数据搜索系统,热门电子元器件搜索 |
|
LTC1159CS-3.3 数据表(PDF) 13 Page - Linear Technology |
|
LTC1159CS-3.3 数据表(HTML) 13 Page - Linear Technology |
13 / 20 page 13 LTC1159/LTC1159-3.3/LTC1159-5 APPLICATIO S I FOR ATIO LTC1159 SENSE+ SENSE – 9 8 1000pF R1 100 Ω R2 100 Ω L RSENSE + COUT R3 LTC1159 • F07 Figure 7. Suppressing Burst Mode Operation low to high to low again, a packet of charge dQ moves from VCC to ground. The resulting dQ/dt is a current out of VCC which is typically much larger than the control circuit current. In continuous mode, IGATECHG ≈ f (QP + QN), where QP and QN are the gate charges of the two MOSFETs. By powering EXTVCC from an output-derived source, the additional VIN current resulting from the driver and control currents will be scaled by a factor of (Duty Cycle)/(Efficiency). For example in a 20V to 5V application, 10mA of VCC current results in approxi- mately 3mA of VIN current. This reduces the mid-current loss from 10% or more (if the driver was powered directly from VIN) to only a few percent. 3. I 2R losses are easily predicted from the DC resistances of the MOSFET, inductor, and current shunt. In con- tinuous mode all of the output current flows through L and RSENSE, but is “chopped” between the P-channel and N-channel MOSFETs. If the two MOSFETs have approximately the same RDS(ON), then the resistance of one MOSFET can simply be summed with the resis- tances of L and RSENSE to obtain I2R losses. For example, if each RDS(ON) = 0.1Ω, RL = 0.15Ω, and RSENSE = 0.05Ω, then the total resistance is 0.3Ω. This results in losses ranging from 3% to 12% as the output current increases from 0.5A to 2A. I2R losses cause the efficiency to roll-off at high output currents. 4. Transition losses apply only to the P-channel MOSFET, and only when operating at high input voltages (typi- cally 20V or greater). Transition losses can be esti- mated from: Transition Loss ≈ 5(VIN)2(IMAX)(CRSS)(f) Other losses including CINandCOUT ESRdissipativelosses, Schottky conduction losses during dead time, and inductor core losses, generally account for less than 2% total additional loss. Auxiliary Windings – Suppressing Burst Mode Operation The LTC1159 synchronous switch removes the normal limitation that power must be drawn from the inductor primary winding in order to extract power from auxiliary windings. With synchronous switching, auxiliary out- puts may be loaded without regard to the primary output load, providing that the loop remains in continuous mode operation. Burst Mode operation can be suppressed at low output currents with a simple external network which cancels the 0.025V minimum current comparator threshold. This tech- nique is also useful for eliminating audible noise from certain types of inductors in high current (IOUT > 5A) applications when they are lightly loaded. An external offset is put in series with the Sense – pin to subtract from the built-in 0.025V offset. An example of this technique is shown in Figure 7. Two 100 Ω resistors are inserted in series with the leads from the sense resistor. With the addition of R3, a current is generated through R1 causing an offset of: VOFFSET = VOUT ) ) R1 R1 + R3 If VOFFSET > 0.025V, the minimum threshold will be cancelled and Burst Mode operation is prevented from occurring. Since VOFFSET is constant, the maximum load current is also decreased by the same offset. Thus, to get back to the same IMAX, the value of the sense resistor must be reduced: RSENSE ≈ m Ω 75 IMAX To prevent noise spikes from erroneously tripping the current comparator, a 1000pF capacitor is needed across the Sense– and Sense+ pins. |
类似零件编号 - LTC1159CS-3.3 |
|
类似说明 - LTC1159CS-3.3 |
|
|
链接网址 |
隐私政策 |
ALLDATASHEETCN.COM |
ALLDATASHEET是否为您带来帮助? [ DONATE ] |
关于 Alldatasheet | 广告服务 | 联系我们 | 隐私政策 | 链接交换 | 制造商名单 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 |