ADM230LAQ View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADM230LAQ Datasheet PDF : 16 Pages
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ADM223/ADM230L–ADM241L
A3
100
90
0.8 V
A3
100
90
0.8 V
10
0%
5V
5V
LBw5
1ms
HO
Figure 30. Charge Pump, V+, V– Exiting Shutdown
A3
100
90
0.8 V
10
0%
5V
LBw5
5µs
HO
Figure 31. Transmitter Output Loaded Slew Rate
10
0%
5V
LBw5
1µs
HO
Figure 32. Transmitter Output Unloaded Slew Rate
GENERAL INFORMATION
The 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. The 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. The
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.
The 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.
The ADM233L and ADM235L are designed for applications
where space saving is important as the charge pump capacitors
are molded into the package.
The ADM231L and ADM239L include only a negative charge
pump converter and are intended for applications where a posi-
tive 12 V is available.
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.
CIRCUIT DESCRIPTION
The internal circuitry in the ADM230L–ADM241L consists of
three main sections. These are:
(a) A charge pump voltage converter
(b) RS-232 to TTL/CMOS receivers
(c) TTL/CMOS to RS-232 transmitters
Charge Pump DC-DC Voltage Converter
The charge pump voltage converter consists of an 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 in Figures 33 and 34.
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.
VCC
GND
S1
C1
S2
S3
C3
S4
V+ = 2VCC
VCC
INTERNAL
OSCILLATOR
Figure 33. Charge-Pump Voltage Doubler
–12–
REV. 0
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