Micrel, Inc.

MAQ5281

Detailed Description

The MAQ5281 voltage regulator accepts a 6V to 120V

input and has an ultra-low 6µA typical quiescent current

while offering an excellent line transient response and

PSRR. These features make it ideal for harsh, noisy

environments. All options of the device offer 25mA of

output current. The MAQ5281YMME offer an adjustable

output voltage from 1.27V to 5.5V. The MAQ5281-

3.3YMME offer fixed 3.3V outputs and the MAQ5281-

5.0YMME offer fixed 5.0V outputs. The YMME packaged

devices feature a heat slug to more effectively remove

heat from the die.

Applications Information

Thermal Protection

The MAQ5281 has an internal thermal shutdown circuit to

protect it from excessive heating of the die. When the

junction temperature exceeds approximately +155°C, the

output is disabled and the device begins to cool down. The

device turns back on when the junction temperature cools

by 15°C. This will result in a cycled output during

continuous thermal-overload conditions.

Current Limit

The MAQ5281 features output current-limit protection. The

output sustains a continuous short circuit to GND without

damage to the device, but thermal shutdown often results.

Input Capacitor

Connect a 1µF capacitor from VIN to GND. Micrel

recommends the C5750X7R2E105M, 1µF, 250V capacitor

made by TDK. When using a different capacitor, assure

that the voltage rating of the capacitor exceeds any

potential transient.

CPSRR Capacitor

Connect a 0.1µF capacitor from CPSRR to GND to

maintain high power supply rejection. The voltage rating of

the capacitor must be at least 14V.

Output Capacitor

Connect a 10µF capacitor from VOUT to GND. Assure that

the voltage rating of the capacitor exceeds the designed

output voltage of the MAQ5281.

Output Voltage Setting

to 5.5V using:













+

×

=

1

R2

R1

V

V

REF

OUT

Typical Applications circuit.

Thermal Measurements

It is always wise to measure an IC’s case temperature to

make sure that it is within operating limits, but it is easy to

get erroneous results. The standard thermocouple that

comes with many voltage meters uses a large wire gauge

that behaves like a heat-sink, resulting in artificially low

case temperature measurements. Use a thermocouple of

36-gauge wire or smaller, such as the Omega (5SC-TT-K-

36-36), to minimize the heat-sinking effect. Also, apply

thermal compound to maximize heat transfer between the

IC and the thermocouple.

An infrared thermometer is a recommended alternative.

The IR thermometer from Optris has a 1mm spot size,

ideal for monitoring small surface mount packages. Also,

the optional stand makes it easy to keep the beam on the

IC for long periods of time.

October 2, 2014

9

Revision 2.0