June 2000

7

MIC5213

MIC5213

Micrel

Applications Information

Input Capacitor

A 0.1

µF 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

0.47

µF 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

Thermal Behavior

The MIC5213 is designed to provide 80mA of continuous

current in a 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 junction-to-ambi-

ent thermal resistance of the device and the following basic

equation:

P

TT

D(max)

J(max)

A

JA

=

−

θ

T

125

°C, and T

the junction-to-ambient thermal resistance ambient of the

regulator. The

θ

The actual power dissipation of the regulator circuit can be

determined using one simple equation.

P

Substituting P

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

−

°

P

222mW

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

222mW = (80mA

× V

462mW = 83mA

× V

IN

V

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

3.0V

3.6V

Li-Ion

Cell

EN

Figure 1. Single-Cell Regulator