MIC2267 Datasheet, PDF (14/19 Pages) Micrel Semiconductor – Input Current Limiting Synchronous Buck Regulator

Micrel Inc.
C_IN
Connect a ceramic capacitor of X5R or X7R dielectric
from the VIN pin to PGND as close to the MIC2267 as
possible to decouple the high di/dt switching current
paths. A minimum value of 10µF is recommended for
most applications. An additional 22µF can be useful in
reducing ringing effects if long power leads are used to
connect power.
C_OUT
Connect a ceramic capacitor of X5R or X7R dielectric
from V_OUT to PGND as close as possible to the inductor
and C_IN ground connection to reduce the effect of high
di/dt ground currents from interfering with internal
signals. A minimum of 47µF is recommended for most
applications. Additional bulk capacitance such as
electrolytic, tantalum or ceramic can be added to
improve transient performance and hold up during large
load transients.
5V Pass Through
Some applications will require a legacy 5v supply to be
available which also benefits from the current limit
protection. The circuit in Figure 5 allows for a low current
bias supply to be provided while still providing current
limit protection.
1A Schottky
VOUT2 = 4.75V
10uF
VIN = 5.0V USB
10k
10uF
22nF
VIN
SW
PGOOD
EN MIC2267
FB
FILTER
FREQ
COMP
SLOPEC LIMIT PGND AGND
11.5k
4.7uH
23k
10k
680pF
100k
75k 110k
15nF
VOUT1 = 3.3V
100µF 150µF 150µF
Figure 3. Standard MIC2267 Circuit with
Protected ~5v Bias Supply
MIC2267
Below are some oscilloscope shots of the Pass through
circuit operating under the following conditions:
Normal operation:
V_OUT1 = 3.3v @ 200mA Continuous Load
V_OUT2 = 4.75v @ 80mA to 200mA Pulsing Load
Over Current peaks applied:
V_OUT1 = 3.3v @ 200mA Continuous Load
V_OUT2 = 4.75V @ 80mA to 600mA Pulsing Load
Normal operation; no Over Current
Over Current Peaks applied on V_OUT2
January 2011
14
M9999-011711-A