MIC45212 Datasheet, PDF (17/31 Pages) Micrel Semiconductor – 26V/14A DC-to-DC Power Module

Micrel, Inc.
Application Information
Setting the Switching Frequency
The MIC45212 switching frequency can be adjusted by
changing the value of resistors R1 and R2.
MIC45212
The switching frequency also depends upon VIN, VOUT
and load conditions as MIC45212 uses and adaptive ON-
time architecture as explained in Theory of Operation.
Output Capacitor Selection
The type of the output capacitor is usually determined by
the application and its equivalent series resistance
(ESR). Voltage and RMS current capability are two other
important factors for selecting the output capacitor.
Recommended capacitor types are MLCC, OS-CON and
POSCAP. The output capacitor’s ESR is usually the main
cause of the output ripple. The MIC45212 requires ripple
injection and the output capacitor ESR affects the control
loop from a stability point of view.
The maximum value of ESR is calculated as in Equation
6:
Figure 6. Switching Frequency Adjustment
Equation 5 gives the estimated switching frequency:
f_SW

f_O

R2
R1 R2
Eq. 5
Where:
f_O = 600kHz(Typical per Electrical Characteristic Table)
R1= 100kΩ is recommended.
R2 needs to be selected in order to set the required
switching frequency.
Switching Frequency
800
700
V_OUT = 5V
600
VIN = 12V
500
400
300
200
R1 = 100kΩ
100
0
10.00
100.00
1000.00
R2 (kΩ)
10000.00
Figure 7. Switching Frequency vs. R2
ESR_COUT

ΔV_OUT(PP)
ΔI_L(PP)
Where:
ΔV_OUT(PP) = Peak-to-peak output voltage ripple
ΔI_L(PP) = Peak-to-peak inductor current ripple
Eq. 6
April 28, 2014
17
Revision-1.0