C 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 C and C2 are charged from Vcc with
their negative terminals initially connected to
ground. C+ is then connected to ground and
the stored charge from C- 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 C is charged from Vcc to
prepare it for its next phase.
The clock rate for the charge pump typically op-
erates at greater than 5kHz allowing the pump
to run efficiently with small 0.1uF capacitors. Ef-
ficient operation depends on rapid charging and
discharging of C 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 .
Shutdown (SD) and Enable (En) features for
the SP310E and SP312E
Both the SP30E and SP32E 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 SP30E, this control line is
the ON/OFF (pin 8) input. Activating the shut-
down mode puts the SP30E transmitter and
receiver ouptuts into a high impedance con-
dition. For the SP32E, this control line is the
SHUTDOWN (pin8) 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 "" on the EN line (pin ).
Wake-Up Feature for the SP312E
The SP32E 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 SP32E 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 SP32E 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 SP32E to a
logic high, taking it out of the shutdown mode.
The receiver propagation delay is typically
us. 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.
DESCRiPTion
SD
0
0
EN
0
0
Power
Receiver
Up/Down outputs
Down
Down
Up
Up
Enabled
Tri-state
Enabled
Tri-state
Table . 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
Two V- pins
Two C2+ pins
Two C- pins
SOICW
0 & 7
2 & 5
& 6
Connect Pins 6 and 9 to
GND
Table 2. Pin Strapping table for SP233E
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (50)668-7000 • www.exar.com SP202E,232E,233E, 30E, 32E_00_0608
6
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