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参数资料
| 型号： | LM5009SD |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 150 mA, 100V Step-Down Switching Regulator |
| 中文描述： | 0.37 A SWITCHING REGULATOR, DSO8 |
| 封装： | 4 X 4 MM, EXPOSED PAD, LLP-8 |
| 文件页数： | 13/14页 |
| 文件大小： | 647K |
| 代理商： | LM5009SD |
Hysteretic Control Circuit
Overview (Continued)
(1)
The output voltage (V
OUT) is programmed by two external
resistors as shown in Figure 1. The regulation point is cal-
culated as follows:
V
OUT =2.5x(R1+R2)/R2
All hysteretic regulators regulate the output voltage based on
ripple voltage at the feedback input, requiring a minimum
amount of ESR for the output capacitor C2. A minimum of
25mV of ripple voltage at the feedback pin (FB) is required
for the LM5009. In cases where the capacitor ESR is too
small, additional series resistance may be required (R3 in
For applications where lower output voltage ripple is re-
quired the output can be taken directly from a low ESR
output capacitor, as shown in Figure 2. However, R3 slightly
degrades the load regulation.
High Voltage Start-Up Regulator
The LM5009 contains an internal high voltage startup regu-
lator. The input pin (VIN) can be connected directly to line
voltages up to 95 Volts, with transient capability to 100 volts.
The regulator is internally current limited at 9.5mA. Upon
power up, the regulator sources current into the external
capacitor at VCC (C3). When the voltage on the VCC pin
reaches the under-voltage lockout threshold of 6.3V, the
buck switch is enabled.
In applications involving a high value for V
IN, where power
dissipation in the V
CC regulator is a concern, an auxiliary
voltage can be diode connected to the VCC pin. Setting the
voltage between 8V and 14V shuts off the internal regulator,
reducing internal power dissipation. See Figure 3. The cur-
rent required into the VCC pin is shown in the Typical Per-
formance Characteristics.
Regulation Comparator
The feedback voltage at FB is compared to an internal 2.5V
reference. In normal operation (the output voltage is regu-
lated), an on-time period is initiated when the voltage at FB
falls below 2.5V. The buck switch will stay on for the pro-
grammed on-time, causing the FB voltage to rise above
2.5V. After the on-time period, the buck switch will stay off
until the FB voltage again falls below 2.5V. During start-up,
the FB voltage will be below 2.5V at the end of each on-time,
resulting in the minimum off-time. Bias current at the FB pin
is less than 5 nA over temperature.
Over-Voltage Comparator
The feedback voltage at FB is compared to an internal
2.875V reference. If the voltage at FB rises above 2.875V
the on-time pulse is immediately terminated. This condition
can occur if the input voltage, or the output load, change
suddenly. The buck switch will not turn on again until the
voltage at FB falls below 2.5V.
ON-Time Generator and Shutdown
The on-time for the LM5009 is determined by the R
ON resis-
tor, and is inversely proportional to the input voltage (Vin),
resulting in a nearly constant frequency as Vin is varied over
its range. The on-time equation is:
T
ON =1.25x10
-10 xR
ON /VIN
(2)
R
ON should be selected for a minimum on-time (at maximum
V
IN) greater than 250 ns, for proper current limit operation.
This requirement limits the maximum frequency for each
application, depending on V
IN and VOUT.
The LM5009 can be remotely disabled by taking the
RON/SD pin to ground. See Figure 4. The voltage at the
RON/SD pin is between 1.7V and 5V, depending on Vin and
the value of the R
ON resistor.
20165805
FIGURE 2. Low Ripple Output Configuration
20165806
FIGURE 3. Self Biased Configuration
LM5009
www.national.com
8
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM5009SDC | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| LM5009SDC/NOPB | 功能描述:直流/直流开关转换器 150 MA 100V STEP-DWN SWITCHING REG RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| LM5009SDC/NOPB | 制造商:Texas Instruments 功能描述:DC/DC Converter IC |
| LM5009SDCNOPB | 制造商:NATIONAL 功能描述:Pb Free |
| LM5009SDCX | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
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