descriptions Option
ADM3311EARS-Reel 2.5 –40°C to +85°C 28-Lead Shrink Small Outline (SSOP) RS-28
ADM3311EARU-Reel 2.5 –40°C to +85°C 28-Lead Thin Shrink Small Outline (TSSOP) RU-28
–3–REV. A
ADM3311E
–Typical Performance Characteristics
90
80
EN 55022 CLASS B
CONDUCTED QUASI-PEAK dBV
70
60
50
40
LEVEL – dBV
30
20
10
100k 10M
1M
FREQUENCY – Hz
Figure 1. EMC Conducted Emissions
70
60
50
RADIATED EMISSIONS dBV/m (EUT at 3m)
40
30
LEVEL – dBV/m
20
EN 55022 CLASS B
10
8
T
HIGH
6
4
2
0
Tx O/P – Volts
–2
–4
–6
–8
OUT
T
OUT
0 2500500
LOW
1000
LOAD CAPACITANCE – pF
1500 2000
Figure 4. Transmitter Output High/Low vs. Load
Capacitance
0.57
0.56
0.55
0.54
– mA
CC
0.53
I
0.52
10
0
20 200
FREQUENCY – MHz
180160140120100806040
Figure 2. EMC Radiated Emissions
8
7
6
5
4
3
2
1
0
–1
VOLTAGE – V
–2
–3
–4
–5
–6
–7
–8
V–
V+
I
LOAD
– mA
12108642
14
16 18 200
Figure 3. Charge Pump V+, V– vs. Load Current
0.51
0.50
2.7
2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6
VCC – Volts
Figure 5. Power Supply Current vs. Power Supply Voltage
(Unloaded)
25
20
15
– mA
CC
I
10
5
0
2.7
2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6
VCC – Volts
Figure 6. Power Supply Current vs. Power Supply Voltage
= 3 kΩ)
(R
L
–4–
REV. A
ADM3311E
40
35
30
25
20
15
SLEW RATE – V/s
10
5
0
0 2500
LOAD CAPACITANCE – pF
200015001000470150
Figure 7. Slew Rate vs. Load Capacitance
40
35
30
25
– mA
20
CC
I
15
12
10
8
6
4
LOAD CURRENT – mA
2
0
0 300
OSCILLATOR FREQUENCY – kHz
25020015010050
Figure 10. Load Current vs. Oscillator Frequency
Tek Stop 500kS/s 429 Acqs
1
2
[
T
T
T
]
SD
Tx O/P HIGH
10
5
0
0 2500
LOAD CAPACITANCE – pF
200015001000500
Figure 8. Supply Current vs. Load Capacitance (RL = 3 kΩ)
30
25
20
15
– mA
CC
I
10
5
0
0 2500
LOAD CAPACITANCE – pF
200015001000500
Figure 9. Supply Current vs. Load Capacitance (RL = ∞)
Ch1 5.00V Ch2 5.00V M 100s Ch1 0V
Figure 11. Transmitter Output (High) Exiting Shutdown
Tek Stop 500kS/s 247 Acqs
1
2
Ch1 5.00V Ch2 5.00V M 100s Ch1 0V
[]
T
T
T
SD
Tx O/P LOW
Figure 12. Transmitter Output (Low) Exiting Shutdown
–5–REV. A
ADM3311E
Tek Stop 500kS/s 101 Acqs
1
2
Ch1 5.00V Ch2 5.00V M 100s Ch1 0V
[
T
T
T
]
SD
V–
Figure 13. Charge Pump V– Exiting Shutdown
GENERAL DESCRIPTION
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.
All RS-232 inputs and outputs contain protection against
electrostatic discharges up to ± 15 kV and electrical fast transients 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.
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.
CIRCUIT DESCRIPTION
The internal circuitry consists of three main sections. These are:
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
The charge pump voltage converter consists of a 180 kHz oscillator 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.
However, it should be noted that, unlike other charge-pump dcdc 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
Tek Stop 500kS/s 244 Acqs
1
2
Ch1 5.00V Ch2 5.00V M 100s Ch1 0V
[
T
T
T
]
SD
V+
Figure 14. Charge Pump V+ Exiting Shutdown
± 9 V in practice. This saves power as well as maintaining a
more constant output voltage.
The tripler operates in two phases. During the oscillator low
phase, S1 and S2 are closed and C1 charges rapidly to V
CC
. 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 V
CC
. This
voltage is used to charge C2. In the absence of any discharge
current, C2 will charge up to 2 V
after a several cycles. Dur-
CC
ing the oscillator high phase, as previously mentioned, S6 and
S7 are closed, so the voltage at the output of S6 will be 3 V
CC
.
This voltage is used to charge C3.
V
CC
GND
INTERNAL
OSCILLATOR
S1
S2
S3
+
C1
S4
S5
V
CC
S6
+
C2
S7
V+ = 3V
+
C4
CC
V
CC
Figure 15. Charge Pump Voltage Tripler
The voltage inverter is illustrated in Figure 14. During the oscillator high phase S10 and S11 are open, S8 and S9 are closed
and (over several cycles) C2 is charged to +3 V
from the out-
CC
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 negative terminal is the V– output. Over several cycles C5 charges to
.
–3 V
CC
FROM
VOLTAGE
TRIPLER
V+
GND
INTERNAL
OSCILLATOR
S8
S9
S10
+
C3
S11
GND
+
C5
V– = –(V+)
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
What Is Green Idle?
Green Idle is a method of minimizing power consumption under
idle (no transmit) conditions while still maintaining the ability
to instantly transmit data.
How Does it Work?
Charge pump type dc-dc converters used in RS-232 line drivers
normally operate open-loop, i.e., the output voltage is not regulated 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.
Even under no-load conditions, the oscillator and charge pump
are operating at a very high frequency with consequent switching losses and current drain.
Green Idle works by monitoring the output voltage and maintaining it at a constant value around 7 V. When the voltage rises
above 7.25 V, the oscillator is turned off. When the supply voltage 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.
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
VOLTAGE
REFERENCE
TRANSCEIVERS
SHUTDOWN
V+ VOLTAGE
COMPARATOR
WITH 250mV
HYSTERESIS
START/STOP
CHARGE
START/STOP
V– VOLTAGE
COMPARATOR
WITH 250mV
HYSTERESIS
PUMP
V+
V–
Figure 17. Block Diagram of Green Idle Circuit
The operation of Green Idle for V+ under various load conditions 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.
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.
Under high load conditions, the oscillator will be on continuously if the charge pump output cannot reach 7.25 V.
OVERSHOOT
7.25V
V+
7V
OSC
LIGHT LOAD
7.25V
V+
7V
OSC
MEDIUM LOAD
7.25V
V+
7V
OSC
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 V
. V– is zero because there is no charge pump
CC
operation to charge C5. This means there is a delay after coming 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.
Doesn’t It Increase Supply Voltage Ripple?
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 frequency will decrease the ripple voltage; decreasing the oscillator
frequency will increase it. Increasing the load current will increase the ripple voltage; decreasing the load current will decrease it. The ripple voltage at light loads will naturally be lower
than that for high load currents.
Using Green Idle, the ripple voltage is determined by the high
and low thresholds of the Green Idle circuit. These are nominally 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.
What About Electromagnetic Compatibility?
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 transceiver 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.
–7–REV. A
ADM3311E
Transmitter (Driver) Section
The drivers convert 3.3 V logic input levels into EIA-232 output
levels. With V
= +3.0 V and driving an EIA-232 load, the
CC
output voltage swing is typically ±6.4 V.
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 V
CC
or left unconnected in order to minimize power consumption.
Receiver Section
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. Unconnected 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.
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
The enable function is intended to facilitate data bus connections 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 shutdown, 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 permitted to connect multiple (RS-232) driver outputs together.
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 shutdown, the charge pump is restarted and it takes approximately
100 µs for it to reach its steady state operating condition.
3V
EN INPUT
RECEIVER
OUTPUT
0V
V
OH
V
OL
t
DR
VOH – 0.1V
V
+ 0.1V
OL
Figure 19. Receiver Disable Timing
3V
EN INPUT
RECEIVER
OUTPUT
0V
V
OH
V
OL
t
ER
3V
0.4V
HIGH BAUD RATE
The ADM3311E features high slew rates permitting data transmission 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 I
modem stan-
SDN
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.
LAYOUT AND SUPPLY DECOUPLING
Because of the high frequencies at which the ADM3311E oscillator 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 Idle
current pulses are taken from V
. For this reason VCC should
CC
operation, large
be decoupled with a parallel combination of 1 F or greater
tantalum and 0.1 F ceramic capacitor, mounted as close to the
pin as possible.
V
CC
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).
ESD/EFT TRANSIENT PROTECTION SCHEME
The ADM3311E uses protective clamping structures on all inputs 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 transmitter outputs and receiver inputs have a similar protection 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.
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.
RECEIVER
INPUT
R
IN
Rx
D1
D2
Figure 20. Receiver Enable Timing
–8–
Figure 21a. Receiver Input Protection Scheme
REV. A
ADM3311E
100
I
PEAK
– %
90
10
TIME t
30ns
60ns
0.1 TO 1ns
Tx
D1
D2
TRANSMITTER
OUTPUT
Figure 21b. Transmitter Output Protection Scheme
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.
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 destruction 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.
I-O lines are particularly vulnerable to ESD damage. Simply
touching or plugging in an I-O cable can result in a static discharge that can damage or completely destroy the interface
product connected to the I-O port. Traditional ESD test methods 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 traditional test and the IEC test:
(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.
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 normally with power applied. For maximum peace of mind however,
both tests should be performed, thus ensuring maximum protection both during handling and later, during field service.
GENERATOR
HIGH
VOLTAGE
ESD TEST METHOD R2 C1
H. BODY MIL-STD883B 1.5k⍀100pF
IEC1000-4-2 330⍀ 150pF
Figure 22. ESD Test Standards
R1 R2
C1
DEVICE
UNDER TEST
100
90
– %
PEAK
I
36.8
10.0
t
RL
t
DL
TIME t
Figure 23. Human Body Model ESD Current Waveform
Figure 24. IEC1000-4-2 ESD Current Waveform
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 contact discharge. This means that the products are able to withstand contact discharges in excess of 8 kV.
Table II. IEC1000-4-2 Compliance Levels
Contact Discharge Air Discharge
Level (kV) (kV)
12 2
24 4
36 8
48 15
Table III. ADM3311E ESD Test Results
ESD Test Method I-O Pins (kV) Other Pins (kV)
MIL-STD-883B ± 15 ± 3
IEC1000-4-2
Contact ± 8
–9–REV. A
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 simulate 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 appearing on the line, therefore, consists of a burst of extremely fast
transient impulses. A similar effect occurs when switching on
fluorescent lights.
The fast transient burst test defined in IEC1000-4-4 simulates
this arcing and its waveform is illustrated in Figure 25. It consists 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.
V
t
300ms
5ns
V
15ms
Test results are classified according to the following:
1. Normal performance within specification limits.
2. Temporary degradation or loss of performance, which is selfrecoverable.
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 transmission during the transient condition is corrupted but it may
be resumed immediately following the EFT event without user
intervention.
Figure 26. IEC1000-4-4 Fast Transient Generator
IEC1000-4-3 RADIATED IMMUNITY
IEC1000-4-3 (previously IEC801-3) describes the measurement
method and defines the levels of immunity to radiated electro-
50ns
magnetic fields. It was originally intended to simulate the electromagnetic fields generated by portable radio transceivers or
t
0.2/0.4ms
Figure 25. IEC1000-4-4 Fast Transient Waveform
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 fluorescent lights, thyristor drives, inductive loads, etc.
Testing for immunity involves irradiating the device with an EM
Table IV.
V Peak (kV) V Peak (kV)
Level PSU I-O
1 0.5 0.25
2 1 0.5
321
442
A simplified circuit diagram of the actual EFT generator is
illustrated in Figure 26.
The transients are coupled onto the signal lines using an EFT
coupling clamp. The clamp is 1 m long and it completely surrounds 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.
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.
1. Normal operation.
2. Temporary degradation or loss of function, which is selfrecoverable when the interfering signal is removed.
3. Temporary degradation or loss of function that requires
operator intervention or system reset when the interfering
signal is removed.
4. Degradation or loss of function that is not recoverable due to
damage.
The ADM3311E easily meets Classification 1 at the most stringent (Level 3) requirement. In fact, field strengths up to 30 V/m
showed no performance degradation and error-free data transmission continued even during irradiation.
Note that this stress is applied while the interface products are
powered up and transmitting data. The EFT test applies hundreds of pulses with higher energy than ESD. Worst case transient current on an I-O line can be as high as 40 A.
HIGH
VOLTAGE
SOURCE
R
C
C
C
L
Z
S
C
D
R
M
50⍀
OUTPUT
–10–
REV. A
Table V. Test Severity Levels (IEC1000-4-3)
1
2
SWITCHING GLITCHES
Field Strength
Level V/m
11
23
310
ADM3311E
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.
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 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 V
and GND which results in conducted
CC
emissions. It is therefore important that the switches in the charge
pump guarantee break-before-make switching under all conditions so that instantaneous short circuit conditions do not occur.
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 specification. No additional filtering/decoupling other than the recommended 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.
V
CC
GND
INTERNAL
OSCILLATOR
S1
S2
S3
+
C1
S4
S5
V
CC
S6
+
C2
S7
V+ = 3V
+
C4
CC
V
CC
Figure 27. Charge Pump Voltage Tripler
Figure 28. Switching Glitches
90
80
EN 55022 CLASS B
CONDUCTED QUASI-PEAK dBV
70
60
50
40
LEVEL – dBV
30
20
10
100k 10M
1M
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 output 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 emission, both conducted and radiated.
The RS-232 outputs on the ADM3311E products feature a
controlled slew rate in order to minimize the level of radiated emissions, yet are fast enough to support data rates up to 230 kBaud.
RADIATED NOISE
DUT
TO
TURNTABLE
ADJUSTABLE
ANTENNA
RECEIVER
Figure 30. Radiated Emissions Test Setup
–11–REV. A
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 components. The ADM3311E was operated at maximum baud rates
and configured as in a typical RS-232 interface.
Testing for radiated emissions was carried out in a shielded
anechoic chamber.
70
60
50
RADIATED EMISSIONS dBV/m (EUT at 3m)
40
30
LEVEL – dBV/m
20
10
0
20 200
EN55022 CLASS B
180160140120100806040
FREQUENCY – MHz
Figure 31. Radiated Emissions Plot
Dimensions shown in inches and (mm).
28 15
0.311 (7.9)
0.301 (7.64)
0.078 (1.98)
0.068 (1.73)
0.008 (0.203)
0.002 (0.050)
PIN 1
0.0256
(0.65)
BSC
0.386 (9.80)
0.378 (9.60)
28
OUTLINE DIMENSIONS
28-Lead SSOP (RS-28)
0.407 (10.34)
0.397 (10.08)
0.212 (5.38)
0.205 (5.21)
141
0.07 (1.79)
0.066 (1.67)
0.015 (0.38)
0.010 (0.25)
SEATING
PLANE
0.009 (0.229)
0.005 (0.127)
28-Lead TSSOP (RU-28)
15
8°
0°
C3434–0–6/00 (rev. A) 00074
0.03 (0.762)
0.022 (0.558)
0.177 (4.50)
0.169 (4.30)
0.006 (0.15)
0.002 (0.05)
SEATING
PLANE
1
PIN 1
0.0256 (0.65)
BSC
0.0118 (0.30)
0.0075 (0.19)
14
0.256 (6.50)
0.246 (6.25)
0.0433
(1.10)
MAX
0.0079 (0.20)
0.0035 (0.090)
8°
0°
0.028 (0.70)
0.020 (0.50)
PRINTED IN U.S.A.
–12–
REV. A
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