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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 00_05308

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

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