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參數(shù)資料
| 型號： | LT3956IUHE#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING REGULATOR, PQCC36 |
| 封裝： | 5 X 6 MM, LEAD FREE, PLASTIC, QFN-36 |
| 文件頁數(shù)： | 2/20頁 |
| 文件大?。?/td> | 1424K |
| 代理商： | LT3956IUHE#TRPBF |
LT3956
0
3956f
applicaTions inForMaTion
INTVCC Regulator Bypassing and Operation
The INTVCC pin requires a capacitor for stable operation
and to store the charge for the switch driver and PWMOUT
pin switching currents. Choose a 10V rated low ESR, X7R
or X5R ceramic capacitor for best performance. A 4.7F
capacitor will be adequate for many applications. Place
the capacitor close to the IC to minimize the trace length
to the INTVCC pin and also to the IC ground.
An internal current limit on the INTVCC output protects
the LT3956 from excessive on-chip power dissipation.
The INTVCC pin has its own undervoltage disable (UVLO)
set to 4.1V (typical) to protect the internal MOSFET from
excessive power dissipation caused by not being fully en-
hanced.IftheINTVCCpindropsbelowtheUVLOthreshold,
the PWMOUT pin will be forced to 0V, the power switch
turned off and the soft-start pin will be reset.
If the input voltage, VIN,willnotexceed7V,thentheINTVCC
pin could be connected to the input supply. This action
allows the LT3956 to operate from as low as 4.5V. Be aware
that a small current (less than 12μA) will load the INTVCC
inshutdown.Otherwise,theminimumoperatingVIN value
isdeterminedbythedropoutvoltageofthelinearregulator
and the 4.4V (4.1V typical) INTVCC undervoltage lockout
threshold mentioned above.
Programming the Turn-On and Turn-Off Thresholds
With the EN/UVLO Pin
ThefallingUVLOvaluecanbeaccuratelysetbytheresistor
divider. A small 2.1A pull-down current is active when
EN/UVLO is below the falling threshold. The purpose of
this current is to allow the user to program the rising
hysteresis. The following equations should be used to
determine the values of the resistors:
V
R R
R
IN FALLING
,
.
=
+
1 22
1
2
V
A R
V
IN RISING
IN FALLING
,
.
=
+
2 1
1
EN/UVLO
LT3956
VIN
R2
3956 F01
R1
Figure 1
LED Current Programming
The LED current is programmed by placing an appropri-
ate value current sense resistor, RLED, between the ISP
and ISN pins. Typically, sensing of the current should
be done at the top of the LED string. If this option is not
available, then the current may be sensed at the bottom
of the string, but take caution that the minimum ISN value
does not fall below 3V, which is the lower limit of the LED
current regulation function. The CTRL pin should be tied
to a voltage higher than 1.2V to get the full-scale 250mV
(typical) threshold across the sense resistor. The CTRL pin
can also be used to dim the LED current to zero, although
relative accuracy decreases with the decreasing voltage
sense threshold. When the CTRL pin voltage is less than
1V, the LED current is:
I
V
mV
R
LED
CTRL
LED
=
100
4
When the CTRL pin voltage is between 1V and 1.2V
the LED current varies with CTRL, but departs from the
previous equation by an increasing amount as the CTRL
voltage increases. Ultimately, above CTRL = 1.2V, the LED
current no longer varies with CTRL. At CTRL = 1.1V, the
actual value of ILED is ~98% of the equation’s estimate.
When VCTRL is higher than 1.2V, the LED current is regu-
lated to:
I
mV
R
LED
=
250
The CTRL pin should not be left open (tie to VREF if not
used). The CTRL pin can also be used in conjunction with
a thermistor to provide overtemperature protection for
the LED load, or with a resistor divider to VIN to reduce
output power and switching current when VIN is low.
The presence of a time varying differential voltage signal
(ripple) across ISP and ISN at the switching frequency
is expected. The amplitude of this signal is increased by
high LED load current, low switching frequency and/or a
smaller value output filter capacitor. Some level of ripple
signal is acceptable: the compensation capacitor on the
VC pin filters the signal so the average difference between
ISP and ISN is regulated to the user-programmed value.
Ripple voltage amplitude (peak-to-peak) in excess of
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LT3957 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Wide Input Voltage Range |
| LT3957A | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Boost, Flyback, SEPIC and Inverting Converter |
| LT3957AEUHE#PBF | 功能描述:IC REG MULTI CONFIG ADJ 5A 36QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:250 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V 輸入電壓:2.05 V ~ 6 V PWM 型:電壓模式 頻率 - 開關(guān):2MHz 電流 - 輸出:500mA 同步整流器:是 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:6-UFDFN 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:6-SON（1.45x1） 產(chǎn)品目錄頁面:1032 (CN2011-ZH PDF) 其它名稱:296-25628-2 |
| LT3957AEUHE#TRPBF | 功能描述:IC REG MULTI CONFIG ADJ 5A 36QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V，1.5V，1.8V，2.5V 輸入電壓:2.7 V ~ 20 V PWM 型:- 頻率 - 開關(guān):- 電流 - 輸出:50mA 同步整流器:是 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬）裸露焊盤 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:10-MSOP 裸露焊盤 |
| LT3957AIUHE#PBF | 功能描述:IC REG MULTI CONFIG ADJ 5A 36QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:250 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V 輸入電壓:2.05 V ~ 6 V PWM 型:電壓模式 頻率 - 開關(guān):2MHz 電流 - 輸出:500mA 同步整流器:是 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:6-UFDFN 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:6-SON（1.45x1） 產(chǎn)品目錄頁面:1032 (CN2011-ZH PDF) 其它名稱:296-25628-2 |
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