Hey,
Our TPS92515 LED driver circuit is exhibiting a power output drop after some power cycles. The power drop is a pretty stable 20mA below what we desire and have observed the circuit provide given our controls. Inputs to the chip such as DAC/IADJ, Vin, PWM, and VCC have been observed to be the same during proper and faulty operational power cycles. After powering down and back up our circuit for 30 times we will see this error show up once or twice and then return to normal operation on the subsequent power cycles. For some of our circuits on the same board we never see this issue arise.
In the below chart you can see our normal linear operation above the faulty operation. We've noticed that the error is not percent based on our expected output but ~20mA decrease for every point.
In this next chart I've graphed the current outputs over the course of the test. We cycle through 11 different DAC settings for every power cycle. We power cycle in this test 30 times. Note that the highlighted section of dots is the only one to exhibit the power drop error and during the next power cycle it has returned to proper output.
At this point we believe there may be a transient issue upon startup that sets an internal voltage reference incorrectly. However we have been unable confirm this suspicion so far. The Coff pin charges up and down constantly during operation so any issue with it should only be visible for an extremely short time. We also believe that the BOOT and SW pins would exhibit the same instantaneous error if any at all. We would also like to note that our Vin ripple is well below both 2V and 10% of total voltage.
Is there some internal voltage reference we have missed or do not fully understand? Is this a known issue or a sign of a defective part? Is it possible some aspect of the circuit design is failing(it exhibits no other issues)?
Please and Thanks
Tyler
