參數(shù)資料
型號： L6997
廠商： 意法半導體
英文描述： STEP DOWN CONTROLLER FOR LOW VOLTAGE OPERATIONS
中文描述： 降壓控制器低電壓運作
文件頁數(shù)： 8/23頁
文件大?。?/td> 291K
代理商： L6997
L6997
8/23
Eq 6
Where
V
OUT
is the output ripple and
V
INT
is the ripple wanted at the INT pin (100mV typ).
Figure 4. Integrator loop block diagram
Respect to a traditional PWM controller, that has an internal oscillator setting the switching frequency, in a hys-
teretic system the frequency can change with some parameters (input voltage, output current). In L6997 is im-
plemented the voltage feed-forward circuit that allows constant switching frequency during steady-sate
operation with the input voltage variation. There are many factors affecting switching frequency accuracy in
steady-state operation. Some of these are internal as dead times, which depend on high side MOSFET driver.
Others related to the external components as high side MOSFET gate charge and gate resistance, voltage
drops on supply and ground rails, low side and high side RDSON and inductor parasitic resistance.
During a positive load transient, (the output current increases), the converter switches at its maximum frequency
(the period is TON+TOFFmin) to recover the output voltage drop. During a negative load transient, (the output
current decreases), the device stops to switch (high side MOSFET remains off).
1.3 Transition from PWM to PFM/PSK
To achieve high efficiency at light load conditions, PFM mode is provided. The PFM mode differs from the PWM
mode essentially for the off section; the on section is the same. In PFM after a turn-on cycle the system turns-
on the low side MOSFET, until the inductor current reaches the zero A value, when the zero-crossing compar-
ator turns off the low side MOSFET. In this way the energy stored in the output capacitor will not flow to ground,
through the low side MOSFET, but it will flow to the load. In PWM mode, after a turn on cycle, the system keeps
the low side MOSFET on until the next turn-on cycle, so the energy stored in the output capacitor will flow
through the low side MOSFET to ground. The PFM mode is naturally implemented in hysteretic controller, in
fact in PFM mode the system reads the output voltage with a comparator and then turns on the high side MOS-
FET when the output voltage goes down a reference value. The device works in discontinuous mode 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 V
IN
, L, and V
OUT
. Note that the higher the in-
C
C
INT1
---------------
V
V
INT
------------------
=
PCB TRACES
LOAD
From Vsense
Q
Cint1
R1
INT
Vref
FB
DS
R
S
Vout
Vin
HGATE
LGATE
Q
OSC
Vref
One-shot generator
FFSR
PWM comparator
Vsense
Gndsense
R2
Cint2
HS
LS
Integrator amplifier
+
-
-
+
+
-
相關(guān)PDF資料
PDF描述
L6997D STEP DOWN CONTROLLER FOR LOW VOLTAGE OPERATIONS
L6997DTR STEP DOWN CONTROLLER FOR LOW VOLTAGE OPERATIONS
L702 2A Quad Darlington Switches(2A四通道達林頓開關(guān))
L70S70 16 Characters x 2 Lines, 5x7 Dot Matrix Character and Cursor
L70S20 16 Characters x 2 Lines, 5x7 Dot Matrix Character and Cursor
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
L6997-28 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT
L6997-5 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT; Accessory Type:Tuning Element; For Use With:High Quality Variable Reactance Tuning Microwave Cavities, Filters & other Resonant Structures
L6997-9 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT
L6997D 功能描述:DC/DC 開關(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 安裝風格: 封裝 / 箱體:CPAK
L6997DTR 功能描述:DC/DC 開關(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 安裝風格: 封裝 / 箱體:CPAK
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