SP502 datasheet(9/30 Pages) SIPEX

9 / 30 page

Rev. 7/21/03

SP502 Multi-Mode Serial Transceiver

tor C

1 is switched to +5V and the negative side

is connected to ground.

Phase 3

— V

DD charge storage — The third phase of the

clock is identical to the first phase — the charge

transferred in C

1 produces –5V in the negative

terminal of C

1, which is applied to the negative

side of capacitor C

2. Since C2

+ is at +5V, the

voltage potential across C

2 is l0V.

Phase 4

— V

DD transfer — The fourth phase of the clock

connects the negative terminal of C

2 to ground

and transfers the generated l0V across C

2 to C4,

the V

DD storage capacitor. Again, simultaneously

with this, the positive side of capacitor C

1 is

switched to +5V and the negative side is con-

nected 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 ap-

VCC = +5V

–5V

+5V

VSS Storage Capacitor

VDD Storage Capacitor

–

Figure 1. Charge Pump Phase 1.

VCC = +5V

–10V

VSS Storage Capacitor

VDD Storage Capacitor

–

Figure 2. Charge Pump Phase 2.

proaches 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. Two

external Schottky diodes connected as in Figure

6 are required for high rate of rise power sup-

plies.

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,

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

Figure 3. Charge Pump Waveforms

+10V

GND

–10V

–

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