MIC23155_12 Datasheet, PDF (14/19 Pages) Micrel Semiconductor – 3MHz PWM 2A Buck Regulator with HyperLight Load® and Power Good

Micrel Inc.
As the load current increases, the MIC23155 goes into
continuous conduction mode (CCM) and switches at a
frequency centered at 3MHz. The equation to calculate
the load when the MIC23155 goes into continuous
conduction mode may be approximated as illustrated in
Figure 7:
I_LOAD
>
 ^(VIN

− V_OUT
2L × f
)
×
D

Eq. 7
As shown in the previous equation, the load at which the
MIC23155 transitions from HyperLight Load mode to
PWM mode is a function of the input voltage (V_IN), output
voltage (V_OUT), duty cycle (D), inductance (L) and
frequency (f). As shown in Figure 5, as the output
current increases, the switching frequency also
increases until the MIC23155 goes from HyperLight
Load mode to PWM mode at approximately 180mA. The
MIC23155 will switch at a relatively constant frequency
around 3MHz once the output current is over 180mA.
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0.1
Switching Frequency
vs. Output Current
L=0.47µH
L=1.0µH
1
10 100 1000 10000
OUTPUT CURRENT (mA)
Figure 5. SW Frequency vs. Output Current
MIC23155
November 2012
14
M9999-110812-A