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RT9198-30PBR Datasheet(PDF) 9 Page - Richtek Technology Corporation |
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RT9198-30PBR Datasheet(HTML) 9 Page - Richtek Technology Corporation |
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9 / 15 page  RT9198/A 9 DS9198/A-10 November 2006 www.richtek.com Applications Information Like any low-dropout regulator, the external capacitors used for the RT9198/A must be carefully selected for regulator stability and performance. Using a capacitor whose value is > 1 μF on the RT9198/A 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 RT9198/A 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 more than 20mΩ on the RT9198/A output ensures stability. The RT9198/A 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 with in 0.5 inch from the VOUT pin of the RT9198/A and returned to a clean analog ground. Thermal Considerations Thermal protection limits power dissipation in RT9198/A. When the operating junction temperature exceeds 165 °C, the OTP circuit starts the thermal shutdown function and turns the pass element off. The pass element turns on again after the junction temperature cools by 30 °C. For continuous operation, do not exceed absolute maximum operatiog junction temperature 125 °C. The power dissipation definition in device is shown as following formula : 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 operating junction temperature 125 °C, TAis the ambient temperature and the θJA is the junction to ambient thermal resistance. Instable Enable Function The RT9198/A features an LDO regulator enable/disable function. To assure the RT9198 LDO regulator will switch on, the EN turn on control level must be greater than 1.2V. The RT9198 LDO regulator will go into shutdown mode when the voltage on the EN pin falls below 0.4V. For RT9198A, the EN turn on control level must be lower than 0.4V to assure the RT9198A LDO regulator switch on. The RT9198A LDO regulator will go into shutdown mode when the voltage on the ENpin is higher than 1.2 V. The RT9198A equips a quick-discharge function to protect the system. When the regulator is turned off by EN pin, the internal MOSFET between VOUT and GND will be turned on to discharge output voltage quickly. If the enable function is not needed in a specific application, it may be tied to GND/VIN to keep the LDO regulator in a continuously on state. Figure 1 Region of Stable COUT ESR vs. Load Current 0.00 0.01 0.10 1.00 10.00 100.00 0 50 100 150 200 250 300 Load Current (mA) COUT = 1uF Instable Stable 100 10 1 RT9198/A-15CU5 COUT = 1 μF, X7R Simulation Verify |
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