SP3223 Sipex, SP3223 Datasheet - Page 12

• Manufacturer Part Number: SP3223
• Description: Intelligent +3.0V to +5.5V RS-232 Transceivers
• Manufacturer: Sipex

Rev. 6/30/03
Receivers are active when the AUTO ON-LINE
circuitry is enabled or when in shutdown.
During the shutdown, the receivers will continue
to be active. If there is no activity present at the
receivers for a period longer than 100µs or when
SHUTDOWN is enabled, the device goes into a
standby mode where the circuit draws 1µA.
Driving EN to a logic HIGH forces the outputs of
the receivers into high-impedance. The truth
table logic of the SP3223 and SP3243 driver and
receiver outputs can be found in Table 2.
The SP3243 includes an additional non-invert-
ing receiver with an output R
extra output that remains active and monitors
activity while the other receiver outputs are
forced into high impedance. This allows Ring
Indicator (RI) from a peripheral to be monitored
without forward biasing the TTL/CMOS inputs
of the other devices connected to the receiver
outputs.
Since receiver input is usually from a transmis-
sion line where long cable lengths and system
interference can degrade the signal, the inputs
have a typical hysteresis margin of 300mV. This
ensures that the receiver is virtually immune to
noisy transmission lines. Should an input be left
unconnected, an internal 5KΩ pulldown resistor
to ground will commit the output of the receiver
to a HIGH state.
Charge Pump
The charge pump is a Sipex–patented design
(U.S. 5,306,954) and uses a unique approach
compared to older less–efficient designs. The
charge pump still requires four external
capacitors, but uses a four–phase voltage
shifting technique to attain symmetrical 5.5V
power supplies. The internal power supply
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.
CC
) over the +3.0V to +5.5V
2
OUT. R
2
SP3223 +3.0V to +5.5V RS-232 Transceivers
OUT is an
®
12
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
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.
1
3
CC
, the positive side of capacitor C
and C
, the voltage potential across capacitor C
CC
DD
DD
SS
SS
charge storage — During this phase of
transfer — The fourth phase of the clock
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
1
. This generated voltage is
2
produces –V
.
–
. Since C
2
. Since C
DD
© Copyright 2003 Sipex Corporation
storage capacitor. This
2
1
is 2 times V
2
is switched to V
+
CC
2
is connected to
+
in the negative
is at V
1
2
is switched
2
CC
to the V
to GND,
. C
CC
CC
4
, the
.
, the
1
l
+
–
2
CC
SS
is
is
is
2