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參數(shù)資料
| 型號： | L4992 |
| 廠商： | STMICROELECTRONICS |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 300 kHz SWITCHING FREQ-MAX, PQFP32 |
| 封裝： | TQFP-32 |
| 文件頁數(shù)： | 6/26頁 |
| 文件大?。?/td> | 296K |
| 代理商： | L4992 |
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offered by manufacturer, also for surface mount assemblies.
+3.3 V Transformer
The primary winding carries the secondary power as well, thus the total primary average current is:
Itot3
= Iout3
+
Vinlin
Iout12
3.3
where Vinlin is the voltage generated during the recirculation of the primary and fed into the input of the
+12V linear regulator. The turns ratio 1:n of the transformer is chosen so that Vinlin is above 13V. To re-
duce the turns ratio in order to minimize stray parameters, the secondary is referred to the 3.3V output,
and therefore the minimum value is given by:
nmin
=
Vinlin
3.3 + Vf
3.3
where Vf is the forward drop across the rectifier (assume 1V to be conservative). Make sure the secon-
dary is connected with the proper polarity (see fig. 6).
The minimum primary inductance value can be expressed as:
L3pmin
=
3
4
3.3
(Vin 3.3)2
Vin
fsw [Itot3
RF (Vin 3.3) n Vin Iout12]
where RF, to get positive values for L3pmin, must satisfy the inequality:
RF
>
n
Vin Iout12
Itot3
(Vin 3.3
)
and where Vin can be either Vinmin or Vinmax, whichever gives the higher value for L3pmin.
With a primary inductance L3p > L3pmin the primary peak current, which must not saturate the magnetic
core, will be:
IL3pk
= Itot3 +
3.3
(Vin max 3.3)
2
fsw L3p Vin max +
n
Iout12
As to the transformer realization, the considerations regarding to the +5.1V inductor can be here repeated.
Power MOSFET’s and Schottky diodes
Since the gate drivers of the L4992 are powered by a 5V bus , the use of logic-level MOSFET’s is highly
recommended, especially for high current applications. Their breakdown voltage V(BR)DSS must be
greater than Vinmax with a certain margin, so the selection will address 20V or 30V devices.
The RDS(ON) can be selected once the allowable power dissipation has been established. By selecting
identical power MOSFET’s as the main switch and the synchronous rectifier, the total power they dissi-
pate does not depend on the duty cycle. Thus, if PON is this power loss (few percent of the rated output
power), the required RDS(ON) (@ 25 °C) can be derived from:
RDS(ON) =
PON
Iout
2
(1 + α T)
where Iout is either Itot3 or Iout5, according to the section under consideration,
α is the temperature coeffi-
cient of RDS(ON) (typically,
α = 5 10-3 °C-1 for these low-voltage classes) and T the admitted tempera-
ture rise.
It is worth noticing, however, that generally the lower RDS(ON), the higher is the gate charge Qg, which
leads to a higher gate drive consumption. In fact, each switching cycle, a charge Qg moves from the in-
put source to ground, resulting in an equivalent drive current:
Ig
= Qg fsw
DESIGN PROCEDURE (continued)
L4992
14/26
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| L4993 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:Low drop voltage regulator |
| L4993D | 功能描述:低壓差穩(wěn)壓器 - LDO Low drop voltage regulator RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| L4993DTR | 功能描述:低壓差穩(wěn)壓器 - LDO Low drop voltage regulator RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| L4993MD | 功能描述:低壓差穩(wěn)壓器 - LDO Low drop voltage regulator RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| L4993MDTR | 功能描述:低壓差穩(wěn)壓器 - LDO 5V 150mA LW DROP VLT REGULATOR RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
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