LM22677 - two in parallel?

Hi Denislav, thanks for that.

I am wanting to run peltiers controlled by having a switched mode supply (little heating as the peltiers do enough of that) from 24V input to output 24V down to zero by changing the voltage below Vref (1V23) resistor divider, from zero upward. - That works well on an LM2575 for a fan control

I have a quick prototype of a buck-boost webbench designed LM5118, but too quick and it isn't working that well.

Not like the 22677 that was fine straight away for another project.  The LM5118 requires some tuning and another board layout I suspect.

I am willing to go to a simpler buck only if it will go to nearly the full 24V out. 

I need 6Amp or more from 24V switched down to zero in a package that can be hand soldered

LM5118 seemed great but it starts to misbehave while entering into buck-boost mode, I had to add another 10mOhm sense resistor in parallel (9A design I tried) to get it to go near 24V out at 2 or 3 Amps only. It would suddenly drop down to about 10V from say 18 or 20 and continue to  provide more current but starts to heat the inductor (which saturates at 23A and allows a bit more more temperature-wise) and I hear something buzzing - can't tell what yet. FET gate control looks reasonable but does start to jump around a bit on the scope - not sure if it is a triggering thing or real yet.

Anyway, any advice on that LM5118, or the buck only that'll do what I want? The high current ones seem to supply lower voltages. I need 24V down to zero into a semi-constant (resistive) load, so higher current at higher voltages.  

I need to get something quickly and the tuning - I'm part way there - of the LM5118 is taking some time and I'd like another board run at that and another option at the same time to cover options at the same board run.

Thanks

Gary 

Hi Gary,

I understand that you have constant 24Vin and would like to get 24V down to zero on the output at around 6A load. For 24Vin to 24Vout, you definetly need a buck boost design otherwise if your output is not fully 24V you can choose one of the high voltage high current bucks.

It seems like you are familiar with Webench, so if you enter an output voltage that is 80-90% of the input voltage you will get a lot of options. since you need something quick, I would suggest using one of the high current controller or low side n-channel driver such as LM3481, lm3488 or lm3478  

Regards

Ismail  

Hello,

for myself I want to use 2 Lm3488, one to create +24V from 100V, the econd +5V from previous 24V.

Can I synchronise them by joining sync pin, with a common resistor to ground?

Thankyou for help

Alain