ADM223/ADM230L–ADM241L
A3
0.8 V
A3
0.8 V
100
90
100
90
10
10
0%
0%
H
H
O
Bw5
1ms
Bw5
L
5µs
O
5V
5V
5V
L
Figure 30. Charge Pum p, V+, V– Exiting Shutdown
Figure 31. Transm itter Output Loaded Slew Rate
A3
0.8 V
100
90
10
0%
H
O
Bw5
1µs
5V
L
Figure 32. Transm itter Output Unloaded Slew Rate
GENERAL INFO RMATIO N
CIRCUIT D ESCRIP TIO N
T he ADM223/ADM230L–ADM241L family of RS-232 drivers/
receivers are designed to solve interface problems by meeting
the EIA-232-E specifications while using a single digital +5 V
supply. T he EIA-232-E standard requires transmitters which
will deliver ±5 V minimum on the transmission channel and
receivers which can accept signal levels down to ±3 V. T he
ADM223/ADM230L–ADM241L meet these requirements by
integrating step up voltage converters and level shifting trans-
mitters and receivers onto the same chip. CMOS technology is
used to keep the power dissipation to an absolute minimum. A
comprehensive range of transmitter/receiver combinations is
available to cover most communications needs.
T he internal circuitry in the ADM230L–ADM241L consists of
three main sections. T hese are:
(a) A charge pump voltage converter
(b) RS-232 to T T L/CMOS receivers
(c) T T L/CMOS to RS-232 transmitters
Char ge P um p D C-D C Voltage Conver ter
T he charge pump voltage converter consists of an oscillator 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 using a
switched capacitor technique as illustrated in Figures 33 and 34.
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 in-
verted to generate –10 V using C2 as the storage element.
T he ADM223, ADM230L, ADM235L, ADM236L and
ADM241L are particularly useful in battery powered systems as
they feature a low power shutdown mode which reduces power
dissipation to less than 5 µW.
S1
S3
V
V+ = 2V
CC
CC
C1
C3
T he ADM233L and ADM235L are designed for applications
where space saving is important as the charge pump capacitors
are molded into the package.
S2
S4
GND
V
CC
INTERNAL
OSCILLATOR
T he ADM231L and ADM239L include only a negative charge
pump converter and are intended for applications where a posi-
tive 12 V is available.
Figure 33. Charge-Pum p Voltage Doubler
To facilitate sharing a common line or for connection to a micro-
processor data bus the ADM235L, ADM236L, ADM239L and
ADM241L feature an enable (EN, EN) function. When disabled,
the receiver outputs are placed in a high impedance state.
REV. 0
–12–
ADI [ ADI ]
