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參數(shù)資料
| 型號： | L6995STR |
| 廠商： | STMICROELECTRONICS |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, PDSO20 |
| 封裝： | MO-153-AC, TSSOP-20 |
| 文件頁數(shù)： | 10/26頁 |
| 文件大?。?/td> | 427K |
| 代理商： | L6995STR |
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L6995S
18/26
6.5 Output voltage setting
To select the output divider network there isn't a specific criteria, but a low divider network value (around 100
)
reduces the efficiency at low current; instead a high value divider network (500K
) increase the noise effects.
A network divider values from 1K to 50K is right. From the Eq4:
R10 = 1K
R9 = 390
The device output voltage is adjustable by connecting a voltage divider from output to VSENSE pin. Minimum
output voltage is VOUT = VREF = 0.9V. Once output divider and frequency divider have been designed as to ob-
tain the required output voltage and switching frequency, the following equation gives the smallest input voltage,
which allows L6995S to regulate (which corresponds to TOFF = TOFF, MIN):
Eq 25
where the KOSC/TOFFMIN ratio worst-case is given in electrical characteristic table (pag. 4).
6.6 Voltage Feed Forward
Choosing the switching frequency around 270KHz from the Eq1. It can be selected the input divider. For exam-
ple:
R3=560K
R4=28K
In order to compensate the comparator delay R4 resistor should be increased around 20%.
R4=33K
6.7 Current limit resistor
From the Eq13 can be set the valley current limit, knowing the low side RDSON. To set the exact current limit it
must be considered the temperature effect. So two STS25NH3LL have 2.75m
@ 25°C, at 100°C can be con-
sidered 3.85m
.
R8 = 47K
6.8 Integrator capacitor
Let it be FU = 15kHz.
Since VREF = 0.9V, from Eq4, it follows
αOUT = 0.72 and, from Eq5 it follows CINT1 = 330pF. Because the ripple
is lower than 150mV the system doesn't need the second integrator capacitor.
6.9 Soft start capacitor
Considering the soft start equations (Eq. 11) at page 10, it can be found:
CSS = 200pF
These equations are valid whitout load. When an active load is present the equantions result more complex;
further some active loads have unexpected effect, as higher current than the expected one during the start up,
that can change the start up time.
In this case the capacitor value can be selected on the application; anyway the Eq11 gives an idea about the
CSS value.
δ 1
α
OSC
α
OUT
---------------
1
K
OSC
T
OFFMIN
------------------------
------------------------------
–
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| L6996 | 功能描述:DC/DC 開關(guān)控制器 Step-Down Contrllr RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| L6996-1 | 制造商:Johanson 功能描述:TUNING ROTOR |
| L6996-13 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
| L6996-16 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
| L6996-17 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
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