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RP500x
13
TIMING
CHART
(1) Soft Start Time
In the case of starting this IC with CE
In the case of starting this IC with CE, the operation can be as in the timing chart below.
When the voltage of CE pin (VCE) is beyond the threshold level, the operation of the IC starts. The threshold
voltage of CE pin is in between CE "H" input voltage (VCEH) and CE "L" input voltage (VCEL) described in the
electrical characteristics table. Soft-start circuit operates, and after the certain time, the reference voltage
inside the IC (VREF) is rising gradually up to the constant value.
VCEH
Soft-start Time
IC Internal Voltage
Reference
VCEL
Threshold Level
Lx Voltage
(VCE)
(VREF)
Soft-start Circuit
operating
(VLX)
Depending on Power supply,
Load Current, External Components
(VOUT)
Output Voltage
CE Pin
Input Voltage
PWM mode operating
during the Soft-start Time
Soft-start time is the time interval from soft start circuit starting point to the reference voltage level reaching
point up to this constant level.
Soft start time is not always equal to the turn-on speed of DC/DC converter.
The power supply capacity for this IC, load current, inductance and capacitance values affect the turn-on
speed.
In the case of starting with power supply
In the case of starting with power supply, when the input voltage (VIN) is larger than UVLO release voltage
(VUVLO2), soft start circuit operates, and after that, the same explanation above is applied to the operation.
Soft-start time is the time interval from soft start circuit starting point to the reference voltage level reaching
point up to this constant level.
Output Voltage
Input Voltage
VUVLO2
IC Internal Voltage
Reference
VUVLO1
Lx Voltage
Set VOUT
Soft-start Time
Depending on Power supply,
Load Current, External Components
PWM mode operating during the Soft-start Time
(VOUT)
(VIN)
(VREF)
(VLX)
Turn-on speed is affected by next conditions;
(a) Input Voltage (VIN) rising speed depending on the power supplier to the IC and input capacitor CIN.
(b) Output Capacitor COUT value and load current value.