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APW7093NI-TUL Datasheet(PDF) 11 Page - Anpec Electronics Coropration |
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APW7093NI-TUL Datasheet(HTML) 11 Page - Anpec Electronics Coropration |
11 / 20 page Copyright © ANPEC Electronics Corp. Rev. A.5 - Jun., 2005 APW7093 www.anpec.com.tw 11 0 200 400 600 800 1000 1200 1400 2.8 3.3 3.8 4.3 4.8 5.3 Function Descriptions(Cont.) Shutdown Drive SHDN to a logic-level low to place the APW7093 in low-power shutdown mode and reduce supply current less than 1µ A. In shutdown, all circuitry and internal MOSFETs turn off, so the LX node becomes high impedance. Drive SHDN to a logic-level high or connect to VCC for normal operation. Power Dissipation Power dissipation in the APW7093 is dominated by conduction losses in the two internal power switches. Power dissipation due to charging and discharging the gate capacitance of the internal switches (i.e., switching losses) is approximately: SW 2 IN D(CAP) f V C P × × = where C = 500pF and fSW is the switching frequency. Resistive losses in the two power switches are approximated by: PMOS 2 OUT D(RES) R I P × = where RPMOS is the on-resistance of the PMOS switch. The junction-to-ambient thermal resistance required to dissipate this amount of power is calculated by: θJA = (TJ,MAX - TA,MAX) / (PD(CAP) + PD(RES)) where: θ JA = junction-to-ambient thermal resistance TJ,MAX = maximum junction temperature TA,MAX = maximum ambient temperature Application Information For typical applications, use the recommended component values in Figure 2. For other applications, take the following steps: 1. Select the desired PWM-mode switching frequency. See Figure 3 for maximum operating frequency. 2. Select the constant off-time as a function of input voltage, output voltage, and switching frequency. 3. Select RTOFF as a function of off-time. 4. Select the inductor as a function of output voltage, off-time, and peak-to-peak inductor current. Fig 3. Maximum Recommended Operation Frequency Setting the Output Voltage An external voltage applied to the EXTREF pin sets the output voltage of the APW7093. This can come directly from another voltage source or external reference. When FB is directly tied to the output (Figure 4), the output voltage range is limited by the external reference’s input voltage limits. VEXTREF should be limited to less than VIN-1.7V. Failure to comply can cause the part to operate abnormally and may cause part damage. Alternatively, the output can be adjusted up to VIN by connecting FB to a resistor- divider between the output voltage and ground (Figure 5). Use 50k Ω for R1. R2 is given by: − ⋅ = 1 V V R1 R2 EXTREF OUT VOUT=2.5V VOUT=1.25V VOUT=1.1V VOUT=3.3V Input Voltage(V) |
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