7

FN3072.7

October 10, 2005

The voltage regulator portion of the ICL7660 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 GROUND, disabling the regulator. For supply

voltages greater than 3.5V the LV terminal must be left open to

insure latchup proof operation, and prevent device damage.

Theoretical Power Efficiency

Considerations

In theory a voltage converter can approach 100% efficiency

if certain conditions are met.

1. The driver circuitry consumes minimal power.

2. The output switches have extremely low ON resistance

and virtually no offset.

3. The impedances of the pump and reservoir capacitors

are negligible at the pump frequency.

The ICL7660 and ICL7660A approach these conditions for

are used.

ENERGY IS LOST ONLY IN THE TRANSFER OF

CHARGE BETWEEN CAPACITORS IF A CHANGE IN

VOLTAGE OCCURS. The energy lost is defined by:

high at the pump frequency (refer to Figure 12) compared to

achieve maximum efficiency of operation.

Do’s And Don’ts

1. Do not exceed maximum supply voltages.

2. Do not connect LV terminal to GROUND for supply

voltages greater than 3.5V.

3. Do not short circuit the output to V+ supply for supply

voltages above 5.5V for extended periods, however,

transient conditions including start-up are okay.

must be connected to pin 2 of the ICL7660 and ICL7660A

5. If the voltage supply driving the ICL7660 and ICL7660A

has a large source impedance (25

Ω - 30Ω), then a 2.2µF

capacitor from pin 8 to ground may be required to limit

rate of rise of input voltage to less than 2V/

µs.

6. User should insure that the output (pin 5) does not go

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

under these conditions. A 1N914 or similar diode placed

under these conditions. (Anode pin 5, Cathode pin 3).

8

3

2

5

3

7

FIGURE 12. IDEALIZED NEGATIVE VOLTAGE CONVERTER

FIGURE 13A. CONFIGURATION

FIGURE 13B. THEVENIN EQUIVALENT

FIGURE 13. SIMPLE NEGATIVE CONVERTER

1

2

3

4

8

7

6

5

+

-

10

µF

ICL7660

V+

+

-

10

µF

ICL7660A

V+

+

-

ICL7660, ICL7660A