Rainbow Electronics MAX1677 - Manual

General Description
The MAX1677 is a compact, high-efficiency, dual-out-
put boost converter for portable devices needing two
regulated supplies, typically for logic and liquid crystal
displays (LCDs). Operation with inputs as low as 0.7V
allows the MAX1677 to accept 1, 2, or 3-cell alkaline,
NiCd, or NiMH batteries as well as 1-cell lithium-ion bat-
teries. The device requires no external FETs and can
maintain regulation while consuming only 20µA, making
it ideal for hand-held pen-input and PDA devices oper-
ating with low-current “sleep” states.
The MAX1677’s primary regulator supplies up to
350mA at either a factory-preset 3.3V or an adjustable
2.5V to 5.5V output. On-chip synchronous rectification
provides efficiencies up to 95%. 300kHz (or externally
clocked) pulse-width-modulation (PWM) operation is
particularly suitable for applications needing low noise,
such as those with wireless features. The primary con-
verter also features pin-selectable pulse-frequency-
modulation (PFM) operation that consumes only 20µA.
A 1µA shutdown state also minimizes battery drain.
The MAX1677’s secondary step-up converter supplies up
to +28V or -28V for LCD bias, varactor tuning, or other
high-voltage, low-current functions. Other MAX1677 fea-
tures include precision reference, logic control inputs for
both regulators, and an uncommitted comparator for
low-battery detection or a reset function. The MAX1677
is supplied in Maxim’s compact 16-pin QSOP package,
which occupies no more space than a standard SO-8.
Applications
PDAs Portable Phones
Hand-Held Terminals Portable Instruments
Features
♦ No External FETs Required
♦ Main Output
Up to 350mA for Logic Supply
Fixed 3.3V or Adjustable (2.5V to 5.5V)
Synchronous Rectification for High Efficiency
(up to 95%)
300kHz (200kHz to 400kHz Synchronizable)
Fixed-Frequency PWM Operation
♦ Secondary Output
Up to +28V or -28V for LCD Bias
Programmable Current Limit
♦ 0.7V to 5.5V Input Voltage Range
♦ 20µA Quiescent Current
♦ 1µA Shutdown Current
♦ Low-Battery Comparator
♦ Small 16-Pin QSOP Package
MAX1677
Compact, High-Efficiency, Dual-Output
Step-Up and LCD Bias DC-DC Converter
________________________________________________________________ Maxim Integrated Products 1
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15
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13
12
11
10
9
1
2
3
4
5
6
7
8
OUT POUT
LX
PGND
LCDGND
LCDLX
ON
LCDFB
GND
TOP VIEW
MAX1677
FB
LBI
LCDON
LBO
CLK/SEL
LCDPOL
REF
QSOP
19-1403; Rev 1; 3/01
PART
MAX1677EEE -40°C to +85°C
TEMP RANGE PIN-PACKAGE
16 QSOP
EVALUATION KIT
AVAILABLE
Pin Configuration
Ordering Information
Typical Operating Circuit
MAX1677
LX POUT
OUT
±28V
LCD
BOOST
OUTPUT
3.3V MAIN
BOOST OUTPUT
LCDFB
REF
FB
LCDGND
GND
LCDLX
LCDON
LBI
ON
OFF
LBO
CLK/SEL
ON
LCDPOL
PGND
PWM
PFM
ON
OFF
+VE OUT
-VE OUT
V IN = 0.7V to 5.5V
(UP TO MAIN OUT )
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.