MAX848 Datasheet, PDF (1/16 Pages) Maxim Integrated Products – 1-Cell to 3-Cell, High-Power, Low-Noise, Step-Up DC-DC Converters

19-1095; Rev 2; 12/97
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
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
o Up to 95% Efficiency
(see Typical Output Selector Guide below)
o 3.3V Dual Mode™ or 2.7V to 5.5V Adj. Output
o 0.7V to 5.5V Input Range
o 0.15mW Standby Mode
o 300kHz PWM Mode or Synchronizable
o Two-Channel ADC with Serial Output
o Power-Good Function
Digital Cordless Phones
Cellular Phones
Palmtop Computers
Local 3.3V to 5V Supplies
Applications
PCS Phones
Hand-Held Instruments
Personal Communicators
PART
MAX848ESE
MAX849ESE
Ordering Information
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 Narrow SO
16 Narrow SO
Typical Operating Circuit
Typical Output Selector Guide
V_IN
V_OUT
MAX849 I_OUT
(V)
(V)
(mA)
3.3
100
0.9
5
70
3.3
300
1.2
5
200
3.3
750
2.4
5
500
3.3
800
2.7
5
600
3.6
5
1000
MAX848 I_OUT
(mA)
70
40
110
70
200
130
250
150
300
INPUT
0.8V TO 5.5V
A/D CHANNEL 1 IN
A/D CHANNEL 2 IN
A/D CHANNEL SELECT
A/D OUTPUT
ON/OFF CONTROL
SYNC INPUT
MAX848
AIN1 ^MAX849
AIN2
AINSEL
DATA
ON1
ON2
CLK/SEL
POKIN
LX
OUT
POUT
POK
FB
REF GND PGND
OUTPUT
VOLTAGE MONITOR
OUTPUT
Pin Configuration appears at end of data sheet.
Dual Mode is a trademark of Maxim Integrated Products.
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