Micrel, Inc.

MIC5528

Application Information

The MIC5528 is a high-performance, low-power 500mA

LDO. The MIC5528 includes an auto-discharge circuit

that is switched on when the regulator is disabled through

the enable pin. The MIC5528 also offers an internal

pulldown resistor on the enable pin to ensure the output

is disabled if the control signal is tri-stated. The MIC5528

regulator is fully protected from damage due to fault

conditions, offering linear current limiting and thermal

shutdown.

Input Capacitor

The MIC5528 is a high-performance, high-bandwidth

device. An input capacitor of 2.2µF 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 MIC5528 requires an output capacitor of 2.2µF 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 2.2µF 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 MIC5528

remains stable and in regulation with no load. This is

especially

important

in

CMOS

RAM

keep-alive

applications.

Enable/Shutdown

The MIC5528 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 an off

mode current state drawing virtually zero current. When

disabled the MIC5528 switches an internal 25Ω load on

the regulator output to discharge the external capacitor.

Forcing the enable pin high enables the output voltage.

The MIC5528 has an internal pull down resistor on the

enable pin to disable the output when the enable pin is

floating.

Thermal Considerations

The

MIC5528

is

designed

to

provide

500mA

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 3.3V, and the output current = 500mA. The

actual power dissipation of the regulator circuit can be

determined using Equation 1:

Eq. 1

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 Equation 2:

(

)

W

150

.

0

P

mA

500

V

3

.

3

V

6

.

3

P

D

D

=

×

−

=

Eq. 2

To

determine

the

maximum

ambient

operating

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

thermal resistance of the device Equation 3:













θ

−

=

JA

A

)

MAX

(

J

)

MAX

(

D

T

T

P

Eq. 3

die, θ

package.

May 5, 2014

8

Revision 1.1