Verifying serial buses and components in embedded designs
The setup shown in Figure 1 below up makes it possible to simultaneously monitor the stimulation (Temperature), the communications (I2C), and the effect on the charger switching power supply (Voltage and Current). The technique of inserting an additional monitoring line in the control loop (Update) is also being employed.
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Figure 1. Operation of a charger over a period of four seconds.
Using the acquired signal information, the first step was to determine when the change in temperature, which occurs between the positions marked at A1 and A2, is read by the charger. The temperature is read by the battery monitoring electronics during the short pulses on the Temperature trace.
The higher temperature reading is shown at A1 (a thermistor is used so the higher temperature is represented by a lower resistance and corresponding lower voltage). Position A2 is where the lower temperature value is first read. The I2C bus is read at the time of the longer pulse on the Temperature trace; also shown as activity on the Clock and Data digital traces.
Figure 2 below shows the I2C bus and decode at the sample which occurs after the temperature change is measured by the battery protection electronics. Now the temperature value read after the (0x17) command at C1 has the value of 0x08D4 representing a change in temperature.
This is the first I2C data reading taken after the temperature reading was taken by the battery protection electronics, so the response is as expected. Note that the perspective on the total time frame is maintained in the upper portion of the screen. This magnified display is taken at position C2.
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Figure 2: The PC bus and decode at the next sample which occurs after the temperature change is measured by the battery protection electronics.
Figure 3 below is the same trace greatly magnified to show the detailed current and voltage wave forms during the operation of the switching power supply charge control. A current probe was used to measure the current in the power transistor.
The drive signal is shown correlated to the analog signals so that the drive delay and the switching times can be measured. This data also shows the current ripple measurement which indicated that the power supply inductor ripple was well controlled during the transition from the higher current to the new lower current level.
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Figure 3: The same trace is further magnified, showing the detailed current and voltage waveforms during the operation of the switching power supply charge control.
This measurement example showed that the battery protection electronics correctly captured the change in temperature and that the charger was able to read this temperature change and promptly reduce the charge current to respond to the change in temperature. All of the information to measure the time intervals and current response was captured in one trace from which the events in the control system could be evaluated by the engineer as needed.
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