Micrel, Inc.

MIC69151/153

July 2010

7

M9999-071210-D

Application Information

The MIC69151/153 is an ultra-high performance low

dropout linear regulator designed for high current

applications requiring a fast transient response. It utilizes

a single input supply, perfect for low-voltage DC-to-DC

conversion. The MIC69151/153 requires a minimum

number of external components.

The MIC69151/153 regulator is fully protected from

damage due to fault conditions offering constant current

limiting and thermal shutdown.

Input Supply Voltage

transistor. The minimum input voltage is 1.65V allowing

conversion from low voltage supplies.

Output Capacitor

The MIC69151/153 requires a minimum of output

capacitance to maintain stability. However, proper

capacitor selection is important to ensure desired

transient response. The MIC69151/153 is specifically

designed to be stable with low ESR ceramic chip

capacitors. A 10µF ceramic chip capacitor should satisfy

most applications. Output capacitor can be increased

without bound. See typical characteristics for examples

of load transient response.

X7R dielectric ceramic capacitors are recommended

because of their temperature performance. X7R-type

capacitors change capacitance by only 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 or a

tantalum capacitor to ensure the same capacitance

value over the operating temperature range. Tantalum

capacitors have a very stable dielectric (10% over their

operating temperature range) and can also be used with

this device.

Input Capacitor

An input capacitor of 1µF or greater is recommended

when the device is more than 4 inches away from the

bulk supply capacitance or when the supply is a battery.

Small, surface mount, ceramic chip capacitors can be

used for the bypassing. The capacitor should be placed

within 1 inch of the device for optimal performance.

Larger values will help to improve ripple rejection by

bypassing the input to the regulator further improving the

integrity of the output voltage.

Minimum Load Current

The MIC69151/153 regulator is specified between finite

loads. If the output current is too small, leakage currents

dominate and the output voltage rises. A 10mA minimum

load current is necessary for proper operation.

Adjustable Regulator Design

The MIC69153 adjustable version allows programming

the output voltage anywhere between 0.5V and 5.5V

the adjust pin should not exceed 10kΩ. Larger values

can cause instability. The resistor values are calculated

by:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

+

∗

=

1

R

R

0.5

V

2

1

OUT

Enable

The fixed output voltage versions of the MIC69151

feature an active high enable input (EN) that allows on-

off control of the regulator. Current drain reduces to near

“zero” when the device is shutdown, with only

microamperes of leakage current. EN may be directly

Thermal Design

Linear regulators are simple to use. The most

complicated design parameters to consider are thermal

characteristics. Thermal design requires the following

application-specific parameters:

First, calculate the power dissipation of the regulator

from these numbers and the device parameters from this

data sheet.

where the ground current is approximated by using

numbers from the “Electrical Characteristics” or “Typical

Characteristics” sections. The maximum allowable

allowable power dissipation will result in excessive die

temperature and the regulator will go into thermal

shutdown.

Refer to “Application Note 9” for further details and

examples on thermal design and heat sink applications.