LT6650 UUWUAPPLICATIO S I FOR ATIO VOUT. RB must be within the following range for proper the parts cycled over the higher temperature extremes operation (the optimal value depends greatly on the direc- exhibit a broader hysteresis distribution. The worst hys- tion and magnitude of the load current): teresis measurements indicate voltage shifts of less than R 1000ppm (0.1%) from their initial value. B > |VS – VOUT|/(200µA + 0.4/RG) RB < |VS – VOUT|/(15µA + 0.4/RG) Limits of OperationHysteresis The LT6650 is a robust bipolar technology part. ESD clamp diodes are integrated into the design and are Due to various mechanical stress mechanisms inherent to depicted in the Simplified Schematic for reference. Diodes integrated-circuit packaging, internal offsets may not pre- are included between the GND pin and the IN, OUT, and FB cisely recover from variations that occur over tempera- pins to prevent reverse voltage stress on the device. ture, and this effect is referred to as hysteresis. Proprietary Unusual modes of operation that forward-bias any these manufacturing steps minimize this hysteresis, though diodes should limit current to 10mA to avoid permanent some small residual error can occur. Hysteresis measure- damage to the device. The LT6650 is fabricated using a ments for the LT6650 can be seen in Figures 11 and 12. relatively high-voltage process, allowing any pin to inde- Figure 11 presents the worst-case data taken on parts pendently operate at up to 20V with respect to GND. The subjected to thermal cycling between 0°C to 70°C, while part does not include any over voltage protection mecha- Figure 12 shows data for –40°C to 85°C cycling. Units nisms; therefore caution should be exercised to avoid were cycled several times over these temperature ranges inadvertent application of higher voltages in circuits in- and the largest changes are shown. As would be expected, volving high potentials. 6 7 LIGHT COLUMNS 0°C TO 25°C LIGHT COLUMNS –40°C TO 25°C DARK COLUMNS 70°C TO 25°C DARK COLUMNS 85°C TO 25°C 5 6 5 4 4 3 3 NUMBER OF UNITS 2 NUMBER OF UNITS 2 1 1 0 0 –400 –200 0 200 400 600 –1000 –750 –500 –250 0 250 500 750 1000 DISTRIBUTION (ppm) DISTRIBUTION (ppm) 6650 F11 6650 F12 Figure 11. Worst-Case 0 ° C to 70 ° C HysteresisFigure 12. Worst-Case –40 ° C to 85 ° C Hysteresis 6650fa 10