Micrel, Inc.

MIC5367/8

June 2010

7

M9999-060110-A

Application Information

MIC5367 and MIC5368 are Low noise 150mA LDOs.

The MIC5368 includes an auto-discharge circuit that is

switched on when the regulator is disabled through the

Enable pin. The MIC5367/8 regulator is fully protected

from damage due to fault conditions, offering linear

current limiting and thermal shutdown.

Input Capacitor

The MIC5367/8 is a high-performance, high bandwidth

device. An input capacitor of 1µF is required from the

input to ground to provide stability. Low-ESR ceramic

capacitors provide optimal performance at a minimum of

space. Additional high-frequency capacitors, such as

small-valued NPO dielectric-type capacitors, help filter

out high-frequency noise and are good practice in any

RF-based

circuit.

X5R

or

X7R

dielectrics

are

recommended for the input capacitor. Y5V dielectrics

lose most of their capacitance over temperature and are

therefore, not recommended.

Output Capacitor

The MIC5367/8 requires an output capacitor of 1µF or

greater to maintain stability. The design is optimized for

use with low-ESR ceramic chip capacitors. High ESR

capacitors are not recommended because they may

cause high frequency oscillation. The output capacitor

can be increased, but performance has been optimized

for a 1µF ceramic output capacitor and does not improve

significantly with larger capacitance.

X7R/X5R

dielectric-type

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 capacitor to ensure the same minimum

capacitance over the equivalent operating temperature

range.

No-Load Stability

Unlike many other voltage regulators, the MIC5367/8 will

remain stable and in regulation with no load. This is

especially

important

in

CMOS

RAM

keep-alive

applications.

Enable/Shutdown

The MIC5367/8 comes with an active-high enable pin

that allows the regulator to be disabled. Forcing the

enable pin low disables the regulator and sends it into a

“zero” off-mode-current state. In this state, current

consumed by the regulator goes nearly to zero. Forcing

the enable pin high enables the output voltage. The

active-high enable pin uses CMOS technology and the

enable pin cannot be left floating; a floating enable pin

may cause an indeterminate state on the output.

Thermal Considerations

The MIC5367/8 is designed to provide 150mA of

continuous current in a very small package. Maximum

ambient operating temperature can be calculated based

on the output current and the voltage drop across the

part. For example if the input voltage is 3.3V, the output

voltage is 1.5V, and the output current = 150mA. The

actual power dissipation of the regulator circuit can be

determined using the equation:

Because this device is CMOS and the ground current is

typically <100µA over the load range, the power

dissipation contributed by the ground current is < 1% and

can be ignored for this calculation.

To

determine

the

maximum

ambient

operating

temperature of the package, use the junction-to-ambient

thermal resistance of the device and the following basic

equation:

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

−

=

JA

A

J(max)

D(max)

T

T

P

θ

package.

operating temperature will give the maximum operating

conditions for the regulator circuit. The junction-to-

ambient thermal resistance for the minimum footprint is

92.4°C/W.

The maximum power dissipation must not be exceeded

for proper operation.