ADM3311 AD [Analog Devices], ADM3311 Datasheet - Page 6

• Manufacturer Part Number: ADM3311
• Manufacturer: AD [Analog Devices]

ADM3311E
GENERAL DESCRIPTION
The ADM3311E is a ruggedized RS-232 line driver/receiver
that operates from a single supply of +2.7 V to +3.6 V. Step-up
voltage converters, coupled with level-shifting transmitters and
receivers, allow RS-232 levels to be developed while operating
from a single supply. Features include low power consumption,
Green Idle operation, high transmission rates and compatibility
with the EU directive on electromagnetic compatibility. EM
compatibility includes protection against radiated and conducted
interference including high levels of electrostatic discharge.
All RS-232 inputs and outputs contain protection against
electrostatic discharges up to ± 15 kV and electrical fast tran-
sients up to ± 4 kV.
The device is ideally suited for operation in electrically harsh
environments or where RS-232 cables are frequently being
plugged/unplugged, and is immune to high RF field strengths
without special shielding precautions.
Emissions are also controlled to within very strict limits. 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 three main sections. These are:
1. A charge pump voltage converter.
2. 3.3 V logic to EIA-232 transmitters.
3. EIA-232 to 3 V logic receivers.
4. Transient protection circuit on all I-O lines.
Charge Pump DC-DC Voltage Converter
The charge pump voltage converter consists of a 180 kHz oscil-
lator and a switching matrix. The converter generates a ± 9 V
supply from the input +3.0 V level. This is done in two stages
using a switched capacitor technique as illustrated below. First,
the +3.0 V input supply is tripled to +9.0 V using capacitor C4
as the charge storage element. The +9.0 V level is then inverted
to generate –9.0 V using C5 as the storage element.
However, it should be noted that, unlike other charge-pump dc-
dc converters, the charge pump on the ADM3311E does not
run open-loop. The output voltage is regulated to ± 7.25 V by
the Green Idle circuit (as described later) and will never reach
1
2
Tek Stop 500kS/s
Ch1 5.00V
[
Ch2
5.00V
101 Acqs
T
T
T
M 100 s
Ch1
]
SD
V–
0V
± 9 V in practice. This saves power as well as maintaining a
more constant output voltage.
The tripler operates in two phases. During the oscillator low
phase, S1 and S2 are closed and C1 charges rapidly to V
S4 and S5 are open. S6 and S7 are closed.
During the oscillator high phase, S1 and S2 are open. S3 and
S4 are closed, so the voltage at the output of S3 is 2 V
voltage is used to charge C2. In the absence of any discharge
current, C2 will charge up to 2 V
ing the oscillator high phase, as previously mentioned, S6 and
S7 are closed, so the voltage at the output of S6 will be 3 V
This voltage is used to charge C3.
The voltage inverter is illustrated in Figure 14. During the oscil-
lator high phase S10 and S11 are open, S8 and S9 are closed
and (over several cycles) C2 is charged to +3 V
put of the voltage tripler. During the oscillator low phase, S8
and S9 are open, while S10 and S11 are closed. C3 is connected
across C5, whose positive terminal is grounded and whose nega-
tive terminal is the V– output. Over several cycles C5 charges to
–3 V
The V+ and V– supplies may also be used to power external
circuitry if the current requirements are small. Please refer to
Figures 13 and 14 in the Typical Performance section.
GND
OSCILLATOR
V
INTERNAL
CC
CC
VOLTAGE
.
TRIPLER
1
2
Tek Stop 500kS/s
FROM
S2
Ch1 5.00V
S1
OSCILLATOR
GND
INTERNAL
V+
C1
+
[
Ch2
S3
S4
S9
S8
5.00V
V
CC
244 Acqs
C3
CC
T
S5
T
T
+
S10
S11
M 100 s
after a several cycles. Dur-
C2
+
C5
S6
S7
Ch1
]
+
CC
C4
from the out-
SD
GND
V– = –(V+)
V+
+
0V
CC
V+ = 3V
V
CC
. This
CC
. S3,
CC
CC
.