Hi,
I would like to use the MC33063 switching regulator in a buck regulator design.
My understanding is that this device drives a maximum of 1.5A into a load.
What I would like to achieve is the following:
V_out = 14.5 Volt
I_out(max) = 1.5A (or as close as possible)
V_in(max) = 18V
The basic parameters are as follows:
V_in(max) = 18V
I_out(max) [desired] = 1.5A
V_out = 14.4V
V_F = 0.6V
V_sat = 1.3V
V_in(min) = 16V
In order to calculate values, I assumed C_T = 1nF.
t_on = C_T / (4E-5) = 1E-9/(4E-5) = 0.000025s
t_on / t_off = (Vout + VF) / (Vin - Vsat - Vout) = (14.4 + 0.6) / (18 - 1.3 - 14.4) = 6.52173913043479
t_off = t_off = t_on / (t_on / t_off) = t_on / 6.52 = 0.0000038333s
1 / f = t_on + t_off = 0.0000288333s
f = 1 / (1 / f) = 34682.0809248555Hz
I_pk(switch) = 2 * I_out(max) = 3A
R_sc = 0.3 / I_pk(switch) = 0.3 / 3 = 0.1 Ohm [according to the datasheet, 0.2 is the minimum value]
L(min) = ((V_in(min) - V_sat - V_out) / I_pk(switch)) * t_on(max) = 0.000025H
C_o = I_pk(switch) * (t_on + t_off) / (8 * V_ripple(p-p)) = 0.000108125F
V_out = 1.25 * (1 + (R2 / R1)) = 1.25 * (1 + (45300 / 4300)) = 14.4186V
I have used both the datasheet for the MC34063 and application note slva252b in an attempt to calculate
various parameters and component values, as shown.
I believe I am possibly misinterpreting something (R_sc may not less than 0.2 Ohm ; nomad design tool complains when I select I_out = 1500mA). Can anyone with knowledge of such devices please assist if possible.
