+5V to ±10V Voltage Converters

4

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_______________Detailed Description

The MAX681 contains all circuitry needed to implement

a dual charge pump. The MAX680 needs only four

capacitors. These may be inexpensive electrolytic

capacitors with values in the 1µF to 100µF range. The

MAX681 contains two 1.5µF capacitors as C1 and C2,

and two 2.2µF capacitors as C3 and C4. See

Typical

Operating Characteristics.

Figure 2a shows the idealized operation of the positive

voltage converter. The on-chip oscillator generates a

50% duty-cycle clock signal. During the first half of the

cycle, switches S2 and S4 are open, S1 and S3 are

closed, and capacitor C1 is charged to the input volt-

open, S2 and S4 are closed, and C1 is translated

load on C3, charge is transferred onto C3 from C1 such

positive supply.

Figure 2b shows the negative converter. The switches

of the negative converter are out of phase from the pos-

itive converter. During the second half of the clock

cycle, S6 and S8 are open and S5 and S7 are closed,

tive charge pump) to GND. In the first half of the clock

MAX680

C1

4.7

µF

C3

10

µF

V+ OUT

V- OUT

GND

C4

10

µF

C2

4.7

µF

C1-

8

7

6

5

C2+

V-

V+

1

2

3

4

C1+

GND

C2-

a)

b)

S1

S3

8kHz

C1+

C1

C3

C1-

S2

S4

S5

S6

S7

S8

C2-

GND

V-

C2+

C4

C2

GND

V+

GND

V+

Figure 1. Test Circuit

Figure 2. Idealized Voltage Quadrupler: a) Positive Charge Pump; b) Negative Charge Pump