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NCV47700 データシート(PDF) 10 Page - ON Semiconductor |
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NCV47700 データシート(HTML) 10 Page - ON Semiconductor |
10 / 12 page NCV47700 www.onsemi.com 10 The output voltage is calculated from the following formula. Ignoring the bias current into the ADJ pin: Vout + VREF1 1 ) R 1 R 2 (eq. 2) Use R2 < 50 k W to avoid significant voltage output errors due to ADJ bias current. Designers should consider the tolerance of R1 and R2 during the design phase. Setting the Output Current Limit The output current limit can be set between 10 mA and 350 mA by external resistor RCSO (see Figure 1). Capacitor CCSO of 1 mF in parallel with RCSO is required for stability of current limit control circuitry (see Figure 1). V CSO + Iout RCSO 1 100 (eq. 3) I LIM + 100 1 2.55 R CSO (eq. 4) R CSO + 100 1 2.55 I LIM (eq. 5) Where RCSO − current limit setting resistor VCSO − voltage at CSO pin proportional to Iout ILIM − current limit value Iout − output current actual value CSO pin provides information about output current actual value. The CSO voltage is proportional to output current according to Equation 3. Once output current reaches its limit value (ILIM) set by external resistor RCSO than voltage at CSO pin is typically 2.55 V. Calculations of ILIM or RCSO values can be done using equations Equation 4 and Equation 5, respectively. Thermal Considerations As power in the NCV47700 increases, it might become necessary to provide some thermal relief. The maximum power dissipation supported by the device is dependent upon board design and layout. Mounting pad configuration on the PCB, the board material, and the ambient temperature affect the rate of junction temperature rise for the part. When the NCV47700 has good thermal conductivity through the PCB, the junction temperature will be relatively low with high power applications. The maximum dissipation the NCV47700 can handle is given by: P D(MAX) + T J(MAX) * TA RqJA (eq. 6) Since TJ is not recommended to exceed 150 °C, then the NCV47700 soldered on 645 mm2, 1 oz copper area, FR4 can dissipate up to 1.8 W (SOIC−8 EP) or 1 W (SOIC−8) and up to 4.3 W (SOIC−8 EP) or 1.6 W (SOIC−8) for 4 layers PCB (all layers are 1 oz) when the ambient temperature (TA) is 25 °C. See Figure 18 for RthJA versus PCB area. The power dissipated by the NCV47700 can be calculated from the following equations: P D + Vin Iq@Iout ) Iout Vin * Vout (eq. 7) or V in(MAX) [ P D(MAX) ) Vout Iout Iout ) Iq (eq. 8) Hints Vin and GND printed circuit board traces should be as wide as possible. When the impedance of these traces is high, there is a chance to pick up noise or cause the regulator to malfunction. Place external components, especially the output capacitor, as close as possible to the NCV47700 and make traces as short as possible. Figure 18. Thermal Resistance vs. PCB Copper Area 40 60 80 100 120 140 160 180 0 100 200 300 400 500 600 700 COPPER HEAT SPREADER AREA (mm2) SO−8 EP 4 layers PCB SO−8 EP single layer PCB 20 200 220 SO−8 single layer PCB 1 oz 2 oz 1 oz 2 oz 1 oz 2 oz 1 oz 2 oz SO−8 4 layers PCB ORDERING INFORMATION Device Output Voltage Marking Package Shipping† NCV47700PDAJR2G Adjustable 47700 SOIC−8 EP (Pb−Free) 2500 / Tape & Reel NCV47700DAJR2G Adjustable 47700 SOIC−8 (Pb−Free) 2500 / Tape & Reel †For information on tape and reel specifications,including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specifications Brochure, BRD8011/D. |
同様の部品番号 - NCV47700_17 |
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同様の説明 - NCV47700_17 |
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