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IRU3037ACS Datasheet(PDF) 7 Page - International Rectifier |
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IRU3037ACS Datasheet(HTML) 7 Page - International Rectifier |
7 / 21 page IRU3037 / IRU3037A 7 Rev. 2.8 03/10/03 www.irf.com For this design, IRF7301 is a good choice. The device provides low on-resistance in a compact SOIC 8-Pin package. The IRF7301 has the following data: The total conduction losses will be: The switching loss is more difficult to calculate, even though the switching transition is well understood. The reason is the effect of the parasitic components and switching times during the switching procedures such as turn-on / turnoff delays and rise and fall times. With a linear approximation, the total switching loss can be ex- pressed as: The switching time waveform is shown in figure 4. Figure 4 - Switching time waveforms. From IRF7301 data sheet we obtain: These values are taken under a certain condition test. For more detail please refer to the IRF7301 data sheet. By using equation (6), we can calculate the switching losses. Feedback Compensation The IRU3037 is a voltage mode controller; the control loop is a single voltage feedback path including error amplifier and error comparator. To achieve fast transient response and accurate output regulation, a compensa- tion circuit is necessary. The goal of the compensation network is to provide a closed loop transfer function with the highest 0dB crossing frequency and adequate phase margin (greater than 45 8). The output LC filter introduces a double pole, –40dB/ decade gain slope above its corner resonant frequency, and a total phase lag of 180 8 (see Figure 5). The Reso- nant frequency of the LC filter expressed as follows: Figure 5 shows gain and phase of the LC filter. Since we already have 180 8 phase shift just from the output filter, the system risks being unstable. Figure 5 - Gain and phase of LC filter. The IRU3037’s error amplifier is a differential-input transconductance amplifier. The output is available for DC gain control or AC phase compensation. The E/A can be compensated with or without the use of local feedback. When operated without local feedback the transconductance properties of the E/A become evi- dent and can be used to cancel one of the output filter poles. This will be accomplished with a series RC circuit from Comp pin to ground as shown in Figure 6. VDSS = 20V ID = 5.2A RDS(ON) = 0.05 V Where: VDS(OFF) = Drain to Source Voltage at off time tr = Rise Time tf = Fall Time T = Switching Period ILOAD = Load Current tr = 42ns tf = 51ns PSW = 0.186W PCON(TOTAL)=PCON(Upper Switch)+PCON(Lower Switch) PCON(TOTAL) = ILOAD 3 RDS(ON) 3 q 2 q = 1.5 according to the IRF7301 data sheet for 150 8C junction temperature PCON(TOTAL) = 1.2W FLC = ---(7) 1 2 p3 LO 3CO PSW = ILOAD ---(6) tr + tf T VDS(OFF) 2 3 3 VDS VGS 10% 90% td(ON) td(OFF) tr tf Gain FLC 0dB Phase 0 8 FLC -180 8 Frequency Frequency -40dB/decade |
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