MIC61300 Datasheet, PDF (12/22 Pages) Micrel Semiconductor – Low Input Voltage, Single-Supply High-Current LDO

Micrel, Inc.
Functional Description
The MIC61300 is an ultra-high-performance, low-dropout
linear regulator designed for high-current applications
that require low input voltage operation. The MIC61300
operates from a single input supply and generates an
internal supply that is higher than the input voltage to
drive an on-chip N-Channel MOSFET. The N-Channel
MOSFET significantly reduces the dropout voltage when
compared to a traditional P-Channel MOSFET.
P-Channel MOSFETs are usually used in single-supply
low-dropout linear voltage regulators. However, for input
voltages below 1.5V, there is not sufficient gate drive to
turn on the P-Channel. To solve this issue, the
MIC61300 uses a simple internal charge pump to drive
the internal N-Channel MOSFET’s gate higher than the
input voltage, see Functional Diagram. The N-Channel
MOSFET greatly reduces the dropout voltage for the
same die area when compared to that of a P-Channel.
Other added benefits of the charge pump include the
ability to control the output voltage rise time and to
improve the power supply rejection ratio (PSRR). This is
accomplished by using the V_CP supply to power the error
amplifier.
The other significant advantage of the MIC61300 over a
P-Channel regulator is its transient response. The N-
Channel in the follower configuration is much faster than
its P-channel counter part and is simpler to compensate.
Any type of output capacitor can be placed in parallel
with it as long as the minimum value output ceramic
capacitor is placed next to the MIC61300. See the
Output Capacitor section for specific details. Also, the
regulator is fully protected from damage due to fault
conditions by offering linear current limiting and thermal
shutdown.
Soft-Start
Soft-start reduces the power supply input surge current
at startup by controlling the output voltage rise time. The
input surge appears while the output capacitor is
charged up. A slower output rise time will draw a lower
input surge current.
The CP pin is the output of the internal charge pump.
The soft-start rise time is controlled by the external
capacitor connected from CP pin-to-GND. During soft-
start, the charge pump feeds a current to C_CP. The
output voltage rise time is dependent upon the value of
C_CP, the input voltage, output voltage and the current
limit. The value of the charge pump external capacitor
selected is recommended in the range of 0.1µF to 1µF.
MIC61300
Input Capacitor
A 10µF ceramic input capacitor is all that is required for
most applications. However, fast load transient and low
headroom (V_IN – V_OUT) requires additional bulk bypass
capacitance to ensure that the regulator does not drop
out of regulation.
The input capacitor must be placed on the same side of
the board and next to the MIC61300 to minimize the
dropout voltage and voltage ringing during transient and
short circuit conditions. It is also recommended to use
two vias for each end of the capacitor to connect to the
power and ground plane.
X7R or 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 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. Tantalum capacitors have a very stable dielectric
(10% over their operating temperature range) and can
also be used in parallel with the ceramic capacitor(s).
See Typical Characteristics section for examples of load
transient response.
Output Capacitor
As part of the frequency compensation, the MIC61300
requires a 47µF ceramic output capacitor. However, any
other type of capacitor can be placed in parallel as long
as the 47µF ceramic output capacitor is placed next to
the MIC61300.
Output voltages below 0.8V require either a 100µF or
2x 47µF output capacitance for large output transients.
The increased output capacitance reduces the output
voltage drop caused by load transients, which increases
as a percentage of the output voltage as the output
voltage is lowered.
The output capacitor type and placement criteria are the
same as the input capacitor. See the Input Capacitor
section for a detailed description.
Minimum Load Current
The MIC61300 requires a minimum load of 10mA to
maintain output voltage regulation.
September 2010
12
M9999-092910-A