 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC1159IS-5 Datasheet(PDF) 8 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC1159IS-5 Datasheet(HTML) 8 Page - Linear Technology |
|
|
8 / 20 page  8 LTC1159 LTC1159-3.3/LTC1159-5 MAXIMUM OUTPUT CURRENT (A) 0 0.12 0.16 0.20 4 LTC1159 • F02 0.08 0.04 0 1 2 3 5 0.10 0.14 0.18 0.06 0.02 Figure 2. RSENSE vs Maximum Output Current APPLICATIO S I FOR ATIO IBURST ≈ 15mV RSENSE ISC(PK) = 150mV RSENSE The LTC1159 automatically extends tOFF during a short circuit to allow sufficient time for the inductor current to decay between switch cycles. The resulting ripple current causes the average short-circuit current ISC(AVG) to be reduced to approximately IMAX. L and CT Selection for Operating Frequency The LTC1159 uses a constant off-time architecture with tOFF determined by an external timing capacitor CT. The value of CT is calculated from the desired continuous mode operating frequency, f: CT = 7.8 • 10–5 f ) )1– VOUT VIN A graph for selecting CT versus frequency including the effects of input voltage is given in Figure 3. As the operating frequency is increased the gate charge losses will be higher, reducing efficiency (see Efficiency Considerations). The complete expression for operating frequency is given by: f = 1 tOFF ) )1– VOUT VIN where tOFF = 1.3 • 104 • CT Once the frequency has been set by CT, the inductor L must be chosen to provide no more than 0.025V/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 LTC1159 may not enter Burst Mode operation and efficiency will be severely degraded at low currents. Inductor Core Selection Once the minimum value for L is known, the type of inductor must be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores, forcing the use of more expensive ferrite, molypermalloy or Kool M µ® cores. Actual core loss is independent of core size for a fixed inductor value, but it is very dependent on the inductance selected. As induc- tance increases, core losses go down but copper (I2R) losses will increase. Ferrite designs have very low core loss, so design goals can concentrate on copper loss and preventing saturation. Ferrite core material saturates “hard,” which means that inductance collapses abruptly when the peak design cur- rent is exceeded. This results in an abrupt increase in FREQUENCY (kHz) 0 0 200 400 600 1400 1000 50 100 1200 800 150 200 250 VOUT = 5V VIN = 48V VIN=12V VIN = 24V LTC1159 • F03 Figure 3. Timing Capacitor Selection Kool M µ is a registered trademark of Magnetics, Inc. |
Similar Part No. - LTC1159IS-5 |
|
Similar Description - LTC1159IS-5 |
|
|
|
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
