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EL7516IYZ Datasheet(PDF) 10 Page - Intersil Corporation |
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EL7516IYZ Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 12 page 10 FN7333.4 March 4, 2005 Schottky Diode In selecting the Schottky diode, the reverse break down voltage, forward current and forward voltage drop must be considered for optimum converter performance. The diode must be rated to handle 1.5A, the current limit of the EL7516. The breakdown voltage must exceed the maximum output voltage. Low forward voltage drop, low leakage current, and fast reverse recovery will help the converter to achieve the maximum efficiency. Input Capacitor The value of the input capacitor depends the input and output voltages, the maximum output current, the inductor value and the noise allowed to put back on the input line. For most applications, a minimum 10µF is required. For applications that run close to the maximum output current limit, input capacitor in the range of 22µF to 47µF is recommended. The EL7516 is powered from the VIN. To. High frequency 0.1µF by-pass cap is recommended to be close to the VIN pin to reduce supply line noise and ensure stable operation. Loop Compensation The EL7516 incorporates an transconductance amplifier in its feedback path to allow the user some adjustment on the transient response and better regulation. The EL7516 uses current mode control architecture which has a fast current sense loop and a slow voltage feedback loop. The fast current feedback loop does not require any compensation. The slow voltage loop must be compensated for stable operation. The compensation network is a series RC network from COMP pin to ground. The resistor sets the high frequency integrator gain for fast transient response and the capacitor sets the integrator zero to ensure loop stability. For most applications, the compensation resistor in the range of 2K to 7.5K and the compensation capacitor in the range of 3nF to 10nF. Soft-Start The soft-start is provided by an internal 6µA current source charges the external CSS, the peak MOSFET current is limited by the voltage on the capacitor. This in turn controls the rising rate of the output voltage. The regulator goes through the start-up sequence as well after the SHDN pin is pulled to HI. Frequency Selection The EL7516 switching frequency can be user selected to operate at either at constant 620kHz or 1.25MHz. Connecting FSEL pin to ground sets the PWM switching frequency to 620kHz. When connect FSEL high or VDD, switching frequency is set to 1.25MHz. Shut-Down Control When Shut-down pin is pulled down, the EL7516 is shut- down reducing the supply current to <3µA. EL7516 does not use a level translator or ground-referenced threshold for the SHDN input. For different supply voltages, please refer the Figure 32 to choose right input threshold voltages for SHDN, where VTP is about 1V. It is recommend that VIH = (VIN-VTP/2) and VIL = (VIN/4). If the consistent SHDN threshold is desired in the application, an external active level shifter must be used, simplest circuit requires 1 NMOS and 1 resistor as shown in Figure 33, where the gate of the NMOS is connected to supply of PWRON logic circuit, and the source of the NMOS goes to PWRON pin of the converter. Maximum Output Current The MOSFET current limit is nominally 1.5A and guaranteed 1.3A. This restricts the maximum output current IOMAX based on the following formula: FIGURE 32. SHDN INPUT THRESHOLD vs INPUT SUPPLY VOLTAGE VIH, UPPER 0V VIN (VIN-VTP) (VIN/2) KEEP OUT VIL, LOWER VIN VIN=3.3V VIN=5.5V LOGIC THRESHOLD LOGIC THRESHOLD FIGURE 33. LEVEL SHIFTER CIRCUIT SUPPLY INPUT VOLTAGE TO EL7516 PIN3 SHDN 20K 3VD 20K PWRON PIN OF THE CONVERTER IL IL-AVG 12 ⁄∆I L × () + = EL7516 |
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