MIC28513 Datasheet, PDF (21/34 Pages) Microchip Technology – 45V, 4A Synchronous Buck Regulator

5.0 APPLICATION INFORMATION
5.1 Output Voltage Setting
Components
The MIC28513 requires two resistors to set the output
voltage as shown in Figure 5-1.
MIC28513
5.2 Setting the Switching Frequency
The MIC28513 switching frequency can be adjusted by
changing the resistor divider network from V_IN.
g_M AMP
V_REF
R1
FB
R2
FIGURE 5-1:
Configuration.
Voltage Divider
The output voltage is determined by Equation 5-1.
EQUATION 5-1:
V_OUT
=
V_F
B



1
+
RR_{----12--}
Where:
V_FB
0.8V
A typical value of R1 used on the standard evaluation
board is 10 kΩ. If R1 is too large, it may allow noise to
be introduced into the voltage feedback loop. If R1 is
too small in value, it will decrease the efficiency of the
power supply, especially at light loads. Once R1 is
selected, R2 can be calculated using Equation 5-2:
EQUATION 5-2:
R2 = ----^V----^F---^B----^-----^R----1-----
V_OUT – V_FB
FIGURE 5-2:
Adjustment.
Switching Frequency
Equation 5-3 gives the estimated switching frequency.
EQUATION 5-3:
Where:
f₀
f_SW
=
f₀



R^{----1---7--R---+-1---7-}R^{----1---9-}
Switching frequency when R17 is open;
typically 600 kHz.
Figure 5-3 shows the switching frequency versus the
resistor R17 when R19 = 100 kΩ.
 2016 Microchip Technology Inc.
FIGURE 5-3:
R17.
Switching Frequency vs.
5.3 Inductor Selection
Values for inductance, peak, and RMS currents are
required to select the output inductor. The input and
output voltages and the inductance value determine
the peak-to-peak inductor ripple current. Generally,
higher inductance values are used with higher input
voltages. Larger peak-to-peak ripple currents will
increase the power dissipation in the inductor and
DS20005522A-page 21