SP202E Datasheet, PDF (6/17 Pages) Sipex Corporation – High-Performance RS-232 Line Drivers/Receivers

C1 is charged from Vcc to prepare it for its next
phase.
Phase 3
Vdd charge store and double: Phase three is
identical to the first phase. The positive termi-
nals of C1 and C2 are charged from Vcc with
their negative terminals initially connected to
ground. C1+ is then connected to ground and
the stored charge from C1- is superimposed
onto C2-. Since C2+ is still connected to Vcc
the voltage potential across capacitor C2 is now
2 x Vcc.
Phase 4
Vdd transfer: The fourth phase connects the
negative terminal of C2 to ground and the posi-
tive terminal of C2 to the Vdd storage capacitor.
This transfers the doubled (V+) voltage onto C3.
Meanwhile, capacitor C1 is charged from Vcc to
prepare it for its next phase.
The clock rate for the charge pump typically op-
erates at greater than 15kHz allowing the pump
to run efficiently with small 0.1uF capacitors. Ef-
ficient operation depends on rapid charging and
discharging of C1 and C2, therefore capacitors
should be mounted as close as possible to the
IC and have low ESR (equivalent series resis-
tance). Inexpensive surface mount, ceramic ca-
pacitors are ideal for using on charge pump. If
polarized capacitors are used the positive and
negative terminals should be connected as
shown in the typical operating circuit. A diagram
of the individual phases are shown in Figure 1.
Shutdown (SD) and Enable (EN) features for
the SP310E and SP312E
Both the SP310E and SP312E have a shutdown
/ standby mode to conserve power in battery-
powered applications. To activate the shutdown
mode, which stops the operation of the charge
pump, a logic "0" is applied to the appropriate
control line. For the SP310E, this control line is
the ON/OFF (pin 18) input. Activating the shut-
down mode puts the SP310E transmitter and
receiver ouptuts into a high impedance con-
dition. For the SP312E, this control line is the
SHUTDOWN (pin18) input; this also puts the
transmitter outputs in a tri-state mode. The re-
ceiver outputs can be tri-stated seperately dur-
ing normal operation or shutdown by applying a
logic "1" on the EN line (pin 1).
DESCRIPTION
Wake-Up Feature for the SP312E
The SP312E has a wake-up feature that keeps
the receivers active when the device is placed
into shutdown. Table 1 defines the truth table for
the Wake-Up function. When only the receivers
are activated, the SP312E typically draws less
than 5uA supply current. In the case of when
a modem is interfaced to a computer in power
down mode, the Ring Indicator (RI) signal from
the modem would be used to "wake-up" the
computer, allowing it to accept data transmis-
sion.
After the ring indicator has propagated
through the SP312E receiver, it can be used
to trigger the power management circuitry of
the computer to power up the microproces-
sor, and bring the SD pin of the SP312E to a
logic high, taking it out of the shutdown mode.
The receiver propagation delay is typically
1us. The enable time for V+ and V- is typi-
cally 2ms. After V+ and V- have settled to their
final values, a signal can be sent back to the
modem on the data terminal ready (DTR) pin
signifying that the computer is ready to accept
the transmit data.
Power Receiver
SD EN Up/Down outputs
0 0 Down Enabled
0 1 Down Tri-state
10
Up
Enabled
11
Up
Tri-state
Table 1. Wake-up Function truth table
Pin Strapping for the SP233E
To operate properly, the following pairs of pins
must be externally wired together as noted in
table 2:
Pins Wired
Together
SOICW
Two V- pins
10 & 17
Two C2+ pins 12 & 15
Two C- pins
11 & 16
Connect Pins 6 and 9 to
GND
Table 2. Pin Strapping table for SP233E
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • www.exar.com SP202E,232E,233E, 310E, 312E_100_110608