參數(shù)資料
型號(hào)： LTC3869IGN-2#PBF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： SWITCHING CONTROLLER, PDSO28
封裝： 0.150 INCH, LEAD FREE, PLASTIC, SSOP-28
文件頁(yè)數(shù)： 10/40頁(yè)
文件大?。?/td> 2705K
代理商： LTC3869IGN-2#PBF
LTC3869/LTC3869-2
18
3869f
ThesynchronousMOSFETlossesaregreatestathighinput
voltage when the top switch duty factor is low or during
a short-circuit when the synchronous switch is on close
to 100% of the period.
The term (1 + d) is generally given for a MOSFET in the
form of a normalized RDS(ON) vs Temperature curve, but
d = 0.005/°C can be used as an approximation for low
voltage MOSFETs.
TheoptionalSchottkydiodesconductduringthedeadtime
betweentheconductionofthetwopowerMOSFETs.These
preventthebodydiodesofthebottomMOSFETsfromturn-
ing on, storing charge during the dead time and requiring
a reverse recovery period that could cost as much as 3%
in efficiency at high VIN. A 1A to 3A Schottky is generally
a good compromise for both regions of operation due to
the relatively small average current. Larger diodes result
in additional transition losses due to their larger junction
capacitance. A Schottky diode in parallel with the bottom
FET may also provide a modest improvement in Burst
Mode efficiency.
Soft-Start and Tracking
The LTC3869 has the ability to either soft-start by itself
with a capacitor or track the output of another channel or
externalsupply.Whenoneparticularchannelisconfigured
to soft-start by itself, a capacitor should be connected to
its TK/SS pin. This channel is in the shutdown state if its
RUN pin voltage is below 1.2V. Its TK/SS pin is actively
pulled to ground in this shutdown state.
Once the RUN pin voltage is above 1.2V, the channel pow-
ers up. A soft-start current of 1.2A then starts to charge
its soft-start capacitor. Note that soft-start or tracking is
achieved not by limiting the maximum output current of
the controller but by controlling the output ramp voltage
according to the ramp rate on the TK/SS pin. Current
foldback is disabled during this phase to ensure smooth
soft-start or tracking. The soft-start or tracking range is
defined to be the voltage range from 0V to 0.6V on the
TK/SS pin. The total soft-start time can be calculated as:
tSOFTSTART = 0.6
CSS
1.2A
Regardless of the mode selected by the MODE/PLLIN pin,
the regulator will always start in pulse-skipping mode
up to TK/SS = 0.5V. Between TK/SS = 0.5V and 0.54V, it
will operate in forced continuous mode and revert to the
selected mode once TK/SS > 0.54V. The output ripple
is minimized during the 40mV forced continuous mode
window ensuring a clean PGOOD signal.
When the channel is configured to track another supply,
the feedback voltage of the other supply is duplicated by
a resistor divider and applied to the TK/SS pin. Therefore,
the voltage ramp rate on this pin is determined by the
ramp rate of the other supply’s voltage. Note that the small
soft-start capacitor charging current is always flowing,
producingasmalloffseterror.Tominimizethiserror,select
the tracking resistive divider value to be small enough to
make this error negligible.
In order to track down another channel or supply after
the soft-start phase expires, the LTC3869 is forced into
continuous mode of operation as soon as VFB is below the
undervoltage threshold of 0.54V regardless of the setting
on the MODE/PLLIN pin. However, the LTC3869 should
always be set in force continuous mode tracking down
when there is no load. After TK/SS drops below 0.1V, its
channel will operate in discontinuous mode.
APPLICATIONS INFORMATION
相關(guān)PDF資料
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
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LTC3872EDDB#TRMPBF 功能描述:IC REG CTRLR BST PWM CM 8-DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無(wú) 升壓:是 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR)
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