Datasheet XCL303, XCL304 (Torex) - 10

XCL303/XCL304 Series
■OPERATIONAL EXPLANATION (Continued) <CE Function> When a “H” voltage (VCEH) is input to the CE terminal, it operates normally after the output voltage is started by the soft start function. When a “L” voltage (VCEL) is input to the CE terminal, it goes to the stand-by state, the quiescent current is suppressed to the stand-by current ISTB (TYP.0 μA) level and the Pch driver transistor turns OFF. <UVLO Function> When the VIN terminal voltage drops below the UVLO detect voltage level (VUVLOD), the UVLO function operates and turns off the Pch driver transistor to prevent any erroneous pulse output due to possible unstable action of the internal circuit. When the VIN terminal voltage increases above the UVLO release voltage level (VUVLOR), the UVLO function is released. After the UVLO function is released, the soft start function starts the output voltage and the IC operates normally. The UVLO function operates even if the VIN terminal momentarily drops below the UVLO detect voltage. In addition, whilst the UVLO function is in operation, rather than being in a stand-by state, the IC is in a switching operation stopped state, so the internal circuit is still operating. <Soft Start Function> This gently starts up the output voltage when the IC starts up and the UVLO function is released to suppress the inrush current. The VREF startup circuit operates after the “H” voltage (VCEH) is input to the CE terminal and after the UVLO function is released. The VREF startup circuit charges the CVREF with current and can gently raise the VREF voltage and FB voltage. In response to this, the output voltage is lowered proportionally to the increase in the VREF voltage and FB voltage. This action makes it possible to prevent input current inrush and to smoothly lower the output voltage. The output voltage startup time (soft start time) is determined by the capacity of the CVREF connected to the VREF terminal. In the stand-by state and during the UVLO function operation, the charge accumulated in the CVREF is discharged and the VREF voltage is made to be 0V. Soft Start Time : tss (Depend on CVREF) Normal operation St and-by 0V VOUT VOUTSET Fall time depends on Iout VREF Voltage V 1.6V (TYP.) REF VFB Voltage VFB 0.5V (TYP.) 0V VCE VCEH VCEL 0V 10/24