MIC5319

Micrel

October 2004

8

M9999-100604

Applications Information

Enable/Shutdown

The MIC5319 features 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, as this

may cause an indeterminate state on the output.

Input Capacitor

The MIC5319 is a high-performance, high bandwidth device.

Therefore, it requires a well-bypassed input supply for opti-

mal performance. A 1µF capacitor is required from the input-

to-ground to provide stability. Low-ESR ceramic capacitors

provide optimal performance at a minimum of space. Addi-

tional high frequency capacitors, such as small-valued NPO

dielectric-type capacitors, help filter out high-frequency noise

and are good design practice in any RF-based circuit.

Output Capacitor

The MIC5319 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 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 recom-

mended because of their temperature performance. X7R-

type capacitors change capacitance by 15% over their oper-

ating 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 capaci-

tor with Y5V dielectric, the value must be much higher than an

X7R ceramic capacitor to ensure the same minimum capaci-

tance over the equivalent operating temperature range.

Bypass Capacitor

A capacitor can be placed from the bypass pin-to-ground to

reduce output voltage noise. The capacitor bypasses the

internal reference. A 0.1µF capacitor is recommended for

applications that require low-noise outputs. The bypass ca-

pacitor can be increased, further reducing noise and improv-

ing PSRR. Turn-on time increases slightly with respect to

bypass capacitance. A unique, quick-start circuit allows the

MIC5319 to drive a large capacitor on the bypass pin without

significantly slowing turn-on time. Refer to the “Typical Char-

acteristics” section for performance with different bypass

capacitors.

No-Load Stability

Unlike many other voltage regulators, the MIC5319 will

remain stable and in regulation with no load. This is especially

important in CMOS RAM keep-alive applications.

Adjustable Regulator Application

Adjustable regulators use the ratio of two resistors to multiply

the reference voltage to produce the desired output voltage.

The MIC5319 can be adjusted from 1.25V to 5.5V by using

two external resistors (Figure 1). The resistors set the output

voltage based on the following equation:

MIC5319BML

VOUT

VIN

ADJ

BYP

GND

R1

2.2

µF

R2

1

µF

EN

Figure 1. Adjustable Voltage Application

Thermal Considerations

The MIC5319 is designed to provide 500mA of continuous

current in a very small MLF package. Maximum ambient

operating temperature can be calculated based on the output

current and the voltage drop across the part. Given an input

voltage of 3.3V, output voltage of 2.8V and output current =

500mA, 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 resis-

tance of the device and the following basic equation:

VV

1

R1

R2

V

1.25V

OUT

REF

REF

=+

⎛

⎝

⎜

⎞

⎠

⎟

=

P(

T (max) – T

D

JA

JA

max) =

⎛

⎝

⎜

⎞

⎠

⎟

θ