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MIC5239-3.0BS Datasheet(PDF) 9 Page - Micrel Semiconductor |
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MIC5239-3.0BS Datasheet(HTML) 9 Page - Micrel Semiconductor |
9 / 14 page Micrel MIC5239 December 2007 9 M9999-121007 Application Information The MIC5239 provides all of the advantages of the MIC2950: wide input voltage range, and reversed- battery protection, with the added advantages of reduced quiescent current and smaller package. Additionally, when disabled, quiescent current is reduced to 0.1µA. Enable A low on the enable pin disables the part, forcing the quiescent current to less than 0.1µA. Thermal shutdown and the error flag are not functional while the device is disabled. The maximum enable bias current is 2µA for a 2.0V input. An open-collector pull-up resistor tied to the input voltage should be set low enough to maintain 2V on the enable input. Figure 1 shows an open-collector output driving the enable pin through a 200kΩ pull-up resistor tied to the input voltage. In order to avoid output oscillations, slow transitions from low-to-high should be avoided. C V V 5V V IN MIC5239 EN 200k 200k OUT GND FLG Figure 1. Remote Enable Input Capacitor An input capacitor may be required when the device is not near the source power supply or when supplied by a battery. Small, surface mount ceramic capacitors can be used for bypassing. Larger values may be required if the source supply has high ripple. Output Capacitor The MIC5239 has been designed to minimize the effect of the output capacitor ESR on the closed loop stability. As a result, ceramic or film capacitors can be used at the output. Figure 2 displays a range of ESR values for a 10µF capacitor. Virtually any 10µF capacitor with an ESR less than 3.4Ω is sufficient for stability over the entire input voltage range. Stability can also be maintained throughout the specified load and line conditions with 4.7µF film or ceramic capacitors. Figure 2. Output Capacitor ESR Error Detection Comparator Output The FLAG pin is an open-collector output which goes low when the output voltage drops 5% below it’s internally programmed level. It senses conditions such as excessive load (current limit), low input voltage, and over temperature conditions. Once the part is disabled via the enable input, the error flag output is not valid. Overvoltage conditions are not reflected in the error flag output. The error flag output is also not valid for input voltages less than 2.3V. The error output has a low voltage of 400mV at a current of 200µA. In order to minimize the drain on the source used for the pull-up, a value of 200kΩ to 1MΩ is suggested for the error flag pull-up. This will guarantee a maximum low voltage of 0.4V for a 30V pull-up potential. An unused error flag can be left unconnected. NOT VALID NOT VALID VALID ERROR Error FLAG Output Input Voltage Output Voltage 4.75V 0V 0V 5V 1.3V Figure 3. Error FLAG Output Timing Thermal Shutdown The MIC5239 has integrated thermal protection. This feature is only for protection purposes. The device should never be intentionally operated near this temperature as this may have detrimental effects on the life of the device. The thermal shutdown may become inactive while the enable input is transitioning from a high to a low. When disabling the device via the enable pin, transition from a high to low quickly. This will insure that the output remains disabled in the event of a thermal shutdown. |
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