adm3101e Analog Devices, Inc., adm3101e Datasheet - Page 8

• Manufacturer Part Number: adm3101e
• Description: ?15 Kv Esd Protected, 3.3 V Single-channel Rs-232 Line Driver/receiver
• Manufacturer: Analog Devices, Inc.

ADM3101E
GENERAL DESCRIPTION
The ADM3101E is a single-channel RS-232 line driver/receiver.
Step-up voltage converters, coupled with level shifting trans-
mitters 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 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 illustrated in
Figure 12 and Figure 13. First, the 3.3 V input supply is doubled
to 6.6 V by using 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.
The C3 and C4 capacitors are used to reduce the output ripple.
The values are not critical and can be increased, if desired.
If desired, larger capacitors (up to 10 μF) can be used in place of
the C1, C2, C3, and C4 capacitors.
±6.6 V supply from the input 3.3 V level, which is done in two
0.1µF
0.1µF
*INTERNAL 5kΩ PULL-DOWN
RESISTOR ON THE RS-232 INPUT.
16V
16V
C1
C2
Charge pump voltage converter
A 3.3 V logic to EIA/TIA-232E transmitter
A EIA/TIA-232E to 3.3 V logic receiver
OUTPUT
+
+
CMOS
INPUT
CMOS
Figure 11. ADM3101E Typical Operating Circuit
C1+
C1–
C2+
C2–
T
R
IN
OUT
VOLTAGE DOUBLER
VOLTAGE INVERTER
+3.3V TO +6.6V
+6.6V TO –6.6V
ADM3101E
GND
T
R
T
V
OUT
R
V+
CC
V–
IN
+3.3V INPUT
EIA/TIA-232E
OUTPUT
EIA/TIA-232E
INPUT*
+
+
C3
0.1µF
6.3V
C4
0.1µF
16V
CC
, but is
+
C5
0.1µF
Rev. A | Page 8 of 12
3.3 V Logic to EIA/TIA-232E Transmitter
The transmitter driver converts the 3.3 V logic input levels into
RS-232 output levels. When driving an RS-232 load with V
3.3 V, the output voltage swing is typically ±6 V. Internally, the
T
open-drain output, but the maximum operating data rate is
reduced when the T
EIA/TIA-232E to 3.3 V Logic Receiver
The receiver is an inverting level shifter that accepts the RS-232
input level and translates it into a 3.3 V logic output level. The
input has an internal 5 kΩ pull-down resistor to ground and is
also protected against overvoltages of up to ±30 V. An uncon-
nected input is pulled to 0 V by the internal 5 kΩ pull-down
resistor, which, therefore, results in a Logic 1 output level for
an unconnected input or for an input connected to GND.
The receiver has a Schmitt trigger input with a hysteresis level
of 0.4 V, which ensures error-free reception for both a noisy
input and for an input with slow transition times.
CMOS Input Voltage Thresholds
The CMOS input and output pins (T
ADM3101E are designed to interface with 1.8 V logic
thresholds when V
The CMOS input and output pins (T
ADM3101E are also designed to interface with TTL/CMOS
logic thresholds when V
ESD Protection on RS-232 and CMOS I/O Pins
All RS-232 (T
outputs are protected against electrostatic discharges (up to
±15 kV).
IN
DOUBLER
VOLTAGE
pin has a weak pull-up that allows it to be driven by an
FROM
OSCILLATOR
GND
INTERNAL
V
CC
OSCILLATOR
GND
INTERNAL
V+
OUT
Figure 12. Charge Pump Voltage Doubler
Figure 13. Charge Pump Voltage Inverter
and R
CC
S1
S2
IN
= 3.3 V.
pin is driven by a open-drain pin.
S1
S2
IN
CC
) and CMOS (T
= 5 V.
+
C1
+
C2
S3
S4
IN
IN
S3
S4
and R
and R
IN
+
and R
C3
OUT
OUT
+
C4
) of the
) of the
V+ = 2V
V
OUT
CC
) inputs and
GND
V– = –(V+)
CC
CC
=