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RT9193-15GQW Datasheet(PDF) 8 Page - Richtek Technology Corporation |
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RT9193-15GQW Datasheet(HTML) 8 Page - Richtek Technology Corporation |
8 / 14 page RT9193 8 DS9193-11 May 2008 www.richtek.com Applications Information Like any low-dropout regulator, the external capacitors used with the RT9193 must be carefully selected for regulator stability and performance. Using a capacitor whose value is > 1 μF on the RT9193 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 RT9193 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 > 25m Ω on the RT9193 output ensures stability. The RT9193 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 RT9193 and returned to a clean analog ground. Figure 1 Bypass Capacitor and Low Noise Connecting a 22nF between the BP pin and GND pin significantly reduces noise on the regulator output, it is critical that the capacitor connection between the BP pin and GND pin be direct and PCB traces should be as short as possible. There is a relationship between the bypass capacitor value and the LDO regulator turn on time. DC leakage on this pin can affect the LDO regulator output noise and voltage regulation performance. Enable Function The RT9193 features an LDO regulator enable/disable function. To assure the LDO regulator will switch on, the EN turn on control level must be greater than 1.2 volts. The LDO regulator will go into the shutdown mode when the voltage on the EN pin falls below 0.4 volts. For to protecting the system, the RT9193 have a quick-discharge function. If the enable function is not needed in a specific application, it may be tied to VIN to keep the LDO regulator in a continuously on state. Thermal Considerations Thermal protection limits power dissipation in RT9193. When the operation junction temperature exceeds 165 °C, the OTP circuit starts the thermal shutdown function turn the pass element off. The pass element turn on again after the junction temperature cools by 30 °C. For continue 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, TA is the ambient temperature and the θJA is the junction to ambient thermal resistance. 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) Simulation Verify Instable Stable 100 10 1 RT9193-15xU5 CIN = COUT = 1uF, X7R |
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