MIC5301 Datasheet, PDF (8/11 Pages) Micrel Semiconductor – Single, 150mA μCap ULDO™

Micrel, Inc.
Applications Information
Enable/Shutdown
The MIC5301 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 MIC5301 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 practice in any RF-
based circuit.
Output Capacitor
The MIC5301 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, but
performance has been optimized for a 1µF 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 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
November 2006
MIC5301
PSRR. Turn-on time increases slightly with respect to
bypass capacitance. A unique, quick-start circuit
allows the MIC5301 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 MIC5301
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 MIC5301 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
MIC5301YML
V_IN
VIN VOUT
V_OUT
R1
1µF
EN ADJ
1µF
GND
R2
Figure 1. Adjustable Voltage Output
Thermal Considerations
The MIC5301 is designed to provide 150mA 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 5.0V, the output voltage is
2.8V and the output current = 150mA.
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
Because this device is CMOS and the ground current
is typically <100µA over the load range, the power
dissipation contributed by the ground current is < 1%
and can be ignored for this calculation.
P_D = (5V – 2.8V) × 150mA
P_D = 0.33W
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M9999-111506