Micrel, Inc.
MIC47050
Functional Description
The MIC47050 is a high-speed, ultra-low dropout, dual
supply NMOS ULDO™ designed to take advantage of
point-of-load applications that use multiple supply rails to
generate a low-voltage, high-current power supply. The
MIC47050 can source 0.5A of output current while only
requiring a 1µF ceramic output capacitor for stability.
The MIC47050 regulator is fully protected from damage
due to fault conditions, offering linear current limiting and
thermal shutdown.
Tantalum capacitors have a very stable dielectric (10%
over their operating temperature range) and can also be
used with this device. See the Typical Characteristic
section for examples of load transient response.
Output Capacitor
The MIC47050 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.
Bias Supply Voltage
VBIAS, requiring relatively light current, provides power to
the control portion of the MIC47050. Bypassing on the
bias pin is recommended to improve performance of the
regulator during line and load transients. Small 0.1µF
ceramic capacitors from VBIAS-to-ground help reduce
high frequency noise from being injected into the control
circuitry from the bias rail and are good design practice.
The output capacitor type and placement criteria are the
same as the input capacitor. See the “Input Capacitor”
subsection for a detailed description.
Minimum Load Current
The MIC47050, unlike most other regulators, does not
require a minimum load to maintain output voltage
regulation.
Input Supply Voltage
VIN provides the supply to power the LDO. The minimum
input voltage is 1.0V. This allows conversion from low
voltage supplies to reduce the power dissipation in the
pass element.
Adjustable Regulator Design
The MIC47050 adjustable version allows programming
the output voltage from 0.4V to 2.0V. Two external
resistors are required. The R1 resistor value between
Input Capacitor
The MIC47050 is a high-performance, high bandwidth
device. Therefore, it requires a well-bypassed input
supply for optimal performance. A 1µF capacitor is the
minimum required for stability. A 10µF ceramic capacitor
is recommended for most applications, especially if the
LDO’s headroom (VIN –VOUT) is small and/or large load
transients are present. Fast load transient and low
headroom requires a larger input filter capacitor to
ensure that the regulator does not drop out of regulation.
A 10µF will better attenuate any voltage glitches from
exceeding the maximum voltage rating of the part.
V
OUT and the ADJ pin should not exceed 10kꢀ, as larger
values can cause instability. R2 connects between the
ADJ pin and ground. The resistor values are calculated
as follows:
VOUT
R1 R2 V
1
REF
Where VOUT is the desired output voltage and VREF is the
internal reference voltage.
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.
Enable/Shutdown
The MIC47050 comes with a single 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.
X7R and X5R dielectric 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 are not recommended since
they 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 or a
tantalum capacitor to ensure the same capacitance
value over the operating temperature range.
M9999-040312-B
April 2012
10
MICREL [ MICREL SEMICONDUCTOR ]
