August 2004 7 MIC5213
MIC5213 Micrel
Applications Information
Input Capacitor
A 0.1µF 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 when a battery is used as the input.
Output Capacitor
Typical PNP-based regulators require an output capacitor to
prevent oscillation. The MIC5213 is ultrastable, requiring only
0.47µF of output capacitance for stability. The regulator is
stable with all types of capacitors, including the tiny, low-ESR
ceramic chip capacitors. The output capacitor value can be
increased without limit to improve transient response.
No-Load Stability
The MIC5213 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.
Enable Input
The MIC5213 features nearly zero off-mode current. When
EN (enable input) is held below 0.6V, all internal circuitry is
powered off. Pulling EN high (over 2.0V) re-enables the
device and allows operation. When EN is held low, the
regulator typically draws only 10nA of current. While the logic
threshold is TTL/CMOS compatible, EN may be pulled as
high as 20V, independent of V
IN
.
Thermal Behavior
The MIC5213 is designed to provide 80mA of continuous
current in a very small profile package. 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 junction-to-ambi-
ent thermal resistance of the device and the following basic
equation:
P
TT
D(max)
J(max) A
JA
=
−
θ
T
J(max)
is the maximum junction temperature of the die,
125°C, and T
A
is the maximum ambient temperature. θ
JA
is
the junction-to-ambient thermal resistance ambient of the
regulator. The θ
JA
of the MIC5213 is 450°C/W.
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)
, determined above, 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 MIC5213-3.0BC5
at room temperature, with a minimum footprint layout, we can
determine the maximum input voltage for a set output current.
P
125 25
450 C / W
D(max)
=
−
°
To prevent the device from entering thermal shutdown,
maximum power dissipation cannot be exceeded. Using the
output voltage of 3.0V, and an output current of 80mA, we can
determine the maximum input voltage. Ground current, maxi-
mum of 3mA for 80mA of output current, can be taken from
the “Electrical Characteristics” section of the data sheet.
222mW = (V
IN
– 3.0V) 80mA + V
IN
× 3mA
222mW = (80mA × V
IN
+ 3mA × V
IN
) – 240mW
462mW = 83mA × V
IN
V
IN
= 5.57V max.
Therefore, a 3.0V application at 80mA of output current can
accept a maximum input voltage of 5.6V in an SC-70-5
package. For a full discussion of heat sinking and thermal
effects on voltage regulators, refer to Regulator Thermals
section of Micrel’s
Designing with Low-Dropout Voltage Regu-
lators
handbook.
Fixed Voltage Regulator
The MIC5213 is ideal for general-purpose voltage regulation
in any handheld device. Applications that are tight for space
can easily use the Teeny™ SC-70 regulator which occupies
half the space of a SOT-23-5 regulator. The MIC5203 offers
a smaller system solution, only requiring a small multilayer
ceramic capacitor for stability.
MIC5213-x.x
IN OUT
GND
0.47µF
V
OUT
3.0V
3.6V
Li-Ion
Cell
EN
Figure 1. Single-Cell Regulator
