 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LT3755-1 Datasheet(PDF) 11 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LT3755-1 Datasheet(HTML) 11 Page - Linear Technology |
|
|
11 / 26 page  LT3755/LT3755-1/LT3755-2 37551fd applicaTions inForMaTion INTVCC Regulator Bypassing and Operation The INTVCC pin requires a capacitor for stable operation and to store the charge for the large GATE switching cur- rents. Choose a 10V rated low ESR, X7R or X5R ceramic capacitor for best performance. A 4.7µF 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 LT3755 from excessive on-chip power dissipation. The minimum value of this current should be considered when choosing the switching NMOS and the operating frequency. IINTVCC can be calculated from the following equation: IINTVCC = QG • fOSC Careful choice of a lower QG FET will allow higher switch- ing frequencies, leading to smaller magnetics. The INTVCC pin has its own undervoltage disable (UVLO) set to 4.1V (typical) to protect the external FETs from excessive power dissipation caused by not being fully enhanced. If the INTVCC pin drops below the UVLO threshold, the GATE and PWMOUT pins will be forced to 0V and the soft-start pin will be reset. If the input voltage, VIN, will not exceed 8V, then the IN- TVCC pin could be connected to the input supply. Be aware that a small current (less than 12μA) will load the INTVCC in shutdown. This action allows the LT3755 to operate from VIN as low as 4.5V. If VIN is normally above, but occasionally drops below the INTVCC regulation voltage, then the minimum operating VIN will be close to 6V. This value is determined by the dropout voltage of the linear regulator and the INTVCC undervoltage lockout threshold mentioned above. Programming the Turn-On and Turn-Off Thresholds with the SHDN/UVLO Pin ThefallingUVLOvaluecanbeaccuratelysetbytheresistor divider. A small 2.1µA pull-down current is active when SHDN/UVLO is below the threshold. The purpose of this currentistoallowtheusertoprogramtherisinghysteresis. SHDN/UVLO LT3755 VIN R2 37551 F01 R1 Figure 1. Resistor Connection to Set VIN Undervoltage Shutdown Threshold The following equations should be used to determine the values of the resistors: VIN,FALLING =1.22• R1 +R2 R2 V IN,RISING = 2.1µA •R1 + VIN,FALLING LED Current Programming The LED current is programmed by placing an appropriate value current sense resistor, RLED, in series with the LED string. The voltage drop across RLED is (Kelvin) sensed by 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 100mV (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: ILED = VCTRL − 100mV RLED • 10 WhentheCTRLpinvoltageisbetween1Vand1.2VtheLED current varies with CTRL, but departs from the equation abovebyanincreasingamountasCTRLvoltageincreases. 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. |
Similar Part No. - LT3755-1_15 |
|
Similar Description - LT3755-1_15 |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.NET |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
