7660AIBA datasheet(6/11 Pages) INTERSIL

6 / 11 page

FN3072.7

October 10, 2005

Detailed Description

The ICL7660 and ICL7660A contain all the necessary

circuitry to complete a negative voltage converter, with the

exception of 2 external capacitors which may be inexpensive

µF polarized electrolytic types. The mode of operation of

the device may be best understood by considering Figure

12, which shows an idealized negative voltage converter.

Capacitor C1 is charged to a voltage, V+, for the half cycle

when switches S1 and S3 are closed. (Note: Switches S2

and S4 are open during this half cycle.) During the second

half cycle of operation, switches S2 and S4 are closed, with

S1 and S3 open, thereby shifting capacitor C1 negatively by

V+ volts. Charge is then transferred from C1 to C2 such that

the voltage on C2 is exactly V+, assuming ideal switches and

no load on C2. The ICL7660 approaches this ideal situation

more closely than existing non-mechanical circuits.

In the ICL7660 and ICL7660A, the 4 switches of Figure 12

are MOS power switches; S1 is a P-Channel device and S2,

S3 and S4 are N-Channel devices. The main difficulty with

this approach is that in integrating the switches, the

substrates of S3 and S4 must always remain reverse biased

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

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

under output short circuit conditions (VOUT = V+), 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 latchup.

This problem is eliminated in the ICL7660 and ICL7660A by a

logic network which senses the output voltage (VOUT) together

with the level translators, and switches the substrates of S3 and

S4 to the correct level to maintain necessary reverse bias.

FIGURE 9. OUTPUT VOLTAGE AS A FUNCTION OF OUTPUT

CURRENT

FIGURE 10. SUPPLY CURRENT AND POWER CONVERSION

EFFICIENCY AS A FUNCTION OF LOAD

CURRENT

NOTE:

6. These curves include in the supply current that current fed directly into the load RL from the V+ (See Figure 11). Thus, approximately half the

supply current goes directly to the positive side of the load, and the other half, through the ICL7660/ICL7660A, to the negative side of the load.

Ideally, VOUT ∼ 2VIN, IS ∼ 2IL, so VIN x IS ∼ VOUT x IL.

NOTE: For large values of COSC (>1000pF) the values of C1 and C2 should be increased to 100µF.

FIGURE 11. ICL7660, ICL7660A TEST CIRCUIT

Typical Performance Curves (Test Circuit of Figure 11) (Continued)

TA = 25°C

V+ = 2V

-1

-2

SLOPE 150

Ω

LOAD CURRENT IL (mA)

100

PEFF

I+

LOAD CURRENT IL (mA)

1.5

3.0

4.5

6.0

7.5

9.0

20.0

18.0

16.0

14.0

12.0

10.0

8.0

6.0

4.0

2.0

TA = 25°C

V+ = 2V

µF

IS V+

(+5V)

-VOUT

µF

ICL7660

COSC

(NOTE)

ICL7660A

ICL7660, ICL7660A

7660AIBA Datasheet(PDF) 6 Page - Intersil Corporation

7660AIBA Datasheet(HTML) 6 Page - Intersil Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11

Datasheet Descarga

Enlace URL