Application information

ST2S06

12/18

DocID13866 Rev 6

7

Application information

The ST2S06A33 and ST2S06B represent a series of dual adjustable current mode PWM

step-down DC-DC converters with an internal 0.5 A power switch, packaged in a QFN12L

(4x4 mm).

It is a complete 0.5 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 the cycle-by-cycle current limiting that provides protection against shorted

outputs.

The output voltage is determined by an external resistor divider, as the ST2S06A33 and

ST2S06B are adjustable regulators. The desired value is given by the following equation:

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

ST2S06A33 and ST2S06B have 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 functionality of the device. Due to the high switching frequency and peak current, it is

important to optimize the application environment by reducing the length of the PCB traces

and placing all the external components near the device.

Figure 23. Reset function

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