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ISL6412IRZ Datasheet(PDF) 9 Page - Intersil Corporation |
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ISL6412IRZ Datasheet(HTML) 9 Page - Intersil Corporation |
9 / 10 page 9 FN9067.1 March 20, 2007 Thermal Overload Protection Thermal overload protection limits total power dissipation in the ISL6412. When the junction temperature (TJ) exceeds +150°C, the thermal sensor sends a signal to the shutdown logic, turning off the pass transistor and allowing the IC to cool. The pass transistor turns on again after the IC’s junction temperature typically cools by 20°C, resulting in a pulsed output during continuous thermal overload conditions. Thermal overload protection protects the ISL6412 against fault conditions. For continuous operation, do not exceed the absolute maximum junction temperature rating of +150°C. Operating Region and Power Dissipation The maximum power dissipation of ISL6412 depends on the thermal resistance of the IC package and circuit board, the temperature difference between the die junction and ambient air, and the rate of air flow. The power dissipated in the device is: PT = P1 + P2 + P3, where P1 = IOUT1 (VIN – VOUT1) P2 = IOUT2 (VIN – VOUT2) P3 = IOUT3 (VIN- VOUT3) The maximum power dissipation is: Pmax = (Tjmax – TA)/θJA Where Tjmax = +150°C, TA = ambient temperature, and θJA is the thermal resistance from the junction to the surrounding environment. The ISL6412 package features an exposed thermal pad on its underside. This pad lowers the thermal resistance of the package by providing a direct heat conduction path from the die to the PC board. Additionally, the ISL6412’s ground (GND/GND3) performs the dual function of providing an electrical connection to system ground and channeling heat away. Connect the exposed backside pad and GND to the system ground using a large pad or ground plane, or through multiple vias to the ground plane layer. Integrator Circuitry The ISL6412 uses an external 33nF compensation capacitor for minimizing load and line regulation errors and for lowering output noise. When the output voltage shifts due to varying load current or input voltage, the integrator capacitor voltage is raised or lowered to compensate for the systematic offset at the error amplifier. Compensation is limited to ±5% to minimize transient overshoot when the device goes out of dropout, current limit, or thermal shutdown. FAULT Functionality Applications Information Capacitor Selection and Regulator Stability Capacitors are required at the ISL6412’s input and output for stable operation over the entire load range and the full temperature range. Use >1µF capacitor at the input of ISL6412. The input capacitor lowers the source impedance of the input supply. Larger capacitor values and lower ESR provides better PSRR and line transient response. The input capacitor must be located at a distance of not more then 0.5 inches from the VIN pins of the IC and returned to a clean analog ground. Any good quality ceramic or tantalum can be used as an input capacitor. The output capacitor must meet the requirements of minimum amount of capacitance and ESR for all three LDO’s. The ISL6412 is specifically designed to work with small ceramic output capacitors. The output capacitor’s ESR affects stability and output noise. Use an output capacitor with an ESR of 50m Ω or less to insure stability and optimum transient response. For stable operation, a ceramic capacitor, with a minimum value of 3.3 μF, is recommended for VOUT1 for 300mA output current, and 2.2μF is recommended for VOUT2 and VOUT3 each at 200mA load current. There is no upper limit to the output capacitor value. Larger capacitor can reduce noise and improve load transient response, stability and PSRR. Higher value of output capacitor (10µF) is recommended for LDO3 when used to power VCO circuitry in wireless chipsets. The output capacitor should be located very close to VOUT pins to minimize impact of PC board inductances and the other end of the capacitor should be returned to a clean analog ground. Input-Output (Dropout) Voltage A regulator’s minimum input-output voltage differential (or dropout voltage) determines the lowest usable supply voltage. Because the ISL6412 uses a P-channel MOSFET pass transistor, its dropout voltage is a function of rDS(ON) (typically 0.5) multiplied by the load current. TABLE 1. EVENT FAULT1 Below UVLO threshold L VOUT1 = 1.8V ±8% typ VOUT2/VOUT3 not in regulation H VOUT1 not in regulation VOUT2 and VOUT3 are in regulation L Thermal Shutdown L Normal Shutdown with SHDN pin L Overcurrent only on LDO1 L Overcurrent only on LDO2/LDO3 H ISL6412 |
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