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LM9074MX Datasheet(PDF) 8 Page - Texas Instruments |
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LM9074MX Datasheet(HTML) 8 Page - Texas Instruments |
8 / 12 page Application Information (Continued) An output bypass capacitor of at least 0.1µF is required for stability (47 µF is recommended). An input capacitor of 1 µF or larger is recommended to improve line transient and noise performance. With the Keep-Alive input, a system microprocessor has the ability to keep the regulator ON (with a logic “0” on Keep- Alive) after the ON/OFF input has been commanded OFF. A power-down sequence, when system variables are typically stored in programmable memory, can be executed and take as much time as necessary. At the end of the operation the micro then pulls Keep-Alive high and the regulator and sys- tem turn OFF and revert to the low quiescent current standby mode. For additional system reliability, consideration has been made for the possibility of a short circuited load at the output of the regulator. When the regulator is switched ON, conven- tional current limiting and thermal shutdown protect the regu- lator. When the regulator is switched OFF however, a grounded V CC supply to the micro (due to the shorted regu- lator output) will force the Keep-Alive input to be low and thus try to maintain the Keep-Alive mode of operation. With a shorted load, the drain on the battery could be as high as 1.5A. A separate internal circuit monitors the output voltage of the regulator. If V OUT is less than 4V, as would be the case with a shorted load, the Keep-Alive function is logically dis- abled to ensure that the regulator turns OFF and reverts to less than a 60 µA load on the battery. Conventional load dump protection is built in to withstand up to +60V and −50V transients. A 1 k Ω resistor in series with the ON/OFF and Keep-Alive inputs are recommended to provide the same level of transient protection for these pins if required. Protection against reverse polarity battery con- nections is also built in. With a reversed battery the output of the LM9074 will not go more negative than one diode drop below ground. This will prevent damage to any of the 5V load circuits. For applications where the control logic is not required the logic pins should be configured as shown in Figure 2.A separate device, called the LM9071, can be used. The LM9071 is available in a 5-lead TO-220 package and does not provide control logic functions, but still retains all of the protection features of the LM9074. RESET FLAG Excessive loading of the output to the point where the output voltage drops by 300 mV to 500 mV will signal a reset flag to the micro. This will warn of a V CC supply that may produce unpredictable operation of the system. On power-up and recovery from a fault condition the delay capacitor is used to 10130523 FIGURE 1. Typical Application Circuit 10130524 FIGURE 2. Control Logic Not Used www.national.com 7 |
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