LT6660 UUWUAPPLICATIO S I FOR ATIO Table 1 gives the maximum output capacitance for vari- Hysteresis ous load currents and output voltages to avoid instability. Hysteresis data shown in Figure 6 and Figure 7 represents Load capacitors with low ESR (effective series resistance) the worst-case data taken on parts from 0°C to 70°C and cause more ringing than capacitors with higher ESR such from –40°C to 85°C. The output is capable of dissipat- as polarized aluminum or tantalum capacitors. ing relatively high power, i.e., for the LT6660-2.5, PD = Table 1. Maximum Output Capacitance 17.5V • 20mA = 350mW. The thermal resistance of the VOLTAGE DFN package is 102°C/W and this dissipation causes a OPTIONIOUT = 100µA IOUT = 1mA IOUT = 10mA IOUT = 20mA 36°C internal rise. This elevated temperature may cause 2.5V >10µF >10µF 2µF 0.68µF the output to shift due to thermal hysteresis. For highest 3V >10µF >10µF 2µF 0.68µF performance in precision applications, do not let the 3.3V >10µF >10µF 1µF 0.68µF LT6660’s junction temperature exceed 85°C. 5V >10µF >10µF 1µF 0.68µF 10V >10µF 1µF 0.15µF 0.1µF Input Capacitance It is recommended that a 0.1µF or larger capacitor be Long-Term Drift added to the input pin of the LT6660. This can help with stability when large load currents are demanded. Long-term drift cannot be extrapolated from accelerated 18 high temperature testing. This erroneous technique WORST-CASE HYSTERESIS 16 ON 40 UNITS gives drift numbers that are wildly optimistic. The only 14 way long-term drift can be determined is to measure itover the time interval of interest. The LT6660 long-term 12 drift data was taken on over 100 parts that were soldered 10 70°C TO 25°C 0°C TO 25°C into PC boards similar to a “real world” application. The 8 boards were then placed into a constant temperature oven NUMBER OF UNITS 6 with TA = 30°C, their outputs were scanned regularly and 4 measured with an 8.5 digit DVM. Figure 5 shows typical 2 long-term drift of the LT6660s. 0 –240 –200 –160 –120 –80 –40 0 40 80 120 160 200 240 HYSTERESIS (ppm) 150 6660 F06 100 Figure 6. 0°C to 70°C Hysteresis 50 9 WORST-CASE HYSTERESIS 8 ON 34 UNITS ppm 0 7 85°C TO 25°C –40°C TO 25°C –50 6 5 –100 4 –150 NUMBER OF UNITS 3 0 100 200 300 400 500 600 700 800 900 1000 HOURS 2 6660 F05 1 Figure 5. Typical Long-Term Drift 0 –600 –500 –400 –300 –200 –100 0 100 200 300 400 500 600 HYSTERESIS (ppm) 6660 F07 Figure 7. –40°C to 85°C Hysteresis 6660fa 9