MAX1843 Datasheet, PDF (1/13 Pages) Maxim Integrated Products – 2.7A, 1MHz, Low-Voltage, Step-Down Regulator with Internal Synchronous Rectification in QFN Package

19-1986; Rev 1; 3/02
EVALUATION ^KIT
AVAILABLE
2.7A, 1MHz, Low-Voltage, Step-Down Regulator with
Internal Synchronous Rectification in QFN Package
General Description
The MAX1843 constant-off-time, pulse-width modulated
(PWM) step-down DC-DC converter is ideal for use in 5V
and 3.3V to low-voltage conversion necessary in note-
book and subnotebook computers. This device features
an internal PMOS power switch and internal synchronous
rectification for high efficiency and reduced component
count. An external Schottky diode is not required. The
internal 90mΩ power switch and 70mΩ NMOS synchro-
nous-rectifier switch easily deliver continuous load cur-
rents up to 2.7A. The MAX1843 produces a preset +2.5V,
+1.8V, or +1.5V output voltage or an adjustable output
from +1.1V to V_IN. It achieves efficiencies as high as
95%.
The MAX1843 uses a unique current-mode, constant-off-
time, PWM control scheme, which includes Idle Mode™
to maintain high efficiency during light-load operation.
The programmable constant-off-time architecture sets
switching frequencies up to 1MHz, allowing the user to
optimize performance trade-offs between efficiency, out-
put switching noise, component size, and cost. The
MAX1843 features an adjustable soft-start to limit surge
currents during startup, a 100% duty-cycle mode for low
dropout operation, and a low-power shutdown mode that
disconnects the input from the output and reduces sup-
ply current below 1µA. The MAX1843 is available in a 28-
pin QFN package with an exposed backside pad.
Applications
5V or 3.3V to Low-Voltage Conversion
CPU I/O Ring
Chipset Supplies
Notebook and Subnotebook Computers
Typical Configuration
INPUT
+3V TO
+5.5V _10Ω
2.2µF
470pF
IN
LX
MAX1843 FB
V_CC
SHDN
COMP
TOFF
PGND
GND
FBSEL
REF
SS
OUTPUT
+1.1V TO
V_IN
1µF
0.01µF
Idle Mode is a trademark of Maxim Integrated Products.
Features
o ±1% Output Accuracy
o Up to 1MHz Switching Frequency
o 95% Efficiency
o Internal PMOS/NMOS Switches
90mΩ/70mΩ On-Resistance at V_IN = +4.5V
110mΩ/80mΩ On-Resistance at V_IN = +3V
o Output Voltage
+2.5V, +1.8V, or +1.5V Pin Selectable
+1.1V to V_IN Adjustable
o +3V to +5.5V Input Voltage Range
o 350µA Operating Supply Current
o <1µA Shutdown Supply Current
o Programmable Constant-Off-Time Operation
o Idle Mode Operation at Light Loads
o Thermal Shutdown
o Adjustable Soft-Start Inrush Current Limiting
o 100% Duty Cycle During Low-Dropout Operation
o Output Short-Circuit Protection
o 28-Pin QFN Package
PART
MAX1843EGI
Ordering Information
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
28 QFN
Pin Configuration
TOP VIEW
28 27
N.C. 1
26 25
24 23
22
21 PGND
IN 2
20 PGND
LX 3
19 LX
IN 4
N.C. 5
MAX1843
18 LX
17 PGND
SS 6
16 VCC
COMP 7
15 FBSEL
8 9 10 11 12 13 14
QFN
________________________________________________________________ Maxim Integrated Products 1
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.