9.3.9 Frequency Selection (FSW)

To get high power density with very small solution size, a high switching frequency allows the use of small external components for the output filter. However switching losses increase with the switching frequency. If efficiency is the key parameter, more than solution size, the switching frequency can be set to half (1.25 MHz typ.) by pulling FSW to High. Running with lower frequency a higher efficiency, but also a higher output voltage ripple, is achieved. Pull FSW to Low for high frequency operation (2.5 MHz typ.). To get low ripple and full output current at the lower switching frequency, it's recommended to use an inductor of at least 2.2uH. The switching frequency can be changed during operation, if needed. A pull down resistor of about 400kOhm is internally connected to the pin, acting the same way as at the DEF Pin (see above).