MIC5319_10 Datasheet, PDF (9/12 Pages) Micrel Semiconductor – 500mA μCap Ultra-Low Dropout High PSRR LDO Regulator

Micrel, Inc.
Applications Information
Enable/Shutdown
The MIC5319 features 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, as this may cause an
indeterminate state on the output.
Input Capacitor
The MIC5319 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. Additional high-
frequency capacitors, such as small-valued NPO
dielectric-type capacitors, help filter out high-frequency
noise and are good design practice in any RF-based
circuit.
Output Capacitor
The MIC5319 requires an output capacitor of 2.2µF 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, but performance has
been optimized for a 2.2µF ceramic output capacitor and
does not improve significantly with larger capacitance.
X7R/X5R dielectric-type ceramic capacitors are
recommended because of their temperature
performance. 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 to ensure the same minimum
capacitance over the equivalent operating temperature
range.
Bypass Capacitor
A capacitor can be placed from the 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.
MIC5319
A unique, quick-start circuit allows the MIC5319 to drive
a large capacitor on the bypass pin without significantly
slowing turn-on time. Refer to the “Typical
Characteristics” section for performance with different
bypass capacitors.
No-Load Stability
Unlike many other voltage regulators, the MIC5319 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 MIC5319 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 Application
Thermal Considerations
The MIC5319 is designed to provide 500mA of
continuous current in a very small MLF^® package.
Maximum ambient operating temperature can be
calculated based on the output current and the voltage
drop across the part. Given an input voltage of 3.3V,
output voltage of 2.8V and 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
9
M9999-052510