ADM202E/ADM1181A
GENERAL D ESCRIP TIO N
and VCC, 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. T his facili-
tates direct substitution with older generation charge pump
RS-232 transceivers.
T he 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.
S1
S3
V
V+ = 2V
CC
CC
C3
C1
S2
S4
V
GND
CC
All inputs and outputs contain protection against Electrostatic
Discharges up to ±15 kV and Electrical Fast T ransients up to
±2 kV. This ensures compliance to IE1000-4-2 and IEC1000-4-4
requirements.
INTERNAL
OSCILLATOR
NOTE: C3 CONNECTS BETWEEN V+ AND GND ON THE ADM1181A
T he devices are ideally suited for operation in electrically harsh
environments or where RS-232 cables are frequently being
plugged/unplugged. T hey are also immune to high RF field
strengths without special shielding precautions.
Figure 1. Charge Pum p Voltage Doubler
S1
S3
V+
GND
FROM
VOLTAGE
DOUBLER
CMOS technology is used to keep the power dissipation to an
absolute minimum allowing maximum battery life in portable
applications.
C4
C2
S2
S4
GND
V– = –(V+)
T he 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.
INTERNAL
OSCILLATOR
Figure 2. Charge Pum p Voltage Inverter
Tr ansm itter (D r iver ) Section
T he drivers convert 5 V logic input levels into RS-232 output
levels. With VCC = +5 V and driving an RS-232 load, the output
voltage swing is typically ±9 V.
CIRCUIT D ESCRIP TIO N
T he internal circuitry consists of four main sections. T hese are:
1. A charge pump voltage converter
2. 5 V logic to EIA-232 transmitters
3. EIA-232 to 5 V logic receivers.
Receiver Section
T he receivers are inverting level shifters which accept RS-232
input levels and translate them into 5 V logic output levels.
T he 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. T his, therefore, results in a Logic 1 output level
for unconnected inputs or for inputs connected to GND.
4. T ransient protection circuit on all I/O lines
Char ge P um p D C-D C Voltage Conver ter
T he charge pump voltage converter consists of an 200 kHz os-
cillator and a switching matrix. T he converter generates a ±10 V
supply from the input +5 V level. T his 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. T he 10 V level is then inverted to
generate –10 V using C2 as the storage element.
T he receivers have Schmitt trigger inputs with a hysteresis level
of 0.5 V. T his ensures error-free reception for both noisy inputs
and for inputs with slow transition times.
Capacitors C3 and C4 are used to reduce the output ripple.
T heir values are not critical and can be increased if desired. On
the ADM202E, capacitor C3 is shown connected between V+
REV. 0
–4–
ADI [ ADI ]
