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RT9270 Datasheet(PDF) 11 Page - Richtek Technology Corporation |
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RT9270 Datasheet(HTML) 11 Page - Richtek Technology Corporation |
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11 / 13 page  RT9270 Preliminary 11 DS9270-09 March 2007 www.richtek.com Output Voltage The regulated output voltage is calculated by : For most applications, R2 is a suggested a value up to 100k Ω. Place the resistor-divider as close to the IC as possible to reduce the noise sensitivity. Loop Compensation The RT9270 voltage feedback loop can be compensated with an external compensation network consisted of R3, C3 and C4 (As shown in Figure 1). Choose R3 to set the high-frequency integrator gain for fast transient response without over or under compensation. Once R3 is determined, C3 is selected to set the integrator zero to maintain loop stability. The purpose of C4 is to cancel the zero caused by output capacitor and the capacitor ESR. If the ceramic capacitor is selected to be the output capacitor, C4 can be taken off because of the small ESR. C2 is the output capacitor as shown in Figure 1. The following equations give approximate calculations of each component : The best criterion to optimize the loop compensation is by inspecting the transient response and adjusting the compensation network. Soft-Start Capacitor The soft-start function begins from VSS=0V to VSS=1.24V with a 4uA constant current charging to the soft-start capacitor, so the capacitor should be large enough to let the output voltage reach regulation inside the soft-start cycle. Typical value of soft-start capacitor range is from 10nF to 200nF. After the cycle finished, the load can start to draw maximum current as required. Layout Guideline For high frequency switching power supplies, the PCB layout is important step in system application design. In order to let IC achieve good regulation, high efficiency and stability, it is strongly recommended the power components should be placed as close as possible. These traces should be wide and short. The feedback pin and the networks of feedback and compensation should be kept away from the power loops, and be shielded with a ground trace or plane to prevent noise coupling. ≅× × OUT RIPPLE RIPPLE(ESR) RIPPLE(C) PEAK OUT IN PEAK C OUT OUT OSC V= V + V IV - V I ESR + ( ) CV f × OUT R1 V = 1.24V (1+ ) R2 × × ×× ×× ×× × -12 -6 O IN ESR 2 C3 = 10 C2 RL VL1 C2 R3 = 2C3 V C4 = C2 R 1 10 (F) (F) ( Ω) |
Similar Part No. - RT9270 |
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Similar Description - RT9270 |
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