Datasheet LT1528 (Analog Devices) - 9

LT1528
APPLICATIONS INFORMATION
The maximum junction temperature will be equal to the several different processors. This application allows the maximum junction temperature rise above ambient plus output voltage to be jumper selectable. the maximum ambient temperature or:
Protection Features
TJMAX = 50°C + 31.4°C = 81.4°C The LT1528 incorporates several protection features, such
Output Capacitance and Transient Performance
as current limiting and thermal limiting, in addition to the normal protection features associated with monolithic The LT1528 is designed to be stable with a wide range regulators. The device is protected against reverse input of output capacitors. The minimum recommended value voltages and reverse voltages from output to input. is 3.3μF with an ESR of 2Ω or less. The LT1528 output transient response will be a function of output capacitance. Current limit protection and thermal overload protection See the Transient Response curves in the Typical Perfor- are intended to protect the device against overload con- mance Characteristics. Larger values of output capacitance ditions. For normal operation the junction temperatures will decrease the peak deviations and provide improved should not exceed 125°C. output transient response for larger load transients. By- The input of the device will withstand reverse voltages pass capacitors, used to decouple individual components of 15V. Current fl ow into the device will be limited to less powered by the LT1528, will increase the effective value than 1mA (typically less than 100μA) and no negative of the output capacitor. voltage will appear at the output. The device will protect both itself and the load.
Microprocessor Applications
The SENSE pin is internally clamped to one diode drop The LT1528 has been optimized for microprocessor ap- below ground. If the SENSE pin is pulled below ground, plications, with the fastest transient response of current with the input open or grounded, current must be limited PNP low dropout regulators. In order to deal with the to less than 5mA. large load transients associated with current generation microprocessors, output capacitance must be increased. Several different input/output conditions can occur in To meet worst-case voltage specifi cations for many regulator circuits. The output voltage may be held up popular processors, four 47μF solid tantalum surface while the input is either pulled to ground, pulled to some mount capacitors are recommended for decoupling at intermediate voltage or is left open circuit. Current fl ow the microprocessor. These capacitors should have an back into the output will vary depending on the conditions. ESR of approximately 0.1Ω to 0.2Ω to minimize transient Many circuits incorporate some form of power manage- response under worst-case load deltas. The Typical Ap- ment. The following information summarized in Table 2 plication shows connections needed to supply power for will help optimize power usage.
Table 2. Fault Conditions INPUT PIN SHDN PIN OUTPUT/SENSE PINS RESULTING CONDITIONS
< VOUT (Nominal) Open (High) Forced to VOUT (Nominal) Reverse Output Current ≈ 150μA (See Figure 3) Input Current ≈ 1μA (See Figure 4) < VOUT (Nominal) Grounded Forced to VOUT (Nominal) Reverse Output Current ≈ 150μA (See Figure 3) Input Current ≈ 1μA (See Figure 4) Open Open (High) > 1V Reverse Output Current ≈ 150μA (See Figure 3) Open Grounded > 1V Reverse Output Current ≈ 150μA (See Figure 3) ≤ 0.8V Open (High) ≤ 0V Output Current = 0 ≤ 0.8V Grounded ≤ 0V Output Current = 0 > 1.5V Open (High) ≤ 0V Output Current = Short-Circuit Current – 15V < VIN < 15V Grounded ≤ 0V Output Current = 0 1528fb 9