ICL7660AIBA datasheet(6/11 Pages) RENESAS

6 / 11 page

ICL7660, ICL7660A

FN3072 Rev.7.00

Page 6 of 11

Oct 5, 2010

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 10

F

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 100F.

FIGURE 11. ICL7660, ICL7660A TEST CIRCUIT

Typical Performance Curves

(Test Circuit of Figure 11) (Continued)

TA = 25°C

V+ = 2V

-1

-2

SLOPE 150



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

F

IS V+

(+5V)

-VOUT

F

ICL7660

COSC

(NOTE)

ICL7660A

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