Learn how to use the ISL28025 digital power monitor evaluation kit to measure the voltage and current performance of the ISL9110 buck-boost regulator.
This is a dongle that converts USB commands to I2C. This is the demo board ISL28025 that measures current draw from a buck-boost regulator. I've started the ISL28023/25 eval software on a Win 7 system. I also have connected, through a USB cable, the computer to the dongle, and the ISL28025 demo board. To connect to the demo board, press "Connect to Device." The software automatically sniffs what's connected to the dongle and as you can see here, is that the software window has elongated. To the left are the controls for the ISL28025 and to the right are the controls to the demo software and the ISL9110 buck-boost regulator.
Applied to the demo board, is a 4V external voltage supply. To ensure that the demo board is powered up through the external voltage supply, the jumper selection has to be chosen such that jumper 1 and 2 are shorted, as opposed to 2 and 3. Two and 3 will power the demo board from the dongles. And as you can see here, there's no load on the regulator itself, the buck-boost regulator, so there's very little current if not any. And you can see 4V is being sourced through the Vbus for the input of the regulator itself.
To turn on the regulator, press the on button. The current sense resistor for this demo board is 50mOhm. You can calibrate your own sense resistor or, you know, unsolder it and solder your own value of sense resistor to change. To do this, to recalibrate your sense resistor, just enter the new ohmic value of the sense resistor and press "Set Res Value." The default state, once the regulator is powered on, is 1V. So no load connected to the regulator, so there's very little current. And as you can see, the Vaux pin is measuring the output regulation voltage which is 1V.
To set the regulation voltage between 1 and 3.5, to set it, just enter 3.3 into the Vreg Out input field, and then press "Set Vreg." This changes the Rg resistor, the gain resistor, for the Buck-Boost Regulator ISL9110. By setting Vreg, the Rg resistor is a digitally controlled pod, the ISL23315. And once you measure once, you can see 3.3V is at the output of the regulator, or the Vaux input. Again, there is no load connected to the buck-boost regulator. To add a load, you know, click in the 'Built In Resistive Loads' circled with my mouse. If you would like to connect your own load, change the jumper position for the output load jumper from 2 to 3, to 1 to 2. That would be shorting 1 to 2 and you can apply a load to the output terminator. I'm gonna choose, for this demo, the 68ohm resistance, to be applied to the buck-boost regulator.
The current is measured at 46.24. This is the current measuring into the buck-boost regulator, with a 4V input. I'm gonna lower the voltage being applied to the buck-boost regulator, such that the buck-boost now becomes a boost. I have lowered it to 2V. As you can see, it's still regulating, the buck-boost regulator, and the input is now at 2V. And now, the buck-boost is now just a boost.
And I brought it back up to 4V. Now, I'm gonna apply a heavier load. And when you apply a heavier load, a dialogue box or a warning box appears. The warning box is warning you as a user to make sure that the Vin select jumper is not connected such that the power's coming from the USB port. The USB port can only source 500mA of current. Again, every time you exceed a current threshold that is near the limitations of the USB port, a dialogue box will warn you saying, "Make sure that the jumper position is in the correct position."
As you can see, I'm sourcing up to almost 700mA of current. The Vbus voltage is measured as 3.915V. The power supply is sourcing out four. There is actually a little bit of a voltage drop due to the amount of current flowing through the jumper cable that connects the power supply to the demo board.
Now, there are three input threshold detectors connected to the primary shunt of the ISL28025. Two comparator are connected to Vbus which measures overvoltage and undervoltage to the input. And one comparator is dedicated to the Vshunt channel or the current channel, which measures for over current conditions.
We're gonna enable the overcurrent detector for this demo. And I'm gonna say well, "I want an alert to happen when there is 20mA, at threshold range of 40mV," so 2. And what it does is that the dialogue box will do is configure a 6-bit DAC, such that it has a 20mV threshold, and monitor the Vshunt input to make sure that current does not exceed the set voltage.
There are two alert pins for the ISL28025. They both share the same digital filter and the same parators. Again, their both connected to the Vbus or the primary input, Vbus and the Vshunt. The SMB Alert 2 is a push-pull pin and the SMB Alert 1 is a open drain pin. There's a selection that the user can choose to get either, monitor the output of the comparator or to signal condition the comparator, such it goes through a glitch filter, where a user can choose a minimum glitch of 2µs, 4µs, or 8µs before it passes the signal to a latch bit, which is more or less a D flip-flop.
The output of the latch bit can either be masked or unmasked before being sent to the foregate. The inverter is really the active state of the alert. Is it an active-high or is it active-low? And for this instance, we're gonna unmask the overcurrent and we're gonna put a glitch filter of 4µs. The SMB Alert 1 pin is connected to the enable pin of the buck-boost regulator, ISL9110.
So what happens is that there is an alert that happens, it automatically shuts down the regulator, or the buck-boost regulator. And it's just an active feedback without even going through the microcontroller. I have enabled the OC regulator, such that it purposefully is in an overcurrent condition.
And now, let's check. It was 34mV which gave you 686mA of current that the regulator was sourcing, or was being sourced to the regulator, prior to the overcurrent condition. Now let's see if there is an overcurrent condition by measuring once. As you can see here, is that you have the backlit is orange, such that it's an overcurrent condition. And you can see that the current draw now is 0, -488µA, and everything has been turned off. The Vaux is at 0V.
The ISL28025 has a temperature sensor integrated into the device. To enable that, check the check box for Chip Temp. The ISL9110 buck-boost regulator is currently sourcing a heavy load. A heavy load, through metal, causes the metal to heat up. Since the ISL28025 is mounted very close to the board itself, it's a good representation of the temperature of the board. And as you can see, is that the temperature will continue to rise while the regulator is sourcing a heavy load.
Once the load is removed from the regulator, the temperature of the board should go down, as shown currently. This concludes our demonstration. Thank you for watching the ISL28025 demonstration.