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| 型号： | LM22673EVAL/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 10/27页 |
| 文件大小： | 0K |
| 描述： | BOARD EVALUATION FOR LM22673 |
| 产品培训模块： | LM315x & LM2267x SIMPLE SWITCHER® and WEBENCH |
| 标准包装： | 1 |
| 系列： | SIMPLE SWITCHER® |
| 主要目的： | DC/DC，步降 |
| 输出及类型： | 1，非隔离 |
| 输出电压： | 3.3V |
| 电流 - 输出： | 3A |
| 输入电压： | 4.5 ~ 42 V |
| 稳压器拓扑结构： | 降压 |
| 频率 - 开关： | 500kHz |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | LM22673 |
| 相关产品： | LM22673TJ-ADJ/NOPBTR-ND - IC REG BUCK ADJ 3A TO263-7 LM22673TJ-5.0-ND - IC REG BUCK 5V 3A TO263-7 LM22673MRX-ADJ-ND - IC REG BUCK ADJ 3A 8PSOP LM22673MR-ADJ/NOPB-ND - IC REG BUCK ADJ 3A 8PSOP LM22673MRX-5.0-ND - IC REG BUCK 5V 3A 8PSOP LM22673MR-5.0/NOPB-ND - IC REG BUCK 5V 3A 8PSOP LM22673TJE-ADJDKR-ND - IC REG BUCK ADJ 3A TO263-7 LM22673TJE-5.0DKR-ND - IC REG BUCK 5V 3A TO263-7 LM22673MRE-ADJDKR-ND - IC REG BUCK ADJ 3A 8PSOP LM22673MRE-5.0DKR-ND - IC REG BUCK 5V 3A 8PSOP 更多... |
| 其它名称： | *LM22673EVAL LM22673EVAL LM22673EVAL-ND |
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SNVS586N – SEPTEMBER 2008 – REVISED APRIL 2013
Soft-Start
The soft-start feature allows the regulator to gradually reach steady-state operation, thus reducing start-up
stresses. The internal soft-start feature brings the output voltage up in about 500 μs. This time can be extended
by using an external capacitor connected to the SS pin. Values in the range of 100 nF to 1 μF are recommended.
The approximate soft-start time can be estimated from the following equation:
(6)
Soft-start is reset any time the part is shut down or a thermal overload event occurs.
Boot-Strap Supply
The LM22673 incorporates a floating high-side gate driver to control the power MOSFET. The supply for this
driver is the external boot-strap capacitor connected between the BOOT pin and SW. A good quality 10 nF
ceramic capacitor must be connected to these pins with short, wide PCB traces. One reason the regulator
imposes a minimum off-time is to ensure that this capacitor recharges every switching cycle. A minimum load of
about 5 mA is required to fully recharge the boot-strap capacitor in the minimum off-time. Some of this load can
be provided by the output voltage divider, if used.
Thermal Protection
Internal thermal shutdown circuitry protects the LM22673 should the maximum junction temperature be
exceeded. This protection is activated at about 150°C, with the result that the regulator will shutdown until the
temperature drops below about 135°C.
Internal Compensation
The LM22673 has internal loop compensation designed to provide a stable regulator over a wide range of
external power stage components. The internal compensation of the -ADJ option is optimized for output voltages
below 5V. If an output voltage of 5V or greater is needed, the -5.0 option with an external resistor divider can be
used.
Ensuring stability of a design with a specific power stage (inductor and output capacitor) can be tricky. The
LM22673 stability can be verified using the WEBENCH? Designer online circuit simulation tool at www.ti.com. A
quick start spreadsheet can also be downloaded from the online product folder.
The complete transfer function for the regulator loop is found by combining the compensation and power stage
transfer functions. The LM22673 has internal type III loop compensation, as detailed in Figure 15 . This is the
approximate "straight line" function from the FB pin to the input of the PWM modulator. The power stage transfer
function consists of a D.C. gain and a second order pole created by the inductor and output capacitor(s). Due to
the input voltage feedforward employed in the LM22673, the power stage D.C. gain is fixed at 20dB. The second
order pole is characterized by its resonant frequency and its quality factor (Q). For a first pass design, the
product of inductance and output capacitance should conform to the following equation:
(7)
Alternatively, this pole should be placed between 1.5kHz and 15kHz and is given by the equation shown below:
(8)
The Q factor depends on the parasitic resistance of the power stage components and is not typically in the
control of the designer. Of course, loop compensation is only one consideration when selecting power stage
components; see the Application Information section for more details.
10
Product Folder Links: LM22673
Copyright ? 2008–2013, Texas Instruments Incorporated
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM22673MR-5.0 | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Inv/Step Down 4.5V to 42V 8-Pin PSOP EP Rail |
| LM22673MR-5.0/NOPB | 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 |
| LM22673MR-ADJ | 制造商:Texas Instruments 功能描述:REGULATOR, ADJ. VOLTAGE, 3A 8PSOP 制造商:Texas Instruments 功能描述:REGULATOR, ADJ. VOLTAGE, 3A 8PSOP; Primary Input Voltage:42V; No. of Outputs:1; Output Current:3A; Voltage Regulator Case Style:SOP; No. of Pins:8; Operating Temperature Min:-40C; Operating Temperature Max:125C; SVHC:No SVHC ;RoHS Compliant: Yes |
| LM22673MR-ADJ/NOPB | 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 |
| LM22673MRE-5.0 | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Inv/Step Down 4.5V to 42V 8-Pin PSOP EP T/R 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述:SIMPLESWITCH 3.0A 4.5~42VIN 8PSOP 制造商:Texas Instruments 功能描述:SIMPLESWITCH, 3.0A 4.5~42VIN, 8PSOP 制造商:Texas Instruments 功能描述:SIMPLESWITCH, 3.0A 4.5~42VIN, 8PSOP, Primary Input Voltage:12V, No. of Outputs:1 制造商:Texas Instruments 功能描述:SIMPLESWITCH, 3.0A 4.5~42VIN, 8PSOP, Primary Input Voltage:12V, No. of Outputs:1, Output Voltage:5V, Output Current:3A, Voltage Regulator Case Style:SOP, No. of Pins:8, Operating Temperature Min:-40C, Operating Temperature , RoHS Compliant: Yes |
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