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EL7584IRZ-T7 Datasheet(PDF) 10 Page - Intersil Corporation |
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EL7584IRZ-T7 Datasheet(HTML) 10 Page - Intersil Corporation |
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10 / 16 page  10 FN7317.2 February 4, 2005 The following table gives typical values: (Margins are considered 10%, 3%, 20%, 10%, and 15% on VIN, VO, L, FS, and ILMT, respectively) TABLE 1. MAXIMUM CONTINUOUS OUTPUT CURRENT VIN (V) VO (V) L (µH) FS (kHz) IOMAX (mA) 3.3 9 10 1000 430 3.3 12 10 1000 320 3.3 15 10 1000 250 5 9 10 1000 650 5 12 10 1000 470 5 15 10 1000 370 12 18 10 1000 830 Component Considerations Input Capacitor It is recommended that CIN is larger than 10µF. Theoretically, the input capacitor has ripple current of ∆IL. Due to high-frequency noise in the circuit, the input current ripple may exceed the theoretical value. Larger capacitor will reduce the ripple further. Boost Inductor The inductor has peak and average current decided by: ILPK ILAVG ∆I L 2 -------- + = ILAVG IO 1 - D ------------- = The inductor should be chosen to be able to handle this current. Furthermore, due to the fixed internal compensation, it is recommended that maximum inductance of 10µH and 15µH to be used in the 5V and 12V or higher output voltage, respectively. The output diode has average current of IO, and peak current the same as the inductor's peak current. Schottky diode is recommended and it should be able to handle those currents. Feedback Resistor Network An external resistor divider is required to divide the output voltage down to the nominal reference voltage. Current drawn by the resistor network should be limited to maintain the overall converter efficiency. The maximum value of the resistor network is limited by the feedback input bias current and the potential for noise being coupled into the feedback pin. A resistor network in the order of 200k Ω is recommended. The boost converter output voltage is determined by the following relationship: VBOOST R1 R2 + R1 --------------------- VFBB × = where VFBB is 1.300V. Schottky Diode Speed, forward voltage drop, and reverse current are the three most critical specifications for selecting the Schottky diode. The entire output current flows through the diode, so the diode average current is the same as the average load current and the peak current is the same as the inductor peak current. When selecting the diode, one must consider the forward voltage drop at the peak diode current. On the Elantec demo board, MBRM120 is selected. Its forward voltage drop is 450mV at 1A forward current. Output Capacitor The EL7584 is specially compensated to be stable with capacitors which have a worst-case minimum value of 10µF at the particular VOUT being set. Output ripple voltage requirements also determine the minimum value and the type of capacitors. Output ripple voltage consists of two components - the voltage drop caused by the switching current though the ESR of the output capacitor and the charging and discharging of the output capacitor: VRIPPLE ILPK ESR VOUT - VIN VOUT -------------------------------- + × IOUT COUT FS × ------------------------------ × = For low ESR ceramic capacitors, the output ripple is dominated by the charging/discharging of the output capacitor. In addition to the voltage rating, the output capacitor should also be able to handle the RMS current is given by: ICORMS 1 ( - D ) D ∆I L 2 ILAVG 2 -------------------- + × 1 12 ------ × ILAVG × = Positive and Negative Charge Pump (VON and VOFF) The EL7584 contains two independent charge pumps (see charge pump block and connection diagram.) The negative charge pump inverts the VDDN supply voltage and provides a regulated negative output voltage. The positive charge pump doubles the VDDP supply voltage and provides a regulated positive output voltage. The regulation of both the negative and positive charge pumps is generated by the internal comparator that senses the output voltage and compares it with and internal reference. The switching frequency of the charge pump is set to ½ the boost converter switching frequency. The pumps use pulse width modulation to adjust the pump period, depending on the load present. The pumps are short- circuit protected to 180mA at 12V supply and can provide 15mA to 60mA for 6V to 12V supply. EL7584 |
Similar Part No. - EL7584IRZ-T7 |
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Similar Description - EL7584IRZ-T7 |
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