MIC5216_07 Datasheet, PDF (8/13 Pages) Micrel Semiconductor – 500mA-Peak Output LDO Regulator

Micrel, Inc.
Application Information
The MIC5216 is designed for 150mA to 200mA output
current applications where a high current spike (500mA)
is needed for short, startup conditions. Basic application
of the device will be discussed initially followed by a
more detailed discussion of higher current applications.
Enable/Shutdown
Forcing EN (enable/shutdown) high (> 2V) enables the
regulator. EN is compatible with CMOS logic. If the
enable/shutdown feature is not required, connect EN to
IN (supply input). See Figure 5.
Input Capacitor
A 1µF capacitor should be placed from IN to GND if
there is more than 10 inches of wire between the input
and the ac filter capacitor or if a battery is used as the
input.
Output Capacitor
An output capacitor is required between OUT and GND
to prevent oscillation. 1µF minimum is recommended.
Larger values improve the regulator’s transient
response. The output capacitor value may be increased
without limit.
The output capacitor should have an ESR (equivalent
series resistance) of about 5Ω or less and a resonant
frequency above 1MHz. Ultralow-ESR capacitors could
cause oscillation and/or underdamped transient
response. Most tantalum or aluminum electrolytic
capacitors are adequate; film types will work, but more
expensive. Many aluminum electrolytics have
electrolytes that freeze at about –30°C, so solid
tantalums are recommended for operation below –25°C.
At lower values of output current, less output
capacitance is needed for stability. The capacitor can be
reduced to 0.47µF for current below 10mA or 0.33µF for
currents below 1mA.
No-Load Stability
The MIC5216 will remain stable and in regulation with no
load (other than the internal voltage divider) unlike many
other voltage regulators. This is especially important in
CMOS RAM keep-alive applications.
Error Flag Output
The error flag is an open-collector output and is active
(low) when an undervoltage of approximately 5% below
the nominal output voltage is detected. A pull-up resistor
from IN to FLAG is shown in all schematics.
If an error indication is not required, FLAG may be left
open and the pull-up resistor may be omitted.
MIC5216
Thermal Considerations
The MIC5216 is designed to provide 200mA of
continuous current in two very small profile packages.
Maximum power dissipation can be calculated based on
the output current and the voltage drop across the part.
To determine the maximum power dissipation of the
package, use the thermal resistance, junction-to-
ambient, of the device and the following basic equation.
( ) _{PD(MAX) =}
T_J(MAX) − T_A
θ _JA
T_J(MAX) is the maximum junction temperature of the die,
125°C, and T_A is the ambient operating temperature. θ_JA
is layout dependent; table 1 shows examples of thermal
resistance, junction-to-ambient, for the MIC5216.
Package
MM8™ (MM)
SOT-23-5 (M5)
θ_JA Recommended
Minimum Footprint
160°C/W
220°C/W
θ_JA 1” Square
Copper Clad
70°C/W
170°C/W
θ_JC
30°C/W
130°C/W
Table 1. MIC5216 Thermal Resistance
The actual power dissipation of the regulator circuit can
be determined using one simple equation.
P_D = (V_IN – V_OUT) I_OUT + V_IN I_GND
Substituting P_D(MAX) for P_D and solving for the operating
conditions that are critical to the application will give the
maximum operating conditions for the regulator circuit.
For example, if we are operating the MIC5216-3.3BM5
at room temperature, with a minimum footprint layout,
we can determine the maximum input voltage for a set
output current.
P_D(MAX)
=
(125°C − 25°C)
220°C/W
P_D(MAX) = 455mW
The thermal resistance, junction-to-ambient, for the
minimum footprint is 220°C/W, taken from table 1. The
maximum power dissipation number cannot be
exceeded for proper operation of the device. Using the
output voltage of 3.3V, and an output current of 150mA,
we can determine the maximum input voltage. Ground
current, maximum of 3mA for 150mA of output current,
can be taken from the Electrical Characteristics section
of the data sheet.
455mW = (V_IN – 3.3V) 150mA + V_IN × 3mA
V_IN
⎜⎛
⎝
455mW + 3.3V(150mA
150mA + 3mA
)
⎟⎞
⎠
March 2007
8
M9999-032307