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Part Number: TPS61196
Dear Ti Team,
Should be used other set of resistors (eg. 10k 2.4k 8.2k ?) or ???
Thank you for help.
Please use our equation 2 in the datasheet to choose the right resistor for the UVLO configuration. What the resistor you have chosen is not right.
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In reply to Sean Zhou:
I read, this. What I paste was the last test.
Ok new one, calculate from equation for
So I choose for R5 200k, 33kx2 for R1 and 37.4k for R2
Starts, but also sometimes (if I "power" twice etc.).
What I observed when I start them work perfectly if I not discharge (leave for longer time, disconnect from other devices - power supply). Eg. I could block output on power supllay switch of function generator, works till I unplug from PS and Generator.
It starts quite good (better but not aceptable) if start voltage is set to 14V or higger
If I exchange R1 to 182k like in proposed schematic, start always from around 14V.
What should I check ?
In reply to Bartosz Reichel:
The calculate method seems ok, I guess the reason is that it may trigger the current limit with the low input voltage. I think you can check the waveform on "ISNS" pin whether it triggers current limit under low supply voltage.
On ISNS I have puls around 200mV then start oscialtion (in 14V case) in 12V case have pulse also around 200mV and nothing,
but when I start with 14V and goes down to 12V everything looks similar like for 14V.
There is two suggestion for the test:
1. Decrease the PWM duty cycle for the test to achieve a light load to check whether it starts normally;
2. Decrease the LED counts for the test.
The suggestion that I proposed is to create a light load condition to check whether it triggers something wrong.
PWN not help (start from 10%) but decresing count helps (start from half, but works with more, now only test chain to prepare / understoot for final one ). Which parameter should be trim in this case (R7 ?). ISET have around 150k now (and fit to this LED).
What's the LED configuration for your test set up? I'm considering maybe it has triggered maximum duty cycle limitation for low Vin and high Vout.
Your ISET is too high, and you have set the current to about 32mA for each channel? You 'd better change the output current of each channel above 50mA. Have triy with ISET=98k.
OK, I made next test, I back to proposed in DS values (200k/182k/24.9k) for which my test setup work. Exchange resistor to 74.5k to have 65mA and plug one of the finall led string which works under 65mA and 47V,
nothing happen (old one also with this resistor still works). PWM duty 50%, 5V, 222Hz.
This is really strange and I don't have much more comments now and please do more test and hope you can find that something that leads to this issue. Anny update please let me know.
I build string array with +/- same voltage. Try to start => nothing.
But when I take half, TPS start, then I take next and next and finally whole string works. Then change to final leds and also strart. But if discharge (eg touch output by finger), nope.
Where could be a probem ? I try with differ inductor (~ same value, but I start from cheap one then use let say better). Power supply (standard lab ax-6003p) ?
Any other idea of test will be welcome !
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