Back light design of cell phone, PWM, PFM or Charge PUMP ?

[Btrend]

pwm in cellur phone

Hi experts,
Could u tell me, what kind of topology is suitable in back light deisgn of cell phone using while LED driver ?
there are a lot of advistments of IC vendor for this, some vendor said that their PWM solution provide lower noise inject to the batter source, but some vendor insist there solution (PFM) is much efficiency then PWM (but they don't address their noise issue ), some others assisit their Charge pump solution need only cap,
(but they don't address power loss in resistors of each branch ).
So, what's the real case in designing such back light of cell phone ?

Thanks in advance!

 

[sunking]

it depend on your system requirement.
For Charge Pump: low noise for rf circuit, but the efficiency power rate is low.
For PWM: provide lower noise inject to the batter source, but the noise big for rf circuit.
For PFM: the efficiency is best in the three kind but noise is biggest.