Rainbow Electronics MAX1677 - Manual (Page 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
ON
OUT
STARTUP OSC
IN
POL
I LCDLX
SUCLK
MAIN DC-DC
839k
QP
501k
QN
CLK/SEL
OUT
POUT
LX
PGND
50% REF
FB
LBO
LBI
LCDON
LCDLX
LCDGND
ON
CLK
EA
ST
EA
LCDDRV
CL
I LCDLX POL
LCD BIAS
ON
ON
REF
ON
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