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XR76203-Q Datasheet(PDF) 15 Page - Exar Corporation |
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XR76203-Q Datasheet(HTML) 15 Page - Exar Corporation |
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15 / 20 page  XR76203-Q/XR76205-Q/XR76208-Q 15 / 20 exar.com/XR76203-Q/XR705-Q/XR76208-Q Rev 1C ©2016-2017 Exar Corporation Feed-Forward Capacitor (CFF) A feed-forward capacitor (CFF) may be necessary depend- ing on the Equivalent Series Resistance (ESR) of COUT. If only ceramic output capacitors are used for COUT then a CFF is necessary. Calculate CFF from: where: R1 is the resistor that CFF is placed in parallel with fLC is the frequency of output filter double-pole fLC frequency must be less than 11kHz when using ceramic COUT. If necessary, increase L and/or COUT in order to meet this constraint. When using capacitors with higher ESR, such as PANA- SONIC TPE series, a CFF is not required provided following conditions are met: 1. The frequency of output filter LC double-pole fLC should be less than 11kHz. 2. The frequency of ESR Zero fZero,ESR should be at least five times larger than fLC. Note that if fZero,ESR is less than 5xfLC, then it is recom- mended to set the fLC at less than 2kHz. CFF is still not required. Maximum Allowable Voltage Ripple at FB pin Note that the steady-state voltage ripple at feedback pin FB (VFB,RIPPLE) must not exceed 50mV in order for the Regu- lator to function correctly. If VFB,RIPPLE is larger than 50mV then COUT should be increased as necessary in order to keep the VFB,RIPPLE below 50mV. Feed-Forward Resistor (RFF) Poor PCB layout can cause FET switching noise at the out- put and may couple to the FB pin via CFF. Excessive noise at FB will cause poor load regulation. To solve this problem place a resistor RFF in series with CFF. RFF value up to 2% of R1 is acceptable. CFF 1 2 R17 fLC ------------------------------------------------ = |
Similar Part No. - XR76203-Q |
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Similar Description - XR76203-Q |
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