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ISL9103AIRUDZ-T Datasheet(PDF) 11 Page - Renesas Technology Corp |
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ISL9103AIRUDZ-T Datasheet(HTML) 11 Page - Renesas Technology Corp |
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11 / 14 page  ISL9103, ISL9103A FN6828 Rev 3.00 Page 11 of 14 December 9, 2015 Overcurrent Protection The overcurrent protection is provided on ISL9103, ISL9103A when overload condition happens. It is realized by monitoring the CSA output with the OCP comparator, as shown in Figure 22. When the current at P-Channel MOSFET is sensed to reach the current limit, the OCP comparator is triggered to turn off the P- Channel MOSFET immediately. Short-Circuit Protection ISL9103, ISL9103A has a Short-Circuit Protection (SCP) comparator, which monitors the FB pin voltage for output short- circuit protection. When the output voltage is sensed to be lower than a certain threshold, the SCP comparator reduces the PWM oscillator frequency to a much lower frequency to protect the IC from being damaged. Undervoltage Lockout (UVLO) When the input voltage is below the Undervoltage Lock Out (UVLO) threshold, ISL9103, ISL9103A is disabled. Soft-Start The soft-start feature eliminates the inrush current during the circuit start-up. The soft-start block outputs a ramp reference to both the voltage loop and the current loop. The two ramps limit the inductor current rising speed as well as the output voltage speed so that the output voltage rises in a controlled fashion. Low Dropout Operation The ISL9103, ISL9103A features low dropout operation to maximize the battery life. When the input voltage drops to a level that ISL9103, ISL9103A can no longer operate under switching regulation to maintain the output voltage, the P-Channel MOSFET is completely turned on (100% duty cycle). The dropout voltage under such condition is the product of the load current and the ON-resistance of the P-Channel MOSFET. Minimum required input voltage VIN under this condition is the sum of output voltage plus the voltage drop cross the inductor and the P-Channel MOSFET switch. Thermal Shut Down The ISL9103, ISL9103A provides built-in thermal protection function. The thermal shutdown threshold temperature is +130°C (typ) with a 30°C (typ) hysteresis. When the internal temperature is sensed to reach +130°C, the regulator is completely shut down and as the temperature drops to +100°C (typ), the ISL9103, ISL9103A resumes operation starting from the soft-start. Applications Information Inductor and Output Capacitor Selection To achieve better steady state and transient response, ISL9103, ISL9103A typically uses a 2.2µH inductor. The peak- to-peak inductor current ripple can be expressed in Equation 1: In Equation 1, usually the typical values can be used but to have a more conservative estimation, the inductance should consider the value with worst case tolerance; and for switching frequency fS, the minimum fS from the “Electrical Specifications” table on page 3 can be used. To select the inductor, its saturation current rating should be at least higher than the sum of the maximum output current and half of the delta calculated from Equation 1. Another more conservative approach is to select the inductor with the current rating higher than the P-Channel MOSFET peak current limit. Another consideration is the inductor DC resistance since it directly affects the efficiency of the converter. Ideally, the inductor with the lower DC resistance should be considered to achieve higher efficiency. Inductor specifications could be different from different manufacturers so please check with each manufacturer if additional information is needed. For the output capacitor, a ceramic capacitor can be used because of the low ESR values, which helps to minimize the output voltage ripple. A typical value of 10µF ceramic capacitor should be enough for most of the applications and the capacitor should be X5R or X7R. Input Capacitor Selection The main function for the input capacitor is to provide decoupling of the parasitic inductance and to provide filtering function to prevent the switching current from flowing back to the battery rail. A 10µF ceramic capacitor (X5R or X7R) is a good starting point for the input capacitor selection. Output Voltage Setting Resistor Selection For ISL9103, ISL9103A adjustable output option, the voltage resistors, R1 and R2, as shown in Figure 21, set the desired output voltage values. The output voltage can be calculated using Equation 2: where VFB is the feedback voltage (typically it is 0.8V). The current flowing through the voltage divider resistors can be calculated as VO/(R1 + R2), so larger resistance is desirable to minimize this current. On the other hand, the FB pin has leakage current that will cause error in the output voltage setting. The leakage current has a typical value of 0.1µA. To minimize the accuracy impact on the output voltage, select the R2 no larger than 200k. I VO 1 VO VIN --------- – LfS --------------------------------------- = (EQ. 1) VO VFB 1 R1 R2 ------- + = (EQ. 2) |
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