MIC2207 Datasheet, PDF (17/21 Pages) Micrel Semiconductor – 3mmx3mm 2MHz 3A PWM Buck Regulator

Micrel
Then, determine the output impedance by looking at
the output impedance vs frequency graph. Then
calculating the voltage deviation times the load step;
∆V_OUT = ∆I_OUT × Z_OUT
The output impedance graph shows the relationship
between supply voltage and output impedance. This
is caused by the lower Rdson of the high side
MOSFET and the increase in gain with increased
supply voltages. This explains why higher supply
voltages have better transient response.
↓Z_TOTAL =
↓
R_DSON + DCR +
↑ GAIN
X_L
X _COUT
MIC2207
Ripple measurements
To properly measure ripple on either input or output
of a switching regulator, a proper ring in tip
measurement is required. Standard oscilloscope
probes come with a grounding clip, or
a long wire with an alligator clip.
Unfortunately, for high frequency
measurements, this ground clip can
pick-up high frequency noise and
erroneously inject it into the measured
output ripple.
The standard evaluation board
accommodates a home made version
by providing probe points for both the
input and output supplies and their
respective grounds. This requires the
removing of the oscilloscope probe
sheath and ground clip from a
standard oscilloscope probe and
wrapping a non-shielded bus wire
around the oscilloscope probe. If there
does not happen to be any non
shielded bus wire immediately available, the leads
from axial resistors will work. By maintaining the
shortest possible ground lengths on the oscilloscope
probe, true ripple measurements can be obtained.
April 2005
17
M9999-040705
www.micrel.com