The UC2903DWG4 is a high-frequency device, and proper layout and placement are crucial for its operation. TI recommends a 4-layer PCB with a solid ground plane, and the device should be placed close to the input capacitors. The output inductor and diode should be placed close to the device as well. A good rule of thumb is to keep the high-frequency nodes (e.g., SW node) as short as possible and away from the low-frequency nodes (e.g., VIN, VOUT).
The inductor selection depends on the output current, output voltage, and switching frequency. TI recommends using an inductor with a low DC resistance (DCR) and high saturation current. A good starting point is to use an inductor with an inductance value between 1-10 μH, and a current rating of at least 1.5 times the maximum output current. The inductor should also be able to handle the peak current during switching.
The UC2903DWG4 has an absolute maximum input voltage rating of 18V. However, the recommended maximum input voltage is 15V to ensure reliable operation and to prevent damage to the device. Exceeding the recommended input voltage may result in reduced performance, increased power dissipation, or even device failure.
The UC2903DWG4 uses a voltage-mode control architecture, and the voltage feedback loop requires compensation to ensure stability. TI recommends using a Type II compensator with a zero at around 10 kHz and a pole at around 100 kHz. The compensation network should be designed to provide a phase margin of at least 45° and a gain margin of at least 10 dB.
The UC2903DWG4 has a built-in soft-start circuit that limits the inrush current during startup. The soft-start time is typically around 1-2 ms, but it can be adjusted by adding an external capacitor between the SS pin and ground. A larger capacitor will increase the soft-start time, while a smaller capacitor will decrease it.
UC2903DWG4 datasheet
by Texas Instruments
