I recently purchased some Microchip TC7660S charge pumps as I plan to use them to generate a -12V DC output from a +12V DC input.
Based on the datasheet, the circuit seems simple enough.
However, I am rather puzzled by Pin 1, which the datasheet refers to as the Switching Frequency boost pin. Now, why would you need to boost the oscillating frequency - I'm guessing this is for when you want to generate a positive voltage multiplier.
Then on the bottom of page 10 (section 5.4 Changing the TC7660S Oscillator Frequency) it then talks about slowing the oscillating frequency using the following method:
For example, the addition of a 100 pF capacitor between pin 7 (OSC) and pin 8 (V +) will lower the oscillator frequency to 1 kHz from its nominal frequency of 10 kHz (a multiple of 10), and necessitate a corresponding increase in the values of C 1 and C 2 (from 10 μF to 100 μF).
So, as a learning exercise I'm also trying to fathom when does one decrease the frequency. I believe a clue is given in the datasheet, but not still not sure why one would want to, that you should only slow down the frequency for low currents. I'm given very little else.
I'm sure there's good reason for all of the above.
I look forward to receiving some insight.
Thanks.
Colin.
