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PDF MAX1831 Data sheet ( Hoja de datos )
| Número de pieza | MAX1831 | |
| Descripción | Step-Down Regulators | |
| Fabricantes | Maxim Integrated | |
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Hay una vista previa y un enlace de descarga de MAX1831 (archivo pdf) en la parte inferior de esta página. Total 13 Páginas | ||
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19-2198; Rev 0; 10/01
EVALUATION KIT
AVAILABLE
3A, 1MHz, Low-Voltage, Step-Down Regulators with
Synchronous Rectification and Internal Switches
General Description
The MAX1830/MAX1831 constant-off-time, pulse-width-
modulated (PWM) step-down DC-DC converters are
ideal for use in 5V and 3.3V to low-voltage conversion
necessary in notebook and subnotebook computers.
These devices feature internal synchronous rectification
for high efficiency and reduced component count. They
require no external Schottky diode. The internal 45mΩ
PMOS power switch and 55mΩ NMOS synchronous-rec-
tifier switch easily deliver continuous load currents up to
3A. The MAX1830 produces preset +2.5V, +1.8V, or
+1.5V output voltage or an adjustable output from +1.1V
to VIN. The MAX1831 produces preset +3.3V, +2.5V, and
+1.5V output voltages and an adjustable output from
+1.1V to VIN. They achieve efficiencies as high as 94%.
The MAX1830/MAX1831 use 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, output switching noise, compo-
nent size, and cost. Both devices are designed for con-
tinuous output currents up to 3A, an internal digital
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 supply current below
1µA.The MAX1830/MAX1831 are available in 16-pin
QSOP packages.
For similar devices that provide continuous output
currents of 1A to 3A, refer to the MAX1644, MAX1623,
and MAX1742/MAX1842/MAX1843 data sheets.
Applications
5V or 3.3V to Low-Voltage Conversion
CPU I/O Supplies
Chipset Supplies
Notebook and Subnotebook Computers
Pin Configuration appears at end of data sheet.
Features
o ±1.5% Output Accuracy
o 94% Efficiency
o Internal PMOS/NMOS Switches
45mΩ/55mΩ On-Resistance at VIN = +4.5V
50mΩ/55mΩ On-Resistance at VIN = +3V
o Output Voltages
+3.3V, +2.5V, or +1.5V Pin Selectable (MAX1831)
+2.5V, +1.8V, or +1.5V Pin Selectable (MAX1830)
+1.1V to VIN Adjustable (Both Devices)
o +3V to +5.5V Input Voltage Range
o 750µA (max) Operating Supply Current
o <1µA Shutdown Supply Current
o Programmable Constant-Off-Time Operation
o Up to 1MHz Switching Frequency
o Idle Mode Operation at Light Loads
o Thermal Shutdown
o Internal Digital Soft-Start Inrush Current Limiting
o 100% Duty Cycle During Low-Dropout Operation
o Output Short-Circuit Protection
o 16-Pin QSOP Package
PART
MAX1830EEE
MAX1831EEE
Ordering Information
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 QSOP
16 QSOP
Typical Configuration
INPUT
+3V TO
+5.5V
IN LX
MAX1830 FB
MAX1831
VCC PGND
SHDN
COMP
TOFF
GND
FBSEL
REF
OUTPUT
+1.1V TO
VIN
Idle Mode is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________ 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.
1 page  
3A, 1MHz, Low-Voltage, Step-Down Regulators with
Synchronous Rectification and Internal Switches
Typical Operating Characteristics (continued)
(Circuit of Figure 1, TA = +25°C, unless otherwise noted.)
NORMALIZED OUTPUT ERROR
vs. OUTPUT CURRENT
0.10
0.05
0
-0.05
-0.10
-0.15
-0.20
VIN = 5.0V
VOUT = 1.5V
L = 1.5µH
VIN = 3.3V
VOUT = 1.5V
L = 1.5µH
-0.25
0.001
0.01 0.1
1
OUTPUT CURRENT (A)
10
SWITCHING FREQUENCY
vs. OUTPUT CURRENT
1200
VIN = 5.0V,
1000 VOUT = 1.5V, L = 1.5µH
800
600
VIN = 3.3V,
400 VOUT = 1.5V, L = 1.5µH
200
0
0 0.5 1.0 1.5 2.0 2.5 3.0
OUTPUT CURRENT (A)
STARTUP AND SHUTDOWN
MAX1830 toc06
IIN
1A/div
VSHDN
5V/div
400µs/div
VIN = 3.3V, VOUT = 1.5V,
ROUT = 0.5Ω, RTOFF = 82kΩ, L = 1.5µH
VOUT
1V/div
LOAD-TRANSIENT RESPONSE
MAX1830 toc07
VOUT
50mV/div
AC-COUPLE
0
10µs/div
VIN = 3.3V, VOUT = 1.5V,
RTOFF = 82kΩ, L = 1.5µH, IOUT = 0.1A TO 3A
IOUT
2A/div
LINE-TRANSIENT RESPONSE
MAX1830 toc08
VIN
2V/div
20µs/div
VOUT = 1.8V, IOUT = 1A,
RTOFF = 75kΩ, L = 1.5µH
VOUT
50mV/div
AC-COUPLED
_______________________________________________________________________________________ 5
5 Page 
3A, 1MHz, Low-Voltage, Step-Down Regulators with
Synchronous Rectification and Internal Switches
MAX1830/MAX1831
MAXIMUM RECOMMENDED CONTINUOUS
OUTPUT CURRENT vs. TEMPERATURE
3.50
3.40
3.30
3.20
3.10
3.00
2.90
2.80
2.70
2.60
2.50 0.7IN2 OF 1-OZ COPPER
2.40
25 35 45 55 65 75 85
TEMPERATURE (°C)
Figure 5. Maximum Recommended Continuous Output Current
vs. Temperature
Integrator Amplifier
An internal transconductance amplifier fine tunes the
output DC accuracy. A capacitor, CCOMP, from COMP
to VCC compensates the transconductance amplifier.
For stability, choose CCOMP = 470pF.
A large capacitor value maintains a constant average
output voltage but slows the loop response to changes
in output voltage. A small capacitor value speeds up
the loop response to changes in output voltage but
decreases stability.
High-Current Thermal Considerations
High ambient temperatures can limit the maximum
current or duty factor of the output current, depending
on the total copper, are connected to the MAX1830/
MAX1831 and available airflow.
Figure 5 shows the maximum recommended continuous
output current vs. ambient temperature. Figure 6 shows
the maximum recommended output current vs. the out-
put current duty cycle at high temperatures. These fig-
ures are based on 0.7in2 of 1oz copper in free air.
Figure 6 assumes that the output current is a square
wave with a 100Hz frequency. The duty cycle is
defined as the duration of the burst current divided by
the period of the square wave. This figure shows the
limitations for continuous bursts of output current.
Note that if the thermal limitations of the MAX1830/
MAX1831 are exceeded, it enters thermal shutdown to
prevent destructive failure.
MAXIMUM RECOMMENDED BURST CURRENT
vs. BURST CURRENT DUTY CYCLE
3.40
3.20 TA = +55°C
TA = +85°C
3.00
2.80
2.60
IOUT IS A 100Hz SQUARE WAVE
FROM 1A TO THE BURST CURRENT
2.40
0
20 40
60 80
DUTY CYCLE (%)
100
Figure 6. Maximum Recommended Burst Current vs. Burst
Current Duty Cycle
Frequency Variation with
Output Current
The operating frequency of the MAX1830/MAX1831 is
determined primarily by tOFF (set by RTOFF), VIN, and
VOUT as shown in the following formula:
[ ( ( ) )]fPWM =
VIN − VOUT − VPMOS
tOFF VIN − VPMOS + VNMOS
However, as the output current increases, the voltage
drop across the NMOS and PMOS switches increases
and the voltage across the inductor decreases. This
causes the frequency to drop. The change in frequency
can be approximated with the following formula:
∆fPWM = -IOUT x RPMOS / (VIN x tOFF)
where RPMOS is the resistance of the internal MOSFETs
(50mΩ typ).
Circuit Layout and Grounding
Good layout is necessary to achieve the MAX1830/
MAX1831s’ intended output power level, high efficien-
cy, and low noise. Good layout includes the use of a
ground plane, careful component placement, and cor-
rect routing of traces using appropriate trace widths.
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet MAX1831.PDF ] | |
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