8

FN3179.7

January 23, 2013

Detailed Description

The ICL7660S and ICL7660A contain all the necessary

circuitry to complete a negative voltage converter, with the

exception of two external capacitors, which may be

inexpensive 10µF polarized electrolytic types. The mode of

operation of the device may best be understood by

considering Figure 14, which shows an idealized negative

and ICL7660A approach this ideal situation more closely

than existing non-mechanical circuits.

In the ICL7660S and ICL7660A, the four switches of

difficulty with this approach is that in integrating the switches,

biased with respect to their sources, but not so much as to

degrade their “ON” resistances. In addition, at circuit start-

the output voltage must be sensed and the substrate bias

adjusted accordingly. Failure to accomplish this would result

in high power losses and probable device latch-up.

This problem is eliminated in the ICL7660S and ICL7660A by

together with the level translators, and switches the

necessary reverse bias.

The voltage regulator portion of the ICL7660S and

ICL7660A is an integral part of the anti-latchup circuitry;

however, its inherent voltage drop can degrade operation at

low voltages. Therefore, to improve low voltage operation,

the “LV” pin should be connected to GND, thus disabling the

regulator. For supply voltages greater than 3.5V, the LV

terminal must be left open to ensure latchup-proof operation

and to prevent device damage.

Theoretical Power Efficiency

Considerations

In theory, a voltage converter can approach 100% efficiency

if certain conditions are met:

1. The drive circuitry consumes minimal power.

2. The output switches have extremely low ON resistance

and virtually no offset.

3. The impedance of the pump and reservoir capacitors are

negligible at the pump frequency.

The ICL7660S and ICL7660A approach these conditions for

used. ENERGY IS LOST ONLY IN THE TRANSFER OF

CHARGE BETWEEN CAPACITORS IF A CHANGE IN

VOLTAGE OCCURS. The energy lost is defined as shown in

Equation 1:

relatively high at the pump frequency (see Figure 14)

voltage ripple, but also to employ a correspondingly large

operation.

Do’s and Don’ts

1. Do not exceed maximum supply voltages.

2. Do not connect LV terminal to GND for supply voltage

greater than 3.5V.

voltages above 5.5V for extended periods; however,

transient conditions including start-up are okay.

be connected to pin 2 of the ICL7660S and ICL7660A, and

5. If the voltage supply driving the ICL7660S and ICL7660A

has a large source impedance (25

Ω to 30Ω), then a

2.2µF capacitor from pin 8 to ground may be required to

limit the rate of rise of input voltage to less than 2V/µs.

6. If the input voltage is higher than 5V and it has a rise rate

to CAP- is needed to prevent latchup (triggered by

forward biasing Q4’s body diode) by keeping the output

(pin 5) from going more positive than CAP- (pin 4).

7. User should ensure that the output (pin 5) does not go

more positive than GND (pin 3). Device latch-up will

occur under these conditions. To provide additional

protection, a 1N914 or similar diode placed in parallel

cathode pin 3).

8

2

4

33

5

7

FIGURE 14. IDEALIZED NEGATIVE VOLTAGE CONVERTER

E

1

2

---

–

()

=

(EQ. 1)

ICL7660S, ICL7660A