Hi,
Seems app notes for 3525 are for the monolithic or paleolithic IC, or whatever term is more appropriate, SG1524.
ST, ST-AN250 (cd00003778) - 'A Second-Generation IC Switch Mode Controller Optimized for High Frequency Power MOS Drive'
p.7: f = 1/(CT x (0.07 RT + 3 RD)), and a bit more oscillator info.
Microsemi, PS-2-SG1524 (an_ps_2_sg1524_rev2) - 'Simplifying Converter Design with a New Integrated Regulating Pulse Width Modulator'
p.2: Oscillator info.
p.3: Comp. pin function/use.
Silicon General, Application Notes - SG1524B (PS-5_SG1524B_AppNote) - 'Converting 1524 Switching Power Supply Designs to the SG1524B'
p.3: pin 9 EA formulas for frequency compensation component values and poles and zeroes.
ST, ST SG2525A SG3525A datasheet
p.3: EA output low and high levels, and so on.
p.4: fOSC formula
p.6: figure 1 and figure 2 are oscillator charge and discharge times with some component values.
It seems RD goes from pin 5 (ramp) to pin 7 (discharge), if used.
To me, it looks like you have to pay attention to the EA and the PWM Comparator electrical specifications about min. and max. in and out levels, use figure 1 and 2 and fOSC formula to set your linear ramp. Nice puzzle... In case it helps to guesstimate ramp peak at '? t':
delta V/delta t = I x C. Linear isn't quite same as RC charging constant to calculate V at '? t'.
Hope not answering things you didn't ask, sorry if have.