I'm doing a new design with LM5176 buck boost. I've run it through web bench and also am doing a sanity check against the recommended equations in the data sheet.
I'd like to get a little more information about the slope capacitance equation. Cslope = gmslope * (L1 / (Rsense * Acs))
gmslope is specified 2us in the datasheet, Acs is also shown on the block diagram as 5 (a unitless gain factor). Rsense is in ohms and Inductor L1 in henries. The product Rsense * Acs is the effective current sense resistance, that is, a 8 milliohm resistor with a gain of 5 behaves like a 40 milliohm resistor. So far, that is how I'm reading the equation.
So, is the relationship between inductance and effective resistance, time here (as in t = L/R)? that is, ignoring gmslope, is L1/(Rsense*Acs) have units of seconds. .If so, multiplying by gmslope results in units of seconds squared. Then, in order to convert to capacitance, we use the relationship sqrt(LC) = seconds or L*C = s^2; however, the datasheet shows result of capacitance rather than product of inductance * capacitance.
Wonder how you are getting from seconds squared to capacitance or did I miss anything in deriving this equation?
I have most equations worked through from the datasheet, and they make a certain amount of sense. This one has me puzzled and wonder if you could explain it's derivation a little more than what the datasheet has to offer. The slope compensation capacitor is unique to TI, and not sure if any of the app notes talk about it.
Thanks, Bob
