Rainbow Electronics MAX849 - Manual

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General Description
The MAX848/MAX849 boost converters set a new stan-
dard of high efficiency and high integration for noise-
sensitive power-supply applications, such as portable
phones and small systems with RF data links. The heart
of the these devices is a synchronous boost-topology
regulator that generates a fixed 3.3V output (or 2.7V to
5.5V adjustable output) from one to three NiCd/NiMH
cells or one Li-Ion cell.
Synchronous rectification provides a 5% efficiency
improvement over similar nonsynchronous boost regu-
lators. In standby mode, pulse-skipping PFM operation
keeps the output voltage alive with only 150µW quies-
cent power consumption. Fixed-frequency PWM opera-
tion ensures that the switching noise spectrum is limited
to the 300kHz fundamental and its harmonics, allowing
easy post-filtering noise reduction. For even tighter
noise spectrum control, synchronize to a 200kHz to
400kHz external clock.
Battery monitoring is provided by a two-channel, volt-
age-to-frequency analog-to-digital converter (ADC).
One channel is intended for a single-cell battery input
(0.625V to 1.875V range), while the other channel is for
monitoring higher voltages (0V to 2.5V range).
Two control inputs are provided for push-on, push-off
control via a momentary pushbutton switch. Upon
power-up, an internal comparator monitors the output
voltage to generate a power-good output (POK).
The devices differ only in the current limit of the
N-channel MOSFET power switch: 0.8A for the
MAX848, and 1.4A for the MAX849.
Features
♦ Up to 95% Efficiency
(see
Typical Output Selector Guide below)
♦ 3.3V Dual Mode™ or 2.7V to 5.5V Adj. Output
♦ 0.7V to 5.5V Input Range
♦ 0.15mW Standby Mode
♦ 300kHz PWM Mode or Synchronizable
♦ Two-Channel ADC with Serial Output
♦ Power-Good Function
Applications
Digital Cordless Phones PCS Phones
Cellular Phones Hand-Held Instruments
Palmtop Computers Personal Communicators
Local 3.3V to 5V Supplies
MAX848/MAX849
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
________________________________________________________________ Maxim Integrated Products 1
AIN1
AIN2
AINSEL
DATA
ON1
ON2
CLK/SEL
POKIN
LX
OUT
POUT
POK
FB
MAX848
MAX849
OUTPUT A/D CHANNEL 1 IN
A/D CHANNEL 2 IN
A/D CHANNEL SELECT
A/D OUTPUT
ON/OFF CONTROL
SYNC INPUT
INPUT
0.8V TO 5.5V
VOLTAGE MONITOR
OUTPUT
REF GND PGND
Typical Operating Circuit
19-1095; Rev 2; 12/97
PART
MAX848 ESE
MAX849 ESE -40°C to +85°C
-40°C to +85°C
TEMP. RANGE PIN-PACKAGE
16 Narrow SO
16 Narrow SO
Ordering Information
Pin Configuration appears at end of data sheet.
Dual Mode is a trademark of Maxim Integrated Products.
Typical Output Selector Guide
V IN
(V)
V OUT
(V)
MAX849 I OUT
(mA)
MAX848 I OUT
(mA)
0.9
3.3 100 70
5 70 40
1.2
3.3 300 110
5 200 70
2.4
3.3 750 200
5 500 130
2.7
3.3 800 250
5 600 150
3.6 5 1000 300