sp3223ebcy-tr Exar Corporation, sp3223ebcy-tr Datasheet - Page 11

• Manufacturer Part Number: sp3223ebcy-tr
• Description: Sp3223eb -intelligent +3.0v To +5.5v Rs-232 Transceivers
• Manufacturer: Exar Corporation

consists of a regulated dual charge pump that
provides output voltages 5.5V regardless of the
input voltage (V
range. This is important to maintain compliant
RS-232 levels regardless of power supply
fluctuations.
The charge pump operates in a discontinuous
mode using an internal oscillator. If the output
voltages are less than a magnitude of 5.5V, the
charge pump is enabled. If the output voltages
exceed a magnitude of 5.5V, the charge pump is
disabled. This oscillator controls the four phases
of the voltage shifting. A description of each
phase follows.
Phase 1
— V
the clock cycle, the positive side of capacitors
C
then switched to GND and the charge in C
transferred to C
V
now 2 times V
Phase 2
— V
connects the negative terminal of C
storage capacitor and the positive terminal of C
to GND. This transfers a negative generated
voltage to C
regulated to a minimum voltage of -5.5V.
Simultaneous with the transfer of the voltage to
C
to V
GND.
Phase 3
— V
clock is identical to the first phase — the charge
transferred in C
terminal of C
side of capacitor C
voltage potential across C
Phase 4
— V
connects the negative terminal of C
and transfers this positive generated voltage
across C
Date: 10/06/06
1
3
CC
, the positive side of capacitor C
and C
, the voltage potential across capacitor C
CC
DD
DD
SS
SS
transfer — The fourth phase of the clock
charge storage — During this phase of
charge storage — The third phase of the
and the negative side is connected to
2
transfer — Phase two of the clock
2
to C
are initially charged to V
1
4
, which is applied to the negative
3
, the V
CC
. This generated voltage is
1
2
produces –V
CC
.
–
. Since C
) over the +3.0V to +5.5V
2
. Since C
DD
storage capacitor. This
2
is 2 times V
2
+
CC
2
is connected to
+
in the negative
is at V
1
2
is switched
2
CC
SP3223 +3.0V to +5.5V RS-232 Transceivers
to the V
to GND,
. C
CC
CC
.
, the
1
l
+
–
2
SS
is
is
is
2
11
voltage is regulated to +5.5V. At this voltage,
the internal oscillator is disabled. Simultaneous
with the transfer of the voltage to C
positive side of capacitor C
and the negative side is connected to GND,
allowing the charge pump cycle to begin again.
The charge pump cycle will continue as long as
the operational conditions for the internal
oscillator are present.
Since both V
from V
be symmetrical. Older charge pump approaches
that generate V
the magnitude of V
inherent inefficiencies in the design.
AUTO ON-LINE
The SP3223 devices have a patent pending
AUTO ON-LINE
power in applications such as laptop computers,
PDA's, and other portable systems.
The SP3223 devices incorporate an AUTO
ON-LINE
itself when the external transmitters are enabled
and the cable is connected. Conversely, the
AUTO ON-LINE
the internal circuitry when the device is not being
used and goes into a standby mode where the
device typically draws 1µA. This function can
also be externally controlled by the ONLINE
pin. When this pin is tied to a logic LOW, the
AUTO ON-LINE
active, the device is enabled until there is no
activity on the receiver inputs. The receiver
input typically sees at least ±3V, which are
generated from the transmitters at the other end
of the cable with a ±5V minimum. When the
external transmitters are disabled or the cable is
disconnected, the receiver inputs will be pulled
down by their internal 5kΩ resistors to ground.
When this occurs over a period of time, the
internal transmitters will be disabled and the
device goes into a shutdown or standby mode.
When ONLINE is HIGH, the AUTO ON-LINE
mode is disabled.
CC
, in a no–load condition V
®
circuit that automatically enables
+
and V
–
from V
®
®
®
®
–
Circuitry
circuitry on board that saves
circuit also disables most of
–
compared to V
function is active. Once
are separately generated
+
© Copyright 2006 Sipex Corporation
will show a decrease in
1
is switched to V
+
+
and V
due to the
4
–
, the
will
CC
®