MIC5281_11 Datasheet, PDF (10/21 Pages) Micrel Semiconductor – 120VIN, 25mA, Ultra-Low IQ, High-PSRR Linear Regulator

Micrel, Inc.
MIC5281
Detailed Description
The MIC5281 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 MIC5281YMM and MIC5281YMME
offer an adjustable output voltage from 1.27V to 5.5V. The
MIC5281-3.3YMME and MIC5281-3.3YMM offer fixed
3.3V outputs and the MIC5281-5.0YMME and MIC5281-
5.0YMM 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
MIC5281 has internal thermal shutdown 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
MIC5281 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 1.0µF capacitor from VIN to GND. Micrel
recommends the C5750X7R2E105M, 1.0µF, 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 MIC5281.
Output Voltage Setting
For the MIC5281YMME and MIC5281YMM, V_OUT is
programmed from 1.27V to 5.5V using:
V_OUT
=
V_REF
×
⎜⎛
⎝
R1
R2
+
1⎟⎞
⎠
where V_REF = 1.267V, and R1 and R2 are shown in the
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 thermal couple 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.
June 2011
10
M9999-062411-A