BD9489F Datasheet, PDF (28/39 Pages) Rohm – DCDC converter with current mode

BD9489F
3.5.4 Soft Start Function
STB
PWM
UVLO
VCCUVLO
REG58UVLO
OVP
RT
2.0V
SS
Datasheet
2.7V
3.0V
7.2V
7.5V
2.3V
2.6V
3.0V
2.8V
4clk
(*1)
(*2)(*3) (*4)
(*5)
(*6)
(*7)
Figure 39. Soft Start Function
(*1)…The SS pin charge does not start by just STB=H. PWM=H is required to start the soft start. In the low SS voltage, the
GATE pin duty depends on the SS voltage. And while the SS is less than 0.4V, the pulse does not output.
(*2)…By the time STB=L, the SS pin is discharged immediately. As REG58UVLO=H, RT is still High.
(*3)…As the STB recovered to STB=H, The SS charge starts immediately by the logic PWM=H in this chart.
(*4)…The SS pin is discharged immediately by the UVLO=L.
(*5)…The SS pin is discharged immediately by the VCCUVLO=L.
(*6)…The SS pin is discharged immediately by the REG58UVLO=L.
(*7)…The SS pin is not discharged by the abnormal detection of the latch off type such as OVP until the latch off.
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29.Oct 2014 Rev.002