Power House - All Comments

Extend battery life in tablets with one chip

Daniel Acevedo — Tue, 21 May 2013 17:49:42 GMT

Devan, for charging from a USB source, a boost converter such as the TPS61087 or the TPS43061 can be used. These devices typically operate with voltage mode control but can be modified to operate with a current mode control loop. This configuration paired with the TPS65090 front-end PMU and it's charger and power path management features allows for charging of the multi-cell battery from a 5V USB source with low and variable current levels. We have tested and documented solutions which will be posted on the TPS65090 landing page as they become available: www.ti.com/.../tps65090.

Extend battery life in tablets with one chip

Devan Lippman — Tue, 21 May 2013 15:57:24 GMT

I like the idea, how does this work with charging over USB (ie. detecting port type and limiting charger current accordingly)?

Engineer It Video Series: Testing Power Supplies

Bob Hanrahan — Thu, 16 May 2013 20:06:48 GMT

Hi Jeff, Thanks for the questions!

1. How much phase and gain margin is acceptable for a power supply?

Acceptable gain and phase margin values depend on the specific application. First off let me state that higher margins typically sacrifice the response time of the control loop thus a design with high margins may not properly react to load changes resulting in unacceptable voltage droops. A design with low margins may have very fast loop response yet potentially over-shoot the desired output voltage during load changes (often showing up as a high frequency ringing during step load changes).

I discuss this and provide industry target values in the EDN article at the following web address:

www.edn.com/.../Testing-a-power-supply---Stability--Part-three-

2. How can I test the stability of an LDO that does not have external feedback components? I recently encountered one that was unstable at low temperatures. I seek a method to determine the control loop margin to predict this possibility.

When you have no way to inject a signal into the control loop you can verify stability by providing a load step onto the output. A load step from minimum to maximum expected load will result in either unacceptable ringing or unacceptable voltage droop if the loop is not properly compensated. Generally speaking, if you observe more than 3 cycles of ringing on the output voltage before settling your margins are likely too low and you may risk instability. In this situation you must adjust the load impedance to increase the margin. Many LDO datasheets will provide output capacitor limitations for just this reason. If you follow guidelines on the datasheet you should realize good results.

3. Can a step load response be used to determine stability?

As described above, a load step can be used to determine stability. By disturbing the output of a power supply one can determine the output impedance of the supply over frequency and use this to plot the phase and gain margins. Companies do make such test equipment and they do have the advantage of not requiring you to open up the control loop for the measurement (adding a resistor in the feedback loop). From what I have seen and read, it appears that these passive methods do not provide the accuracy of the traditional loop response measurement technique I describe in the EDN article and video. You want to inject and observe inside the control loop for the real picture. By carefully adding the injection point resistor you can make stability measurements with your actual system load in place.

Bob

Engineer It Video Series: Testing Power Supplies

Jeff Weslowski — Thu, 16 May 2013 00:16:43 GMT

Hi Bob,

This is a great set of video tutorials on power supply testing. Thanks.

I have a few questions regarding power supply stability measurements:

1. How much phase and gain margin is acceptable for a power supply?

3. Can a step load response be used to determine stability?

Thanks,

Jeff

Engineer It Video Series: Testing Power Supplies

Brian Wang0928 — Wed, 15 May 2013 02:22:32 GMT

Nice video. it's really helpful for the flash engineers who designs the power supply.

Engineer It Video Series: Testing Power Supplies

Bob Hanrahan — Tue, 14 May 2013 01:16:13 GMT

Thanks very much for all the nice comments, I appreciate the feedback and am very glad to hear that the material was beneficial.

Yura:

A few examples of problems that I discovered with an efficiency graph are as follows. When a power supply starts going into current limiting you will see a sharp change of slope with a fairly linear down-turn as the voltage drops off. Sometimes people miscalculate and find that the peak switch current is higher than they figured, especially in a boost converter design. Once you see the spot where the slope changes you can study that specific condition. Another example is where a power circuit goes unstable. Most often when a power control loop is even marginally unstable the efficiency will suffer. This is again shown by an abrupt change in slope of the graph, sometimes only with specific input voltages and output currents. Again the graph will pinpoint the conditions where the problem exists; often a look at the switch node waveform will show some instability (jitter or unexpected oscillation). Instability can be caused by many things, yet if it's simply a marginal control loop, the measurements explained in part 4 of this video series, or in part 3 of the EDN series on the subject should help.

Thanks for the question! Bob

Engineer It Video Series: Testing Power Supplies

Curtis Roberson — Sat, 11 May 2013 22:24:42 GMT

Yes these video's were very helpful and should be implemented thoroughly over all TI's component portfolios.

Engineer It Video Series: Testing Power Supplies

Robert Scott — Fri, 10 May 2013 19:36:38 GMT

Hello,

I really appreciated these videos. They presented information on power supply characterization in an exceptionally practical and helpful manner. I look forward to viewing further videos from this contributor. Thank you.

Engineer It Video Series: Testing Power Supplies

Iurii Vlasenko — Fri, 10 May 2013 11:12:15 GMT

Hi,

Thanks for a very clear and informative videos!

In the part 2 you speak about the design problems we can find with the help of efficiency plot. Can you possibly give an example of such a problem?

Best regards,

Yura

Testing power supply: Measuring stability

Power House — Tue, 07 May 2013 16:01:29 GMT

Last week, I posted part 1 of a 3 part series on how to test your power supply design: Testing power

Testing power supply: Measuring efficiency

Power House — Tue, 07 May 2013 16:01:26 GMT

Last week, I posted part 1 of a 3 part series on how to test your power supply design: Testing power

Testing power supply: Measuring stability

Power House — Tue, 07 May 2013 16:00:45 GMT

During my normal activity as an Analog Field Applications Engineer, I am called to help a customer solve

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Testing power supply: Measuring Noise

Power House — Wed, 24 Apr 2013 16:40:30 GMT

Previously, I posted part 1 and 2 of a 3 part series on how to test your power supply design: measuring

Testing power supply: Measuring efficiency

Power House — Wed, 24 Apr 2013 16:40:29 GMT

Previously, I posted part 1 and 2 of a 3 part series on how to test your power supply design: measuring