MIC23451 Datasheet, PDF (16/20 Pages) Micrel Semiconductor – 3MHz, 2A Triple Synchronous Buck Regulator

Micrel, Inc.
increases, the MIC23451 goes into continuous
conduction mode (CCM) and switches at a frequency
centered at 3MHz. The equation to calculate the load
when the MIC23451 goes into continuous conduction
mode is approximated in Equation 11.
I_LOAD
> _{} ^(VIN
− V_OUT
2L × f
)
×
D

Eq. 11
As shown in Equation 11, the load at which the
MIC23451 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). Figure 4 shows that as the output current
increases, the switching frequency also increases until
the MIC23451 goes from HyperLight Load mode to PWM
mode at approximately 120mA. The MIC23451 will switch
at a relatively constant frequency around 3MHz after the
output current is over 120mA.
10000
Switching Frequency
vs. Load Current
1000
100
10
V_IN = 3V
V_IN = 3.6V
V_IN = 5V
1
0.1
0.0001
V_OUT = 1.8V
0.001 0.01
0.1
1
10
OUTPUT CURRENT (A)
Figure 4. SW Frequency vs. Output Current
MIC23451
Multiple Sources
The MIC23451 provides all the pins necessary to operate
the three regulators from independent sources. This can
be useful in partitioning power within a multi-rail system.
For example, two supplies may be available within a
system: 3.3V and 5V. The MIC23451 can be connected
to use the 3.3V supply to provide two, low-voltage
outputs (for example, 1.2V and 1.8V) and use the 5V rail
to provide a higher output (for example, 2.5V), resulting in
the power blocks shown in Figure 5.
Figure 5. Multi-Source Power Block Diagram
November 5, 2013
16
Revision 1.2