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參數(shù)資料
| 型號： | MAX1927 |
| 廠商： | Maxim Integrated Products, Inc. |
| 元件分類： | 數(shù)字信號處理 |
| 英文描述： | Fixed-Point Digital Signal Processor 288-FCBGA |
| 中文描述： | 低輸出電壓、800mA、PWM降壓型DC-DC轉換器 |
| 文件頁數(shù)： | 9/12頁 |
| 文件大小： | 303K |
| 代理商： | MAX1927 |
Applications Information
Output Voltage Selection
The MAX1927/MAX1928 have preset output voltages.
In addition, the MAX1927R has an adjustable output.
To set the output voltage at the preset voltage, connect
FB to the output. See Table 1 for a list of the preset volt-
ages and their corresponding part numbers.
The output voltage for the MAX1927R is adjustable
from 0.75V to the input voltage by connecting FB to a
resistor-divider between the output and GND (Figure
2). To determine the values of the resistor-divider, first
select a value for feedback resistor R2 between 5k
to
50k
. R1 is then given by:
where V
FB
is 0.75V.
Input Capacitor Selection
Capacitor equivalent series resistance (ESR) is a major
contributor to input ripple in high-frequency DC-DC
converters. Ordinary aluminum-electrolytic capacitors
have high ESR and should be avoided. Low-ESR alu-
minum electrolytic capacitors are acceptable and rela-
tively inexpensive. Low-ESR tantalum capacitors or
polymer capacitors are better and provide a compact
solution for space-constrained surface-mount designs.
Ceramic capacitors have the lowest ESR overall.
The input filter capacitor reduces peak currents and
noise at the input voltage source. Connect a low-ESR
bulk capacitor (
≥
10μF typ) to the input. Select this bulk
capacitor to meet the input ripple requirements and
voltage rating rather than capacitance value. Use the
following equation to calculate the maximum RMS input
current:
Compensation, Stability, and
Output Capacitor
The MAX1927/MAX1928 are externally compensated
with a resistor and a capacitor (see Figure 3, R
C
and
C
C
) in series from COMP to GND. An additional capaci-
tor (C
f
) may be required from COMP to GND if high-
ESR output capacitors are used. The capacitor inte-
grates the current from the transimpedance amplifier,
averaging output capacitor ripple. This sets the device
speed for transient response and allows the use of
small ceramic output capacitors because the phase-
shifted capacitor ripple does not disturb the current
regulation loop. The resistor sets the proportional gain
of the output error voltage by a factor g
m
R
C
.
Increasing this resistor also increases the sensitivity of
the control loop to output ripple.
The resistor and capacitor set a compensation zero
that defines the system
’
s transient response. The load
creates a dynamic pole, shifting in frequency with
changes in load. As the load decreases, the pole fre-
quency decreases. System stability requires that the
compensation zero must be placed to ensure adequate
phase margin (at least 30
°
at unity gain). The following
is a design procedure for the compensation network:
1) Select an appropriate converter bandwidth (f
C
) to
stabilize the system while maximizing transient
response. This bandwidth should not exceed 1/10
of the switching frequency.
2) Calculate the compensation capacitor, C
C
, based
on this bandwidth:
For the MAX1927:
C
V
I
R
g
R
+
1
R
R
f
C
OUT
(
OUT MAX
CS
m
C
=
×
×
×
)
1
2
2
1
2
π
I
I
V
V
V
V
RMS
OUT
IN
OUT
IN
OUT
=
×
×
(
)
R
R
V
V
OUT
FB
1
2
1
=
×
M
Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
_______________________________________________________________________________________
9
LX
FB
R1
R2
50k
MAX1927R
Figure 2. Setting the Adjustable Output Voltage
PART
PRESET OUTPUT VOLTAGE
0.75V, Adjustable
1.5 V
1.8 V
2.5 V
MAX1927R
MAX1928-15
MAX1928-18
MAX1928-25
Table 1. FB Regulation Voltages
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1927REUB | 功能描述:直流/直流開關轉換器 800mA PWM Step-Down DC/DC Converter 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 |
| MAX1927REUB+ | 功能描述:直流/直流開關轉換器 800mA PWM Step-Down DC/DC Converter 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 |
| MAX1927REUB+T | 功能描述:直流/直流開關轉換器 800mA PWM Step-Down DC/DC Converter 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 |
| MAX1927REUB-G05 | 功能描述:直流/直流開關轉換器 800mA PWM Step-Down DC/DC Converter 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 |
| MAX1927REUB-T | 功能描述:直流/直流開關轉換器 800mA PWM Step-Down DC/DC Converter 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 |
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