MIC29302AWUTR View Datasheet(PDF) - Micrel

Part Name

Description

Manufacturer

MIC29302AWUTR

High-Current Low-Dropout Regulators

Micrel 

Micrel, Inc.

For example, given an expected maximum ambient

temperature (TA) of 75°C with VIN = 3.3V, VOUT = 2.5V,

and IOUT = 1.5A, first calculate the expected PD using

Equation 3:

PD=(3.3V–2.5V)1.5A–(3.3V)(0.016A)=1.1472W

Eq. 3

Next, calcualte the junction temperature for the expected

power dissipation.

TJ=(θJA×PD)+TA=(56°C/W×1.1472W)+75°C

=139.24°C

Eq. 4

Now determine the maximum power dissipation allowed

that would not exceed the IC’s maximum junction

temperature (125°C) without the useof a heat sink by:

PD(MAX) = (TJ(MAX)–TA)/θJA

= (125°C–75°C)/(56°C/W) = 0.893W

Eq. 5

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. The

MIC29150/29300/29500/29750 regulators are stable

with the following minimum capacitor values at full load,

as noted in Table 1:

Device

MIC29150

MIC29300

MIC29500

MIC29750

Full Load Capacitor

10µF

10µF

10µF

22µF

Table 1. Minimum Capacitor Values 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.

MIC29150/29300/29500/29750

Where the regulator is powered from a source with high

AC impedance, a 0.1µF capacitor connected between

Input and GND is recommended. This capacitor should

have good characteristics to above 250kHz.

Minimum Load Current

The MIC29150–29750 regulators are specified between

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

currents dominate and the output voltage rises. The

following minimum load current swamps any expected

leakage current across the operating temperature range,

as shown in Table 2:

Device

MIC29150

MIC29300

MIC29500

MIC29750

Minimum Load

5mA

7mA

10mA

10mA

Table 2. Minimum Load Currents

Adjustable Regulator Design

The adjustable regulator versions, MIC29xx2 and

MIC29xx3, allow programming the output voltage

anywhere between 1.25V and the 25V. Two resistors are

used. The resistor values are calculated by Equation 6:

R1

=

R2

×



VOUT

1.240

− 1

Eq. 6

where VOUT is the desired output voltage. Figure 4 shows

component definition. Applications with widely varying

load currents may scale the resistors to draw the

minimum load current required for proper operation (see

“Minimum Load Current” sub-section).

December 2012

20

M9999-122012-B

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