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參數(shù)資料
| 型號(hào)： | LM25007 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 42V, 0.5A Step-Down Switching Regulator |
| 中文描述： | 42V的0.5A的降壓型開關(guān)穩(wěn)壓器 |
| 文件頁數(shù)： | 7/12頁 |
| 文件大?。?/td> | 615K |
| 代理商： | LM25007 |
Detailed Operating Description
The LM25007 is a monolithic step-down switching regulator
featuring all of the functions needed to implement low cost,
efficient, power supply. Capable of driving a 0.5Amp load
over a 9-42V input voltage range, this device is easy to apply
and is provided in the small MSOP-8 and the thermally
enhanced LLP-8 packages. Ultra-fast transient response is
achieved through the use of a constant on-time architecture
with Vin feed forward. This feature provides and almost
constant operating frequency over load and input voltage
variations. The operating frequency may be adjusted up to
800kHz depending on input and output voltages. This archi-
tecture is easy to use and tolerant of component selection.
An intelligent current limit is implemented in the LM25007
with forced off time that is inversely proportional to Vout to
ensure recovery from fault conditions. The output voltage
may be set from 2.5V to
>
30V. To improve efficiency in light
load applications, the Vcc pin can be tied to an external
voltage source thus eliminating the drop through the inte-
grated internal regulator. Additional protection features in-
clude: thermal shutdown, Vcc under-voltage lockout, gate
drive under-voltage lockout, and max duty cycle limiter.
Hysteretic Control Circuit
Overview
The LM25007 is a Buck DC-DC regulator that uses a con-
stant on-time control scheme. The on-time is programmed
by an external resistor and varies inversely with line input
voltage (Vin). The core regulation elements of the LM25007
are the feedback comparator and the on-time one-shot. The
regulator output voltage is sensed at the feedback pin (FB)
and is compared to an internal reference voltage (2.5V). If
the FB signal is below the reference voltage, the buck switch
is turned on for a fixed time pulse determined by the line
voltage and a programming resistor (R
). Following the on
period the switch will remain off for at least the minimum off
timer period of 300ns. If the FB pin voltage is still below the
reference after the 300ns off-time, the switch will turn on
again for another on time period. This switching behavior will
continue until the FB pin voltage reaches the reference
voltage level.
The LM25007 operates in discontinuous conduction mode at
light load currents or continuous conduction mode at heavier
load currents. In discontinuous conduction mode, current
through the output inductor starts at zero and ramps up to a
peak value during the buck switch on-time and then back to
zero during the off-time. The inductor current remains at zero
until the next on-time period starts when FB falls below the
internal reference. In discontinuous mode the operating fre-
quency is relatively low and will vary with load. Therefore at
light loads the conversion efficiency is maintained, since the
switching losses decrease with the reduction in load current
and switching frequency. The approximate discontinuous
mode operating frequency can be calculated as follows:
In continuous conduction mode, current flows continuously
through the inductor and never ramps down to zero. In this
mode the operating frequency is greater than the discontinu-
ous mode frequency and remains relatively constant with
load and line variations. The approximate continuous mode
operating frequency can be calculated as follows:
The output voltage (Vout) can be programmed by two exter-
nal resistors as shown in
Figure 1
. The regulated voltage is
calculated as follows:
V
OUT
= 2.5 x (R3 + R4) / R4
The feedback comparator in hysteretic regulators depends
on the output ripple voltage to switch the output transistor on
and off at regular intervals. In order for the internal compara-
tor to respond quickly to changes in output voltage, propor-
tional to inductor current, a minimum amount of capacitor
Equivalent Series Resistance (ESR) is required. A ripple
voltage of 25mV is recommended at the feedback pin (FB)
for stable operation. In cases where the intrinsic capacitor
ESR is too small, additional series resistance may be added.
For applications where lower output voltage ripple is re-
quired the load can be connected directly to the low ESR
output capacitor, as shown in
Figure 1
. The series resistor
(R5) will degrade the load regulation. Another technique for
enhancing the ripple voltage at the FB pin is to place a
capacitor in parallel with the feedback divider resistor R3.
The addition of the capacitor reduces the attenuation of the
ripple voltage from the feedback divider.
High Voltage Bias Regulator (VCC)
The LM25007 contains an internal high voltage bias regula-
tor. The input pin (Vin) can be connected directly to line
voltages from 9 to 42 Volts. To avoid supply voltage tran-
sients due to long lead inductances on the input pin (VIN), it
is always recommended to connect a low ESR ceramic chip
capacitor (
)
0.1μF) between VIN and RTN pins located
close to the LM25007. The regulator is internally current
limited to 11mA. Upon power up, the regulator is enabled
and sources current into an external capacitor connected to
the VCC pin. When the voltage on the VCC pin reaches its
UVLO level (6.3V), the controller output is enabled.
An external auxiliary supply voltage can be diode connected
to the Vcc pin. If the auxiliary voltage is greater than 7 Volts
the internal regulator will shutoff, thus reducing internal
power dissipation. Do not exceed 14V at VCC. See
Figure 2
.
L
www.national.com
7
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| LM25007_08 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:42V, 0.5A Step-Down Switching Regulator |
| LM25007_11 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Boot Capacitor Regulation in LM25007 Constant-On-Time (COT) Converter |
| LM25007EVAL | 功能描述:電源管理IC開發(fā)工具 LM25007 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| LM25007MM | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)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(fēng)格:SMD/SMT |
| LM25007MM/NOPB | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 42V,0.5A STEP-DOWN SWITCHING REG RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
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