MIC45205 Datasheet, PDF (17/31 Pages) Micrel Semiconductor – 26V/6A DC-to-DC Power Module

Micrel, Inc.
Application Information
Setting the Switching Frequency
The MIC45205 switching frequency can be adjusted by
changing the value of resistors R1 and R2.
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 the Electrical Characteristics⁽⁵⁾
table)
R1= 100kΩ is recommended.
R2 needs to be selected in order to set the required
switching frequency.
Switching Frequency
800
700 ^VOUT ^{= 5V}
600
V_IN = 12V
500
400
300
200
100
R1 = 100kΩ
0
10.00
100.00
1000.00
R2 (kΩ)
10000.00
Figure 7. Switching Frequency vs. R2
MIC45205
The switching frequency also depends upon VIN, VOUT
and load conditions as MIC45205 uses and adaptive ON-
time architecture as explained in the “Theory of
Operation” subsection in the Functional Description.
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 MIC45205 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:
ESR_COUT
≤
ΔV_OUT(PP)
ΔI_L(PP)
Eq. 6
Where:
ΔV_OUT(PP) = Peak-to-peak output voltage ripple
ΔI_L(PP) = Peak-to-peak inductor current ripple
April 15, 2014
17
Revision 1.0