|
|
PDF MAX1842 Data sheet ( Hoja de datos )
| Número de pieza | MAX1842 | |
| Descripción | Step-Down Regulators | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de MAX1842 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
|
No Preview Available !
19-1760; Rev 2; 9/05
EVAALVUAAILTAIOBNLEKIT
1A/2.7A, 1MHz, Step-Down Regulators with
Synchronous Rectification and Internal Switches
General Description
The MAX1742/MAX1842 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 neces-
sary 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 90mΩ PMOS
power switch and 70mΩ NMOS synchronous-rectifier
switch easily deliver continuous load currents up to 1A.
The MAX1742/MAX1842 produce a preset 2.5V, 1.8V, or
1.5V output voltage or an adjustable output from 1.1V to
VIN. They achieve efficiencies as high as 95%.
The MAX1742/MAX1842 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 architec-
ture sets switching frequencies up to 1MHz, allowing the
user to optimize performance trade-offs between effi-
ciency, output switching noise, component size, and
cost. Both devices are designed for continuous output
currents up to 1A. The MAX1742 uses a peak current
limit of 1.3A (min) and is suitable for applications requir-
ing small external component size and high efficiency.
The MAX1842 has a higher current limit of 3.1A (min)
and is intended for applications requiring an occasional
burst of output current up to 2.7A. Both devices also fea-
ture an adjustable soft-start to limit surge currents during
startup, a 100% duty cycle mode for low-dropout opera-
tion, and a low-power shutdown mode that disconnects
the input from the output and reduces supply current
below 1µA. The MAX1742/MAX1842 are available in 16-
pin QSOP packages.
For similar devices that provide continuous output cur-
rents up to 2A and 3A, refer to the MAX1644 and
MAX1623 data sheets.
Applications
5V or 3.3V to Low-Voltage Conversion
CPU I/O Ring
Chipset Supplies
Notebook and Subnotebook Computers
Pin Configuration appears at end of data sheet.
Idle Mode is a trademark of Maxim Integrated Products.
Features
♦ ±1% Output Accuracy
♦ 95% Efficiency
♦ Internal PMOS and NMOS Switches
90mΩ On-Resistance at VIN = 4.5V
110mΩ On-Resistance at VIN = 3V
♦ Output Voltage
2.5V, 1.8V, or 1.5V Pin Selectable
1.1V to VIN Adjustable
♦ 3V to 5.5V Input Voltage Range
♦ 600μA (max) Operating Supply Current
♦ <1μA Shutdown Supply Current
♦ Programmable Constant-Off-Time Operation
♦ 1MHz (max) Switching Frequency
♦ 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
♦ 16-Pin QSOP Package
Ordering Information
PART
MAX1742EEE
TEMP RANGE
-40°C to +85°C
MAX1742EEE+
MAX1842EEE
MAX1842EEE+
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
+ Denotes lead-free package.
PIN-PACKAGE
16 QSOP
16 QSOP
16 QSOP
16 QSOP
Typical Configuration
INPUT
3V TO
5.5V
10Ω
2.2μF
470pF
IN LX
MAX1742 FB
MAX1842
VCC PGND
SHDN
COMP
TOFF
GND
FBSEL
REF
SS
OUTPUT
1.1V TO
VIN
0.01μF
1μF
________________________________________________________________ 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  
1A/2.7A, 1MHz, Step-Down Regulators with
Synchronous Rectification and Internal Switches
(Circuit of Figure 1, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics
MAX1742
EFFICIENCY vs. OUTPUT CURRENT
(VIN = 5.0V, L = 6.0μH)
100
95 VOUT = 2.5V, RTOFF = 47kΩ, f = 926kHz
90 VOUT = 1.8V, RTOFF = 75kΩ,
85 f = 833kHz
80
75
70
65
60
55
50
0.001
VOUT = 1.5V, RTOFF = 100kΩ, f = 692kHz
0.01 0.1
OUTPUT CURRENT (A)
1
MAX1742
EFFICIENCY vs. OUTPUT CURRENT
(VIN = 3.3V, L = 3.9μH)
100
95 VOUT = 2.5V, RTOFF = 36kΩ, f = 456kHz
90
85
80
75
70 VOUT = 1.8V, RTOFF = 43kΩ, f = 869kHz
65
60
55 VOUT = 1.5V, RTOFF = 56kΩ, f = 833kHz
50
0.001
0.01
0.1
OUTPUT CURRENT (A)
1
MAX1742
EFFICIENCY vs.OUTPUT CURRENT
(fPWM = 270kHz)
100
95
VIN = 5V, VOUT = 1.8V,
L = 15μH, RTOFF = 240kΩ
90
85
80
75
70
65
60 VIN = 3.3V, VOUT = 1.8V,
L = 10μH, RTOFF = 160kΩ
55
50
0.001
0.01 0.1
OUTPUT CURRENT (A)
1
MAX1742
NORMALIZED OUTPUT ERROR
vs. OUTPUT CURRENT
0.5
0.4
0.3
0.2 VIN = 5V, VOUT = 1.5V, L = 6μH
0.1
0
-0.1
-0.2 VIN = 3.3V, VOUT = 1.5V
-0.3
-0.4
-0.5
0.001
0.01 0.1
OUTPUT CURRENT (A)
1
MAX1742
SWITCHING FREQUENCY
vs. OUTPUT CURRENT
1100
1000
VIN = 5V, VOUT = 2.5V, L = 6μH
900
800
700
600
500
400 VIN = 5V, VOUT = 1.5V, L = 6μH
300
200 VIN = 3.3V, VOUT = 1.5V, L = 3.9μH
100
0
0 0.2 0.4 0.6 0.8 1.0
OUTPUT CURRENT (A)
_______________________________________________________________________________________ 5
5 Page 
1A/2.7A, 1MHz, Step-Down Regulators with
Synchronous Rectification and Internal Switches
constant-off-time mode, the synchronous-rectifier
switch turns off just prior to the PMOS power switch
turning on. While both switches are off, inductor current
flows through the internal body diode of the NMOS
switch. The internal body diode’s forward voltage is rel-
atively high.
Thermal Resistance
Junction-to-ambient thermal resistance, θJA, is highly
dependent on the amount of copper area immediately
surrounding the IC leads. The MAX1742 evaluation kit
has 0.5in2 of copper area and a thermal resistance of
80°C/W with no forced airflow. Airflow over the board
significantly reduces the junction-to-ambient thermal
resistance. For heatsinking purposes, evenly distribute
the copper area connected at the IC among the high-
current pins.
Power Dissipation
Power dissipation in the MAX1742/MAX1842 is domi-
nated by conduction losses in the two internal power
switches. Power dissipation due to supply current in the
control section and average current used to charge
and discharge the gate capacitance of the internal
switches (i.e., switching losses) is approximately:
PDS = C x VIN2 x fPWM
where C = 2.5nF and fPWM is the switching frequen-
cy in PWM mode.
This number is reduced when the switching frequency
decreases as the part enters Idle Mode. Combined con-
duction losses in the two power switches are approxi-
mated by:
PD = IOUT2 x RPMOS
where RPMOS is the on-resistance of the PMOS switch.
The junction-to-ambient thermal resistance required to
dissipate this amount of power is calculated by:
θJA = (TJ,MAX - TA,MAX) / PD(TOT)
where: θJA = junction-to-ambient thermal resistance
TJ,MAX = maximum junction temperature
TA,MAX = maximum ambient temperature
PD(TOT) = total losses
__________________Design Procedure
For typical applications, use the recommended compo-
nent values in Tables 1 or 2. For other applications,
take the following steps:
1) Select the desired PWM-mode switching frequency;
1MHz is a good starting point. See Figure 3 for maxi-
mum operating frequency.
Table 1. MAX1742 Recommended
Component Values (IOUT = 1A)
VIN VOUT fPWM
(V) (V) (kHz)
L
(μH)
RTOFF
(kΩ)
5 3.3 850
5.6
39
5 2.5 1070
5 1.8 910
5.6
5.6
47
75
5 1.5 770
5.6
100
3.3 2.5 610
3.9
39
3.3 1.8 1050
3.3 1.5 1000
3.9
3.9
43
56
Table 2. MAX1842 Recommended
Component Values (Continuous Output
Current = 1A, Burst Output Current = 2.7A)
VIN VOUT fPWM
(V) (V) (kHz)
5 3.3 800
5 2.5 1180
5 1.8 850
5 1.5 715
3.3 2.5 570
3.3 1.8 985
3.3 1.5 940
L
(μH)
2.2
2.2
2.2
2.2
1.5
1.5
1.5
RTOFF
(kΩ)
39
47
75
100
39
43
56
MAXIMUM RECOMMENDED
OPERATING FREQUENCY vs. INPUT VOLTAGE
1400
VOUT = 1.5V
1200
1000
800 VOUT = 1.8V
600 VOUT = 2.5V
400 VOUT = 3.3V
200
0
2.6 3.1 3.6 4.1 4.6 5.1 5.6
VIN (V)
Figure 3. Maximum Recommended Operating Frequency vs.
Input Voltage
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet MAX1842.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| MAX184 | High-Speed 12-Bit A/D Converters With External Refernce input | Maxim Integrated |
| MAX1840 | Low-Voltage SIM/Smart Card Level Translators | Maxim Integrated |
| MAX1841 | Low-Voltage SIM/Smart Card Level Translators | Maxim Integrated |
| MAX1842 | Step-Down Regulators | Maxim Integrated |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |