ADM202E/ADM1181A
GENERAL DESCRIPTION
The ADM202E/ADM1181E are ruggedized RS-232 line drivers/
receivers. 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 inputs and outputs contain protection against Electrostatic
Discharges up to
±
15 kV and Electrical Fast Transients 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.
CMOS technology is used to keep the power dissipation to an
absolute minimum allowing maximum battery life in portable
applications.
The ADM202E/ADM1181A is a modification, enhancement
and improvement to the AD230–AD241 family and its deriva-
tives. It is essentially plug-in compatible and does not have ma-
terially different applications.
CIRCUIT DESCRIPTION
and V
CC
, while it is connected between V+ and GND on the
ADM1181A. It is acceptable to use either configuration with
both the ADM202E and ADM1181A. If desired, larger capaci-
tors (up to 47
µF)
can be used for capacitors C1–C4. This facili-
tates direct substitution with older generation charge pump
RS-232 transceivers.
S1
V
CC
C1
S2
GND
S4
V
CC
C3
S3
V+ = 2V
CC
INTERNAL
OSCILLATOR
NOTE: C3 CONNECTS BETWEEN V+ AND GND ON THE ADM1181A
Figure 1. Charge Pump Voltage Doubler
S1
V+
FROM
VOLTAGE
DOUBLER
GND
C2
S2
S4
V– = –(V+)
C4
S3
GND
INTERNAL
OSCILLATOR
Figure 2. Charge Pump Voltage Inverter
Transmitter (Driver) Section
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 drivers convert 5 V logic input levels into RS-232 output
levels. With V
CC
= +5 V and driving an RS-232 load, the output
voltage swing is typically
±
9 V.
Receiver Section
The charge pump voltage converter consists of an 200 kHz os-
cillator and a switching matrix. The converter generates a
±
10 V
supply from the input +5 V level. This is done in two stages us-
ing 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 inverted to
generate –10 V using C2 as the storage element.
Capacitors C3 and C4 are used to reduce the output ripple.
Their values are not critical and can be increased if desired. On
the ADM202E, capacitor C3 is shown connected between V+
The receivers are inverting level shifters which accept RS-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
±
30 V. Un-
connected 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 inputs with a hysteresis level
of 0.5 V. This ensures error-free reception for both noisy inputs
and for inputs with slow transition times.
–4–
REV. 0
AD [ ANALOG DEVICES ]
