When reviewing the TPS62112 converter with a customer today, they expressed some concern over the startup transient.
Specifically, Figure 14 of the TPS62111 data sheet has several traces labeled CH1, CH2, CH3, and CH4, all having to do with startup and soft start, but there isn't a legend that tells us what each channel represents.
Can you please review/clarify this portion of the data sheet so we can make a better recommendation to the customer?
Steven Dunbar, AFA Colorado
This info will be forwarded to the product line so that the data sheet can be updated.
Figure 14—Start-Up Timing
Figure 13—Output Ripple
CH1—Output Ripple Voltage
Bill Johns, Applications Engineer
bqTESLA Wireless Power Products
Texas Instruments Inc
Please elaborate on the answer in light of the soft start description contained in the DS.
1. Trace 3 and 4 are confusing. Trace 3 looks more like I would have expected the inductor ripple current to look like.
2. If trace 3 is input current (per answer above), then why is there significant input current initially and a constant output voltage (~0.4v)? Where is the input power going?
3. There is an apparent discrepancy between the magnitudes of the two current waveforms. The peak input current should be the same as the peak inductor current.
4. Please verify that the scale for CH3 is 500mA/div (not 5V/div as labeled).
5. Was this test run with an active load set to constant current? It doesn't look like what I would have expected with a resistive load, which would have been a better load for this curve.
Mark,The scales for Trace 3 and 4 are in fact switched. CH3 is the inductor current with 500 mA/div. I was not able to recreate the exact waveform on CH4 but it is similar to what I observed at the SW pin. I will post a reply when I can confirm what is shown by CH4. You are also correct that it is done with an active load set to constant current. The attached powerpoint includes my measured startup into both an active load and resistive load. These were taken with the TPS62110 on its EVM.If you have any additional questions I'm happy to answer them for you.Anthony
DC/DC Power Applications Engineer
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