Application information

ST1S10

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5

Application information

5.1

Description

The ST1S10 is a high efficiency synchronous step-down DC-DC converter with inhibit

function. It provides up to 3 A over an input voltage range of 2.5 V to 18 V, and the output

voltage can be adjusted from 0.8 V up to 85% of the input voltage level. The synchronous

rectification removes the need for an external Schottky diode and allows higher efficiency

even at very low output voltages.

A high internal switching frequency (0.9 MHz) allows the use of tiny surface-mount

components, as well as a resistor divider to set the output voltage value. In typical

application conditions, only an inductor and 3 capacitors are required for proper operation.

The device can operate in PWM mode with a fixed frequency or synchronized to an external

frequency through the SYNC pin. The current mode PWM architecture and stable operation

with low ESR SMD ceramic capacitors results in low, predictable output ripple. No external

compensation is needed.

To maximize power conversion efficiency, the ST1S10 works in pulse skipping mode at light

load conditions and automatically switches to PWM mode when the output current

increases.

The ST1S10 is equipped with thermal shut down protection activated at 150°C (typ.).

Cycle-by-cycle short circuit protection provides protection against shorted outputs for the

application and the regulator. An internal soft start for start-up current limiting and power ON

delay of 275 µs (typ.) helps to reduce inrush current during start-up.

5.2

External components selection

5.2.1

Input capacitor

drivers.

and reduces switching noise in the IC. A high power supply source impedance requires

larger input capacitance.

higher than the RMS input current. The maximum RMS input current can be calculated

using the following equation:

where

current. The duty cycle can be derived using the equation:

η

D

η

D

2

-

D

I

I

2

2

O

RMS

+

⋅

⋅

=

η

D

η

D

2

-

D

I

I

2

2

O

RMS

+

⋅

⋅

=