參數(shù)資料
型號(hào)： LTC3850EUF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： 0.1 A DUAL SWITCHING CONTROLLER, 860 kHz SWITCHING FREQ-MAX, PQCC28
封裝： 4 X 4 MM, PLASTIC, QFN-28
文件頁(yè)數(shù)： 9/32頁(yè)
文件大?。?/td> 474K
代理商： LTC3850EUF
LTC3850
17
3850f
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
owing, producing a small offset error. To minimize this
error, 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 LTC3850 is forced into
continuous mode of operation as soon as VFB is below the
undervoltage threshold of 0.74V regardless of the setting
on the MODE/PLLIN pin. However, the LTC3850 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.
Output Voltage Tracking
The LTC3850 allows the user to program how its out-
put ramps up and down by means of the TK/SS pins.
Through these pins, the output can be set up to ei-
ther coincidentally or ratiometrically track another
supply’s output, as shown in Figure 3. In the following
discussions, VOUT1 refers to the LTC3850’s output 1 as a
master channel and VOUT2 refers to the LTC3850’s output
2 as a slave channel. To implement the coincident track-
ing in Figure 3a, connect an additional resistive divider to
VOUT1 and connect its midpoint to the TK/SS pin of the
slave channel. The ratio of this divider should be the same
as that of the slave channel’s feedback divider shown in
Figure 4a. In this tracking mode, VOUT1 must be set higher
than VOUT2. To implement the ratiometric tracking, the
ratio of the VOUT2 divider should be exactly the same as
the master channel’s feedback divider. By selecting differ-
ent resistors, the LTC3850 can achieve different modes of
tracking including the two in Figure 3.
So which mode should be programmed? While either
mode in Figure 4 satises most practical applications,
some tradeoffs exist. The ratiometric mode saves a pair
of resistors, but the coincident mode offers better output
regulation. This can be better understood with the help
of Figure 5. At the input stage of the slave channel’s error
amplier, two common anode diodes are used to clamp
the equivalent reference voltage and an additional diode
is used to match the shifted common mode voltage. The
top two current sources are of the same amplitude. In the
coincident mode, the TK/SS voltage is substantially higher
than 0.8V at steady state and effectively turns off D1. D2
and D3 will therefore conduct the same current and offer
tight matching between VFB2 and the internal precision
0.8V reference. In the ratiometric mode, however, TK/SS
equals 0.8V at steady state. D1 will divert part of the bias
current to make VFB2 slightly lower than 0.8V.
Although this error is minimized by the exponential I-V
characteristic of the diode, it does impose a nite amount
of output voltage deviation. Furthermore, when the master
channel’s output experiences dynamic excursion (under
load transient, for example), the slave channel output will
be affected as well. For better output regulation, use the
coincident tracking mode instead of ratiometric.
INTVCC Regulators and EXTVCC
The LTC3850 features an NPN low dropout linear regulator
(LDO) that supplies power to INTVCC from the VIN supply.
INTVCC powers the gate drivers and much of the LTC3850’s
internal circuitry. The LDO regulates the voltage at the
INTVCC pin to 5V when VIN is greater than 6.5V. EXTVCC
connects to INTVCC through a P-channel MOSFET and can
supply the needed power when its voltage is higher than
4.7V. Each of these can supply a peak current of 100mA
and must be bypassed to ground with a minimum of 1F
ceramic capacitor or low ESR electrolytic capacitor. No mat-
ter what type of bulk capacitor is used, an additional 0.1F
ceramic capacitor placed directly adjacent to the INTVCC
and PGND pins is highly recommended. Good bypassing
is needed to supply the high transient currents required
by the MOSFET gate drivers and to prevent interaction
between the channels.
High input voltage applications in which large MOSFETs
are being driven at high frequencies may cause the maxi-
mum junction temperature rating for the LTC3850 to be
exceeded. The INTVCC current, which is dominated by the
gate charge current, may be supplied by either the 5V LDO
or EXTVCC. When the voltage on the EXTVCC pin is less
than 4.7V, the LDO is enabled. Power dissipation for the
IC in this case is highest and is equal to VIN IINTVCC. The
gate charge current is dependent on operating frequency
as discussed in the Efciency Considerations section. The
junction temperature can be estimated by using the equa-
tions given in Note 3 of the Electrical Characteristics. For
APPLICATIONS INFORMATION
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參數(shù)描述
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LTC3850EUF#PBF 制造商:Linear Technology 功能描述:IC SYNC STEP-DOWN CONTROLLER QFN-28
LTC3850EUF#TRPBF 功能描述:IC REG CTRLR BUCK PWM CM 28-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 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)
LTC3850EUFD#PBF 功能描述:IC REG CTRLR BUCK PWM CM 28-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 特色產(chǎn)品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標(biāo)準(zhǔn)包裝:1 系列:PowerWise® PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:81% 電源電壓:4.5 V ~ 18 V 降壓:是 升壓:無(wú) 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:-5°C ~ 125°C 封裝/外殼:32-WFQFN 裸露焊盤 包裝:Digi-Reel® 產(chǎn)品目錄頁(yè)面:1303 (CN2011-ZH PDF) 其它名稱:LM3754SQDKR
LTC3850EUFD#TRPBF 功能描述:IC REG CTRLR BUCK PWM CM 28-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 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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