SP502 View Datasheet(PDF) - Signal Processing Technologies

Part Name

Description

Manufacturer

SP502

Multi–Mode Serial Transceiver

Signal Processing Technologies 

VCC = +5V

+

C1 –

–5V

+5V

+

C2 –

–5V

C4

+ – VDD Storage Capacitor

– + VSS Storage Capacitor

C3

VCC = +5V

+

C1 –

+

C2 –

–10V

C4

+ – VDD Storage Capacitor

– + VSS Storage Capacitor

C3

Figure 1. Charge Pump Phase 1.

tor C 1 is switched to +5V and the negative side

is connected to ground.

Phase 3

— VDD charge storage — The third phase of the

clock is identical to the first phase — the charge

transferred in C1 produces –5V in the negative

terminal of C1, which

side of capacitor C2.

is applied

Since C2+

to

is

the negative

at +5V, the

voltage potential across C2 is l0V.

Phase 4

— VDD transfer — The fourth phase of the clock

connects the negative terminal of C2 to ground

and transfers the generated l0V across C2 to C4,

the VDD storage capacitor. Again, simultaneously

with this, the positive side of capacitor C1 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 VCC in a no–load condition, V+ and V–

will be symmetrical. Older charge pump ap-

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 22µF 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

+10V

C2+

GND

GND

C2–

–10V

Figure 3. Charge Pump Waveforms

Rev. 7/21/03

SP502 Multi-Mode Serial Transceiver

9

a)

b)

© Copyright 2003 Sipex Corporation

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