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參數(shù)資料
| 型號： | LM25574Q0MT |
| 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)： | 3/20頁 |
| 文件大小： | 394K |
| 代理商： | LM25574Q0MT |
30071008
FIGURE 6. Composition of Current Sense Signal
The sample & hold DC level illustrated in Figure 6 is derived
from a measurement of the re-circulating Schottky diode an-
ode current. The re-circulating diode anode should be con-
nected to the IS pin. The diode current flows through an
internal current sense resistor between the IS and PGND
pins. The voltage level across the sense resistor is sampled
and held just prior to the onset of the next conduction interval
of the buck switch. The diode current sensing and sample &
hold provide the DC level of the reconstructed current signal.
The positive slope inductor current ramp is emulated by an
external capacitor connected from the RAMP pin to AGND
and an internal voltage controlled current source. The ramp
current source that emulates the inductor current is a function
of the Vin and Vout voltages per the following equation:
I
RAMP = (10 x (Vin – Vout)) + 50A
Proper selection of the RAMP capacitor depends upon the
selected value of the output inductor. The value of C
RAMP can
be selected from: C
RAMP = L x 5 x 10
-6
, where L is the value
of the output inductor in Henrys. With this value, the scale
factor of the emulated current ramp will be approximately
equal to the scale factor of the DC level sample and hold
(2.0V / A). The C
RAMP capacitor should be located very close
to the device and connected directly to the pins of the IC
(RAMP and AGND).
For duty cycles greater than 50%, peak current mode control
circuits are subject to sub-harmonic oscillation. Sub-harmonic
oscillation is normally characterized by observing alternating
wide and narrow pulses at the switch node. Adding a fixed
slope voltage ramp (slope compensation) to the current sense
signal prevents this oscillation. The 50A of offset current
provided from the emulated current source adds some fixed
slope to the ramp signal. In some high output voltage, high
duty cycle applications, additional slope may be required. In
these applications, a pull-up resistor may be added between
the V
CC and RAMP pins to increase the ramp slope compen-
sation.
For V
OUT > 7.5V:
Calculate optimal slope current, I
OS = VOUT x 10A/V.
For example, at V
OUT = 10V, IOS = 100A.
Install a resistor from the RAMP pin to V
CC:
R
RAMP = VCC / (IOS - 50A)
30071045
FIGURE 7. R
RAMP to VCC for VOUT > 7.5V
11
www.national.com
LM25574Q0
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM25574Q0MT/NOPB | 功能描述:直流/直流開關轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率: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 安裝風格:SMD/SMT |
| LM25574Q0MTX | 制造商:TI 制造商全稱:Texas Instruments 功能描述:LM25574/LM25574-Q1 SIMPLE SWITCHER 42V, 0.5A Step-Down Switching Regulator |
| LM25574Q0MTX/NOPB | 功能描述:直流/直流開關轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率: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 安裝風格:SMD/SMT |
| LM25574-Q1 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:LM25574/LM25574-Q1 SIMPLE SWITCHER 42V, 0.5A Step-Down Switching Regulator |
| LM25574QMT | 制造商:TI 制造商全稱:Texas Instruments 功能描述:LM25574/LM25574-Q1 SIMPLE SWITCHER 42V, 0.5A Step-Down Switching Regulator |
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