General information

ST2S08B

10/18

Doc ID 18290 Rev 2

7

General information

The ST2S08B is a dual adjustable current mode PWM step-down DC-DC converter.

It is a complete 1.5 A switching regulator with internal compensation that eliminates the

need for additional components.

The constant frequency, current mode, PWM architecture and stable operation with ceramic

capacitors, results in low, predictable output ripple.

To clamp the error amplifier reference voltage, a soft-start control block, generating a

voltage ramp, has been implemented. Other circuits fitted to the device protection are the

thermal shut-down block, which turns off the regulator when the junction temperature

exceeds 150 °C (typ.), and cycle-by-cycle switching current limiting.

Operation of the device requires few components: 2 inductors, 3 capacitors, and a resistor

divider. The chosen inductor must be capable of not saturating at the peak current level. Its

value should be selected keeping in mind that a large inductor value increases the efficiency

at low output current and reduces output voltage ripple, while a smaller inductor can be

chosen when it is important to reduce package size and total application cost.

Finally, the ST2S08 has been designed to work properly with X5R or X7R SMD ceramic

capacitors both at input and at 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 needs of the application, without compromising the correct

functioning of the device.