Application notes

ST1S12XX, ST1S12XX12, ST1S12XX18

10/20

Doc ID 14314 Rev 3

6

Application notes

The ST1S12Gxx is an adjustable current mode PWM step-down DC-DC converter with

internal 0.7 A power switch, packaged in TSOT23-5L. This device is a complete 0.7 A

switching regulator, with its internal compensation eliminating the need for additional

components.

Because the ST1S12Gxx an adjustable regulator, the output voltage is determined by an

external resistor divider. The desired value is derived by the following equation:

Equation 1

For the device to function only a few component are required: an inductor, two capacitors

and the resistor divider. The inductor selected must be capable of non saturation at peak

current level. Moreover, its value can be selected taking into account that a large inductor

value increases efficiency at low output current and reduces output voltage ripple, while a

smaller inductor can be used when it is important to reduce package size and the total cost

of the application. Finally, the ST1S12Gxx has been designed to work properly with X5R or

X7R SMD ceramic capacitors both at the input and at the output. These types of capacitors,

due to their very low series resistance (ESR), minimize the output voltage ripple. Other low

ESR capacitors can be used according to the need of the application without compromising

the correct functioning of the device.