 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LT3475 Datasheet(PDF) 8 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LT3475 Datasheet(HTML) 8 Page - Linear Technology |
|
|
8 / 20 page  LT3475/LT3475-1 8 3475fb Open Circuit Protection The LT3475 has internal open-circuit protection. If the LED is absent or is open circuit, the LT3475 clamps the voltage on the LED pin at 14V. The switching regulator then oper- ates at a very low frequency to limit the input current. The LT3475-1 has no internal open circuit protection. With the LT3475-1, be careful not to violate the ABSMAX voltage of th BOOST pin; if VIN > 25V, external open circuit protection circuitry (as shown in Figure 1) may be necessary.The output voltage during an open LED condition is shown in the Typical Performance Characteristics section. Undervoltage Lockout Undervoltage lockout (UVLO) is typically used in situations where the input supply is current limited, or has high source resistance. A switching regulator draws constant power from the source, so the source current increases as the source voltage drops. This looks like a negative resistance load to the source and can cause the source to current limit or latch low under low source voltage conditions. UVLO prevents the regulator from operating at source voltages where these problems might occur. An internal comparator will force the part into shut- down when VIN falls below 3.7V. If an adjustable UVLO threshold is required, the SHDN pin can be used. The threshold voltage of the SHDN pin comparator is 2.6V. An internal resistor pulls 9μA to ground from the SHDN pin at the UVLO threshold. Choose resistors according to the following formula: R2 = 2.6V VTH –2.6V R1 –9μA VTH = UVLO Threshold Example: Switching should not start until the input is above 8V. VTH = 8V R1=100k R2 = 2.6V 8V – 2.6V 100k –9μA = 57.6k Figure 2. Undervoltage Lockout GND 9μA 2.6V VIN VC LT3475 R1 C1 R2 VIN SHDN 3475 F02 Table 1. Switching Frequencies SWITCHING FREQUENCY (MHz) RT (kΩ) 2 4.32 1.5 6.81 1.2 9.09 1 11.8 0.8 16.9 0.6 24.3 0.4 40.2 0.3 57.6 0.2 100 Keep the connections from the resistors to the SHDN pin short and make sure the coupling to the SW and BOOST pins is minimized. If high resistance values are used, the SHDN pin should be bypassed with a 1nF capacitor to prevent coupling problems from switching nodes. Setting the Switching Frequency The LT3475 uses a constant frequency architecture that can be programmed over a 200kHz to 2MHz range with a single external timing resistor from the RT pin to ground. A graph for selecting the value of RT for a given operating frequency is shown in the Typical Applications section. VC 100k 10k 22V OUT 3475 F01 Figure 1. External Overvoltage Protection Circuitry for the LT3475-1 APPLICATIONS INFORMATION |
Similar Part No. - LT3475_15 |
|
Similar Description - LT3475_15 |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | 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
