adm3232e Analog Devices, Inc., adm3232e Datasheet - Page 8

• Manufacturer Part Number: adm3232e
• Description: ?15 Kv Esd Protected, 3.3 V, Rs-232 Line Driver/receiver
• Manufacturer: Analog Devices, Inc.

ADM3232E
THEORY OF OPERATION
The ADM3232E is a single-channel RS-232 line driver/receiver.
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.
CIRCUIT DESCRIPTION
The internal circuitry consists of the following main sections:
•
•
•
Charge Pump DC-DC Voltage Converter
The charge pump voltage converter consists of a 200 kHz
oscillator and a switching matrix. The converter generates a
stages by using a switched capacitor technique as shown in
Figure 10. 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 V
equally effective if connected between V+ and GND.
Capacitor C3 and Capacitor 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
acceptable to connect this capacitor between V+ and GND.
If desired, larger capacitors (up to 10 μF) can be used for
Capacitor C1 to Capacitor C4.
±6.6 V supply from the input 3.3 V level. This is done in two
TTL/CMOS
OUTPUTS
TTL/CMOS
INPUTS
A charge pump voltage converter
A 3.3 V logic to RS-232 transmitter
An RS-232 to 3.3 V logic receiver
0.1µF
0.1µF
R1
R2
10V
10V
T1
T2
OUT
OUT
IN
IN
+
+
Figure 10. Typical Operating Circuit
GND
C1+
C1–
C2+
C2–
+3.3V TO +6.6V
+6.6V TO –6.6V
ADM3232E
DOUBLER
INVERTER
T1
VOLTAGE
VOLTAGE
T2
R1
R2
*INTERNAL 5kΩ PULL-DOWN RESISTOR
ON EACH RS-232 INPUT.
V
5kΩ
5kΩ
CC
V+
V–
+3.3V INPUT
+
+
T1
T2
R1
R2
C3
0.1µF
6.3V
C4
0.1µF
10V
OUT
OUT
IN
IN
RS-232
INPUTS*
CC
RS-232
OUTPUTS
+
CC
, but it is
C5
0.1µF
. It is also
Rev. 0 | Page 8 of 12
Transmitter (Driver) Section
The drivers convert 3.3 V logic input levels into RS-232 output
levels. With V
voltage swing is typically ±6 V.
Receiver Section
The receivers are inverting level-shifters that accept RS-232 input
levels and translate them into 3 V logic output levels. The inputs
have internal 5 kΩ pull-down resistors to ground and are also
protected against overvoltages up to ±30 V. Unconnected inputs
are pulled to 0 V by the internal 5 kΩ pull-down resistor. This
results in a Logic 1 output level for unconnected inputs or for
inputs connected to GND.
The receivers have Schmitt trigger inputs with a hysteresis level
of 0.4 V. This ensures error-free reception for both noisy inputs
and for inputs with slow transition times.
ESD Protection on RS-232 and TTL/CMOS I/O Pins
All RS-232 (T_
inputs and outputs are protected against electrostatic discharges
(up to ±15 kV). This ensures compliance with IEC 1000-4-2
requirements.
HIGH BAUD RATE
The ADM3232E features high slew rates, permitting data trans-
mission at rates well in excess of the EIA-232E specifications.
RS-232 voltage levels are maintained at data rates up to 460 kbps,
even under worst-case loading conditions. This allows high
speed data links between two terminals and is suitable for the
new generation ISDN modem standards that require data rates
of 230 kbps. The slew rate is internally controlled to less than
30 V/μs to minimize EMI interference.
DOUBLER
VOLTAGE
FROM
OSCILLATOR
GND
V
INTERNAL
CC
OSCILLATOR
GND
INTERNAL
V+
CC
Figure 11. Charge Pump Voltage Doubler
OUT
Figure 12. Charge Pump Voltage Inverter
= 3.3 V and driving an RS-232 load, the output
S2
S1
and R_
S2
S1
C1
IN
) and TTL/CMOS (T_
C2
+
+
S4
S3
S4
S3
C3
C4
+
+
V+ = 2V
V
CC
IN
GND
V– = –(V+)
and R_
CC
OUT
)