BD9489F Datasheet, PDF (26/39 Pages) Rohm – DCDC converter with current mode

BD9489F
3.5.2 PWM Start Up 2 (Input STB Signal after Inputted PWM Signal)
Datasheet
Figure 37. PWM Start Up 2 (Input STB Signal after Inputted PWM Signal)
(*1)…REG58 starts up when STB=H.
(*2)…When REG58UVLO releases or PWM is inputted to the edge of PWM=L→H, SS charge starts and soft start period is
started. And while the SS is less than 0.4V, the pulse does not output. The pin SS continues charging in spite of the
assertion of PWM or OVP level. Please refer the section “2.8 the Retaining Function of The Output Voltage” in detail.
(*3)…The soft start interval will end if the voltage of the pin SS, Vss reaches 3.7V. By this time, it boosts V_OUT to the point where
the set LED current flows. The abnormal detection of FBMAX starts to be monitored.
(*4)…As STB=L, the boost operation is stopped instantaneously (GATE=L, SS=L). (Discharge operation works in the state of
STB=L and REG58UVLO=H. Please refer to the section 3.5.3)
(*5)…In this diagram, before the discharge period is completed, STB is changed to High again. As STB=H again, operation will
be the same as the timing of (*1).
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29.Oct 2014 Rev.002