This User Guide supports the evaluation kit for the FAN2103 TinyBuck(TM) Integrated Synchronous Buck. This guide should be used in conjunction with the FAN2103 datasheet, located at Fairchild’s website (www.fairchildsemi.com). This board (version FAN2103_1A, FEB207) is configured for light-load, power-saving mode of operation. It provides 1.8VOUT, 0-3A from 8-20VIN at a 500KHz switching rate using low-cost ceramic output capacitors.

• A ground strap is provided near the lower left corner of the evaluation board to facilitate oscilloscope probe connections.
• Switching Waveform Connect an oscilloscope probe to test point marked SW to view the switching waveform. Since the MOSFETs are integrated, gate/drive waveforms cannot be viewed.
• Enable / Inhibit The momentary push-button switch S1 establishes a connection from EN to GND, inhibiting the FAN2103 when, switching ceases and only standby current is consumed. A new soft-start cycle commences upon release of S1.
• Current Limit -- The current limit threshold can be set lower by reducing R9. This feature is useful in applications where <3Ais required, allowing the designer to select passive external components with lower current ratings. With R9 open, the FAN2103 enforces a maximum default current limit in excess of 3A.
• Auto-Restart -- The board is configured for auto-restart with a delay (C7). Delay increases linearly with C7. Refer to the device datasheet for auto-restart or latch-off options.
• Power-Saving Mode -- The board is provisioned for light-load power-saving mode. For continuous PWM operation, remove R8.
• Switching Frequency -- Switching frequency is set by R10 (RT). Frequency may be lowered to 200 KHz or raised to >600 KHz. Large changes in frequency may warrant additional component value changes for the output filter and compensation network.
• Input Voltage -- The demo board is currently optimized to work with 8V to 20Vinput voltage range. For operating between 3V to 8V, modifications to output filter, compensation network component values and R7 will need to be done. Consult Excel based calculator to get new values.
• Output Voltage -- The output voltage is determined by the ratio of R1 and R4. For minor output voltage changes, adjust R4. Larger VOUT changes may impact output filter and compensation network component value selection.
• Feedback Loop Response -- R5 opens the feedback loop for closed-loop response measurement. Remove R5 and connect a network analyzer or injection transformer in its place.