FC

Open

FC = V+

Open

SYNC

Open

Open

External

Clock

Oscillator Frequency

5kHz

50kHz

External Clock

Frequency

CMOS Monolithic Voltage Converter

Impala Linear Corporation

4

(408) 574-3939

www.impalalinear.com

May 2000

ILC6660 1.8

Advance

The ILC6660 capacitive charge-pump circuit either

inverts, splits or doubles the input voltage (see Typical

Circuits).

For highest performance, low effective series

resistance (ESR) capacitors should be used (see

Capacitor Selection section for more details). When using

the inverting mode with a supply voltage less than 2V, LV

may be connected to VSS.

This bypasses the internal

regulator circuitry and provides best performance in low-

voltage applications. When using the inverter mode with

a supply voltage above 2V, LV must be left open.

Negative Voltage Converter

The most common application of the ILC6660 is as a

charge-pump voltage inverter. The operating circuit uses

only two external capacitors, C1 and C2 (see Typical

Circuits). Even though its output is not actively regulated,

the ILC6660 is very insensitive to load current changes. A

typical output source resistance of 5

Ω means that with an

input of +5V the output voltage is -5V under light load, and

decreases only to 4.5V with a load of 100mA.

Capacitors selection

Low ESR capacitors should be used at the output of

ILC6660 to minimize output ripple. This can be achieved

using ceramic capacitors, but may also be met with certain

types of tantalum capacitors.

Output ripple voltage is calculated taking into account that

the output current is solely supplied from capacitor C2 dur-

ing one-half of the charge-pump cycle. This introduces a

peak-to-peak ripple of:

V RIPPLE =

I VSH

+ I VSH (ESRC2)

2(f PUMP)(C2)

For a nominal fPUMP of 5kHz and C2 = 100µF with an

ESR of 0.05

Ω, ripple is approximately 100mV with a

100mA load current. If C2 is raised to 470µF, the ripple

drops to approximately 25mV.

Positive Voltage Doubler

The ILC6660 operates in the voltage-doubling mode as

Positive Voltage Splitter

The ILC6660 operates in voltage splitting mode as shown in

Changing Oscillator Frequency

Three modes control the ILC6660's clock frequency,

as listed below:

When FC and SYNC are unconnected (open), the

Oscillator runs at 5kHz typically. When FC is connected to

V+, the charge and discharge current change from 1.0µA

to 10.0µA, thus increasing the Oscillator frequency 10

times. In the inverter mode, SYNC may also be overdriv-

en by an external clock source. A square wave signal of

maximum 2V peak-to-peak may be applied to SYNC via

a 2…5nF capacitor to overdrive the internal oscillator.

When SYNC is overdriven, FC has no effect.

In some

applications, the 5kHz output ripple frequency may be low

enough to interfere with other circuitry.

If desired, the

Oscillator frequency can then be increased through use of

the FC pin or an external Oscillator as described above.

Increasing the clock frequency increases the ILC6660's

quiescent current, but also allows smaller capacitance val-

ues to be used for C1 and C2.

Applications Information

Detailed Description

+

1

2

3

4

8

7

6

5

FC

CAP+

ILC6660

VSS

CAP-

SYNC

LV

VSH

V+

C2

C1

R

L

V+

+

V+ (5V)

N/C

Figure 1: Test Circuit