TPS 54427 Project

[Torkemada]

Hi all,
I have an ideea to build a stepdown with this Ti IC (4.5V to 18 V Input, 4-A Output Single Synchronous Step-Down Switcher with Integrated FET (SWIFT™).

Schematic:
Imageshack - tps54427schematic.jpg

,in a few days i'll have all components and start testing

 

[iuseaspork]

I'm trying to understand why you have a bunch of caps in parallel.

 

[Torkemada]

Caps gives circuit stability and Ti recommend that in datasheet and i think is a solution for better heat exchange.
One 22 uf cap in enough for imput and one for output.(atty doesnt care about ripple)

 

[iuseaspork]

Why not use 1 - 47uf cap instead of 2 - 22uf caps?

 

[CraigHB]

Parallel output caps cut ESR in half which reduces output ripple. Output ripple in not an issue for atomizer power, but it can be for the controller since output voltage is fed back to it. Depending on the caps, it can also be a matter of capacitor current ratings. It's usually not a concern for SMD MLCC caps since they're limited only by heat, but it definitiely is for tantalum polymer caps.

 

[iuseaspork]

...Uh... Oh, there IS a reason. LOL

 

[jhonutz]

seems to be good IC, and it`s brand new

 

[Torkemada]

IC is small and easy to solder,have enable pin (pin EN - R=10k - to +) and i intend to put a touch switch with a protected SMD P channel Mosfet (i'm looking for a good one for this project,R1=100m ohm,R2=1-47k ohm-i'll test here).
Now i'm working to a double sided proper PCB .

 

[Torkemada]

i fond this mosfet ,seems to be good for touch -FDS6679AZ
i want to use this schematic into my car direct at 12v too

 

[Torkemada]

Touch :

 

[CraigHB]

That's a great MOSFET. I've used it as a switch for a direct 5V passthru. It's ESD protected. The threshold voltage is a little high for a single cell mod though. Might work okay anyway, you'd have to try it and see.

 

[Torkemada]

Imput voltage will be 7.4 V (2*14500) or 12 V (in the car).......you think will work?

 

[CraigHB]

Yes, that voltage is just right for that part. I was talking about using it for a switch with a single cell at 3.7 Volts.

 

[Torkemada]

Yes, that voltage is just right for that part. I was talking about using it for a switch with a single cell at 3.7 Volts.

for single cell NTJS3151P AND FDY101PZ is interesting (not tested yet)

 

[Torkemada]

is working with few modification with the touch

 

[Torkemada]

Touch :

View attachment 77975

wrong schematic enable pin -5678 pins
vcc -pin 1
i use 47k rez

 

[jhonutz]

i made a pcb with TPS54427, works well, very well i can say...Good luck with your projects

 

[slimest]

Torkemada, great!
About a separate mosfet switch. According to datasheet Ren (resistance of ENABLE pin to ground) typically is 450 kOhm and ENABLE voltage is just 1.6V. Seems to me that in most cases simple touch contacts between + and ENABLE pin should work...

 

[Torkemada]

The pcb is ready,works great in 1 v-6.4 v range with touch sensor (+ ESD) ,i have a little delay after i press the touch contact (on shutdown)
maybe i use too big value for soft start capacitor
i think is the best new solution for mods that i tested until now

 

[Torkemada]

..............Seems to me that in most cases simple touch contacts between + and ENABLE pin should work...

yap,if u touch en and + the coverter will be ON...any switch will work