Micrel, Inc.

MIC94310

February 2012

9

M9999-020612-A

Application Information

The MIC94310 is a very-high PSRR, fixed-output,

200mA LDO utilizing Ripple Blocker™ technology. The

MIC94310 is fully protected from damage due to fault

conditions, offering linear current limiting and thermal

shutdown.

Input Capacitor

The MIC94310 is a high-performance, high-bandwidth

device. An input capacitor of 0.47µF 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

In order to maintain stability, the MIC94310 requires an

output capacitor of 0.47µF or greater. For optimal ripple

rejection performance a 1µF capacitor is recommended.

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 their value by as much

as 50% and 60%, respectively, over their operating

temperature ranges. To use a ceramic chip capacitor

with the 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

The MIC94310 will remain stable and in regulation with

no load. This is especially important in CMOS RAM

keep-alive applications.

Enable/Shutdown

Forcing the enable (EN) pin low disables the MIC94310

and sends it into a “zero” off mode current state. In this

state, current consumed by the MIC94310 goes nearly to

zero. Forcing EN high enables the output voltage. The

EN pin uses CMOS technology and cannot be left

floating as it could cause an indeterminate state on the

output.

Thermal Considerations

The MIC94310 is designed to provide 200mA 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 2.5V, the output

voltage is 1.8V, and the output current = 200mA. The

actual power dissipation of the Ripple Blocker™ can be

determined using the equation:

Because this device is CMOS and the ground current is

typically <170µA 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

®

package.

operating temperature will give the maximum operating

conditions for the regulator circuit.

The maximum power dissipation must not be exceeded

for proper operation.