MIC5353 Datasheet, PDF (7/12 Pages) Micrel Semiconductor – 500mA LDO in 1.6mm × 1.6mm Package

Micrel, Inc.
Applications Information
Enable/Shutdown
The MIC5353 comes with an active-high enable pin that
allows the regulator to be disabled. Forcing the enable
pin low disables the regulator and sends it into a “zero”
off-mode-current state. In this state, current consumed
by the regulator goes nearly to zero. Forcing the enable
pin high enables the output voltage. The active-high
enable pin uses CMOS technology and the enable pin
cannot be left floating; a floating enable pin may cause
an indeterminate state on the output.
Input Capacitor
The MIC5353 is a high-performance, high bandwidth
device. Therefore, it requires a well-bypassed input
supply for optimal performance. A 1µF capacitor is
required from the input-to-ground to provide stability.
Low-ESR ceramic capacitors provide optimal
performance at a minimum of space. The use of
additional high-frequency capacitors, such as small-
valued NPO dielectric-type capacitors, help filter out
high-frequency noise and are good practice in any RF-
based circuit.
Output Capacitor
The MIC5353 requires an output capacitor of 1µF or
greater to maintain stability. The design is optimized for
use with low-ESR ceramic chip capacitors. High-ESR
capacitors may cause high-frequency oscillation. The
output capacitor can be increased, although
performance has been optimized for a 1µF ceramic
output capacitor and doing so does not improve
significantly with larger capacitance.
X7R/X5R dielectric-type ceramic capacitors are
recommended because of their temperature
performance. The X7R-type capacitors change
capacitance by 15% over their operating temperature
range and are the most stable type of ceramic
capacitors. Z5U and Y5V dielectric capacitors change
value by as much as 50% and 60%, respectively, over
their operating temperature ranges. To use a ceramic
chip capacitor with Y5V dielectric, the value must be
much higher than an X7R ceramic capacitor thereby
ensuring the same minimum capacitance over the
equivalent operating temperature range.
Bypass Capacitor
A capacitor can be placed from the noise bypass pin-to-
ground to reduce output voltage noise. The capacitor
bypasses the internal reference. A 0.1μF capacitor is
recommended for applications that require low-noise
outputs. The bypass capacitor can be increased, further
reducing noise and improving PSRR. Turn-on time
increases slightly with respect to bypass capacitance.
MIC5353
A unique, quick-start circuit allows the MIC5353 to drive
a large capacitor on the bypass pin without significantly
slowing turn-on time.
No-Load Stability
Unlike many other voltage regulators, the MIC5353 will
remain stable and in regulation with no load. This is
especially important in CMOS RAM keep-alive
applications.
Adjustable Regulator Application
Adjustable regulators use the ratio of two resistors to
multiply the reference voltage to produce the desired
output voltage. The MIC5353 can be adjusted from
1.25V to 5.5V by using two external resistors (Figure 1).
The resistors set the output voltage based on the
following equation:
V_OUT
=
V_REF
⎜⎛1
⎝
+
R1 _⎟⎞
R2 _⎠
V_REF = 1.25V
Figure 1. Adjustable Voltage Output
Thermal Considerations
The MIC5353 is designed to provide 500mA of
continuous current. Maximum ambient operating
temperature can be calculated based on the output
current and the voltage drop across the part. Given that
the input voltage is 3.3V, the output voltage is 2.8V and
the output current = 500mA.
The actual power dissipation of the regulator circuit can
be determined using the equation:
P_D = (V_IN – V_OUT) I_OUT + V_IN I_GND
May 2010
7
M9999-052510