Electronic Components Datasheet Search |
|
ADP3179JRU Datasheet(PDF) 10 Page - Analog Devices |
|
ADP3179JRU Datasheet(HTML) 10 Page - Analog Devices |
10 / 16 page REV. A –10– ADP3159/ADP3179 Surface mount MOSFETs are preferred in CPU core converter applications due to their ability to be handled by automatic assembly equipment. The TO-263 package offers the power handling of a TO-220 in a surface-mount package. However, this package still needs adequate copper area on the PCB to help move the heat away from the package. The junction temperature for a given area of 2-ounce copper can be approximated using: TP T AD A JJ =× ()+ θ (21) assuming: θ JA = 45 °C/W for 0.5 in2 θJA = 36°C/W for 1 in2 θJA = 28°C/W for 2 in2 For 1 in 2 of copper area attached to each transistor and an ambient temperature of 50 °C: TJHSF = (36 °C/W × 1.48 W ) + 50°C = 103°C TJLSF = (36 °C/W × 1.08 W ) + 50°C = 89°C All of the above-calculated junction temperatures are safely below the 175 °C maximum specified junction temperature of the selected MOSFETs. CIN Selection and Input Current di/dt Reduction In continuous inductor-current mode, the source current of the high-side MOSFET is approximately a square wave with a duty ratio equal to VOUT/VIN and an amplitude of one-half of the maximum output current. To prevent large voltage transients, a low ESR input capacitor sized for the maximum rms current must be used. The maximum rms capacitor current is given by: II D D AA C RMS O HSF HSF () . – .. =− = = 2 2 15 0 36 0 36 7 2 (22) For a ZA-type capacitor with 1000 µF capacitance and 6.3 V voltage rating, the ESR is 24 m Ω and the maximum allowable ripple current at 100 kHz is 2 A. At 105 °C, at least four such capacitors must be connected in parallel to handle the calculated ripple current. At 50 °C ambient, however, a higher ripple cur- rent can be tolerated, so three capacitors in parallel are adequate. The ripple voltage across the three paralleled capacitors is: VI ESR n D nC f VA m F kHz mV C IN RIPPLE O CIN C HSF C IN MAX C IN RIPPLE () () () % =× + ×× =× Ω + ×µ × = 15 24 3 36 3 1000 195 129 (23) To further reduce the effect of the ripple voltage on the system supply voltage bus, and to reduce the input-current di/dt to below the recommended maximum of 0.1 A/ms, an additional small inductor (L > 1 µH @ 10 A) should be inserted between the converter and the supply bus. Feedback Compensation for Active Voltage Positioning Optimized compensation of the ADP3159 allows the best pos- sible containment of the peak-to-peak output voltage deviation. Any practical switching power converter is inherently limited by the inductor in its output current slew rate to a value much less than the slew rate of the load. Therefore, any sudden change of load current will initially flow through the output capacitors, and this will produce an output voltage deviation equal to the ESR of the output capacitor array times the load current change. CH2 TEK RUN: 200kS/s SAMPLE 100mV CH1 M 250 s CH2 680mV 2 TRIG'D Figure 4. Transient Response of the Circuit of Figure 3 0 0 2 OUTPUT CURRENT – A 10 20 30 40 50 60 70 80 90 100 46 8 10 12 14 16 18 20 Figure 5. Efficiency vs. Load Current of the Circuit of Figure 3 To correctly implement active voltage positioning, the low fre- quency output impedance (i.e., the output resistance) of the converter should be made equal to the maximum ESR of the output capacitor array. This can be achieved by having a single- pole roll-off of the voltage gain of the gm error amplifier, where the pole frequency coincides with the ESR zero of the output capacitor. A gain with single-pole roll-off requires that the gm amplifier output pin be terminated by the parallel combination of a resistor and capacitor. The required resistor value can be calculated from the equation: R RR RR Mk Mk k COMP OGM TOTAL OGM TOTAL = × = Ω× Ω ΩΩ =Ω – . – . . 19 1 19 1 92 (24) where: R nR gR m mmho m k TOTAL I SENSE m E MAX = × × = ×Ω ×Ω =Ω () . . 25 4 22 5 91 (25) In Equations 24 and 25, ROGM is the internal resistance of the gm amplifier, nI is the division ratio from the output voltage to signal of the gm amplifier to the PWM comparator, and gm is the transconductance of the gm amplifier itself. |
Similar Part No. - ADP3179JRU |
|
Similar Description - ADP3179JRU |
|
|
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 |