Other Parts Discussed in Thread: TPS92692
Dear Sir/Ms.
Now the lamp has a new test specification, the input power voltage will drop from 12V to 5V for 20ms. Samples were made, this test item failed. The customer DEPO applied for TPS92692EVM test. The input voltage waveform is as follows. The test results in TPS92692EVM, TPS92692EVM Buck-boost's topology can not pass the test, Boost's topology can pass the test.
Out put spec. in the experiment is 0.68A/ LED x 8 in series (around 24V).
The EVB customer RD did a basic test, and the lowest steady-state input voltage was actually measured at 6.4V. Below this voltage, the output began to decrease brightness.
In the voltage drop experiment,
Customer connected the output to the BUCK-BOOST port, the output current was increased to 680mA (output R1 = 0.3R in parallel with 3 1R resistors), and 8 white LEDs were output,
The input voltage is 13.5V for testing, the voltage will flash from 13.5V-> 5.5V-> 13.5V, and the fall time of 13.5V-> 5.5V is 0.03s.
I tried to parallel four 1R resistors under the MOS resistor (R10 = 0.06R) to increase the OCP protection current, but to no avail.
The following needs you to help confirm
1. Why is the output R1 connected in parallel with three 1Rs and the output is only 680mA? (Theoretical value ILED = 0.1707 / 0.158 = 1.08A)
2. How to reduce the minimum steady-state voltage to 5.5V?
3. How to improve the problem that 13.5V-> 5.5V will flicker?
Would you please guide us how to modify EVM to fit customer's spec? attached excel calcification any missing?
TPS92692_BuckBoost_Design_Calculator.xlsx
Best Regards,
Kami Huang
