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參數(shù)資料
| 型號： | MAX1790 |
| 廠商： | Maxim Integrated Products, Inc. |
| 元件分類： | DC/DC變換器 |
| 英文描述： | Low-Noise Step-Up DC-DC Converter(低噪聲步升DC-DC轉換器) |
| 中文描述： | 低噪聲、升壓型DC-DC轉換器 |
| 文件頁數(shù)： | 9/12頁 |
| 文件大小： | 405K |
| 代理商： | MAX1790 |
M
Low-Noise Step-Up DC-DC Converter
_______________________________________________________________________________________
9
breakdown voltage exceeds V
OUT
. Schottky diodes are
recommended.
Input and Output Capacitor Selection
Low-ESR capacitors are recommended for input
bypassing and output filtering. Low-ESR tantalum
capacitors are a good compromise between cost and
performance. Ceramic capacitors are also a good
choice. Sanyo OS-CON types are also recommended
for their low ESR. Avoid standard aluminum electrolytic
capacitors. A simple equation to estimate input and
output capacitor values for a given voltage ripple is as
follows:
where V
RIPPLE
is the peak-to-peak ripple voltage on the
capacitor.
Output Voltage
The MAX1790 operates with an adjustable output from
V
IN
to 12V. Connect a resistor voltage divider to FB
(Typical Operating Circuit)
from the output to GND.
Select the resistor values as follows:
where V
FB
, the boost-regulator feedback set point, is
1.24V. Since the input bias current into FB is typically 0,
R2 can have a value up to 100k
without sacrificing
accuracy. Connect the resistor-divider as close to the IC
as possible.
Loop Compensation
The voltage feedback loop needs proper compensation
to prevent excessive output ripple and poor efficiency
caused by instability. This is done by connecting a
resistor (R
COMP
) and capacitor (C
COMP
) in series from
COMP to GND, and another capacitor (C
COMP2
) from
COMP to GND. R
COMP
is chosen to set the high-fre-
quency integrator gain for fast transient response, while
C
COMP
is chosen to set the integrator zero to maintain
loop stability. The second capacitor, C
COMP2
, is cho-
sen to cancel the zero introduced by output capaci-
tance ESR. For optimal performance, choose the
components using the following equations:
R
COMP
(200
/ A
2
)
·
V
OUT2
·
C
OUT
/ L
C
COMP
(0.4
·
10
-3
A /
) L / V
IN
C
COMP2
(0.005 A
2
/
) R
ESR
·
L / V
OUT2
For the ceramic output capacitor, where ESR is small,
C
COMP2
is optional. Table 1 shows experimentally verified
external component values for several applications.
The best gauge of correct loop compensation is by
inspecting the transient response of the MAX1790.
Adjust R
COMP
and C
COMP
as necessary to obtain opti-
mal transient performance.
Soft-Start Capacitor
The soft-start capacitor should be large enough that it
does not reach final value before the output has
reached regulation. Calculate C
SS
to be:
where:
C
OUT
= total output capacitance including any bypass
capacitor on the output bus
V
OUT
= maximum output voltage
I
INRUSH
= peak inrush current allowed
I
OUT
= maximum output current during power-up stage
V
IN
= minimum input voltage
The load must wait for the soft-start cycle to finish
before drawing a significant amount of load current.
The duration after which the load can begin to draw
maximum load current is:
t
MAX
= 6.77
·
10
5
C
SS
Application Circuits
1-Cell to 3.3V SEPIC Power Supply
Figure 3 shows the MAX1790 in a single-ended primary
inductance converter (SEPIC) topology. This topology is
useful when the input voltage can be either higher or
lower than the output voltage, such as when converting
a single lithium-ion (Li+) cell to a 3.3V output. L1A and
L1B are two windings on a single inductor. The coupling
capacitor between these two windings must be a low-
ESR type to achieve maximum efficiency, and must also
be able to handle high ripple currents. Ceramic capaci-
tors are best for this application. The circuit in Figure 3
provides 400mA output current at 3.3V output when
operating with an input voltage from +2.6V to +5.5V.
AMLCD Application
Figure 4 shows a power supply for active matrix (TFT-
LCD) flat-panel displays. Output voltage transient per-
formance is a function of the load characteristic. Add or
remove output capacitance (and recalculate compen-
sation network component values) as necessary to
meet transient performance. Regulation performance
C
21 10
C
V
V V
I
OUT
V I
V
SS
6
OUT
OUT2
INRUSH
OUT
OUT
>
R
R
V
V
OUT
FB
1
2
1
=
C
0.5
L I
V
V
PK
2
RIPPLE
OUT
≥
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1790ESA+ | 制造商:Maxim Integrated Products 功能描述:- Rail/Tube |
| MAX1790EUA | 功能描述:直流/直流開關轉換器 Integrated Circuits (ICs) RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| MAX1790EUA+ | 功能描述:直流/直流開關轉換器 Low-Noise Step-Up RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| MAX1790EUA+T | 功能描述:直流/直流開關轉換器 Low-Noise Step-Up RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| MAX1790EUA+-T | 制造商:Maxim Integrated Products 功能描述:CONV DC-DC SGL-OUT STEP UP 8PIN UMAX - Tape and Reel |
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