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參數(shù)資料
| 型號(hào)： | LTC3803HS6-3#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1 A SWITCHING CONTROLLER, 330 kHz SWITCHING FREQ-MAX, PDSO6 |
| 封裝： | 1 MM HEIGHT, LEAD FREE, PLASTIC, MO-193, TSOT-23, 6 PIN |
| 文件頁數(shù)： | 2/16頁 |
| 文件大小： | 170K |
| 代理商： | LTC3803HS6-3#PBF |
LTC3803-3
10
38033fd
APPLICATIONS INFORMATION
CURRENT SENSE RESISTOR CONSIDERATIONS
The external current sense resistor (RSENSE in Figure 2)
allows the user to optimize the current limit behavior for
the particular application. As the current sense resistor
is varied from several ohms down to tens of milliohms,
peak switch current goes from a fraction of an ampere to
several amperes. Care must be taken to ensure proper
circuit operation, especially with small current sense
resistor values.
For example, a peak switch current of 5A requires a sense
resistor of 0.020Ω. Note that the instantaneous peak
power in the sense resistor is 0.5W and it must be rated
accordingly. The LTC3803-3 has only a single sense line
to this resistor. Therefore, any parasitic resistance in the
ground side connection of the sense resistor will increase
its apparent value. In the case of a 0.020Ω sense resis-
tor, one milliohm of parasitic resistance will cause a 5%
reduction in peak switch current. So the resistance of
printed circuit copper traces and vias cannot necessarily
be ignored.
PROGRAMMABLE SLOPE COMPENSATION
The LTC3803-3 injects a ramping current through its SENSE
pin into an external slope compensation resistor (RSL in
Figure 2). This current ramp starts at zero right after the
NGATE pin has been high for the LTC3803-3’s minimum
duty cycle of 8%. The current rises linearly towards a
peak of 5μA at the maximum duty cycle of 80%, shutting
off once the NGATE pin goes low. A series resistor (RSL)
connecting the SENSE pin to the current sense resistor
(RSENSE) thus develops a ramping voltage drop. From
the perspective of the SENSE pin, this ramping voltage
adds to the voltage across the sense resistor, effectively
reducing the current comparator threshold in proportion
to duty cycle. This stabilizes the control loop against
subharmonic oscillation. The amount of reduction in the
current comparator threshold (ΔVSENSE) can be calculated
using the following equation:
ΔVSENSE =
Duty Cycle – 8%
80%
5μA RSL
Note: LTC3803-3 enforces 8% < Duty Cycle < 80%.
A good starting value for RSL is 5.9k, which gives a 30mV
drop in current comparator threshold at 80% duty cycle.
Designs not needing slope compensation may replace RSL
with a short circuit.
INTERNAL WIDE HYSTERESIS UNDERVOLTAGE
LOCKOUT
The LTC3803-3 is designed to implement DC/DC converters
operating from input voltages of typically 48V or more. The
standard operating topology employs a third transformer
winding (LBIAS in Figure 2) on the primary side that pro-
vides power for the LTC3803-3 via its VCC pin. However,
this arrangement is not inherently self-starting. Start-up
is affected by the use of an external trickle-charge resistor
(RSTART in Figure 2) and the presence of an internal wide
hysteresis undervoltage lockout circuit that monitors VCC
pin voltage. Operation is as follows:
Trickle-charge resistor RSTART is connected to VIN and
supplies a small current, typically on the order of 100μA,
to charge CVCC. After some time, the voltage on CVCC
reaches the VCC turn-on threshold. The LTC3803-3 then
turns on abruptly and draws its normal supply current.
The NGATE pin begins switching and the external MOSFET
(Q1) begins to deliver power. The voltage on CVCC begins
to decline as the LTC3803-3 draws its normal supply
current, which exceeds that delivered by RSTART. After
some time, typically tens of milliseconds, the output volt-
age approaches its desired value. By this time, the third
transformer winding is providing virtually all the supply
current required by the LTC3803-3.
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相關(guān)代理商/技術(shù)參數(shù) |
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| LTC3803HS6-5#PBF | 制造商:Linear Technology 功能描述:Bulk |
| LTC3803HS6-5#TRMPBF | 功能描述:IC REG CTRLR FLYBK PWM TSOT23-6 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 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3803HS6-5#TRMPBF | 制造商:Linear Technology 功能描述:IC REG CTRLR FLYBK PWM TSOT23-6 |
| LTC3803HS6-5#TRPBF | 功能描述:IC REG CTRLR FLYBK PWM TSOT23-6 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 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3803IS6 | 制造商:Linear Technology 功能描述:DC DC Cntrlr Single-OUT Flyback Controller 9.2V to 75V Input 6-Pin TSOT-23 |
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