Understanding Smart Sensors - Nomads.usp

254 Understanding Smart SensorsFigure 11.2 Photomicrograph of eight-output PIC. (Courtesy of Motorola, Inc.)As shown in Figure 11.3, the eight outputs of the device have individualtemperature sensors, which allow each device to turn off independently whenthe thermal limit of 170°C is exceeded. All the outputs were shorted to 16Vsupply at a room temperature ambient. A total current of almost 30A initiallyflowed through the device. Note that each device turns off independently, withthe hottest device turning off first. Variations can result from differences in currentlevel and thermal efficiencies. As each device turns off, the total power dissipationin the chip decreases and the devices that are still on heat up slower.The hard short could have been diagnosed by short-circuit (current limit)sensing. However, a soft short, which by definition is below the current limitbut exceeds the power-dissipating capability of the chip, can be an extremely