參數(shù)資料
型號(hào)： L6997D
廠商： STMICROELECTRONICS
元件分類： 穩(wěn)壓器
英文描述： SWITCHING CONTROLLER, PDSO20
封裝： MO-153AC, TSSOP-20
文件頁(yè)數(shù)： 30/30頁(yè)
文件大?。?/td> 591K
代理商： L6997D
Obsolete
Product(s)
- Obsolete
Product(s)
9/30
L6997
at light load and in continuous mode at high load. The transition from PFM to PWM occurs when load current is
around half the inductor current ripple. This threshold value depends on VIN, L, and VOUT. Note that the higher
the inductor value is, the smaller the threshold is. On the other hand, the bigger the inductor value is, the slower
the transient response is. The PFM waveforms may appear more noisy and asynchronous than normal opera-
tion, but this is normal behaviour mainly due to the very low load. If the PFM is not compatible with the applica-
tion it can be disabled connecting to VCC the NOSKIP pin.
4.4 Softstart
After the device is turned on the SS pin voltage begins to increase and the system starts to switch. The softstart
is realized by gradually increasing the current limit threshold to avoid output overvoltage. The active soft start
range for the VSS voltage (where the output current limit increase linearly) is from 0.6V to 1V. In this range an
internal current source (5
A Typ) charges the capacitor on the SS pin; the reference current (for the current limit
comparator) forced through ILIM pin is proportional to SS pin voltage and it saturates at 5
A (Typ.). When SS
voltage is close to 1V the maximum current limit is active. Output protections OVP & UVP are disabled until the
SS pin voltage reaches 1V (see figure 8).
Once the SS pin voltage reaches the 1V value, the voltage on SS pin doesn't impact the system operation any-
more. If the SHDN pin is turned on before the supplies, the power section must be turned on before the logic
section. While if the supplies are applied with the SHND pin off, the start up sequence doesn't meter.
Figure 8. Soft -Start Diagram
Because the system implements the soft start by controlling the inductor current, the soft start capacitor should
be selected based on of the output capacitance, the current limit and the soft start active range (
VSS).
In order to select the softstart capacitor it must be imposed that the output voltage reaches the final value before
the soft start voltage reaches the under voltage value (1V). After this UVP and OVP are enable.
The time necessary to charge the SS capacitor up to 1V is given by:
(7)
In order to calculate the output voltage chargin time it should be considered that the inductor current function
can be supposed linear function of the time.
(8)
Time
0.6V
Maximum current limit
Soft-start active range
5
A
4.1V
1V
Ilim current
Vss
T
SS CSS
()
1V
Iss
-------- C
SS
=
I
L t,CSS
()
R
ilim/Rdson
K
ILIM
I
SS
t
()
V
SS
C
SS
()
---------------------------------------------------------------------------
=
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
L6997DTR 功能描述:DC/DC 開(kāi)關(guān)控制器 Adjustable Step-Down RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開(kāi)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
L6997S 功能描述:DC/DC 開(kāi)關(guān)控制器 STEP DOWN CONTROLLER Lo Vltg Operations RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開(kāi)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
L6997STR 功能描述:DC/DC 開(kāi)關(guān)控制器 3.0 to 5.5V Step-Dwn RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開(kāi)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
L6998-0 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT
L6998-1 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT
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