7

TGoddard/SP332/9617R0

SP332 RS-232/RS-485 Multi-Mode Serial Transceiver

© Copyright 2000 Sipex Corporation

RS-232 Mode

RS-485 Mode

Phase 3

-Vdd charge storage- The third phase of the

clock is identical to the first phase- the trans-

ferred charge in C1 produces -5V in the negative

terminal of C1, which is applied to the negative

side of capacitor C2. Since C2+ is at +5V, the

voltage potential across C2 is 10V.

Phase 4

-Vdd transfer- The fourth phase of the clock

connects the negative terminal of C2 to ground

and transfers the generated 10V across C2 to C4,

the Vdd storage capacitor. Simultaneously with

this, the positive side of capacitor C1 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 Vcc 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 0.1

µF with a 16V breakdown rating.

SP332 TYPICAL OPERATING CIRCUIT

+5V

GND

TTL/CMOS

TTL/CMOS

TTL/CMOS

TTL/CMOS

TTL/CMOS

0.1

µF

0.1

µF

VCC

V+

V-

TTL/CMOS

SHUT

DOWN

RS-232

TTL/CMOS

TTL/CMOS

TTL/CMOS

TTL/CMOS

T1

T2

T3

T4

TX1

TX2

TX3

TX4

TI1

TI2

TI3

TI4

RI1

RI2

RI3

RI4

RX1

RX2

RX3

RX4

1

3

4

5

6

7

8

10

0.1

µF

0.1

µF

C1+

C1-

C2+

C2-

9

11

12

13

14

15

16

17

18

19

20

21

22

23

SEL B

2

SEL A

24

25

26

27

28

R1

R2

R3

R4

5K

Ω

5K

Ω

5K

Ω

5K

Ω

400K

Ω

Vcc

400K

Ω

Vcc

400K

Ω

Vcc

400K

Ω

Vcc

RS-232

RS-232

RS-232

RS-232

RS-232

RS-232

RS-232

LOOP

BACK

0V

0V

SEL A

TTL/CMOS

TTL/CMOS

TTL/CMOS

0.1

µF

0.1

µF

C1+

C1-

C2+

C2-

1

SEL B

2

+5V

VCC

5

GND

8

9

11

12

13

19

20

22

24

26

27

28

TTL/CMOS

TTL/CMOS

TTL/CMOS

TTL/CMOS

T1

T3

R1

RS-485

RS-485

RS-485

TTL/CMOS

0.1

µF

0.1

µF

V+

V-

TTL/CMOS

SHUT

DOWN

RS-485

RS-485

RS-485

4

6

7

10

14

15

16

23

25

3

RI1

RI2

TX3

TX4

TX1

TX2

TI1

TI2

TI3

TI4

RX1

RX2

TTL/CMOS

21

R3

17

18

RI4

RI3

RX3

RX4

15K

Ω

15K

Ω

15K

Ω

15K

Ω

400K

Ω

Vcc

400K

Ω

Vcc

LOOP

BACK

RS-485

RS-485

+5V

+5V

SP332

SP332