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SC4525DEVB датащи(PDF) 15 Page - Semtech Corporation |
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SC4525DEVB датащи(HTML) 15 Page - Semtech Corporation |
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15 / 21 page ![]() © 2011 Semtech Corp. www.semtech.com SC4525D 15 Applications Information (Cont.) (13) The temperature rise of the SC4525D is the product of the total power dissipation (Equation (13)) and q JA (36 o C/W), which is the thermal impedance from junction to ambient for the SOIC-8 EDP package. It is not recommended to operate the SC4525D above 125oC junction temperature. PCB Layout Considerations In a step-down switching regulator, the input bypass capacitor, the main power switch and the freewheeling diode carry pulse current (Figure 9). For jitter-free operation,thesizeoftheloopformedbythesecomponents should be minimized. Since the power switch is already integrated within the SC4525D, connecting the anode of the freewheeling diode close to the negative terminal of the input bypass capacitor minimizes size of the switched current loop. The input bypass capacitor should be placed close to the IN pin. Shortening the traces of the SW and BST nodes reduces the parasitic trace inductance at these nodes. This not only reduces EMI but also decreases switching voltage spikes at these nodes. The exposed pad should be soldered to a large ground plane as the ground copper acts as a heat sink for the device. To ensure proper adhesion to the ground plane, avoid using vias directly under the device. O C E S AT C I V D P ⋅ ⋅ = 40 I V D P O B S T B S T ⋅ ⋅ = DC 2 O IND R I ) 3 . 1 ~ 1 . 1 ( P ⋅ ⋅ = O D D I V ) D 1 ( P ⋅ ⋅ − = S W O IN S S W F I V t 2 1 P ⋅ ⋅ ⋅ ⋅ = Q B S T S W C T OT AL P P P P P + + + = mA 2 V P IN Q ⋅ = O C E S AT C I V D P ⋅ ⋅ = 40 I V D P O B S T B S T ⋅ ⋅ = DC 2 O IND R I ) 3 . 1 ~ 1 . 1 ( P ⋅ ⋅ = O D D I V ) D 1 ( P ⋅ ⋅ − = S W O IN S S W F I V t 2 1 P ⋅ ⋅ ⋅ ⋅ = Q B S T S W C T OT AL P P P P P + + + = mA 2 V P IN Q ⋅ = Figure 9. Heavy lines indicate the critical pulse current loop. Thes stray inductance of this loop should be minimized. Vout Vin + + Currents in Power Section IN V OUT V L Z Vout Vin + + Currents in Power Section IN V OUT V L Z |
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