Micrel, Inc.

MIC5388/9

July 2011

8

M9999-071211-A

Application Information

MIC5388/9 is a dual 150mA LDO in a miniature 6-bump

WLCSP package. The MIC5389 includes an auto-

discharge circuit for each of the LDO outputs that are

activated when the output is disabled. The MIC5388/9

regulator is fully protected from damage due to fault

conditions through linear current limiting and thermal

shutdown.

Input Capacitor

The MIC5388/9 is a high-performance, high-bandwidth

device. An input capacitor of 1µF capacitor 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 MIC5388/9 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.

No-Load Stability

Unlike many other voltage regulators, the MIC5388/9 will

remain stable and in regulation with no load. This is

especially

important

in

CMOS

RAM

keep-alive

applications.

Enable/Shutdown

The MIC5388/9 comes with two active high enable pins

that allow each regulator to be disabled independently.

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.

When disabled the MIC5389 switches a 30Ω (typical)

load on the regulator output to discharge the external

capacitor.

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 MIC5388/9 is designed to provide 150mA of

continuous current for both outputs 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

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.

150mA

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