STELPD01 datasheet(8/27 Pages) STMICROELECTRONICS

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Functional description

6.1

Turn-on and soft start-up feature

When the input voltage is applied and it reaches VUVLO (undervoltage lockout threshold) value, the EN/Fault pin

goes up to the high state (if left floating) and the internal control circuitry is enabled to perform the output start-up

ramp. See the figure below.

Figure 5. Typical startup sequence for STELPD01 and STELPD01A

The start-up procedure starts with an initial delay time of typically 165 µs, then the output voltage is supplied with

a slope defined by the internal dV/dt circuitry. If no additional capacitor is connected to dV/dt pin, the ramp-up time

(VOUT from 10% to 90%) is around 500 µs with VIN = 5 V.

The inrush current profile can be controlled through a dedicated soft-start circuit. Connecting a capacitor between

the CdV/dt pin and GND allows the modification of the output voltage ramp-up time. Given the desired time interval

Δt during which the output voltage goes from 10% to 90% of VOUT, the capacitance to be added on the CdV/dt pin

can be calculated using the following theoretical formula.

Δtms =0.0024×VINV ×CdV/dtpF +0.1×VINV

(1)

STELPD01

Functional description

DS13254 - Rev 1

page 8/27

STELPD01 Datasheet(PDF) 8 Page - STMicroelectronics