CMOS Monolithic Voltage Converter

6

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______________Detailed Description

The MAX660 capacitive charge-pump circuit either

inverts or doubles the input voltage (see

Typical

Operating 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 3V, LV must be connected to GND. This

bypasses the internal regulator circuitry and provides

best performance in low-voltage applications. When

using the inverter mode with a supply voltage above

3V, LV may be connected to GND or left open. The part

is typically operated with LV grounded, but since LV

may be left open, the substitution of the MAX660 for the

ICL7660 is simplified. LV must be grounded when over-

driving OSC (

see Changing Oscillator Frequency sec-

tion). Connect LV to OUT (for any supply voltage) when

using the doubling mode.

__________Applications Information

Negative Voltage Converter

The most common application of the MAX660 is as a

charge-pump voltage inverter. The operating circuit

uses only two external capacitors, C1 and C2 (see

Typical Operating Circuits).

Even though its output is not actively regulated, the

MAX660 is very insensitive to load current changes. A

typical output source resistance of 6.5

Ω means that

with an input of +5V the output voltage is -5V under

light load, and decreases only to -4.35V with a load of

100mA. Output source resistance vs. temperature and

supply voltage are shown in the

Typical Operating

Characteristics graphs.

Output ripple voltage is calculated by noting the output

current supplied is solely from capacitor C2 during

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

peak-to-peak ripple of:

10kHz oscillator frequency) and C2 = 150µF with an

ESR of 0.2

Ω, ripple is approximately 90mV with a

100mA load current. If C2 is raised to 390µF, the ripple

drops to 45mV.

Positive Voltage Doubler

The MAX660 operates in the voltage-doubling mode as

shown in the

Typical Operating Circuit. The no-load

Other Switched-Capacitor Converters

Please refer to Table 1, which shows Maxim’s charge-

pump offerings.

Changing Oscillator Frequency

Four modes control the MAX660’s clock frequency, as

listed below:

FC

OSC

Oscillator Frequency

Open

Open

10kHz

FC = V+

Open

80kHz

Open or

External

See

Typical Operating

FC = V+

Capacitor

Characteristics

Open

External

External Clock Frequency

Clock

When FC and OSC are unconnected (open), the oscil-

lator runs at 10kHz typically. When FC is connected to

V+, the charge and discharge current at OSC changes

from 1.0µA to 8.0µA, thus increasing the oscillator

MAX829

MAX861

MAX1044

Package

SOT 23-5

SO-8,

µMAX

SO-8,

µMAX

Op. Current

(typ, mA)

0.15

0.3 at 13kHz,

1.1 at 100kHz,

2.5 at 250kHz

0.03

Output

Ω

(typ)

20

12

6.5

Pump Rate

(kHz)

35

13, 100, 150

5

Input (V)

1.25 to 5.5

1.5 to 5.5

1.5 to 10

ICL7662

SO-8

0.25

125

10

1.5 to 10

MAX660

SO-8

0.12 at 5kHz,

1 at 40kHz

6.5

5, 40

1.5 to 5.5

MAX860

SO-8,

µMAX

0.2 at 6kHz,

0.6 at 50kHz,

1.4 at 130kHz

12

6, 50, 130

1.5 to 5.5

MAX828

SOT 23-5

0.06

20

12

1.25 to 5.5

ICL7660

SO-8,

µMAX

0.08

55

10

1.5 to 10

Table 1. Single-Output Charge Pumps