Other Parts Discussed in Thread: LM5118
Hi,
I'm currently working with the LM34936. We want an input varying between 9 to 19V, to output 18V. The maximum output current is 2A.
We used the schematic proposed by the webench TI power designer as a starting point. Then we fine-tuned the value of each component after verification and recomputation of each component value based on the datasheet:
- TI tool propose a 2k resistance in series with the VISNS pin, but since our appplication has an input voltage of maximum 19V, we placed a 0 ohm instead;
- We use a 10µH inductor instead of the 3.3µH, since we will mostly be in Buck mode;
- Rsense value is 20 mOhm instead of 15m;
- Cslope has been increased up to 200pF instead of 150pF;
- Cc2 has been increase up to 172 pF instead of 82pF, according to our re-computation
- Rc1 has been reduced to 12k instead of 15K according to our re-computation;
The main problems are that the LM is not woking in buck mode, and cannot boost when input voltage goes above 16,9 V.
Cboot1 and 2 have been increased to 200nF but without any result. We also played with the Rcc1, Cc1 and Cc2, but very little imrovement (increasing input voltage boots range up to 16.9V, as opposed to 16.3V at first)
From our investigations, it seems that the LM switch to a buck/boost hybrid mode around 16V (instead of 18V).
You can find the schematic generated by the tool here
Could you please help me out ?
Thank you in advance,
Regards,
