ADM205 AD [Analog Devices], ADM205 Datasheet - Page 9

• Manufacturer Part Number: ADM205
• Description: 0.1 uF, +5 V Powered CMOS RS-232 Drivers/Receivers
• Manufacturer: AD [Analog Devices]

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GENERAL INFORMATION
The ADM205-ADM211 and ADM213 family of RS-232 driv-
ers/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 re-
ceivers which can accept signal levels down to 3 V. The
ADM205-ADM211 and ADM213 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 ADM205–
ADM211 and ADM213 are modifications, enhancements and
improvements to the AD230–AD241 family and derivatives
thereof. They are essentially plug-in compatible and do not have
materially different applications.
Figure 22. Transmitter Output Unloaded Slew Rate
Figure 20. Charge Pump, V+, V– Exiting Shutdown
Figure 21. Transmitter Output Loaded Slew Rate
100
90
10
0%
100
90
10
0%
100
90
10
0%
A3
5V
A3
5V
A3
5V
0.8 V
0.8 V
0.8 V
5V
L w
B
L w
B
5
L w
B
5
5
1Ms
5 s
1 s
H
O
H
O
H
O
–9–
The ADM205, ADM206, ADM211, and ADM213 are particu-
larly useful in battery powered systems as they feature a low
power shutdown mode which reduces power dissipation to less
than 5 W.
The ADM205 is designed for applications where space saving is
important as the charge pump capacitors are molded into the
package.
The ADM209 includes only a negative charge pump converter
and are intended for applications where a positive 12 V is available.
To facilitate sharing a common line or for connection to a mi-
croprocessor data bus the ADM205, ADM206, ADM209,
ADM211 and ADM213 feature an enable (EN) function. When
disabled, the receiver outputs are placed in a high impedance
state.
CIRCUIT DESCRIPTION
The internal circuitry in the ADM205-ADM211 and ADM213
consists of three main sections. These are:
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 23 and 24.
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.
Their values are not critical and can be reduced if higher levels
of ripple are acceptable. The charge pump capacitors C1 and
C2 may also be reduced at the expense of higher output imped-
ance on the V+ and V– supplies.
The V+ and V– supplies may also be used to power external cir-
cuitry if the current requirements are small.
DOUBLER
VOLTAGE
(a) A charge pump voltage converter
(b) RS-232 to TTL/CMOS receivers
(c) TTL/CMOS to RS-232 transmitters
OSCILLATOR
GND
V
INTERNAL
FROM
CC
OSCILLATOR
INTERNAL
Figure 23. Charge-Pump Voltage Doubler
Figure 24. Charge-Pump Voltage Inverter
GND
V+
S1
S2
ADM205–ADM211/ADM213
S1
S2
C1
C2
S3
S4
S3
S4
C3
C4
V+ = 2V
GND
V– = – (V+)
V
CC
CC