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:
V
O
= V
FB
[1+R1/R2]
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
V
TL
V
TH
V
IN
Reset
t
DEL
V
TL
V
TH
V
IN
Reset
t
DEL
