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Exar Corporation 48720 Kato Road, Fremont CA, 94538 (50)668-7000 Fax (50)668-707 www.exar.com SP233A,30A,32A 0_0603
DESCRiPTion
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 SP310A and SP312A
Both the SP30A and SP32A 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 SP30A, this control line is
the ON/OFF (pin 8) input. Activating the shut-
down mode puts the SP30A transmitter and re-
ceiver ouptuts into a high impedance condition.
For the SP32A, this control line is the SHUT-
DOWN (pin8) input; this also puts the transmit-
ter outputs in a tri-state mode. The receiver out-
puts can be tri-stated seperately during normal
operation or shutdown by applying a logic "" on
the EN line (pin ).
Wake-Up Feature for the SP312A
The SP32A 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 SP32A 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 SP32A 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 SP32A 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.
SD EN
Power
Up/Down
Receiver
outputs
0
Down
Enabled
0
Down
Tri-state
0
Up
Enabled
Up
Tri-state
Table . Wake-up Function truth table
Pin Strapping for the SP233ACT/ACP
The SP233A packaged in a 20 pin SOICW
package (SP233ACT) has a slightly different
pinout than the SP233A in PDIP packaging
(SP233ACP). To operate properly, the fol-
lowing pairs of pins must be externally wired
together as noted in table 2:
Pins Wired
Together
SOICW
PDIP
Two V- pins
0 & 7
2 & 7
Two C2+ pins 2 & 5
& 5
Two C- pins
& 6
0 & 6
No Connections for
Pins 8, 3 and 4
Connect Pins 6 and 9
to GND
Table 2. Pin Strapping table for SP233A