 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LT3487 Datasheet(PDF) 11 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LT3487 Datasheet(HTML) 11 Page - Linear Technology |
|
|
11 / 16 page  LT3487 11 3487f Figure 4. VCE vs I of Output Disconnect Choosing a Feedback Node The positive channel feedback resistor, R1, may be con- nected to the VPOS pin or to the CAP pin (see Figure 5). Regulating the VPOS pin eliminates the output offset result- ing from the voltage drop across the output disconnect. However, in the case of a short-circuit fault at the VPOS pin, the LT3487 will switch continuously because the FBP pin is low. While operating in this open-loop condition, the rising voltage at the CAP pin is limited only by the current limit of the output disconnect. Given worst-case parameters this voltage may reach 18V in a Li-Ion application. Care must be taken in high VIN applications when regulating from the VPOS pin. When the short-circuit is removed, the VPOS pin will bounce up to the voltage on the CAP pin, potentially exceeding the programmed output voltage until the capacitor voltages fall back into regulation. While this is harmless to the LT3487, this should be considered in the context of the external circuitry if short-circuit events are expected. Regulating the CAP pin ensures that the voltage on the VPOS pin never exceeds the set output volt- age after a short-circuit event. However, this setup does not compensate for the voltage drop across the output disconnect, resulting in an output voltage that is slightly lower than the voltage set by the feedback resistor. This voltage drop (VDISC) can be accounted for when using the CAP pin as the feedback node by setting the output voltage according to the following formula (using VDISC from Figure 4): R V µA DISC 1 123 25 = + VPOS –. VBAT The VBAT pin is a new innovation in the LT3487 that allows output disconnect operation in a wide range of applica- tions. The VBAT pin allows the part to stay on until CAP is less than 1.2V above VBAT. This ensures that the positive bias doesn’t fall before the negative bias discharges. In some applications it may be useful to power the inductors from a different source than VIN. In this case, connect VBAT to the source powering the inductors to allow proper operation of the disconnect. For example, in an automotive system there may already be a buck regulator producing 3.3V from a 12V battery. The LT3487 enables the user to power VIN from the 3.3V rail, but power the VBAT pin APPLICATIO S I FOR ATIO Figure 5. Feedback Connection Using the VPOS and CAP Pins DISCONNECT CURRENT (mA) 0 0 50 100 150 200 250 300 20 40 60 80 2400 G31 100 SWN VIN CAP FBP VPOS VBAT LT3487 GND SWP DN FBN RUN/SS 3487 F05 VPOS SWN VIN CAP FBP VPOS VBAT LT3487 GND SWP DN FBN RUN/SS VPOS |
Similar Part No. - LT3487_15 |
|
Similar Description - LT3487_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
