9.2.1 General Application
Figure 21 shows a general application schematic. FPWM, SYNC and EN are digital inputs. RESET is an open-drain output. FB connection is different for the fixed output options and the adjustable option.
- The FPWM pin can be connected to GND to enable light-load PFM operation. Select this option if current consumption at light load is critical. The pin can be connected to VCC or VIN for forced 2-MHz operation. Select this option if constant switching frequency is critical over the entire load range. The pin can also be driven by an external signal and can be toggled while the part is in operation (by an MCU for example.) Refer to the Electrical Characteristics and Device Functional Modes for more details on the operation and signal requirements of the FPWM pin.
- The SYNC pin can be used to control the switching frequency and the phase of the converter. If the function is not needed, tie the SYNC pin to GND or 3 V.
- The RESET pin can be left floating if the function is not required. If the function is needed, the pin must be connected to a DC rail through a pullup resistor (100 kΩ is the typical recommended value). Check Electrical Characteristics and RESET Flag Output for the details of the RESET-pin function.
- If the device is a fixed-output version (3.3 V or 5 V output option), connect the FB pin directly to the output. In the case of an adjustable-output part, connect the output to the FB pin through a voltage divider. See Detailed Design Procedure for details on component selection.
- The BIAS pin can be connected directly to the output except in applications that can experience inductive shorts (such as cases with long leads on the output). In those cases, a 3 Ω or so is necessary between the output and the BIAS pin, and a small capacitor to GND is necessary close to the BIAS pin (CBIAS). Alternatively, a Schottky diode can be connected between the OUT and GND to limit the negative voltage that can arise on the output during inductive shorts. In addition, BIAS can also be connected to an external rail if necessary and if available. The typical current into the bias pin is 15 mA when the device is operating in PWM mode at 2.1 MHz.
- Power components must be chosen carefully for proper operation of the converter. Detailed Design Procedure discusses the details of the process of choosing the input capacitors, output capacitors, and inductor for the application.
Figure 21. General Application Circuit