ICL7660AIBA datasheet(10/11 Pages) RENESAS

10 / 11 page

ICL7660, ICL7660A

FN3072 Rev.7.00

Page 10 of 11

Oct 5, 2010

Positive Voltage Doubling

The ICL7660 and ICL7660A may be employed to achieve

positive voltage doubling using the circuit shown in Figure 19.

In this application, the pump inverter switches of the ICL7660

and ICL7660A are used to charge C1 to a voltage level of V+ -

VF (where V+ is the supply voltage and VF is the forward

voltage drop of diode D1). On the transfer cycle, the voltage on

C1 plus the supply voltage (V+) is applied through diode D2 to

capacitor C2. The voltage thus created on C2 becomes (2V+) -

(2VF) or twice the supply voltage minus the combined forward

voltage drops of diodes D1 and D2.

The source impedance of the output (VOUT) will depend on the

output current, but for V+ = 5V and an output current of 10mA it

will be approximately 60

.

Combined Negative Voltage Conversion

and Positive Supply Doubling

Figure 20 combines the functions shown in Figures 13 and

Figure 19 to provide negative voltage conversion and positive

voltage doubling simultaneously. This approach would be, for

example, suitable for generating +9V and -5V from an existing

+5V supply. In this instance capacitors C1 and C3 perform the

pump and reservoir functions respectively for the generation of

the negative voltage, while capacitors C2 and C4 are pump

and reservoir respectively for the doubled positive voltage.

There is a penalty in this configuration which combines both

functions, however, in that the source impedances of the

generated supplies will be somewhat higher due to the finite

impedance of the common charge pump driver at pin 2 of the

device.

Voltage Splitting

The bidirectional characteristics can also be used to split a

higher supply in half, as shown in Figure 21. The combined

load will be evenly shared between the two sides. Because the

switches share the load in parallel, the output impedance is

much lower than in the standard circuits, and higher currents

can be drawn from the device. By using this circuit, and then

the circuit of Figure 16, +15V can be converted (via +7.5, and -

7.5) to a nominal -15V, although with rather high series output

resistance (

~250).

Regulated Negative Voltage Supply

In some cases, the output impedance of the ICL7660 and

ICL7660A can be a problem, particularly if the load current

varies substantially. The circuit of Figure 22 can be used to

overcome this by controlling the input voltage, via an ICL7611

low-power CMOS op amp, in such a way as to maintain a nearly

constant output voltage. Direct feedback is inadvisable, since

the ICL7660s and ICL7660As output does not respond

instantaneously to change in input, but only after the switching

delay. The circuit shown supplies enough delay to

accommodate the ICL7660 and ICL7660A, while maintaining

adequate feedback. An increase in pump and storage

capacitors is desirable, and the values shown provides an

output impedance of less than 5

 to a load of 10mA.

VOUT

V+

COSC

ICL7660

ICL7660A

FIGURE 18. LOWERING OSCILLATOR FREQUENCY

V+

VOUT =

(2V+) - (2VF)

ICL7660

ICL7660A

FIGURE 19. POSITIVE VOLT DOUBLER

V+

VOUT = (2V+) -

(VFD1) - (VFD2)

VOUT =

- (nVIN - VFDX)

ICL7660

ICL7660A

FIGURE 20. COMBINED NEGATIVE VOLTAGE CONVERTER

AND POSITIVE DOUBLER

F

RL1

VOUT = V+ - V-

V+

RL2

ICL7660

ICL7660A

FIGURE 21. SPLITTING A SUPPLY IN HALF

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