ADM3222 View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADM3222 Datasheet PDF : 16 Pages
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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 are modifications,
enhancements, and improvements of the AD230 to AD241
family and derivatives. They are essentially plug-in compatible
and do not have any materially different applications.
CIRCUIT DESCRIPTION
The internal circuitry consists of these main sections:
• A charge pump voltage converter
• 3.3 V logic to EIA-232 transmitters
• EIA-232 to 5 V logic receivers
Charge Pump DC to DC Voltage Converter
The charge pump voltage converter consists of a 200 kHz
oscillator 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 by using a switched capacitor technique as illustrated in
Figure 18 and Figure 19. First, the 3.3 V input supply is doubled
to 6.6 V by 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
VCC but is equally effective 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 VCC. It is
also acceptable to connect this capacitor between V+ and GND.
If desired, larger capacitors (up to 10 μF) can be used for
Capacitors C1 to C4.
+3.3V INPUT
0.1µF +
10V
0.1µF +
10V
CMOS
INPUTS
T1IN
T2IN
C1+
+3.3V TO +6.6V
VOLTAGE
VCC
C1– DOUBLER V+
C2+ +6.6V TO –6.6V V–
VOLTAGE
C2– INVERTER
T1
T2
C3
0.1µF
6.3V
C5
0.1µF
C4
0.1µF
10V
T1OUT
T2OUT
EIA/TIA-232
OUTPUTS
CMOS
OUTPUTS
R1OUT
R2OUT
R1
R2
GND ADM3202
R1IN
R2IN
EIA/TIA-232
INPUTS*
*INTERNAL 5kΩ PULL-DOWN RESISTOR
ON EACH RS-232 INPUT
Figure 15. ADM3202 Typical Operating Circuit
+3.3V INPUT
0.1µF +
10V
0.1µF +
10V
CMOS
INPUTS
T1IN
T2IN
C1+
+3.3V TO +6.6V
VOLTAGE
VCC
C1– DOUBLER V+
C2+ +6.6V TO –6.6V V–
VOLTAGE
C2– INVERTER
T1
T2
C3
0.1µF
6.3V
C5
0.1µF
C4
0.1µF
10V
T1OUT
T2OUT
EIA/TIA-232
OUTPUTS
CMOS R1OUT
OUTPUTS
R2OUT
R1
R2
R1IN
R2IN
EIA/TIA-232
INPUTS*
EN
GND
SD
ADM3222
*INTERNAL 5kΩ PULL-DOWN RESISTOR
ON EACH RS-232 INPUT
Figure 16. ADM3222 Typical Operating Circuit
+3.3V INPUT
0.1µF +
10V
0.1µF +
10V
CMOS
INPUTS
T1IN
T2IN
C1+
+3.3V TO +6.6V
VOLTAGE
VCC
C1– DOUBLER V+
C2+ +6.6V TO –6.6V V–
VOLTAGE
C2– INVERTER
T1
T2
C3
0.1µF
C4 10V
0.1µF
10V
C5
0.1µF
T1OUT
T2OUT
EIA/TIA-232
OUTPUTS
CMOS
OUTPUTS
R1OUT
R2OUT
R1
R2
R1IN
R2IN
EIA/TIA-232
INPUTS*
DD
GND
SD
ADM1385
*INTERNAL 5kΩ PULL-DOWN RESISTOR
ON EACH RS-232 INPUT
Figure 17. ADM1385 Typical Operating Circuit
VCC
GND
S1
S3
V+ = 2VCC
+
C1
+
C3
S2
S4
VCC
INTERNAL
OSCILLATOR
Figure 18. Charge Pump Voltage Doubler
V+
FROM
VOLTAGE
DOUBLER
GND
S1
S3
GND
+
C2
+
C4
S2
S4
V– = –(V+)
INTERNAL
OSCILLATOR
Figure 19. Charge Pump Voltage Inverter
Rev. E | Page 8 of 16
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