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參數(shù)資料
| 型號： | MAX1651 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | 5V/3.3V or Adjustable, High-Efficiency, Low-Dropout, Step-Down DC-DC Controllers |
| 中文描述： | 5V/3.3V或可調(diào)、高效率、低壓差、降壓型DC-DC控制器 |
| 文件頁數(shù)： | 9/12頁 |
| 文件大小： | 167K |
| 代理商： | MAX1651 |
M
5V /3.3V or Adjustable, High-Effic ienc y,
Low-Dropout, S tep-Down DC-DC Controllers
_______________________________________________________________________________________
9
To maximize efficiency and reduce the size and cost
of external components, minimize the peak current.
However, since the available output current is a func-
tion of the peak current, the peak current must not be
too low.
To choose the proper current-sense resistor for a par-
ticular output voltage, determine the minimum input
voltage and the maximum load current. Next, refer-
ring to Figures 5a or 5b, using the minimum input volt-
age, find the curve with the largest sense resistor that
provides sufficient output current. It is not necessary
to perform worst-case calculations. These curves take
into account the sense-resistor (±5%) and inductor
(47μH ±10%) values, the diode drop (0.4), and the
IC’s current-sense trip level (85mV); an external MOS-
FET on-resistance of 0.07
is assumed for V
GS
= -5V.
Standard wire-wound and metal-film resistors have an
inductance high enough to degrade performance.
Surface-mount (chip) resistors have very little inductance
and are well suited for use as current-sense resistors.
A U-shaped wire resistor made by IRC works well in
through-hole applications. Because this resistor is a
band of metal shaped as a “U”, its inductance is less
than 10nH (an order of magnitude less than metal film
resistors). Resistance values between 5m
and 0.1
are available (see Table 1).
Induc tor S elec tion
The MAX1649/MAX1651 operate with a wide range of
inductor values, although for most applications coils
between 10μH and 68μH take best advantage of the con-
trollers’ high switching frequency. With a high inductor
value, the MAX1649/MAX1651 will begin continuous-cur-
rent operation (see Detailed Description at a lower frac-
tion of full-load current. In general, smaller values pro-
duce higher ripple (see below) while larger values require
larger size for a given current rating.
In both the continuous and discontinuous modes, the
lower limit of the inductor is important. With a too-small
inductor value, the current rises faster and overshoots the
desired peak current limit because the current-limit com-
parator has a finite response time (300ns). This reduces
efficiency and, more importantly, could cause the current
rating of the external components to be exceeded.
Calculate the minimum inductor value as follows:
(V+(max) - V
OUT
) x 0.3μs
L(min) = ——————————––——
I x I
LIM
where
I is the inductor-current overshoot factor,
I
LIM
= V
CS
/R
SENSE
, and 0.3μs is the time it takes the com-
parator to switch. Set
I
=
0.1 for an overshoot of 10%.
For highest efficiency, use a coil with low DC resis-
tance; a value smaller than 0.1V/I
LIM
works best. To
minimize radiated noise, use a toroid, pot core, or
shielded-bobbin inductor. Inductors with a ferrite core
or equivalent are recommended. Make sure the induc-
tor’s saturation-current rating is greater than I
LIM
(max).
However, it is generally acceptable to bias the inductor
into saturation by about 20% (the point where the
inductance is 20% below its nominal value).
5.0
5.4
5.8
6.2
6.6
16.0
1
INPUT VOLTAGE (V)
M
3.0
2.5
2.0
1.5
1.0
0
0.5
r
s
= 0.030
V
OUT
= 5V
r
s
= 0.040
r
s
= 0.050
r
s
= 0.060
r
s
= 0.080
r
s
= 0.100
Figure 5a. MAX1649 Current-Sense Resistor Graph
3.0
3.4
3.8
4.2
4.6
16.0
1
INPUT VOLTAGE (V)
M
3.0
2.5
2.0
1.5
1.0
0
0.5
r
s
= 0.030
r
s
= 0.040
r
s
= 0.050
r
s
= 0.060
r
s
= 0.080
r
s
= 0.100
V
OUT
= 3.3V
Figure 5b. MAX1651 Current-Sense Resistor Graph
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| MAX1649EPA | 5V/3.3V or Adjustable, High-Efficiency, Low-Dropout, Step-Down DC-DC Controllers |
| MAX1649ESA | Circular Connector; Body Material:Aluminum Alloy; Series:D38999; No. of Contacts:100; Connector Shell Size:23; Connecting Termination:Grounded; Gender:Male |
| MAX1649 | 5V/3.3V or Adjustable, High-Efficiency,Low-Dropout, Step-Down DC-DC Controllers(5V或可調(diào),降壓型，輸出電流2A,DC-DC變換器,MAX649的改進(jìn)型) |
| MAX1651CPA | 5V/3.3V or Adjustable, High-Efficiency, Low-Dropout, Step-Down DC-DC Controllers |
| MAX1651CSA | 5V/3.3V or Adjustable, High-Efficiency, Low-Dropout, Step-Down DC-DC Controllers |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1651CPA | 功能描述:DC/DC 開關(guān)控制器 5/3.3/Adj Low-Drop Step-Down RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| MAX1651CSA | 功能描述:DC/DC 開關(guān)控制器 5/3.3/Adj Low-Drop Step-Down RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| MAX1651CSA+ | 功能描述:DC/DC 開關(guān)控制器 5/3.3/Adj Low-Drop Step-Down RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| MAX1651CSA+T | 功能描述:DC/DC 開關(guān)控制器 5/3.3/Adj Low-Drop Step-Down RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| MAX1651CSA-T | 功能描述:DC/DC 開關(guān)控制器 5/3.3/Adj Low-Drop Step-Down RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
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