MIC2128 Evaluation Board User’s Guide
DS50002533A-page 16 2016 Microchip Technology Inc.
2.3.4 Loop Gain Measurement
Resistor R14 is placed in series with the regulator feedback path. The control loop gain
can be measured by connecting an impedance analyzer across the resistor and
selecting the resistor value between 20 to 50.
2.3.5 Setting the Switching Frequency
The MIC2128 Evaluation Board is an adjustable-frequency, synchronous buck
controller featuring a unique adaptive on-time control architecture. The switching
frequency can be adjusted between 270 kHz and 800 kHz by changing the resistor
divider network consisting of R2 and R3.
The following formula provides the estimated switching frequency:
EQUATION 2-4: EQUATION 4
The evaluation board design is optimized for a switching frequency of 300 kHz. If the
switching frequency is programmed to either lower end or higher end, the design needs
optimization. The switching frequency adjustment is depicted in Figure 2-2:
FIGURE 2-2: Switching Frequency Adjustment.
where:
f
0
= Switching Frequency when R2 is 100and R3 is open, f
O
is typically
800 kHz. For a more precise setting, it is recommended to use the
Switching Frequency graph from the data sheet.
f
SW
f
0
R3
R2 R3+
-------------------- -=
V
IN
FREQ
A
GND
MIC2128
V
VIN
R2
R3
11
16
14
