Page 51

EETE OCT 2015

Fig. 5: LTC2946 fault alert generation. signs. The most apparent digital feature is the integration of a digital multiplier and accumulator which provide users with 24- bit power and 32-bit energy and charge values, alleviating the host of polling voltage and current data and performing extra computations. The chip calculates power by multiplying 12-bit measured current with 12-bit measured voltage. In continuous mode, the differential sense voltage is measured to obtain the load current data. However, the voltage data can be selected between the supply voltage, positive sense voltage, or spare ADC input voltage. A 24-bit power value is then calculated every time a current measurement is made. Lastly, energy and charge accumulators are incremented with power and current data and capable of storing several months’ worth of data at nominal current and power levels. The LTC2946 has minimum and maximum registers for current, voltage, and power, which eliminate the need for continuous software polling and free the I2C bus and host to perform other tasks. In addition to detecting and storing min/max values, the circuit has min/max limit registers that can be used to issue an alert in the event any of the limits are exceeded, again, eliminating the need for the microprocessor to constantly poll the LTC2946 and analyze data. The LTC2946 can also be configured to generate an overflow alert after a specified amount of energy or charge has been delivered or when a preset amount of time has elapsed. For an energy monitor, an alert response can be equally as valuable as minimum and maximum registers. Figure 5 shows how the LTC2946 generates an alert signal via software and hardware. Measured data is compared against user defined thresholds; overvoltage, undervoltage, overcurrent, undercurrent, overpower, and underpower thresholds can all be defined and simultaneously monitored. Then, a status register informs the user which parametric thresholds have been exceeded, while actual fault values are logged in another register and can be interrogated at a later time. A separate alert register allows users to select which parameters will respond in accordance with the SMBus alert response protocol, where the Alert Response Address (ARA) is broadcasted and the /ALERT pin is pulled low to notify the host of an alert event. The LTC2946 uses a standard I2C interface with very unique enhancements to communicate with the outside world. Nine I2C device addresses are available so multiple LTC2946s can be easily designed into the same system. All LTC2946 devices respond to a common address, which allows the bus master to write to several LTC2946s simultaneously, regardless of their individual address. A stuck-bus reset timer resets the internal I2C state machine to allow normal communication to resume in the event that I2C signals are held low for over 33ms (stuck bus condition). A split I2C data line conveniently eliminates the need to use I2C splitters or combiners for bidirectional transmission and receiving of data across an isolation boundary. Furthermore, the LTC2946-1 option has an inverted data output for use with inverting opto-isolator configurations. PCB-POOL® is a registered trademark of Beta LAYOUT GmbH Flex PCB Prototypes & Small Series NEW ! Flexible PCBs: • Favourable pricing – thanks to PCB-POOL ® production • Online Calculation • Made in Germany Email: sales@pcb-pool.com www.pcb-pool.com www.electronics-eetimes.com Electronic Engineering Times Europe October 2015 31


EETE OCT 2015
To see the actual publication please follow the link above