 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
EL7571CM-T13 Datasheet(PDF) 10 Page - Intersil Corporation |
|
||||||||||||||||||||||||||||||
EL7571CM-T13 Datasheet(HTML) 10 Page - Intersil Corporation |
|
|
10 / 19 page  10 Input Capacitor, C1 In a buck converter, where the output current is greater than 10A, significant demand is placed on the input capacitor. Under steady state operation, the high side FET conducts only when it is switched “on” and conducts zero current when it is turned “off”. The result is a current square wave drawn from the input supply. Most of this input ripple current is supplied from the input capacitor C1. The current flow through C1’s equivalent series resistance (ESR) can heat up the capacitor and cause premature failure. Maximum input ripple current occurs when the duty cycle is 50%, a current of IOUT/2 RMS. Worst case power dissipation is: where: ERSIN = input capacitor ESR For safe and reliable operation, PD must be less than the capacitor’s data sheet rating. Input Inductor, L2 The input inductor (L2) isolates switching noise from the input supply line by diverting buck converter input ripple current into the input capacitor. Buck regulators generate high levels of input ripple current because the load is connected directly to the supply through the top switch every cycle, chopping the input current between the load current and zero, in proportion to the duty cycle. The input inductor is critical in high current applications where the ripple current is similarly high. An exclusively large input inductor degrades the converter’s load transient response by limiting the maximum rate of change of current at the converter input. A 1.5µH input inductor is sufficient in most applications. Output Capacitor, C2 During steady state operation, output ripple current is much less than the input ripple current since current flow is continuous, either via the top switch or the bottom switch. Consequently, output capacitor power dissipation is less of a concern than the input capacitor’s. However, low ESR is still required for applications with very low output ripple voltage or transient response requirements. Output ripple voltage is given by: where: IRIP = output ripple current ESROUT = output capacitor ESR During a transient response, the output voltage spike is determined by the ESR and the equivalent series inductance (ESL) of the output capacitor in addition to the rate of change and magnitude of the load current step. The output voltage transient is given by: where: ESROUT = output capacitor ESR ESL = output capacitor ESL ∆I OUT = output current step di/dt = rate of change of output current Power MOSFET, Q1 and Q2 The EL7571 incorporates a boot-strap gate drive scheme to allow the usage of N-channel MOSFETs. N-channel MOSFETs are preferred because of their relative low cost and low on resistance. The largest amount of the power loss occurs in the power MOSFETs, thus low on resistance should be the primary characteristic when selecting power MOSFETs. In the boot-strap gate drive scheme, the gate drive voltage can only go as high as the supply voltage, therefore in a 5V system, the MOSFETs must be logic level type, VGS<4.5V. In addition to on resistance and gate to source threshold, the gate to source capacitance is also very important. In the region when the output current is low (below 5A), switching loss is the dominant factor. Switching loss is determined by: where: C is the gate to source capacitance of the MOSFET V is the supply voltage F is the switching frequency Another undesirable reason for a large MOSFET gate to source capacitance is that the on resistance of the MOSFET driver can not supply the peak current required to turn the MOSFET on and off fast. This results in additional MOSFET conduction loss. As frequency increases, this loss also increases which leads to more power loss and lower efficiency. Finally, the MOSFET must be able to conduct the maximum current and handle the power dissipation. The EL7571 is designed to boot-strap to 12V for 12V only input converters. In this application, logic level MOSFETs are not required. The following table below lists a few popular MOSFETs and their critical specifications. P D I OUT 2 ------------- 2 ESR IN • = V RIP I RIP ESR OUT × = ∆V OUT ESR OUT ∆I OUT ESL d i d t ----- × + × = PC V 2 F × × = EL7571 |
Similar Part No. - EL7571CM-T13 |
|
Similar Description - EL7571CM-T13 |
|
|
|
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
