MIC69301_11 Datasheet, PDF (9/13 Pages) Micrel Semiconductor – Single Supply VIN, Low VIN, Low VOUT, 3ALDO

Micrel, Inc.
Application Information
The MIC69301/2/3 is an ultra-high performance low
dropout linear regulator designed for high current
applications requiring a fast transient response. It utilizes
a single input supply and has a very low dropout voltage
perfect for low-voltage DC-to-DC conversion. The
MIC69301/2/3 requires a minimum number of external
components.
The MIC69301/2/3 regulator is fully protected from
damage due to fault conditions offering constant current
limiting and thermal shutdown.
Input Supply Voltage
V_IN provides a high current to the collector of the pass
transistor. The minimum input voltage is 1.65V allowing
conversion from low voltage supplies.
Output Capacitor
The MIC69301/2/3 requires a minimum of output
capacitance to maintain stability. However, proper
capacitor selection is important to ensure desired
transient response. The MIC69301/2/3 is specifically
designed to be stable with low ESR ceramic chip
capacitors. A 10µF ceramic chip capacitor should satisfy
most applications. Output capacitance can be increased
without bound. See typical characteristics for examples
of load transient response.
X7R dielectric ceramic capacitors are recommended
because of their temperature performance. X7R-type
capacitors change capacitance by only 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 with
this device.
Input Capacitor
An input capacitor of 1µF or greater is recommended
when the device is more than 4 inches away from the
bulk supply capacitance or when the supply is a battery.
Small, surface mount, ceramic chip capacitors can be
used for the bypassing. The capacitor should be placed
within 1 inch of the device for optimal performance.
Larger values will help to improve ripple rejection by
bypassing the input to the regulator further improving the
integrity of the output voltage.
MIC69301/2/3
Minimum Load Current
The MIC69301/2/3 regulator is specified between finite
loads. If the output current is too small, leakage currents
dominate and the output voltage rises. A 10mA minimum
load current is necessary for proper operation.
Adjustable Regulator Design
The MIC69302 and MIC69303 adjustable version allows
programming the output voltage anywhere between 0.5V
and 5.0V with two resistors. The resistor value between
V_OUT and the adjust pin should not exceed 10kΩ. Larger
values can cause instability. The resistor values are
calculated by:
V_OUT
=
0.5
×
⎜⎜⎝⎛
R₁
R₂
+ 1_{⎟⎟⎠⎞}
where V_OUT is the desired output voltage.
Enable
The fixed output voltage versions of the MIC69301
feature an active high enable input (EN) that allows on-
off control of the regulator. Current drain reduces to near
“zero” when the device is shutdown, with only
microamperes of leakage current. EN may be directly
tied to V_IN and pulled up to the maximum supply voltage.
Thermal Design
Linear regulators are simple to use. The most
complicated design parameters to consider are thermal
characteristics. Thermal design requires the following
application-specific parameters:
• Maximum ambient temperature (T_A)
• Output current (I_OUT)
• Output voltage (V_OUT)
• Input voltage (V_IN)
• Ground current (I_GND)
First, calculate the power dissipation of the regulator
from these numbers and the device parameters from this
data sheet.
P_D = (V_IN – V_OUT) x I_OUT + V_IN x I_GND
where the ground current is approximated by using
numbers from the “Electrical Characteristics” or “Typical
Characteristics” sections. The heat sink thermal
resistance is then determined with this formula:
θ_SA = ((T_J(max) – T_A)/ P_D) – (θ_JC + θ_CS)
Where T_J(max) ≤125°C and θ_CS is between 0°C and
2°C/W.
March 2011
9
M9999-032111-F