參數(shù)資料
型號(hào)： L6997
廠商： 意法半導(dǎo)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(yùn)作
文件頁(yè)數(shù)： 11/23頁(yè)
文件大?。?/td> 291K
代理商： L6997
11/23
L6997
1.6 Protection and fault
Sensing VSENSE pin voltage performs output protection. The nature of the fault (that is, latched OV or latched
UV) is given by the PGOOD and OVP pins. If the output voltage is between the 89% (typ.) and 110% (typ) of
the regulated value, PGOOD is high. If a hard overvoltage or an undervoltage occurs, the device is latched: low
side MOSFET and, high side MOSFET are turned off and PGOOD goes low. In case the system detects an
overvoltage the OVP pin goes high.
To recover the functionality the device must be shut down and restarted thought the SHDN pin, or the supply
has to be removed, and restart with the correct sequence.
These features are useful to protect against short-circuit (UV fault) as well as high side MOSFET short (OV
fault).
1.7 Drivers
The integrated high-current drivers allow using different size of power MOSFET, maintaining fast switching tran-
sition. The driver for the high side MOSFET uses the BOOT pin for supply and PHASE pin for return (floating
driver). The driver for the low side MOSFET uses the VDR pin for the supply and PGND pin for the return. The
main feature is the adaptive anti-cross-conduction protection, which prevents from both high side and low side
MOSFET to be on at the same time, avoiding a high current to flow from VIN to GND. When high side MOSFET
is turned off the voltage on the pin PHASE begins to fall; the low side MOSFET is turned on only when the volt-
age on PHASE pin reaches 250mV. When low side is turned off, high side remains off until LGATE pin voltage
reaches 500mV. This is important since the driver can work properly with a large range of external power MOS-
FETS.
The current necessary to switch the external MOSFETS flows through the device, and it is proportional to the
MOSFET gate charge and the switching frequency. So the power dissipation of the device is function of the ex-
ternal power MOSFET gate charge and switching frequency.
Eq 14
The maximum gate charge values for the low side and high side are given from:
Eq 15
Eq 16
Where f
SW0
= 500Khz. The equations above are valid for T
J
= 150°C. If the system temperature is lower the Q
G
can be higher.
For the Low Side driver the max output gate charge meets another limit due to the internal traces degradation;
in this case the maximum value is Q
MAXLS
= 125nC.
The low side driver has been designed to have a low resistance pull-down transistor, around 0.5 ohms. This
prevents the voltage on LGATE pin raises during the fast rise-time of the pin PHASE, due to the Miller effect.
Because the driver voltage can be very low it should be considered also the ULTRA LOW VOLTAGE MOSFET.
This kind of MOSFET has very low threshold voltage, so the overdrive voltage can be enough to ensure correct
transition and low enough RDS
ON
.
P
driver
V
cc
Q
gTOT
F
SW
=
Q
MAXHS
f
f
SW
------------
75nC
=
Q
MAXLS
f
f
SW
------------
125nC
=
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(dá)林頓開(kāi)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(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
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
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