I am looking at pg. 12 of the LTM4638 datasheet:
https://www.analog.com/media/en/technical-documentation/data-sheets/ltm4638.pdf
There is a formula relating RFSET to free-running switching frequency. The claimed range (sentence below) is 400 kHz to 3 MHz. I think this is incorrect:
- The lowest possible switching frequency, according to the formula, uses an open (infinite) RFSET resistor. However, when I calculate the resulting switching frequency, it is a minimum of 609 kHz. (It is physically impossible to produce a higher parallel resistance than 274k!)
- The paragraph above states that the default operating frequency is 600 kHz.
Assuming, then, that 400 kHz is a typo - I think the lowest free-running switching frequency is 609 kHz. Can you confirm this interpretation?
If correct, then: assume we are operating with a 609 kHz oscillator and are now supplying an external clock at CLKIN. This clock must satisfy the +/-30% constraint described in the datasheet - hence, the part cannot be synchronized below about 0.7 * 609 kHz = 425 kHz. Can you also confirm this interpretation?
thanks,
Graeme
