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參數(shù)資料
| 型號： | LM25575Q0MHX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING REGULATOR, PDSO16 |
| 封裝： | TSSOP-16 |
| 文件頁數(shù)： | 10/22頁 |
| 文件大?。?/td> | 401K |
| 代理商： | LM25575Q0MHX |
PCB LAYOUT AND THERMAL CONSIDERATIONS
The circuit in Figure 1 serves as both a block diagram of the
LM25575Q0 and a typical application board schematic for the
LM25575Q0. In a buck regulator there are two loops where
currents are switched very fast. The first loop starts from the
input capacitors, to the regulator VIN pin, to the regulator SW
pin, to the inductor then out to the load. The second loop starts
from the output capacitor ground, to the regulator PGND pins,
to the regulator IS pins, to the diode anode, to the inductor
and then out to the load. Minimizing the loop area of these
two loops reduces the stray inductance and minimizes noise
and possible erratic operation. A ground plane in the PC
board is recommended as a means to connect the input filter
capacitors to the output filter capacitors and the PGND pins
of the regulator. Connect all of the low power ground connec-
tions (C
SS, RT, CRAMP) directly to the regulator AGND pin.
Connect the AGND and PGND pins together through the top-
side copper area covering the entire underside of the device.
Place several vias in this underside copper area to the ground
plane.
The two highest power dissipating components are the re-
circulating diode and the LM25575Q0 regulator IC. The eas-
iest method to determine the power dissipated within the
LM25575Q0 is to measure the total conversion losses (Pin –
Pout) then subtract the power losses in the Schottky diode,
output inductor and snubber resistor. An approximation for
the Schottky diode loss is P = (1-D) x Iout x Vfwd. An approx-
imation for the output inductor power is P = I
OUT
2
x R x 1.1,
where R is the DC resistance of the inductor and the 1.1 factor
is an approximation for the AC losses. If a snubber is used,
an approximation for the damping resistor power dissipation
is P = Vin2 x Fsw x Csnub, where Fsw is the switching fre-
quency and Csnub is the snubber capacitor. The regulator
has an exposed thermal pad to aid power dissipation. Adding
several vias under the device to the ground plane will greatly
reduce the regulator junction temperature. Selecting a diode
with an exposed pad will aid the power dissipation of the
diode.
The most significant variables that affect the power dissipated
by the LM25575Q0 are the output current, input voltage and
operating frequency. The power dissipated while operating
near the maximum output current and maximum input volatge
can be appreciable. The operating frequency of the
LM25575Q0 evaluation board has been designed for 300kHz.
When operating at 1.5A output current with a 42V input the
power dissipation of the LM25575Q0 regulator is approxi-
mately 0.9W.
The
junction-to-ambient
thermal
resistance
of
the
LM25575Q0 will vary with the application. The most signifi-
cant variables are the area of copper in the PC board, the
number of vias under the IC exposed pad and the amount of
forced air cooling provided. Referring to the evaluation board
artwork, the area under the LM25575Q0 (component side) is
covered with copper and there are 5 connection vias to the
solder side ground plane. Additional vias under the IC will
have diminishing value as more vias are added. The integrity
of the solder connection from the IC exposed pad to the PC
board is critical. Excessive voids will greatly diminish the ther-
mal dissipation capacity. The junction-to-ambient thermal re-
sistance of the LM25575Q0 mounted in the evaluation board
varies from 50°C/W with no airflow to 28°C/W with 900 LFM
(Linear Feet per Minute). With a 25°C ambient temperature
and no airflow, the predicted junction temperature for the
LM25575Q0 will be 25 + (50 x 0.9) = 70°C. If the evaluation
board is operated at 1.5A output current, 70V input voltage
and high ambient temperature for a prolonged period of time
the thermal shutdown protection within the IC may activate.
The IC will turn off allowing the junction to cool, followed by
restart with the soft-start capacitor reset to zero.
www.national.com
18
LM25575Q0
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM25575Q0MHX/NOPB | 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 |
| LM25575-Q1 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:LM25575/LM25575-Q1 SIMPLE SWITCHER?? 42V, 1.5A Step-Down Switching Regulator |
| LM25575QMH | 制造商:TI 制造商全稱:Texas Instruments 功能描述:LM25575/LM25575-Q1 SIMPLE SWITCHER?? 42V, 1.5A Step-Down Switching Regulator |
| LM25575QMH/NOPB | 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 |
| LM25575QMHX | 制造商:TI 制造商全稱:Texas Instruments 功能描述:LM25575/LM25575-Q1 SIMPLE SWITCHER?? 42V, 1.5A Step-Down Switching Regulator |
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