参数资料
型号: MAX1649ESA
厂商: Maxim Integrated Products
文件页数: 10/12页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM 8-SOIC
产品培训模块: Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program
标准包装: 100
PWM 型: 控制器
输出数: 1
频率 - 最大: 300kHz
占空比: 96.5%
电源电压: 3 V ~ 16 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 85°C
封装/外壳: 8-SOIC(0.154",3.90mm 宽)
包装: 管件
5V/3.3V or Adjustable, High-Efficiency,
Low-Dropout, Step-Down DC-DC Controllers
Table 1. Component Selection Guide
PRODUCTION
METHOD
Surface Mount
INDUCTORS
Sumida
CDRH125-470 (1.8A)
CDRH125-220 (2.2A)
Coilcraft
DO3316-473 (1.6A)
DO3340-473 (3.8A)
CAPACITORS
AVX
TPS series
Sprague
595D series
DIODES
Motorola
MBRS340T3
Nihon
NSQ series
CURRENT-SENSE
RESISTORS
Dale
WSL Series
IRC
LRC series
MOSFETS
Siliconix
Little Foot series
Motorola
medium-power
surface-mount products
Sanyo
Miniature
Through-Hole
Sumida
RCH875-470M (1.3A)
OS-CON series
low-ESR organic
IRC
OAR series
Motorola
semiconductor
Nichicon
Motorola
United Chemi-Con
Low-Cost
Through-Hole
Coilcraft
PCH-45-473 (3.4A)
PL series
low-ESR electrolytics 1N5817 to
1N5823
Motorola
TMOS power MOSFETs
LXF series
The peak current of Figure 1 is 2.35A for a 1.5A output.
The inductor used in this circuit is specified to drop by
10% at 2.2A (worst case); a curve provided by the
manufacturer shows that the inductance typically drops
by 20% at 2.7A. Using a slightly underrated inductor
can sometimes reduce size and cost, with only a minor
impact on efficiency.
Table 1 lists inductor types and suppliers for various
applications. The efficiencies of the listed surface-
mount inductors are nearly equivalent to those of the
larger size through-hole versions.
Diode Selection
The MAX1649/MAX1651 ’s high switching frequency
demands a high-speed rectifier. Schottky diodes, such
as the 1N5817 through 1N5823 (and their surface-
mount equivalents), are recommended. Choose a
diode with an average current rating equal to or greater
than I LIM (max) and a voltage rating higher than
V+(max).
External Switching Transistor
The MAX1649/MAX1651 drive P-channel enhancement-
mode MOSFET transistors only. The choice of power
transistor is primarily dictated by the input voltage and
the peak current. The transistor’s on-resistance, gate-
source threshold, and gate charge must also be appro-
priately chosen. The drain-to-source and gate-to-
source breakdown voltage ratings must be greater than
V+. The total gate-charge specification is normally not
critical, but values should be less than 100nC for best
efficiency. The MOSFET should be capable of handling
the peak current and, for maximum efficiency, have a
very low on-resistance at that current. Also, the on-
resistance must be low for the minimum available V GS ,
which equals V+(min). Select a transistor with an on-
resistance between 50% and 100% of the current-
sense resistor. The Si9430 transistor chosen for the
Typical Operating Circuit has a drain-to-source rating
of -20V and a typical on-resistance of 0.070 Ω at 2A with
V GS = -4.5V. Tables 1 and 2 list suppliers of switching
transistors suitable for use with these devices.
Capacitor Selection
Output Filter Capacitor
The primary criterion for selecting the output filter
capacitor is low equivalent series resistance (ESR),
rather than high capacitance. An electrolytic capacitor
with low enough ESR will automatically have high
enough capacitance. The product of the inductor-cur-
rent variation and the output filter capacitor ’s ESR
determines the amplitude of the high-frequency ripple
seen on the output voltage. When a 330μF, 10V
Sprague surface-mount capacitor (595D series) with
ESR = 0.15 Ω is used, 40mV of output ripple is typically
observed when stepping down from 10V to 5V at 1A.
The output filter capacitor's ESR also affects efficiency.
Again, low-ESR capacitors perform best. Table 1 lists
some suppliers of low-ESR capacitors.
10
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