Datasheet LTC1798 (Analog Devices) - 7

LTC1798 Series
APPLICATIONS INFORMATION
to reduce the output ringing. Figure 2 illustrates the use of These references consume only 4µA of quiescent current a damping resistor for capacitive loads greater than 1µF. under light and heavy loads as well as in dropout; whereas, Figure 3 shows the resistor and capacitor values required PNP-based references waste considerable amounts of cur- to achieve critical damping. rent when the pass transistor is saturated. In addition, the LTC1798 series provides a lower dropout voltage (200mV
Internal P-Channel Pass Transistor
max) than PNP-based references. The LTC1798 series features an internal P-channel MOSFET 10k pass transistor. This provides several advantages over similar designs using a PNP bipolar pass transistor. 1k LTC1798-5 5.2V 2 6 TO IN OUT 5V 12.6V COUT >1µF 100 GND 0.1µF DAMPING RESISTOR RESISTOR VALUE (Ω) 4 <1k 1798 F02 10
Figure 2. Adding a Damping Resistor with
1 10 100 1000 OUTPUT CAPACITOR VALUE (µF)
Output Capacitors Greater Than 1µF
1798 F03
Figure 3. Damping Resistance vs Output Capacitor Value
1798fc 7 Document Outline FEATURES DESCRIPTION APPLICATIONS TYPICAL APPLICATION ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION ORDER INFORMATION AVAILABLE OPTIONS ELECTRICAL CHARACTERISTICS TYPICAL PERFORMANCE CHARACTERISTICS PIN FUNCTIONS BLOCK DIAGRAM APPLICATIONS INFORMATION PACKAGE DESCRIPTION REVISION HISTORY TYPICAL APPLICATION RELATED PARTS