ADM206E/ADM207E/ADM208E/ADM211E/ADM213E
GENERAL DESCRIPTION
S1
V+
FROM
VOLTAGE
DOUBLER
GND
C2
S2
S4
V– = –(V+)
C4
S3
GND
The ADM206E/ADM207E/ADM208E/ADM211E/ADM213E
are ruggedized RS-232 line drivers/receivers which operate from
a single +5 V supply. Step-up voltage converters coupled with
level shifting transmitters and receivers allow RS-232 levels to
be developed while operating from a single +5 V supply.
Features include low power consumption, high transmission
rates and compatibility with the EU directive on electromag-
netic 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 tran-
sients up to
±
2 kV. This ensures compliance to IE1000-4-2 and
IEC1000-4-4 requirements.
The devices are ideally suited for operation in electrically harsh
environments or where RS-232 cables are frequently being
plugged/unplugged. They are also 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. The ADMxxE is a modification, enhancement and
improvement to the AD230–AD241 family and derivatives
thereof. It is essentially plug-in compatible and does not have
materially different applications.
CIRCUIT DESCRIPTION
INTERNAL
OSCILLATOR
Figure 21. Charge Pump Voltage Inverter
Transmitter (Driver) Section
The drivers convert 5 V logic input levels into EIA-232 output
levels. With V
CC
= +5 V and driving an EIA-232 load, the out-
put voltage swing is typically
±
9 V.
Unused inputs may be left unconnected, as an internal 400 kΩ
pull-up resistor pulls them high forcing the outputs into a low
state. The input pull-up resistors typically source 8
µA
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 which accept EIA-232
input levels and translate them into 5 V logic output levels.
The inputs have internal 5 kΩ pull-down resistors to ground and
are also protected against overvoltages of up to
±
25 V. The
guaranteed switching thresholds are 0.4 V minimum and 2.4 V
maximum. Unconnected inputs are pulled to 0 V by the internal
5 kΩ 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 input with a hysteresis level
of 0.5 V. This ensures error-free reception for both noisy inputs
and for inputs with slow transition times.
ENABLE AND SHUTDOWN
The internal circuitry consists of four main sections. These are:
1. A charge pump voltage converter.
2. 5 V logic to EIA-232 transmitters.
3. EIA-232 to 5 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 an 200 kHz
oscillator and a switching matrix. The converter generates a
±
10 V supply from the input +5 V level. This is done in two
stages using a switched capacitor technique as illustrated below.
First, the 5 V input supply is doubled to 10 V using capacitor
C1 as the charge storage element. The 10 V level is then in-
verted to generate –10 V using C2 as the storage element.
Capacitors C3 and C4 are used to reduce the output ripple. If
desired, larger capacitors (up to 47
µF)
can be used for capaci-
tors C1–C4. This facilitates direct substitution with older gen-
eration charge pump RS-232 transceivers.
The V+ and V– supplies may also be used to power external
circuitry if the current requirements are small. Please refer to
Figure 19 in the Typical Performance section.
S1
V
CC
C1
S2
GND
S4
V
CC
C3
S3
V+ = 2V
CC
Table II and Table III show the truth tables for the enable and
shutdown control signals. 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 quies-
cent current. In shutdown, all transmitters are disabled and all
receivers on the ADM211E are three-stated. On the ADM213E,
receivers R4 and R5 remain enabled in shutdown. Note that the
transmitters are disabled but are not three-stated in shutdown,
so it is not permitted to connect multiple (RS-232) driver out-
puts together.
The shutdown feature is very useful in battery operated systems
since it reduces the power consumption to 1
µW.
During shut-
down the charge pump is also disabled. The shutdown control
input is active high on the ADM211E, and it is active low on
the ADM213E. When exiting shutdown, the charge pump is
restarted and it takes approximately 100
µs
for it to reach its
steady state operating conditions.
High Baud Rate
INTERNAL
OSCILLATOR
Figure 20. Charge Pump Voltage Doubler
The ADM2xxE feature high slew rates permitting data transmis-
sion at rates well in excess of the EIA-232-E specifications.
RS-232 levels are maintained at data rates up to 230 kb/s even
under worst case loading conditions. This allows for high speed
data links between two terminals or indeed it is suitable for the
REV. B
–9–
AD [ ANALOG DEVICES ]
