 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LT1578IS8 Datasheet(PDF) 8 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LT1578IS8 Datasheet(HTML) 8 Page - Linear Technology |
|
|
8 / 28 page  8 LT1578/LT1578-2.5 APPLICATIONS INFORMATION Figure 2. Frequency and Current Limit Foldback – + 1.21V VSW VC GND TO SYNC CIRCUIT 1578 F02 TO FREQUENCY SHIFTING R3 1k R4 1k R1 R2 5k OUTPUT 5V R5 5k ERROR AMPLIFIER FB 1.4V Q1 LT1578 Q2 + FEEDBACK PIN FUNCTIONS The feedback (FB) pin on the LT1578 is used to set output voltage and provide several overload protection features. The first part of this section deals with selecting resistors to set output voltage and the remaining part talks about foldback frequency and current limiting created by the FB pin. Please read both parts before committing to a final design. The fixed 2.5V LT1578-2.5 has internal divider resistors and the FB pin, renamed SENSE, is connected directly to the 2.5V output. The suggested value for the output divider resistor (see Figure 2) from FB to ground (R2) is 5k or less, and a formula for R1 is shown below. The output voltage error caused by ignoring the input bias current on the FB pin is less than 0.25% with R2 = 5k. Please read the following if divider resistors are increased above the suggested values. R RVOUT 1 21 21 121 = − () . . More Than Just Voltage Feedback The feedback pin is used for more than just output voltage sensing. It also reduces switching frequency and current limit when output voltage is very low (see the Frequency Foldback graph in Typical Performance Characteristics). This is done to control power dissipation in both the IC and the external diode and inductor during short-circuit con- ditions. A shorted output requires the switching regulator to operate at very low duty cycles, and the average current through the diode and inductor is equal to the short-circuit current limit of the switch (typically 2A for the LT1578, folding back to less than 0.77A). Minimum switch on time limitations would prevent the switcher from attaining a sufficiently low duty cycle if switching frequency were maintained at 200kHz, so frequency is reduced by about 5:1 when the feedback pin voltage drops below 0.7V (see Frequency Foldback graph). This does not affect operation with normal load conditions; one simply sees a gear shift in switching frequency during start-up as the output voltage rises. |
Similar Part No. - LT1578IS8 |
|
Similar Description - LT1578IS8 |
|
|
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
