High efficiency step down conventer?

[asrock70]

Parameter
- input voltage 8-30V
- output voltage adjust (1.8V / 3.3 / 5.0 V)
- output current min 500uA max 800mA
- high efficiency around 95%
- package SO-8 or smaller
- ideally On/Off input
- low cost ~1$ 1000pcs

To cut a long story short, some as LM2675, but low cost or smaller size or synchronous with integrated FET.
Advise?

 

[FvM]

As you probably know, you have several conflicting requirements:
- large Vin/Vout ratio and high efficiency
- effective synchronous switching and high input voltage

It's probably a good specification for a next generation simple switcher. But I fear, the performance of present solutions is far off.

 

[asrock70]

It may be.
Input voltage in reality will be 12V or 24V + - 15% from external sources.
I chose the LM2675 yet, but our country is about 2.6 $.
However you say, maybe there is something like TPS6229x for higher input voltage
or
a Chinese manufacturer makes a copy of the LM2675 with the price of $ 0.5

 

[FvM]

O.K., I forgot price among conflicting requirements. Seriously, I don't see a solution.

 

[asrock70]

Unfortunately, I have reached the same conclusion.:sad:
Why?
Everywhere the same talk on the environment and saving energy.
In my country goes crazy energy as far as latitude 53 to build solar power plants to produce power electricity.Horrible.
On the other hand.
Even the LM2675 have RdsOn 0.25 Ohm. 20mOhm 40V MOSFET is commonly available, why not integrate into these areas, synchrony models with two transistors to mention.

 

[FvM]

Interestingly, Fairchildsemi has used a multichip design with their FAN210x high voltage synchronous buck converters. Apparently, it's not so easy to merge analog IC and state-of-the-art MOSFET. Using large area FETs is bringing drawbacks, that are possibly not obvious at first sight:

- increased gate drive charge and respective idle current
- increased switching losses from increased output node charge

It still seems difficult for synchronous buck converters with large Vin/Vout ratio to achieve higher efficiency than 85 %.

Resonant converter toplogies with zero-voltage or zero-current switching can achieve higher efficiency, but they don't seem appropriate for small, low power converters.

 

[eem2am]

FvM is right.

there is nothing out there.

i have resorted to SEPIC to meet a similar requirement as yours.

https://www.edaboard.com/threads/194278/