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MAX15010ATJ+ Datasheet(PDF) 19 Page - Maxim Integrated Products |
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MAX15010ATJ+ Datasheet(HTML) 19 Page - Maxim Integrated Products |
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19 / 23 page 
Calculate the discharge time, t1, using the following equation: where t1 is in ms, VOV is the adjusted overvoltage threshold in volts, ILOAD is the external load current in mA, and IGATEPD is the 63mA (typ) internal pulldown current of GATE. CSOURCE is the value of the capacitor connected between the source of the MOSFET and PGND in µF. GATE Delay Time (t2) When SOURCE falls 4% below the overvoltage threshold voltage, the internal current sink is disabled and the internal charge pump begins recharging the external GATE voltage. Due to the external load, the SOURCE voltage continues to drop until the gate of the MOSFET is recharged. The time needed to recharge GATE and re- enhance the external MOSFET is approximately: where t2 is in µs, Ciss is the input capacitance of the MOSFET in pF, and VGS(TH) is the gate-to-source thresh- old voltage of the MOSFET in volts. VF is the 0.7V (typ) internal clamp diode forward voltage of the MOSFET in volts, and IGATE is the charge-pump current 45µA (typ). Any external capacitance between GATE and PGND will add up to Ciss. During t2, the SOURCE capacitance, CSOURCE, loses charge through the output load. The voltage across CSOURCE, ΔV2, decreases by ΔV2 until the MOSFET reaches its VGS(TH) threshold. Approximate ΔV2 using the following formula: SOURCE Output Charge Time (t3) Once the GATE voltage exceeds the gate-to-source thresh- old, VGS(TH), of the external MOSFET, the MOSFET turns on and the charge through the internal charge pump with respect to the drain potential, QG, determines the slope of the output-voltage rise. The time required for the SOURCE voltage to rise again to the overvoltage threshold is: where ΔVSOURCE = (VOV x 0.04) + ΔV2 in volts, and Crss is the MOSFET’s reverse transfer capacitance in pF. Any external capacitance between GATE and PGND adds up to Crss. Power Dissipation/Junction Temperature During normal operation, the MAX15008/MAX15010 has two main sources of internal power dissipation: the LDO and the voltage tracker. Calculate the power dissipation due to the LDO as: PLDO = (VIN - VOUT_LDO) x IOUT_LDO where VIN is the LDO input supply voltage in volts, VOUT_LDO is the output voltage of the LDO in volts, and IOUT_LDO is the LDO total load current in mA. Calculate power dissipation due to the tracker as: PTRK = (VTRACK - VOUT_TRK) x IOUT_TRK where VTRACK is the tracker input supply voltage in volts, VOUT_TRK is the output voltage of the tracker in volts, and IOUT_TRK is the tracker load current in mA. The total power dissipation PDISS in mW as: PDISS = PLDO + PTRK For prolonged exposure to overvoltage events, use the VIN and VTRACK voltages expected during overvoltage conditions. Under these circumstances the corre- sponding internal power dissipation contribution, POVP, calculated in the Overvoltage-Limiter Mode Switching Frequency section should also be included in the total power dissipation, PDISS. For a given ambient temperature, TA, calculate the junction temperature, TJ, as follows: TJ = TA + PDISS x θJA where TJ and TA are in °C and θJA is the junction-to- ambient thermal resistance in °C/W as listed in the Absolute Maximum Ratings section. The junction temperature should never exceed +150°C during normal operation. Thermal Protection When the junction temperature exceeds TJ = +160°C, the MAX15008/MAX15010 shut down to allow the device to cool. When the junction temperature drops to +140°C, the thermal sensor turns all enabled blocks on again, resulting in a cycled output during continu- ous thermal-overload conditions. Thermal protection protects the MAX15008/MAX15010 from excessive power dissipation. For continuous operation, do not exceed the absolute maximum junction temperature rating of +150°C. t CV I rss SOURCE GATE 3 = ×Δ ΔV It C LOAD SOURCE 2 2 = × tC VV I iss GS TH F GATE 2 =× + () tC 0.04 V II 1 SOURCE OV LOAD GATEPD =× × + Automotive 300mA LDO Voltage Regulators with Tracker Output and Overvoltage Protector ______________________________________________________________________________________ 19 |
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