Electronic Components Datasheet Search |
|
LTC1159CG-5 Datasheet(PDF) 7 Page - Linear Technology |
|
LTC1159CG-5 Datasheet(HTML) 7 Page - Linear Technology |
7 / 20 page 7 LTC1159/LTC1159-3.3/LTC1159-5 APPLICATIO S I FOR ATIO both track IMAX. Once RSENSE has been chosen, IBURST and ISC(PK) can be predicted from the following equations: 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. The LTC1159 Compared to the LTC1148/LTC1149 Families The LTC1159 family is closest in operation to the LTC1149 and shares much of the applications information. In addi- tion to reduced quiescent and shutdown currents, the LTC1159 adds an internal switch which allows the driver and control sections to be powered from an external source for higher efficiency. This change affects Power MOSFET Selection, EXTVCC Pin Connection, Important Information About LTC1159 Adjustable Applications, and Efficiency Considerations found in this section. The basic LTC1159 application circuit shown in Figure 1 is limited to a maximum input voltage of 30V due to MOSFET breakdown. If the application does not require greater than 18V operation, then the LTC1148 or LTC1148HV should be used. For higher input voltages where quiescent and shutdown current are not critical, the LTC1149 may be a better choice since it is set up to drive standard threshold MOSFETs. RSENSE Selection for Output Current RSENSE is chosen based on the required output current. The LTC1159 current comparator has a threshold range which extends from a minimum of 0.025V/RSENSE to a maximum of 0.15V/RSENSE. The current comparator threshold sets the peak of the inductor ripple current, yielding a maximum output current IMAX equal to the peak value less half the peak-to-peak ripple current. For proper Burst Mode opera- tion, IRIPPLE(P-P) must be less than or equal to the minimum current comparator threshold. Since efficiency generally increases with ripple current, the maximum allowable ripple current is assumed, i.e., IRIPPLE(P-P) = 0.025V/RSENSE (see CT and L Selection for Operating Frequency). Solving for RSENSE and allowing a margin for variations in the LTC1159 and external component values yields: RSENSE = m Ω 100 IMAX A graph for selecting RSENSE versus maximum output current is given in Figure 2. The LTC1159 series works well with values of RSENSE from 0.02Ω to 0.2Ω. The load current below which Burst Mode operation com- mences, IBURST, and the peak short-circuit current, ISC(PK), 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: 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 |
Similar Part No. - LTC1159CG-5 |
|
Similar Description - LTC1159CG-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 |