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參數(shù)資料
| 型號(hào)： | L4985D |
| 元件分類(lèi)： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | Voltage-Mode SMPS Controller |
| 中文描述： | 電壓模式開(kāi)關(guān)電源控制器 |
| 文件頁(yè)數(shù)： | 20/23頁(yè) |
| 文件大?。?/td> | 415K |
| 代理商： | L4985D |
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The delay (Trd)is programmed by an externalca-
pacitor connected to pin 20 and SGND according
to the approximaterate:
Trd= 250ms/
μ
F
Soft Start (pin14)
Soft-start, essential to assure a correct and safe
start-up of converters, is performed by means of
an external capacitor, Css. The soft-start time is
relatedto Css by theapproximate rate:
Tss = 30 Vout/ Vin [ms/
μ
F] .
AuxiliaryConverter (pins 11 & 12)
The auxiliary section includes, as a power switch,
an NDMOS with grounded source and open
drain, thus allowing the implementation of either
boost or transformer coupled converters. That re-
quires, besides the magnetics and the output
stage, only a resistor divider to fix the output volt-
age.No frequencycompensationis needed.
BOARD LAYOUT CONSIDERATIONS.
To prevent degraded performances or, worse, in-
stabilities and oscillations, a careful board layout
is mandatory. With this aim, the following points
should be considered.
1)Separate ground paths of signals and load
currents of the main converter.The two paths
should have their common point in the (-)
plate of theoutput capacitor.
2)Separatethe ground path of the auxiliarycon-
verter from that of the main converter. The
former runs from the (-) plate of its output ca-
pacitor to PWGND. The (-) plates of the two
output capacitors should be connected.
3)Make separate supply paths for the IC (pin
17), the internalstep-up and the auxiliary con-
verter, all leading to the (+) plate of the input
capacitor.
4)The anode of the Schottky diode (the drain of
the synchronous rectifier, when used) should
be placed as close as possible to pin 4 in or-
der to reduce stray inductance which causes
ringing spikes at MOS turn-off.
5)Place the input capacitor as close as possible
to the IC so to reduce the effect of the pulsed
current absorbed.
6)Make copper tracks carrying high currents
(either pulsed or DC) as large as possible, in
order not to impair efficiency and load regula-
tion. Concerning this, it is important to use
copper layers as thick as possible. Some of
these tracks could be doubled on the other
side of the board.
7)Make copper trackscarrying smallsignals run
far from points with quickly swinging voltages.
8)Widen as much as possible the copper area
to which the four central ground pins are con-
nected, in order to make easier heat dissipa-
tion. Also ground paths could be widened to
form groundplanes.
L4985
20/23
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| L4987 | 制造商:STMICROELECTRONICS 制造商全稱(chēng):STMicroelectronics 功能描述:VERY LOW DROP VOLTAGE REGULATORS WITH INHIBIT AND DROPOUT CONTROL FLAG |
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| L4987CPT33 | 功能描述:IC REG LDO 3.3V .2A P-PAK RoHS:是 類(lèi)別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 線性 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:- 穩(wěn)壓器拓?fù)浣Y(jié)構(gòu):正，固定式 輸出電壓:3.1V 輸入電壓:最高 5.5V 電壓 - 壓降（標(biāo)準(zhǔn)）:- 穩(wěn)壓器數(shù)量:1 電流 - 輸出:300mA 電流 - 限制（最?。?420mA 工作溫度:-40°C ~ 85°C 安裝類(lèi)型:表面貼裝 封裝/外殼:SOT-23-5 細(xì)型，TSOT-23-5 供應(yīng)商設(shè)備封裝:TSOT-23-5 包裝:帶卷 (TR) |
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