ADM3222 AD [Analog Devices], ADM3222 Datasheet - Page 6

• Manufacturer Part Number: ADM3222
• Description: Low Power, +3.3 V, RS-232 Line Drivers/Receivers
• Manufacturer: AD [Analog Devices]

ADM3202/ADM3222/ADM1385
GENERAL DESCRIPTION
The ADM3202/ADM3222/ADM1385 are 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 +3.3 V supply.
CMOS technology is used to keep the power dissipation to an
absolute minimum, allowing maximum battery life in portable
applications.
The ADM3202/ADM3222/ADM1385 is a modification, en-
hancement and improvement to the AD230–AD241 family and
its derivatives. It is essentially plug-in compatible and does not
have materially different applications.
CIRCUIT DESCRIPTION
The internal circuitry consists of three main sections. These are:
1. A charge pump voltage converter
2. 3.3 V logic to EIA-232 transmitters
3. EIA-232 to 5 V logic receivers.
Charge Pump DC-DC Voltage Converter
The charge pump voltage converter consists of a 200 kHz oscil-
lator and a switching matrix. The converter generates a ± 6.6 V
supply from the input +3.3 V level. This is done in two stages
using a switched capacitor technique as illustrated below. First,
the +3.3 V input supply is doubled to +6.6 V using capacitor
C1 as the charge storage element. The +6.6 V level is then
inverted to generate –6.6 V using C2 as the storage element. C3
is shown connected between V+ and V
tive if connected between V+ and GND.
Capacitors C3 and C4 are used to reduce the output ripple.
Their values are not critical and can be increased if desired.
Capacitor C3 is shown connected between V+ and V
also acceptable to connect this capacitor between V+ and GND.
If desired, larger capacitors (up to 10 µF) can be used for
capacitors C1–C4.
1 s/DIV
CC
, but is equally effec-
T1
2V/DIV
T1
5V/DIV
IN
OUT
CC
. It is
OUTPUTS
OUTPUTS
OUTPUTS
INPUTS
INPUTS
INPUTS
CMOS
CMOS
CMOS
CMOS
CMOS
CMOS
0.1 F
0.1 F
0.1 F
0.1 F
0.1 F
0.1 F
R1
R2
R1
R2
R1
R2
10V
10V
10V
10V
10V
10V
T1
T2
T1
T2
T1
T2
OUT
OUT
OUT
OUT
OUT
OUT
IN
IN
IN
IN
IN
IN
+
+
+
+
+
+
DD
EN
C1+
C1–
C2+
C2–
C1+
C1–
C2+
C2–
C1+
C1–
C2+
C2–
+6.6V TO –6.6V
+6.6V TO –6.6V
+6.6V TO –6.6V
+3.3V TO +6.6V
+3.3V TO +6.6V
+3.3V TO +6.6V
GND
GND
GND
INVERTER
INVERTER
INVERTER
VOLTAGE
T1
T2
VOLTAGE
T1
T2
VOLTAGE
T1
T2
DOUBLER
DOUBLER
DOUBLER
VOLTAGE
VOLTAGE
VOLTAGE
R1
R2
R1
R2
R1
R2
ADM3222
ADM1385
INTERNAL 5k
ON EACH RS-232 INPUT
INTERNAL 5k
ON EACH RS-232 INPUT
INTERNAL 5k
ON EACH RS-232 INPUT
ADM3202
V
V
V
V+
V–
V+
V–
V+
V–
CC
CC
CC
+3.3V INPUT
+3.3V INPUT
+3.3V INPUT
SD
SD
PULL-DOWN RESISTOR
PULL-DOWN RESISTOR
PULL-DOWN RESISTOR
+
C4
0.1 F
10V
+
+
+
+
T1
T2
R1
R2
T1
T2
R1
R2
T1
T2
R1
R2
C3
0.1 F
6.3V
C4
0.1 F
10V
C3
0.1 F
6.3V
C4
0.1 F
10V
OUT
OUT
OUT
OUT
OUT
OUT
IN
IN
IN
IN
IN
IN
+
C3
0.1 F
6.3V
EIA/TIA-232
OUTPUTS
EIA/TIA-232
INPUTS
EIA/TIA-232
OUTPUTS
EIA/TIA-232
INPUTS
EIA/TIA-232
OUTPUTS
EIA/TIA-232
INPUTS
+
+
+
C5
0.1 F
C5
0.1 F
C5
0.1 F