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參數(shù)資料
| 型號： | LTC3445EUF#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.8 A SWITCHING REGULATOR, 1800 kHz SWITCHING FREQ-MAX, PQCC24 |
| 封裝： | 4 X 4 MM, LEAD FREE, PLASTIC, MO-220-WGGD, QFN-24 |
| 文件頁數(shù)： | 13/24頁 |
| 文件大小： | 470K |
| 代理商： | LTC3445EUF#TRPBF |
20
LTC3445
3445fa
prevent oscillations. The LTC3445 LDOs are micropower
devices and output transient response will be a function of
output capacitance. Larger values of output capacitance
decrease the peak deviations and provide improved tran-
sient response for larger load current changes.
PowerPath CONTROLLER
The PowerPath circuitry in the LTC3445 is used to provide
backup power from VBACKUP to the VCC BATT pin when
VCC1 is low or disconnected. When VCC1 is below 2.8V, the
PowerPath routes VBACKUP, typically a coin cell, to the VCC
BATT pin. While VBACKUP is selected there is no current
limiting except for a small (<5
) resistance from the
VBACKUP input to the VCC BATT output. The LTC3445 sinks
less than 6.5
A from VBACKUP whenitisselectedandsinks
less than 0.1
A from VBACKUP when it is not selected.
When VCC1 exceeds 2.8V, VBACKUP is disconnected from
VCC BATT and an internal LDO regulates the VCC BATT
voltage to the minimum of VCC1 or typically 3V. The
internal LDO is current limited to less than 50mA, but
greater than 10mA. Capacitance on the VCC BATT pin
should be at least 2
F with an ESR less than 3.
VBACKUP will be routed to the VCC BATT output when the
main battery voltage falls below 2.4V. As the main battery,
VCC1, voltage drops from 3V to 2.4V, the LDO will be in
dropout, VCC BATT will follow VCC1 down, rebounding to
VBACKUP when VCC1 falls below 2.4V. If VCC1 is removed
quickly, the capacitor on VCC BATT will limit the VCC BATT
droop until VBACKUP is switched in.
The VTRACK input offers the capability of the VCC BATT
voltage to follow the voltage on VTRACK up to VCC1. In
effect, VTRACK overrides the internal reference of the LDO,
resulting in the LDO output (VCC BATT) having a gain of 1
relative to VTRACK once VTRACK exceeds a typical value of
3V. VCC BATT will follow VTRACK to within 200mV provid-
ing VTRACK does not exceed the dropout voltage of the
LDO, which is powered by VCC1.
VBACKUP should be present prior to VCC1 being connected.
VBACKUP provides power to the BATTFAULT driver which
APPLICATIO S I FOR ATIO
WU
UU
is used to detect an absent or low VCC1. If VBACKUP is not
present, the LTC3445 will be unable to pull the BATTFAULT
pin low to signal a VCC1 fault condition.
Output Capacitance and Transient Response
The LDO used LTC3445 PowerPath is designed to be
stable with a wide range of output capacitors. A minimum
output capacitor of 2.2
F with an ESR of 3 or less is
recommended to prevent oscillations. The LTC3445
PowerPath LDO is a micropower device and output tran-
sient response will be a function of output capacitance.
Larger values of output capacitance decrease the peak
deviations and provide improved transient response for
larger load current changes.
THERMAL CONSIDERATIONS
In most applications the LTC3445 does not dissipate
much heat due to its high efficiency. But, in applications
where the LTC3445 is running at high ambient tempera-
ture with low supply voltage and high duty cycles, such as
in dropout, the heat dissipated may exceed the maximum
junction temperature of the part. If the junction tempera-
ture reaches approximately 150
°C, both power switches
will be turned off and the SW node will become high
impedance. The remaining regulators will also turn off.
To ensure the LTC3445 doesn’t exceed the maximum
junction temperature, the user will need to do some
thermal analysis. The goal of the thermal analysis is to
determine whether the power dissipated exceeds the
maximum junction temperature of the part. The tempera-
ture rise is given by:
TR = θJA (PDBUCK + PDLDO1 + PDLDO2 + PDPowerPath)
where PD is the power dissipated by the regulator and θJA
is the thermal resistance from the junction of the die to the
ambient temperature.
The junction temperature, TJ, is given by:
TJ = TA + TR
where TA is the ambient temperature.
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| LTC3446 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Monolithic Buck Regulator with Dual VLDO Regulators |
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| LTC3446EDE#PBF | 功能描述:IC REG TRPL BCK/LINEAR 14-DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 線性 + 切換式 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 拓?fù)?降壓（降壓）同步（3），線性（LDO）（2） 功能:任何功能 輸出數(shù):5 頻率 - 開關(guān):300kHz 電壓/電流 - 輸出 1:控制器 電壓/電流 - 輸出 2:控制器 電壓/電流 - 輸出 3:控制器 帶 LED 驅(qū)動器:無 帶監(jiān)控器:無 帶序列發(fā)生器:是 電源電壓:5.6 V ~ 24 V 工作溫度:-40°C ~ 85°C 安裝類型:* 封裝/外殼:* 供應(yīng)商設(shè)備封裝:* 包裝:* |
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