SP503CF datasheet(9/29 Pages) SIPEX

9 / 29 page

Date: 7/29/04

SP503 Multiprotocol Transceiver

Figure 3. Charge Pump Waveforms

+10V

GND

–10V

–

VCC = +5V

–10V

VSS Storage Capacitor

VDD Storage Capacitor

–

Figure 2. Charge Pump Phase 2.

and RS-423 drivers. For the RS-232 driver, the

current requirement will be 3.5mA per driver,

and for the RS-423 driver, the worst case current

drain will be 11mA per driver. The external

power supplies should provide a power supply

sequence of : +l0V, then +5V, followed by –l0V.

Drivers

The SP503 has seven (7) independent drivers,

two of which have separate active–low tri–state

controls. If a half-duplex channel is required,

this can be achieved with external connections.

Control for the mode selection is done via a

four–bit control word. The SP503 does not have

a latch; the control word must be externally

latched either high or low to write the appropri-

ate code into the SP503. The drivers are pre-

arranged such that for each mode of operation

the relative position and functionality of the

drivers are set up to accommodate the selected

interface mode. As the mode of the drivers is

changed, the electrical characteristics will change

to support the requirements of clock, data, and

control line signal levels. Table 1 shows a sum-

mary of the electrical characteristics of the driv-

ers in the different interface modes. Unused

driver inputs can be left floating; however, to

ensure a desired state with no input signal, pull–

up resistors to +5V or pull–down resistors to

ground are suggested. Since the driver inputs

are both TTL or CMOS compatible, any value

resistor less than 100k

Ω will suffice.

simultaneously with this, the positive side of

capacitor C

1 is switched to +5V and the negative

side is connected to ground, and the cycle begins

again.

Since both V+ and V– are separately generated

from V

CC in a no–load condition, V+ and V

– will

be symmetrical. Older charge pump approaches

that generate V– from V+ will show a decrease

in the magnitude of V– compared to V+ due to

the inherent inefficiencies in the design.

The clock rate for the charge pump typically

operates at 15kHz. The external capacitors must

be 22

µF with a 16V breakdown rating.

External Power Supplies

For applications that do not require +5V only,

external supplies can be applied at the V+ and

V– pins. The value of the external supply volt-

ages must be no greater than

±l0V. The current

drain for the

±10V supplies is used for RS-232,

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