 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LT1375 Datasheet(PDF) 9 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LT1375 Datasheet(HTML) 9 Page - Linear Technology |
|
|
9 / 28 page  9 LT1375/LT1376 13756fd APPLICATIONS INFORMATION – + 2.4V VSW VC GND 1375/76 F02 TO FREQUENCY SHIFTING R3 1k R4 1k R1 R2 5k OUTPUT 5V R5 5k ERROR AMPLIFIER FB 1.6V Q1 LT1375/LT1376 Q2 + Figure 2. Frequency and Current Limit Foldback Please read the following if divider resistors are increased above the suggested values. R RVOUT 1 22 42 242 = − () . . Table 1 OUTPUT R1 % ERROR AT OUTPUT VOLTAGE R2 (NEAREST 1%) DUE TO DISCREET 1% (V) (k Ω)(kΩ) RESISTOR STEPS 3 4.99 1.21 + 0.23 3.3 4.99 1.82 + 0.08 5 4.99 5.36 + 0.39 6 4.99 7.32 – 0.5 8 4.99 11.5 – 0.04 10 4.99 15.8 + 0.83 12 4.99 19.6 – 0.62 15 4.99 26.1 + 0.52 More Than Just Voltage Feedback The feedback (FB) 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 Char- acteristics). This is done to control power dissipation in both the IC and in the external diode and inductor during short-circuit conditions. 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 (typi- cally 2A for the LT1376, folding back to less than 1A). Minimum switch on time limitations would prevent the switcher from attaining a sufficiently low duty cycle if switching frequency were maintained at 500kHz, so fre- quency is reduced by about 5:1 when the feedback pin voltage drops below 1V (see Frequency Foldback graph). This does not affect operation with normal load condi- tions; one simply sees a gear shift in switching frequency during start-up as the output voltage rises. In addition to lower switching frequency, the LT1376 also operates at lower switch current limit when the feedback pin voltage drops below 1.7V. Q2 in Figure 2 performs this function by clamping the VC pin to a voltage less than its normal 2.3V upper clamp level. This foldback current limit greatly reduces power dissipation in the IC, diode and inductor during short-circuit conditions. Again, it is nearly transparent to the user under normal load conditions. The only loads which may be affected are current source loads which maintain full load current with output voltage less than 50% of final value. In these rare situations the Feedback pin can be clamped above 1.5V with an external diode to defeat foldback current limit. Caution: clamping the feedback pin means that frequency shifting will also be defeated, so a combination of high input voltage and dead shorted output may cause the LT1376 to lose control of current limit. The internal circuitry which forces reduced switching frequency also causes current to flow out of the feedback |
Similar Part No. - LT1375_15 |
|
Similar Description - LT1375_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
