MAX1044 Просмотр технического описания (PDF) - Maxim Integrated

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MAX1044

Switched-Capacitor Voltage Converters

Maxim Integrated 

MAX1044/ICL7660

Switched-Capacitor Voltage Converters

S1

S2

V+

C1

S3

S4

C2

VOUT = -(V+)

Figure 2. Ideal Voltage Inverter

f

V+

C1

VOUT

C2

RLOAD

Figure 3a. Switched Capacitor Model

REQUIV

V+

REQUIV =

1

f x C1

C2

VOUT

RLOAD

Figure 3b. Equivalent Circuit

where f is one-half the oscillator frequency. This resis-

tance is a major component of the output impedance of

switched-capacitor circuits like the MAX1044/ICL7660.

As shown in Figure 4, the MAX1044/ICL7660 contain

MOSFET switches, the necessary transistor drive cir-

cuitry, and a timing oscillator.

V+

pin 8

S1

CAP+

pin 2

S2

1M

BOOST

pin 1

OSC

pin 7

Q

2Q

LV

pin 6

S3

S4

GND

CAP-

pin 3

pin 4

VOUT

pin 5

Figure 4. MAX1044 and ICL7660 Functional Diagram

Design Information

The MAX1044/ICL7660 are designed to provide a simple,

compact, low-cost solution where negative or doubled

supply voltages are needed for a few low-power com-

ponents. Figure 5 shows the basic negative voltage

converter circuit. For many applications, only two external

capacitors are needed. The type of capacitor used is not

critical.

Proper Use of the Low-Voltage (LV) Pin

Figure 4 shows an internal voltage regulator inside

the MAX1044/ICL7660. Use the LV pin to bypass this

regulator, in order to improve low-voltage performance

and allow operation down to 1.5V. For low-voltage opera-

tion and compatibility with the industry-standard LTC1044

and ICL7660, the LV pin should be connected to ground

for supply voltages below 3.5V and left open for supply

voltages above 3.5V.

The MAX1044’s LV pin can be grounded for all operat-

ing conditions. The advantage is improved low-voltage

performance and increased oscillator frequency. The

disadvantage is increased quiescent current and reduced

efficiency at higher supply voltages. For Maxim’s ICL7660,

the LV pin must be left open for supply voltages above 5V.

When operating at low supply voltages with LV open,

connections to the LV, BOOST, and OSC pins should

be short or shielded to prevent EMI from causing

oscillator jitter.

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