During device initialization, a resistor-to-digital converter in the device determines the state of the FSEL pin and sets the switching frequency of the DC/DC converter according to Table 9-2.
|Resistor at FSEL (1%)||Switching Frequency|
|Short to GND||1.5 MHz|
|6.2 kΩ to GND||2.25 MHz|
|47 kΩ to VIN||2.5 MHz|
|Short to VIN||3 MHz|
Detection of the state of the FSEL pin works as follows:
To detect the most significant bit (MSB), the circuit opens S1 and S2, and the input buffer detects if a high or a low level is connected to the FSEL pin.
To detect the least significant bit (LSB):
The propagation delay of the current-sensing comparator limits the minimum on time of the device, meaning the maximum switching frequency the device can support decreases with small duty cycles. Figure 8-5 shows the practical operating range of the device with 3.3-V and 5-V supplies.