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PDF MAX5025 Data sheet ( Hoja de datos )
| Número de pieza | MAX5025 | |
| Descripción | PWM Step-Up DC-DC Converters | |
| Fabricantes | Maxim Integrated | |
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19-2239; Rev 2; 3/09
EVAALVUAAILTAIOBNLEKIT
500kHz, 36V Output, SOT23,
PWM Step-Up DC-DC Converters
General Description
The MAX5025–MAX5028 constant-frequency, pulse-
width modulating (PWM), low-noise boost converters
are intended for low-voltage systems that often need a
locally generated high voltage. These devices are
capable of generating low-noise, high output voltages
required for varactor diode biasing in TV tuners, set-top
boxes, and PCI cable modems. The MAX5025–
MAX5028 operate from as low as 3V and switch at
500kHz.
The constant-frequency, current-mode PWM architec-
ture provides for low output noise that is easy to filter. A
40V lateral DMOS device is used as the internal power
switch, making the devices ideal for boost converters
up to 36V. The MAX5025/MAX5026 adjustable versions
require the use of external feedback resistors to set the
output voltage. The MAX5027/MAX5028 offer a fixed
30V output. These devices are available in a small, 6-
pin SOT23 package.
Applications
TV Tuner Power Supply
Low-Noise Varactor Diode Biasing
Set-Top Box Tuner Power Supply
PCI Cable Modem
Voice-Over-Cable
LCD Power Supply
Avalanche Photodiode Biasing
Features
♦ Input Voltage Range:
3V to 11V (MAX5026/MAX5028)
4.5V to 11V (MAX5025/MAX5027)
♦ Wide Output Voltage Range: VCC to 36V
♦ Output Power: 120mW (max)
♦ User-Adjustable Output Voltage with
MAX5025/MAX5026 Using External Feedback
Resistors
♦ Fixed 30V Output Voltage: MAX5027/MAX5028
♦ Internal 1.3Ω (typ), 40V Switch
♦ Constant PWM Frequency Provides Easy Filtering
in Low-Noise Applications
♦ 500kHz (typ) Switching Frequency
♦ 1μA (max) Shutdown Current
♦ Small, 6-Pin SOT23 Package
PART
MAX5025EUT-T
MAX5026EUT-T
MAX5027EUT-T
MAX5028EUT-T
Ordering Information
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
6 SOT23-6
6 SOT23-6
6 SOT23-6
6 SOT23-6
Typical Operating Circuit
VCC = 4.5V TO 11V
(MAX5027)
VCC = 3V TO 11V
(MAX5028)
L1
VCC LX
MAX5027
MAX5028
SHDN
C1
FB
PGND
GND
D1
VOUT
30V
C2
Selector Guide appears at end of data sheet.
Pin Configuration
TOP VIEW
PGND 1
6 LX
MAX5025–
GND 2 MAX5028 5 VCC
FB 3
4 SHDN
SOT23-6
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
1 page  
500kHz, 36V Output, SOT23,
Step-Up DC-DC Converters
Typical Operating Characteristics (continued)
(VCC = 5V, VOUT = 30V, TA = +25°C, unless otherwise noted.)
OUTPUT
VOLTAGE
20V/div
5V
EXITING SHUTDOWN
MAX5025-28 toc10
30V
INDUCTOR
CURRENT
50mA/div
SHUTDOWN
VOLTAGE
5V/div
2ms/div
MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 1mA.
CIRCUIT OF FIGURE 3
5V
ENTERING SHUTDOWN
MAX5025-28 toc11
30V
OUTPUT
VOLTAGE
20V/div
SHUTDOWN
VOLTAGE
5V/div
5V
5V
0V
100ms/div
MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 1mA.
CIRCUIT OF FIGURE 3
LIGHT-LOAD SWITCHING WAVEFORM
WITHOUT RC FILTER
MAX5025-28 toc12
LIGHT-LOAD SWITCHING WAVEFORM
WITH RC FILTER
MAX5025-28 toc13
VOUT
2mV/div
AC-COUPLED
VOUT
1mV/div
AC-COUPLED
LX PIN
20V/div
LX PIN
20V/div
0V
0V
IL
100mA/div
0mA
1μs/div
MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 0.1mA.
CIRCUIT OF FIGURE 2
MEDIUM-LOAD SWITCHING WAVEFORM
WITHOUT RC FILTER
MAX5025-28 toc14
VOUT
5mV/div
AC-COUPLED
IL
100mA/div
0mA
1μs/div
MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 0.1mA.
CIRCUIT OF FIGURE 3
MEDIUM-LOAD SWITCHING WAVEFORM
WITH RC FILTER
MAX5025-28 toc15
VOUT
1mV/div
AC-COUPLED
LX PIN
20V/div
LX PIN
20V/div
0V
0V
IL
200mA/div
0mA
1μs/div
MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 2mA.
CIRCUIT OF FIGURE 2
IL
200mA/div
1μs/div
MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 2mA.
CIRCUIT OF FIGURE 3
0mA
_______________________________________________________________________________________ 5
5 Page 
500kHz, 36V Output, SOT23,
Step-Up DC-DC Converters
trace lengths to reduce stray capacitance, trace resis-
tance, and radiated noise. The trace between the out-
put voltage-divider (MAX5025/MAX5026) and the FB
pin must be kept short, as well as the trace between
GND and PGND.
Inductor Layout
The shielded drum type inductors have a small air gap
around the top and bottom periphery. The incident fring-
ing magnetic field from this air gap to the copper plane
on the PC board tends to reduce efficiency. This is a
result of the induced eddy currents on the copper plane.
To minimize this effect, avoid laying out any copper
planes under the mounting area of these inductors.
30V Boost Application Circuit
Figures 2 and 3 show the MAX5025/MAX5026 operat-
ing in a 30V boost application. Figure 3 has an RC filter
to reduce noise at the output. These circuits provide
output currents greater than 4mA with an input voltage
of 5V or greater. They are designed by following the
Design Procedure section. Operating characteristics of
these circuits are shown in the Typical Operating
Characteristics section.
VCC = 4.5V TO 11V
(MAX5025)
VCC = 3V TO 11V
(MAX5026)
C1
4.7μF
L1 TOKO 47μH INDUCTOR
47μH A915BY-470M ZETEX SCHOTTKY DIODE
D1 ZHCS500
VCC LX
VOUT
+30V
MAX5025
MAX5026
SHDN
FB
R1
147kΩ
C2
1μF
PGND GND
R2
6.34kΩ
Figure 2. Adjustable 30V Output Circuit
VCC = 4.5V TO 11V
(MAX5025)
VCC = 3V TO 11V
(MAX5026)
C1
4.7μF
L1 TOKO 47μH INDUCTOR
47μH A915BY-470M ZETEX SCHOTTKY DIODE R3
D1 ZHCS500
100Ω
VCC LX
MAX5025
MAX5026
SHDN
FB
PGND GND
R1
147kΩ
R2
6.34kΩ
C2
1μF
VOUT
+30V
C3
1μF
Figure 3. Adjustable 30V Output Circuit with RC Filter
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet MAX5025.PDF ] | |
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