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RT9013-33PB Datasheet(PDF) 8 Page - Richtek Technology Corporation |
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RT9013-33PB Datasheet(HTML) 8 Page - Richtek Technology Corporation |
8 / 12 page RT9013 Preliminary 8 DS9013-05 August 2007 www.richtek.com Applications Information Like any low-dropout regulator, the external capacitors used with the RT9013 must be carefully selected for regulator stability and performance. Using a capacitor whose value is > 1 μF on the RT9013 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 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 RT9013 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 RT9013 output ensures stability. The RT9013 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 RT9013 and returned to a clean analog ground. Figure 1 Enable The RT9013 goes into sleep mode when the EN pin is in a logic low condition. During this condition, the RT9013 has an EN pin to turn on or turn off regulator, When the EN pin is logic hight, the regulator will be turned on. The supply current to 0.7 μA typical. The EN pin may be directly tied to VIN to keep the part on. The Enable input is CMOS logic and cannot be left floating. PSRR The power supply rejection ratio (PSRR) is defined as the gain from the input to output divided by the gain from the supply to the output. The PSRR is found to be ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × = ΔSupply Error ΔGain log 20 PSRR Note that when heavy load measuring, Δsupply will cause Δtemperature. And Δtemperature will cause Δoutput voltage. So the heavy load PSRR measuring is include temperature effect. Current limit The RT9013 contains an independent current limiter, which monitors and controls the pass transistor's gate voltage, limiting the output current to 0.6A (typ.). The output can be shorted to ground indefinitely without damaging the part. Thermal Considerations Thermal protection limits power dissipation in RT9013. 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 30 °C. 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 Region of Stable COUT ESR vs. Load Current 0.001 0.01 0.1 1 10 100 0 100 200 300 400 500 Load Current (mA) RT9013-33PB, VIN = 5V CIN = COUT = 1 μF/X7R Stable Range Unstable Range Unstable Range |
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