ADM3311EARSZ Analog Devices Inc, ADM3311EARSZ Datasheet - Page 13

• Manufacturer Part Number: ADM3311EARSZ
• Description: IC TXRX RS-232 3:5 2.7V 28SSOP
• Manufacturer: Analog Devices Inc
• Type: Transceiverr

Specifications of ADM3311EARSZ

• Number Of Drivers/receivers: 3/5
• Protocol: RS232
• Voltage - Supply: 2.7 V ~ 3.6 V
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Device Type: Transceiver
• Ic Interface Type: RS232
• No. Of Drivers: 1
• Supply Voltage Range: 2.7V To 3.6V
• Driver Case Style: SSOP
• No. Of Pins: 28
• Operating Temperature Range: -40°C To +85°C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

CIRCUIT DESCRIPTION
The internal circuitry consists mainly of four sections. These
include the following:
• A charge pump voltage converter
• 3.3 V logic to EIA-232 transmitters
• EIA-232 to 3.3 V logic receivers
• Transient protection circuit on all I/O lines
Charge Pump DC-to-DC Voltage Converter
The charge pump voltage converter consists of a 250 kHz (300 kHz
for ADM3307E) oscillator 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. 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-
to-dc converters, the charge pump on the ADM3307E does not
run open-loop. The output voltage is regulated to ±7.25 V (or
±6.5 V for the ADM3310E and ADM3315E) by the Green Idle
circuit and never reaches ±9 V in practice. This saves power as
well as maintains 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, and S6 and S7 are closed.
During the oscillator high phase, S1 and S2 are open, and S3
and S4 are closed, so the voltage at the output of S3 is 2V
voltage is used to charge C2. In the absence of any discharge
current, C2 charges up to 2V
oscillator high phase, as previously mentioned, S6 and S7 are
closed, so the voltage at the output of S6 is 3V
then used to charge C3. The voltage inverter is illustrated in
Figure 25.
OSCILLATOR
GND
INTERNAL
V
CC
VOLTAGE
TRIPLER
FROM
OSCILLATOR
GND
INTERNAL
S1
S2
V
CC
Figure 25. Charge Pump Voltage Inverter
Figure 24. Charge Pump Voltage Tripler
C1
+
S8
S9
S3
S4
CC
C3
V
CC
after several cycles. During the
+
S10
S11
S5
C2
C5
+
S6
S7
+
CC
. This voltage is
ADM3307E/ADM3310E/ADM3311E/ADM3312E/ADM3315E
GND
V– = –(V+)
C4
V+ = 3V
+
CC
CC
V
. S3,
CC
CC
. This
Rev. H | Page 13 of 24
During the oscillator high phase, S10 and S11 are open, while
S8 and S9 are closed. C3 is charged to 3V
the voltage tripler over several cycles. 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 negative 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. See Figure 12 in
the Typical Performance Characteristics section.
What Is Green Idle?
Green Idle is a method of minimizing power consumption
under idle (no transmit) conditions while still maintaining the
ability to transmit data instantly.
How Does it Work?
Charge pump type dc-to-dc converters used in RS-232 line
drivers normally operate open-loop, that is, the output voltage
is not regulated in any way. Under light load conditions, the
output voltage is close to twice the supply voltage for a doubler
and three times the supply voltage for a tripler, with very little
ripple. As the load current increases, the output voltage falls and
the ripple voltage increases.
Even under no-load conditions, the oscillator and charge pump
operate at a very high frequency with consequent switching
losses and current drain.
Green Idle works by monitoring the output voltage and
maintaining it at a constant value of around 7 V
voltage rises above 7.25 V
voltage falls below 7 V
charging pulses is sent to the reservoir capacitor. When the
oscillator is turned off, the power consumption of the charge
pump is virtually zero, so the average current drain under light
load conditions is greatly reduced.
1
2
For ADM3310E and ADM3315E, replace with 6.5 V.
For ADM3310E and ADM3315E, replace with 6.25 V.
CC
.
1
, the oscillator is turned on and a burst of
2
the oscillator is turned off. When the
CC
from the output of
1
. When the