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参数资料
| 型号： | MAX1744EUB+T |
| 厂商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分类： | 稳压器 |
| 英文描述： | High-Voltage, Step-Down DC-DC Controller in µMAX |
| 中文描述： | SWITCHING CONTROLLER, 330 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封装： | MICRO MAX PACKAGE-10 |
| 文件页数： | 3/14页 |
| 文件大小： | 256K |
| 代理商： | MAX1744EUB+T |
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controller in MAX
______________________________________________________________________________________
11
where VREF = 1.25V. Since the input bias current at FB
has a maximum value of 50nA, large values (10k
to
200k
) can be used for R3 with no significant accuracy
loss. For 1% error, the current through R2 should be at
least 100 times FB’s input bias current.
Current-Sense-Resistor Selection
The current-sense comparator limits the peak switching
current to VCS/RSENSE, where RSENSE is the value of
the current-sense resistor and VCS is the current-sense
threshold. VCS is typically 100mV. Minimizing the peak
switching current will increase efficiency and reduce
the size and cost of external components. However,
since available output current is a function of the peak
switching current, the peak current limit must not be set
too low.
Set the peak current limit to 1.3 times the maximum
load current by setting the current-sense resistor to:
Inductor Selection
The essential parameters for inductor selection are
inductance and current rating. The MAX1744/MAX1745
operate with a wide range of inductance values. In many
applications, values between 4.7H and 100H take
best advantage of the controller’s high switching fre-
quency.
Calculate the minimum inductance value as follows:
where 1s is the minimum on-time. Inductor values
between 2 and 10 times L(MIN) are recommended. With
high inductor values, the MAX1744/MAX1745 begin
continuous-conduction operation at a lower fraction of
the full load (see the Detailed Description section).
The inductor’s saturation and heating current ratings
must be greater than the peak switching current to pre-
vent overheating and core saturation. Saturation occurs
when the inductor’s magnetic flux density reaches the
maximum level the core can support, and inductance
starts to fall. The heating current rating is the maximum
DC current the inductor can sustain without overheating.
For optimum efficiency, the inductor windings’ resis-
tance should be less than the current-sense resistance.
If necessary, use a toroid, pot-core, or shielded-core
inductor to minimize radiated noise. Table 1 lists induc-
tor types and suppliers for various applications.
External Switching Transistor
The MAX1744/MAX1745 drive a P-channel enhance-
ment-mode MOSFET. The EXT output swings from VH
to IN. Be sure that the MOSFET’s on-resistance is spec-
ified for 5V gate drive or less. Table 1 recommends
MOSFET suppliers.
Four important parameters for selecting a P-channel
MOSFET are drain-to-source breakdown voltage, cur-
rent rating, total gate charge (Qg), and RDS(ON). The
drain-to-source breakdown voltage rating should be at
least a few volts higher than VIN. Choose a MOSFET
with a maximum continuous drain-current rating higher
than the peak current limit:
The Qg specification should be 80nC or less to ensure
fast drain voltage rise and fall times, and reduce power
losses during transition through the linear region. Qg
specifies all of the capacitances associated with charg-
ing the MOSFET gate. EXT pin rise and fall times vary
with different capacitive loads, as shown in the Typical
Operating Characteristics. RDS(ON) should be as low as
practical to reduce power losses while the MOSFET is
on. It should be equal to or less than the current-sense
resistor.
ID(MAX
LIM MAX
CS MAX
SENSE
I
V
R
)(
)
()
≥=
L
=
V
- V
(MIN)
IN
OUT
()
xs
V
R
CS MIN
CS
1
R
=
V
1.3 x I
CS
CS(MIN)
OUT(MAX)
R3
R2
FROM
OUTPUT
TO FB
Figure 5. Adjustable-Output Operation Using the MAX1745
相关PDF资料 |
PDF描述 |
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| MAX1745AUB+T | High-Voltage, Step-Down DC-DC Controller in µMAX |
| MAX1745EUB+T | High-Voltage, Step-Down DC-DC Controller in µMAX |
| MAX1744AUB+ | High-Voltage, Step-Down DC-DC Controller in µMAX |
| MAX1744EUB+ | High-Voltage, Step-Down DC-DC Controller in µMAX |
| MAX1745AUB+ | High-Voltage, Step-Down DC-DC Controller in µMAX |
相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1744EVKIT | 功能描述:DC/DC 开关控制器 Evaluation Kit for the MAX1744 MAX1745 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1745AUB | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1745AUB+ | 功能描述:DC/DC 开关控制器 Step-Down DC/DC Controller RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1745AUB+T | 功能描述:DC/DC 开关控制器 Step-Down DC/DC Controller RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1745AUB-T | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
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