MIC69301 datasheet(11/26 Pages) MICROCHIP

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

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DS20006625A-page 11

MIC69301/2/3

4.0

FUNCTIONAL DESCRIPTION

The MIC69301/2/3 are ultra-high performance low

dropout linear regulators designed for high current

applications that require a fast transient response. It

utilizes a single input supply and has a very low dropout

voltage that is perfect for low-voltage DC-to-DC

conversions. The MIC69301/2/3 require a minimum

number of external components.

The MIC69301/2/3 regulators are fully protected from

damage due to fault conditions offering constant

current limiting and thermal shutdown.

4.1

Input Supply Voltage

VIN provides a high current to the collector of the pass

transistor. The minimum input voltage is 1.65V,

allowing conversion from low voltage supplies.

4.2

Output Capacitor

The MIC69301/2/3 require a minimum of output

capacitance to maintain stability. However, proper

capacitor selection is important to ensure desired

transient response. The MIC69301/2/3 are specifically

designed to be stable with low-ESR ceramic chip

capacitors. A 10 µF ceramic chip capacitor should

satisfy most applications. Output capacitance can be

increased without bound. See the Typical Performance

Curves 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.

4.3

Input Capacitor

An input capacitor of 1 µF 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.

4.4

Minimum Load Current

The MIC69301/2/3 regulator is specified between finite

loads. If the output current is too small, leakage

currents dominate and the output voltage rises. A

10 mA minimum load current is necessary for proper

operation.

4.5

Adjustable Regulator Design

The MIC69302 and MIC69303 adjustable version

allows programming the output voltage anywhere

between 0.5V and 5.0V with two resistors. The resistor

value between VOUT and the adjust pin should not

exceed 10 kΩ. Larger values can cause instability. The

resistor values are calculated by:

EQUATION 4-1:

4.6

Enable

The fixed output voltage versions of the MIC69301

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

tied to VIN and pulled up to the maximum supply

voltage.

4.7

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:

• Maximum ambient temperature (TA)

• Output current (IOUT)

• Output voltage (VOUT)

• Input voltage (VIN)

• Ground current (IGND)

First, calculate the power dissipation of the regulator

from these numbers and the device parameters from

this data sheet.

EQUATION 4-2:

VOUT 0.5 R1

------- 1











Where:

VOUT = Desired output voltage.

VIN VOUT

–





IOUT



VIN

IGND



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