Question 22.15: n the buck regulator of Fig. 22-29, R1 = 2.21 kΩ and R2 = 2....
n the buck regulator of Fig. 22-29, R_1 = 2.21 \ kΩ and R_2 = 2.8 \ kΩ. What is the output voltage? What is the minimum input voltage that can be used with the output voltage?
With Eq. (22-24), we can calculate:
V_{out}=\frac{R_1+R_2}{R_1} V_{REF}=\frac{2.21 \ kΩ + 2.8 \ kΩ}{2.21 \ kΩ}(2.21 \ V) = 5.01 \ V
Because of the drop across the switching device of an LT1074, the input voltage has to be at least 2 V greater than the output of 5 V, which means a minimum input voltage of 7 V. A more comfortable headroom will use an input voltage of 8 V.
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