ST1S03AIPMR STMICROELECTRONICS [STMicroelectronics], ST1S03AIPMR Datasheet - Page 7

• Manufacturer Part Number: ST1S03AIPMR
• Description: 1.5A, 1.5 MHz Adjustable, with inhibit function Step-down switching regulator in DFN6 3x3
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

ST1S03A
Typical application
5
Typical application
Figure 3.
Application circuit
Application notes
The ST1S03A is an adjustable current mode PWM step-down DC/DC converter with internal 1.5A power
switch, packaged in a 6-lead DFN 3x3.
It’s a complete 1.5A 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 250mA 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=100µs 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 ST1S03A 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 other four external components are required: an inductor a schottky and
two capacitors. 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 ST1S03A 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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