 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LT1107 Datasheet(PDF) 8 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LT1107 Datasheet(HTML) 8 Page - Linear Technology |
|
|
8 / 16 page  8 LT1107 1107fa In this mode the switch is arranged in common collector or step-down mode. The switch drop can be modeled as a 0.75V source in series with a 0.65 Ω resistor. When the switch closes, current in the inductor builds according to: where R ′ = 0.65Ω + DCRL VL = VIN – 0.75V As an example, suppose –5V at 50mA is to be generated from a 4.5V to 5.5V input. Recalling Equation (14), Energy required from the inductor is: Picking an inductor value of 100 µH with 0.2Ω DCR results in a peak switch current of: Substituting IPEAK into Equation (04) results in: Since 5.28 µJ > 3.82µJ, the 100µH inductor will work. With this relatively small input range, RLIM is not usually necessary and the ILIM pin can be tied directly to VIN. As in the step-down case, peak switch current should be limited to ~650mA. Step-Up (Boost Mode) Operation A step-up DC/DC converter delivers an output voltage higher than the input voltage. Step-up converters are not short-circuit protected since there is a DC path from input to output. P f mW kHz J L OSC == 275 63 44 17 .( ) µ It V R e L L Rt L ()= ′ − − ′ 115 () where DC = duty cycle (0.50 in step-down mode) VSW = switch drop in step-down mode VD = diode drop (0.5V for a 1N5818) IOUT = output current VOUT = output voltage VIN = minimum input voltage VSW is actually a function of switch current which is in turn a function of VIN, L, time, and VOUT. To simplify, 1.5V can be used for VSW as a very conservative value. Once IPEAK is known, inductor value can be derived from: where tON = switch ON time (7µs). Next, the current limit resistor RLIM is selected to give IPEAK from the Maximum Switch Current vs RLIM curve. The addition of this resistor keeps maximum switch cur- rent constant as the input voltage is increased. As an example, suppose 5V at 300mA is to be generated from a 12V to 24V input. Recalling Equation (10): Next, inductor value is calculated using Equation (11): L mA sH = −− = 12 1 5 5 600 764 13 . () µµ Use the next lowest standard value (56 µH). Then pick RLIM from the curve. For IPEAK = 600mA, RLIM = 56 Ω. Inductor Selection –– Positive-to-Negative Converter Figure 4 shows hookup for positive-to-negative conver- sion. All of the output power must come from the inductor. In this case, P (14) L =+ ()() VV I OUT D OUT L VV V I t IN MIN SW OUT PEAK ON = −− × () () 11 I mA mA PEAK = () + −+ = 2 300 050 50 5 12 15 05 600 12 . . .. () P = 275mW (16 ) L =− + ()() 50 5 50 VV mA . I VV e mA PEAK s H = − () + () − = − 45 075 065 0 2 1 325 18 085 9 100 .. .. () .• ΩΩ Ωµ µ EH A J L = ()( ) = 1 2 100 0 325 5 28 19 2 µµ .. ( ) S APPLICATI I FOR ATIO |
Similar Part No. - LT1107_15 |
|
Similar Description - LT1107_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
