 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC1147CN8-5 Datasheet(PDF) 8 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC1147CN8-5 Datasheet(HTML) 8 Page - Linear Technology |
|
|
8 / 16 page  8 LTC1147-3.3 LTC1147-5/LTC1147L sn1147 1147fds series will delay entering Burst Mode operation and effi- ciency will be degraded at low currents. Inductor Core Selection Once the minimum value for L is known, the type of inductor must be selected. Highest efficiency will be obtained using ferrite, Kool M µ® (from Magnetics, Inc.) or molypermalloy (MPP) cores. Lower cost powdered iron cores provide suitable performance but cut efficiency by 3% to 5%. Actual core loss is independent of core size for a fixed inductor value, but it is very dependent on induc- tance selected. As inductance increases, core losses go down. Unfortunately, increased inductance requires more turns of wire and therefore copper losses will increase. Ferrite designs have very low core loss, so design goals can concentrate on copper loss and preventing satura- tion. Ferrite core material saturates “hard,” which means that inductance collapses abruptly when the peak design current is exceeded. This results in an abrupt increase in inductor ripple current and consequent output voltage ripple which can cause Burst Mode operation to be falsely triggered in the LTC1147. Do not allow the core to saturate! Kool M µ is a very good, low loss core material for toroids with a “soft” saturation characteristic. Molypermalloy is slightly more efficient at high (>200kHz) switching fre- quencies but quite a bit more expensive. Toroids are very space efficient, especially when you can use several layers of wire. Because they generally lack a bobbin, mounting is more difficult. However, new designs for surface mount are available from Coiltronics, Sumida and Beckman Industrial Corp. which do not increase the height significantly. Power MOSFET Selection An external P-channel power MOSFET must be selected for use with the LTC1147 series. The main selection criteria for the power MOSFET are the threshold voltage VGS(TH) and “on” resistance RDS(ON). The minimum input voltage determines whether a stan- dard threshold or logic-level threshold MOSFET must be FREQUENCY (kHz) 0 0 200 400 600 100 200 LTC1147 • F03 800 1000 300 VSENSE– = VOUT = 5V VIN = 10V VIN = 7V VIN = 12V Figure 3. Timing Capacitor Value is given by: f ≈ 1 tOFF ) )1– VOUT VIN where: tOFF = (1.3)(104)(CT) ) )VREG VOUT VREG is the desired output voltage (i.e., 5V, 3.3V). VOUT is the measured output voltage. Thus VREG/VOUT = 1 in regulation. Note that as VIN decreases, the frequency decreases. When the input to output voltage differential drops below 1.5V, the LTC1147 reduces tOFF by increasing the discharge current in CT. This prevents audible opera- tion prior to dropout. Once the frequency has been set by CT, the inductor L must be chosen to provide no more than 25mV/RSENSE of peak-to-peak inductor ripple current. This results in a minimum required inductor value of: LMIN = (5.1)(105)(RSENSE)(CT)(VREG) As the inductor value is increased from the minimum value, the ESR requirements for the output capacitor are eased at the expense of efficiency. If too small an inductor is used, the inductor current will become discontinuous before the LTC1147 series enters Burst Mode operation. A consequence of this is that the LTC1147 Kool M µ is a registered trademark of Magnetics, Inc. APPLICATIO S I FOR ATIO |
Similar Part No. - LTC1147CN8-5 |
|
Similar Description - LTC1147CN8-5 |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.NET |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | 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
