MIC29710 View Datasheet(PDF) - Micrel

Part Name

Description

Manufacturer

MIC29710

7.5A Fast-Response LDO Regulator

Micrel 

Micrel, Inc.

MIC29710/29712

Application Information

The MIC29710 and MIC29712 are high performance

low-dropout voltage regulators suitable for all moderate

to high-current voltage regulator applications. Their

700mV of drop-out voltage at full load make them

especially valuable in battery powered systems and as

high efficiency noise filters in “post-regulator” applica-

tions. Unlike older NPN-pass transistor designs, where

the minimum dropout voltage is limited by the base-

emitter voltage drop and collector-emitter saturation

voltage, dropout performance of the PNP output of these

devices is limited merely by the low VCE saturation

voltage. Output regulation is excellent across the input

voltage, output current, and temperature ranges.

A trade-off for the low dropout voltage is a varying base

drive requirement. But Micrel’s Super ßeta PNP®

process reduces this drive requirement to merely 2 to

5% of the load current.

MIC29710/712 regulators are fully protected from

damage due to fault conditions. Current limiting is

provided. The output current under overload conditions

is limited to a constant value. Thermal shutdown

disables the device when the die temperature exceeds

the maximum safe operating temperature. Transient

protection allows device (and load) survival even when

the input voltage spike above and below nominal. The

MIC29712 version offers a logic level ON/OFF control:

when disabled, the devices draw nearly zero current.

An additional feature of this regulator family is a common

pinout: a design’s current requirement may change up or

down yet use the same board layout, as all of Micrel’s

high-current Super ßeta PNP® regulators have identical

pinouts.

Figure 3. The MIC29710 requires only two capacitors for

operation

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.

First, we calculate the power dissipation of the regulator

from these numbers and the device parameters from this

datasheet.

PD = IOUT × (1.03VIN – VOUT)

Where the ground current is approximated by 3% of

IOUT. Then the heat sink thermal resistance is

determined with this formula:

( ) θSA

=

TJMAX − TA

PD

−

θ JC

+ θCS

Where TJMAX ≤ 125°C and θCS is between 0 and 2°C/W.

The heat sink may be significantly reduced in

applications where the minimum input voltage is known

and is large compared with the dropout voltage. Use a

series input resistor to drop excessive voltage and

distribute the heat between this resistor and the

regulator. The low dropout properties of Micrel Super

ßeta PNP regulators allow very significant reductions in

regulator power dissipation and the associated heat sink

without compromising performance. When this technique

is employed, a capacitor of at least 0.1µF is needed

directly between the input and regulator ground.

Please refer to Application Note 9 for further details and

examples on thermal design and heat sink specification.

Capacitor Requirements

For stability and minimum output noise, a capacitor on

the regulator output is necessary. The value of this

capacitor is dependent upon the output current; lower

currents allow smaller capacitors. MIC29710/2 regula-

tors are stable with a minimum capacitor value of 47µF

at full load.

This capacitor need not be an expensive low ESR type:

aluminum electrolytics are adequate. In fact, extremely

low ESR capacitors may contribute to instability.

Tantalum capacitors are recommended for systems

where fast load transient response is important.

Where the regulator is powered from a source with a

high AC impedance, a 0.1µF capacitor connected

between Input and GND is recommended. This capacitor

should have good characteristics to above 250kHz.

Transient Response and 5V to 3.3V Conversion

The MIC29710/2 have excellent response to variations

in input voltage and load current. By virtue of their low

dropout voltage, these devices do not saturate into

dropout as readily as similar NPN-based designs. A 3.3V

output Micrel LDO will maintain full speed and

performance with an input supply as low as 4.2V, and

will still provide some regulation with supplies down to

3.8V, unlike NPN devices that require 5.1V or more for

good performance and become nothing more than a

resistor under 4.6V of input. Micrel’s PNP regulators

provide superior performance in “5V to 3.3V” conversion

applications, especially when all tolerances are

considered.

October 2006

8

M9999-101906

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