R1517 Datasheet, PDF (14/38 Pages) RICOH electronics devices division – Input Voltage Range (Maximum Rating) 3.5 V to 36.0 V (50.0V)

R1517x
NO. EA−304−170112
Soft-start Function
R1517x is equipped with a constant slope circuit, which achieves a soft-start function. This circuit allows the output
voltage to start up gradually when the CE is turned on. The constant slope circuit minimizes the inrush current at
the start-up and also prevents the overshoot of the output voltage. For R1517xxxxB/C/D, the capacitor to create
the start-up slope is built in this device that does not require any external components. The start-up time and the
start-up slope angle are fixed inside the device. In R1517xxxxE/F, the soft-start time is adjustable by inserting the
external capacitor to DELAY pin. By using the following equation, the relation between the soft-start time tD [s]
and DELAY pin capacitor CD [F] is determined.
tD = ((CD + 90 x 10^-12) / IDELAY) x 0.73
When the capacitor CD is not used in R1517xxxxE/F, use the DELAY pin as OPEN. At that time, CD = 0 in the
above equation, therefore the start-up time is about 26 µs. However, be sure to consider approximately 50 µs of
CE delay time.
Conventional Inrush Current Limit Circuit
(Diagrammatic sketch)
CE Delay Time
CE Input Voltage
Output Voltage
Constant Slope Circuit
(Diagrammatic sketch)
CE Input Voltage
CE Delay Time
Soft-start Time
Output Voltage
Inrush Current
Inrush Current
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