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RT9011-EEPQWC Datasheet(PDF) 9 Page - Richtek Technology Corporation |
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RT9011-EEPQWC Datasheet(HTML) 9 Page - Richtek Technology Corporation |
9 / 12 page RT9011 Preliminary 9 DS9011-05 August 2007 www.richtek.com Applications Information Like any low-dropout regulator, the external capacitors used with the RT9011 must be carefully selected for regulator stability and performance. Using a capacitor whose value is > 1 μF on the RT9011 input and the amount of capacitance can be increased without limit. The input capacitor must be located a distance of not more than 0.5 inch from the input pin of the IC and returned to a clean analog ground. Any good quality ceramic or tantalum can be used for this capacitor. The capacitor with larger value and lower ESR (equivalent series resistance) provides better PSRR and line-transient response. The output capacitor must meet both requirements for minimum amount of capacitance and ESR in all LDOs application. The RT9011 is designed specifically to work with low ESR ceramic output capacitor in space-saving and performance consideration. Using a ceramic capacitor whose value is at least 1 μF with ESR is > 20mΩ on the RT9011 output ensures stability. The RT9011 still works well with output capacitor of other types due to the wide stable ESR range. Figure 1. shows the curves of allowable ESR range as a function of load current for various output capacitor values. Output capacitor of larger capacitance can reduce noise and improve load transient response, stability, and PSRR. The output capacitor should be located not more than 0.5 inch from the VOUT pin of the RT9011 and returned to a clean analog ground. Figure 1. Stable Cout ESR Range V OUT Short to GND 0.4V V OUT I OUT TSD OTP Trip Point 170 C ° 110 C ° 110 C ° 80 C ° IC Temperature Figure 2. Short Circuit Thermal Folded Back Protection when Output Short Circuit Occurs (Patent) Thermal Considerations Thermal protection limits power dissipation in RT9011. When the operation junction temperature exceeds 170 °C, the OTP circuit starts the thermal shutdown function and turns the pass element off. The pass element turn on again after the junction temperature cools by 40 °C. RT9011 lowers its OTP trip level from 170 °C to 110°C when output short circuit occurs (VOUT < 0.4V) as shown in Figure 2. It limits IC case temperature under 100 °C and provides maximum safety to customer while output short circuit occurring. For continuous operation, do not exceed absolute maximum operation junction temperature 125 °C. The power dissipation definition in device is : PD = (VIN-VOUT) x IOUT + VIN x IQ The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surroundings airflow and temperature difference between junction to ambient. The maximum power dissipation can be calculated by following formula : PD(MAX) = ( TJ(MAX) - TA ) / θJA Where TJ(MAX) is the maximum operation junction temperature 125 °C, TAis the ambient temperature and the θJA is the junction to ambient thermal resistance. Region of Stable COUT ESR vs. Load Current 0.001 0.01 0.1 1 10 100 0 50 100 150 200 250 300 Load Current (mA) Unstable Range Stable Range Simulation Verify RT9014-FM, VIN = 5V CIN = COUT1 = COUT2 = 1uF/X7R |
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