Datasheet LT1581, LT1581-2.5 (Analog Devices) - 5

LT1581/LT1581-2.5
W BLOCK DIAGRA
CONTROL POWER + – SENSE OUTPUT FOR FIXED VOLTAGE DEVICE 1581 BD ADJ GND
U U W U APPLICATIONS INFORMATION
The LT1581 is a low dropout regulator designed to power control voltage is relatively small, equal to approximately the new generation of microprocessors. Low dropout 1% of the output current or about 100mA for a 10A load. regulators have become more common in desktop com- The bulk of this current is drive current for the NPN output puter systems as microprocessor manufacturers have transistor. This drive current becomes part of the output moved away from 5V only CPUs. A wide range of supply current. requirements exists today with new voltages just over the The control voltage must be at least 1V greater than the horizon. In many cases the input/output differential is very output voltage to obtain optimum performance. The maxi- small, effectively disqualifying many of the low dropout mum voltage on the V regulators on the market today. The LT1581 is designed to CONTROL pin is 13V. The maximum voltage at the V make use of multiple power supplies present in most POWER pin is limited to 7V. GND pin current for fixed voltage devices is 6mA (typ) and is constant as a systems to reduce the dropout voltage. This 2-supply function of load. ADJUST pin current for adjustable de- approach maximizes efficiency. vices is 60µA at 25°C and varies proportional to absolute The second supply, at least 1V greater than the output temperature. voltage, is used to provide power for the control circuitry The LT1581 has improved frequency compensation which and supply the drive current to the NPN output transistor. permits the use of capacitors with very low ESR. This is This allows the NPN to be driven into saturation, thereby critical in addressing the needs of modern, low voltage, reducing the dropout voltage by a VBE compared to high speed microprocessors. Current generation micro- conventional designs. The current requirement for the 5