Electronic Components Datasheet Search |
|
ISL6224 Datasheet(PDF) 9 Page - Intersil Corporation |
|
ISL6224 Datasheet(HTML) 9 Page - Intersil Corporation |
9 / 13 page 9 FN9042.8 June 8, 2006 could cancel the usefulness of these low inductance components. Consult with the manufacturer of the load circuitry for specific decoupling requirements. Use only specialized low-ESR capacitors intended for switching-regulator applications, at 300kHz, for the bulk capacitors. In most cases, multiple electrolytic capacitors of small case size perform better than a single large case capacitor. The stability requirement on the selection of the output capacitor is that the ‘ESR zero’, fZ, be between 1.2kHz and 30kHz. This range is set by an internal, single compensation zero at 6kHz. The ESR zero can be a factor of five on either side of the internal zero and still contribute to increased phase margin of the control loop. Therefore: In conclusion, the output capacitors must meet three criteria: 1. They must have sufficient bulk capacitance to sustain the output voltage during a load transient while the output inductor current is slewing to the value of the load transient 2. The ESR must be sufficiently low to meet the desired output voltage ripple due to the output inductor current, and 3. The ESR zero should be placed, in a rather large range, to provide additional phase margin. Output Inductor Selection The output inductor is selected to meet the output voltage ripple requirements. The inductor value determines the converter’s ripple current and the ripple voltage is a function of the ripple current and output capacitor(s) ESR. The ripple voltage expression is given in the capacitor selection section and the ripple current is approximated by the following equation: where Fs is the switching frequency. Input Capacitor Selection The important parameters for the bulk input capacitor(s) are the voltage rating and the RMS current rating. For reliable operation, select bulk input capacitors with voltage and current ratings above the maximum input voltage and largest RMS current required by the circuit. The capacitor voltage rating should be at least 1.25 times greater than the maximum input voltage and 1.5 times is a conservative guideline. The AC RMS input current varies with load. Depending on the specifics of the input power and it’s impedance, most (or all) of this current is supplied by the input capacitor(s). Use a mix of input bypass capacitors to control the voltage ripple across the MOSFETs. Use ceramic capacitors for the high frequency decoupling and bulk capacitors to supply the RMS current. Small ceramic capacitors can be placed very close to the upper MOSFET to suppress the voltage induced in the parasitic circuit impedances. For board designs that allow through-hole components, the Sanyo OS-CON® series offer low ESR and good temperature performance. For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rating. These capacitors must be capable of handling the surge-current at power-up. The TPS series available from AVX is surge current tested. MOSFET Considerations The logic level MOSFETs are chosen for optimum efficiency given the potentially wide input voltage range and output power requirements. One dual N-Channel or two N-Channel MOSFETs are used in each of the synchronous rectified buck converters for the outputs. These MOSFETs should be selected based upon rDS(ON) , gate supply requirements, and thermal management considerations. The power dissipation includes two loss components; conduction loss and switching loss. These losses are distributed between the upper and lower MOSFETs according to duty cycle (see the following equations). The conduction losses are the main component of power dissipation for the lower MOSFETs. Only the upper MOSFET has significant switching losses, since the lower device turns on and off into near-zero voltage. The equations assume linear voltage-current transitions and do not model power loss due to the reverse-recovery of the lower MOSFET’s body diode. The gate-charge losses are dissipated by the ISL6224 and do not heat the MOSFETs. However, a large gate-charge increases the switching time, tSW which increases the upper MOSFET switching losses. Ensure that both MOSFETs are within their maximum junction temperature at high ambient temperature by calculating the temperature rise according to package thermal-resistance specifications. C OUT 1 2 π ESR f Z × × × ------------------------------------------- = ∆IL V IN V OUT – F S L × -------------------------------- V OUT V IN ---------------- × = P UPPER I O 2 r DS ON () × V OUT × V IN ------------------------------------------------------------ I O V IN × t SW × F S × 2 ---------------------------------------------------- + = P LOWER I O 2 r DS ON () × V IN V OUT – () × V IN --------------------------------------------------------------------------------- = ISL6224 |
Similar Part No. - ISL6224_06 |
|
Similar Description - ISL6224_06 |
|
|
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 |