st1s06 STMicroelectronics, st1s06 Datasheet - Page 14

• Manufacturer Part Number: st1s06
• Description: Synchronous Rectification With Inhibit, 1.5a, 1.5 Mhz Fixed Or Adjustable, Step-down Switching Regulator In Dfn6 3x3
• Manufacturer: STMicroelectronics

Application notes
ST1S06xx
7
Application notes
The ST1S06 is an adjustable current mode PWM step-down DC-DC converter with internal 1.5 A power
switch, packaged in a 6-lead DFN 3x3.
It’s a complete 1.5 A switching regulator with its internal compensation eliminating additional component.
The constant frequency, current mode, PWM architecture and stable operation with ceramic capacitors
results in low, predictable output ripple. However, in order to maximize the power conversion efficiency
with light load, the regulator reduces automatically the switching frequency when the output load
becomes less than 250 mA typically.
To clamp the error amplifier reference voltage a soft start control block generating a voltage ramp, has
been implemented. Besides an on-chip power on reset of 50 = 100 µs ensure the proper operation when
switching on the power supply. Other circuits fitted to the device protection are the thermal shut down
block which turn off the regulator when the junction temperature exceeds 150 °C typically and the cycle-
by-cycle current limiting that provides protection against shorted outputs.
Being the ST1S06 an adjustable regulator, the output voltage is determined by an external resistor
divider. The desired value is given by the following equation:
V
= V
[1+R1/R2]
O
FB
To make the device working, only few component are required: an inductor and two capacitors and the
resistor divider. The chosen inductor must be able to not saturate at the peak current level. Besides, its
value can be selected keeping in account 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 the package size and the total cost of the application. Finally, the ST1S06 has been
designed to work properly with X5R or X7R SMD ceramic capacitors both at the input and at the output.
this kind of capacitors, thanks 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 invalidate
the right functioning of the device.
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