L7985
 current limit 2.5A -> fsw <= 500kHz

Vref = 0.6V
Vout = Vref * ( 1 + Rb / Rt )

 estimated values from figure
 Rsw  Fsw
kOhm  kHz
  33 1000
  70  640
  80  570
  90  510
 100  490
 110  480
 120  470
open  250