Rainbow Electronics MAX1843 User Manual
General description, Applications, Features
MAX1843
2.7A, 1MHz, Low-Voltage, Step-Down Regulator with
Internal Synchronous Rectification in QFN Package
________________________________________________________________ Maxim Integrated Products
1
19-1986; Rev 1; 3/02
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 90m
Ω 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
Features
♦ ±1% Output Accuracy
♦ Up to 1MHz Switching Frequency
♦ 95% Efficiency
♦ Internal PMOS/NMOS Switches
90m
Ω/70mΩ On-Resistance at V
IN
= +4.5V
110m
Ω/80mΩ On-Resistance at V
IN
= +3V
♦ Output Voltage
+2.5V, +1.8V, or +1.5V Pin Selectable
+1.1V to V
IN
Adjustable
♦ +3V to +5.5V Input Voltage Range
♦ 350µA Operating Supply Current
♦ <1µA Shutdown Supply Current
♦ Programmable Constant-Off-Time Operation
♦ Idle Mode Operation at Light Loads
♦ Thermal Shutdown
♦ Adjustable Soft-Start Inrush Current Limiting
♦ 100% Duty Cycle During Low-Dropout Operation
♦ Output Short-Circuit Protection
♦ 28-Pin QFN Package
PART
TEMP RANGE
PIN-PACKAGE
Ordering Information
Idle Mode is a trademark of Maxim Integrated Products.
EVALUATION KIT
AVAILABLE
MAX1843EGI
-40°C to +85°C
28 QFN
MAX1843
25
26
27
28
22
23
24
8
9
10
11
12
13
14
15
16
17
18
19
20
21
1
2
3
4
5
6
7
REF
TOFF
FB
N.C.
N.C.
N.C.
GND
N.C.
N.C.
N.C.
LX
N.C.
LX
LX
IN
SS
COMP
IN
N.C.
LX
LX
PGND
V
CC
FBSEL
PGND
PGND
QFN
TOP VIEW
N.C.
SHDN
Pin Configuration
TOFF
COMP
V
CC
FBSEL
SHDN
IN
PGND
GND
REF
SS
LX
FB
MAX1843
OUTPUT
+1.1V TO
V
IN
INPUT
+3V TO
+5.5V
0.01
µF
1
µF
2.2
µF
470pF
10
Ω
Typical Configuration
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.