Part Number: TPS63070
We have some problem with power save mode of TPS63070 in our device. Our device has been in production for several months, and a few days ago we notice a problem, because our customer wants to change a standard power supply (so far it was 12V) to 15V. We assumed that the input voltage range is from 9V to 16V (16V is the maximum input voltage of TPS63070), output voltage of TPS63070 is set to 3.3V. Current consumption isn't constant. When radio module transmits data it is about 130mA, otherwise a few mA, so the average current consumption is about 15-20mA (depends on input voltage). When exetrnal supply fails, the device is supply from internal backup battery (LiFePO4 3.2V). The TPS63070 has enough wide input voltage range. It works fine only to 13.5-14V of power supply. Above 13.5V-14V power save mode doesn't work. Once TPS63070 switches to PWM mode, it remains in PWM mode forever. So the averange current consumption increased from 15-20mA (at 9-13.5V of input voltage) to more than 50mA (at input voltage >13.5V) and is not accepted.
I appreciate any suggestion why it works so strange.
Thanks for asking.
Firstly, please share the schematic for us, including the input ORing.
Then may I know how do you judge if the device enters PFM or not? From the current consume or waveform? And what if remove all load?
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In reply to Minqiu Xie:
Because of a specific purpose of our devices I shouldn't share a complete schematics. Any changes in existed devices are a little bit complicated, because devices are encapsulated. Moreover any relevant changes reqiure re-certificate. There is a simplified schematic of a power circuit below. Battery backup circuit is negligible. F1, D2-D4, D6, D7 are necessary to fulfill safety regulations. D1 and T2 switches the power supply between external 9-16V and battery.
I made a few tests with a real load (other parts of our device), one resistor (simulating current consumption of real load) as well as without load. I observed a current consumption. Then I cutted off PS/SYNC track and pull to low (for forced PWM) and I made the same tests. The current consumption with forced PWM mode and with PWM/PFM mode (PWM/PFM mode at input voltage higher than about 13.5V) were very similar.
Observed current consumption (rounded values):1) PWM/PFM mode, Vcc < 13.5V,- no load, Icc = 1mA- after attached and detached a resistive load, Icc = 1mA2) PWM/PFM mode, Vcc > 13.5V- no load, Icc=1mA (I turned it on many times and sometimes it started with Icc=25-30mA)- after attached and detached a resistive load, Icc = 35mA3) forced PWM- no load, Icc=25-35mA (depends on Vcc)
In reply to Wojciech W.:
Thanks for your supplement. Please allow me do a quick reply first.
What's the resistance you use to simulate? I'll try to reproduce the issue in our lab on EVM if the equipment is available today.
Rload = 10 Ohm, I think that it's a good approximation of the maximum current consumption. The average current is a few times smaller.
When you switch the load very slowly, you may not observe the problem. Sometimes Icc falls to 1mA, and sometimes to 35mA. I'm not sure why. In our case the load changes from 3 to 100 times per second. It depends on the frequency of data package sending by a radio module.
I'll appreciate if you try simulate this in two ways:1) turn the power on with no load and then attach and detach the load2) turn the power on with load and then detach the load
In both cases I've got similar results
On how many boards do you observe this behavior?
For more information on buck-boost devices have a look at www.ti.com/buckboost
In reply to Brigitte:
Our customer checked 3 devices and reported a problem to me. Probably most of the 170 provided devices are already installed and working (with lower Vcc=12V). I checked 4 devices in our office (2 pcs from production part and 2 prototypes), with two different marking numbers. In all cases I observed the same behavior.
With the same behavior you mean that input voltages above 13.5V cause the device to not enter PFM mode, correct?
To be honest, I did not observe this behavior up to now and wanted to be absolutely sure and checked 3 EVMs in the lab with 16V on the input and 3.3V on the output and all of them behaved as expected and entered PFM mode at startup.
Could you please check if there is possibly a connection issue for the PS/SYNC pin?
Please share the part number of your inductor. Please check if the problem disappears when you are using a different inductor with higher current rating.
Yes, input voltage above 13.5V causes the device do not enter PFM mode. Sometimes the device enter PFM mode at startup, but after change of a load current it remains in PWM mode. I also observed an output waveform (not only current consumption) and it confirms that the device do not enter PFM mode.
I wanted to eliminate the influence of the rest of my circuit and I cutted off the whole circuit behind TPS63070 (I left only a resistor to simulate any load), as well as the whole input circuit and applied the input voltage behind a ferrite bead L2. I also tried to change the value of input and output capacitors, but the problem remains.
Connection of the PS/SYNC pin seems to be fine. The voltage on this pin is equal to the input voltage.
The part number of my inductor is LQM2HPN1R5MG0L. I will try another inductor soon.
If you have the ability to measure the current through the inductor with a current probe or a shunt resistor, this would be very helpful to dig a little more into the issue you face.
There are waveforms of inductor current below, measured with a shunt resistor of 0R1.
Fig. 1. Vin = 12V, attached load R = 10R
Fig. 2. Vin = 12V, detached load
Fig. 3. Vin = 15V, attached load R = 10R
Fig. 4. Vin = 15V, detached load
All above waveforms are for an inductor of L = 1.5uH, Isat = 1.5A (LQM2HPN1R5MG0L).
I repeated this test with a different inductor (L = 2.2uH, Isat = 2.5A, it was the only inductor suitable for this application in our stock). The inductor ripple current is smaller, but the problem remains. First I thought that the problem is a saturation of the inductor. But as you can see, the maximum current is smaller than Isat. I may buy a few different inductors with a higher current but I'm not sure that it is a right way.
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