Micrel, Inc.

MIC5304

November 2008

9

M9999-111908-A

Application Information

The MIC5304 is a low quiescent current voltage selectable

LDO. The regulator is capable of sourcing 150mA of output

current with a low quiescent current of 24µA. A logic input

signal selects the output between two preset voltages. The

MIC5304 regulator is fully protected from damage due to

fault conditions, offering linear current limiting and thermal

shutdown.

Input Capacitor

The MIC5304 is a high-performance, high bandwidth device.

Therefore, it requires a well bypassed input supply for

optimal performance. 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 MIC5304 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 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.

Enable/Shutdown

The MIC5304 is provided with an active-high enable pin that

allows the regulator to be enabled. 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. 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.

Voltage Select

The voltage select pin is used to select the output voltage

between two voltages. A logic high signal sets the output to

the higher voltage; while a logic low signal selects the lower

output voltage. The voltage select pin cannot be left floating;

a floating pin may cause an indeterminate state on the

output.

Thermal Considerations

The MIC5304 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 3.6V, the output voltage is

output current = 150mA. The lower output voltage should be

used for power dissipation calculations as this is the worst

case situation. 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)

θ

T

T

P

operating temperature will give the maximum operating

conditions for the regulator circuit. The junction-to-ambient

thermal resistance for the minimum footprint is 92°C/W.

The maximum power dissipation must not be exceeded for

proper operation.

For example, when operating the MIC5304-XDYMT at an

input voltage of 3.6V and 150mA load with a minimum

footprint

layout,

the

maximum

ambient

operating

Therefore, a 3.15/1.85V application with a 150mA output

current can accept an ambient operating temperature of

100°C in a 1.6mm x 1.6mm MLF

discussion of heat sinking and thermal effects on voltage

regulators, refer to the “Regulator Thermals” section of

Micrel’s Designing with Low-Dropout Voltage Regulators

handbook. This information can be found on Micrel's website

at: http://www.micrel.com/_PDF/other/LDOBk_ds.pdf