数据搜索系统,热门电子元器件搜索 |
|
LTC3704 数据表(PDF) 17 Page - Linear Technology |
|
LTC3704 数据表(HTML) 17 Page - Linear Technology |
17 / 28 page 17 LTC3704 sn3704 3704fs The RTH(JA) to be used in this equation normally includes the RTH(JC) for the device plus the thermal resistance from the case to the ambient temperature (RTH(CA)). This value of TJ can then be compared to the original, assumed value used in the iterative calculation process. Output Diode Selection To maximize efficiency, a fast switching diode with low forward drop and low reverse leakage is desired. The output diode in a positive-to-negative converter conducts current during the switch off-time. The peak reverse voltage that the diode must withstand is equal to VIN(MAX) – VO. The average forward current in normal operation is equal to the output current, and the peak current is equal to the peak inductor current. II D D PEAK O MAX MAX () ( ) –• – =+ 1 2 1 1 χ The power dissipated by the diode is: PD = IO(MAX) • VD and the diode junction temperature is: TJ = TA + PD • RTH(JA) The RTH(JA) to be used in this equation normally includes the RTH(JC) for the device plus the thermal resistance from the board to the ambient temperature in the enclosure. Remember to keep the diode lead lengths short and to observe proper switch-node layout (see Board Layout Checklist) to avoid excessive ringing and increased dissipation. Selecting the DC Coupling Capacitor The voltage on the coupling capacitor in a positive-to- negative converter is VIN(MAX) – VO, plus any additional ∆V due to the ripple currents in the inductors. Generally, the DC coupling capacitor is dimensioned based on the high RMS ripple which flows in it, as shown in Figure 13. The minimum RMS current rating of this capacitor must exceed: II D D RMS CAP O MAX MAX MAX () ( ) –• – = 1 A low ESR and ESL, X5R- or X7R-type ceramic capacitor is recommended here. Selecting the Output Capacitor The output ripple voltage appears as a triangular wave- form riding on VO, due to the ripple current of L2 (the DC component of the current in L2 equals the output current). This ripple current flows through the ESR and bulk capaci- tance of the output capacitor to produce the overall ripple voltage on this node. Using the off-time to calculate this ripple current results in the following equation for ∆IL2: ∆I D f V L L MAX O 2 1 2 = – – • where VO is a negative number. The output ripple voltage is therefore: ∆V D f V L ESR fC OP P MAX O O (– ) – • –– •• = 1 2 1 8 The ESR can be minimized by using high quality, X5R- or X7R-dielectric ceramic capacitor in parallel with a larger value tantalum or aluminum electrolytic bulk capacitor. Depending upon the application, it may be that the ceramic capacitor alone will be sufficient. The RMS ripple current rating of the output capacitor needs to be greater than: APPLICATIO S I FOR ATIO Figure 13. Ripple Current in the DC Coupling Capacitor 1A/DIV 500ns/DIV 3704 F13 |
类似零件编号 - LTC3704 |
|
类似说明 - LTC3704 |
|
|
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 |