Rainbow-electronics MAX1677 Manual do Utilizador descarregar pdf (Página 9)

MAX1677

Compact, High-Efficiency, Dual-Output

Step-Up and LCD Bias DC-DC Converter

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Main Boost Converter (MBC)

The MBC operates either in PFM mode, 300kHz PWM

mode, or externally synchronized PWM mode as select-

ed by the CLK/SEL input (Table 2). PWM mode offers

fixed-frequency operation and maximum output power.

PFM mode offers the lowest IC operating current. LX

current limit is reduced in PFM mode to increase effi-

ciency and minimize output ripple.

PWM Mode

When CLK/SEL is high, the MAX1677 operates in its

high-power, low-noise PWM mode, switching at the

300kHz internal oscillator frequency. The MOSFET

switch pulse-width is modulated to control the power

transferred on each switching cycle and regulate the

Table 1. Main Boost Converter Available

Output Current

OUT

STARTUP OSC

POL

LCDLX

SUCLK

MAIN DC-DC

839k

501k

CLK/SEL

OUT

POUT

PGND

50% REF

LBO

LBI

LCDON

LCDLX

LCDGND

CLK

LCDDRV

LCDLX

POL

LCD BIAS

REF

LCDPOL

LCDFB

GND

REF

90% REF

2.25V

START-UP

LCD ON

REFERENCE

ISET/POL SENSE

MAX1677

Figure 1. Functional Block Diagram

NUMBER OF

CELLS

1 Alk/NiCd/NiMH 140/150

MBC OUTPUT

CURRENT

(mA)

PWM/PFM

1 Alk/NiCd/NiMH 1.2

1.2

INPUT

VOLTAGE

(V)

MBC

OUTPUT

VOLTAGE

(V)

3.3

5 100/70

2 Alk/NiCd/NiMH 2.4 3.3 350/170

2 Alk/NiCd/NiMH 2.4 5 260/125

1 Alk/NiCd/NiMH

or 1 Li-Ion

3.6 5 350/170

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

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