MCP1702-1502ESLASHMB datasheet(20/32 Pages) MICROCHIP

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MCP1702

DS22008D-page 20

6.3

Voltage Regulator

Internal power dissipation, junction temperature rise,

junction temperature and maximum power dissipation

are calculated in the following example. The power

dissipation, as a result of ground current, is small

enough to be neglected.

6.3.1

POWER DISSIPATION EXAMPLE

Device Junction Temperature Rise

The internal junction temperature rise is a function of

internal power dissipation and the thermal resistance

from junction to ambient for the application. The

thermal resistance from junction to ambient (R

JA) is

derived from an EIA/JEDEC standard for measuring

thermal resistance for small surface mount packages.

The EIA/JEDEC specification is JESD51-7, “High

Effective Thermal Conductivity Test Board for Leaded

Surface Mount Packages”. The standard describes the

test method and board specifications for measuring the

thermal resistance from junction to ambient. The actual

thermal resistance for a particular application can vary

depending on many factors, such as copper area and

thickness. Refer to AN792, “A Method to Determine

How Much Power a SOT-23 Can Dissipate in an

Application”,

(DS00792),

for

information

regarding this subject.

Junction Temperature Estimate

To estimate the internal junction temperature, the

calculated temperature rise is added to the ambient or

offset temperature. For this example, the worst-case

junction temperature is estimated below.

Maximum Package Power Dissipation at +40°C

Ambient Temperature

6.4

Voltage Reference

The MCP1702 can be used not only as a regulator, but

also as a low quiescent current voltage reference. In

many microcontroller applications, the initial accuracy

of the reference can be calibrated using production test

equipment or by using a ratio measurement. When the

initial accuracy is calibrated, the thermal stability and

line regulation tolerance are the only errors introduced

by the MCP1702 LDO. The low-cost, low quiescent

current and small ceramic output capacitor are all

advantages when using the MCP1702 as a voltage

reference.

FIGURE 6-2:

Using the MCP1702 as a

Voltage Reference.

Package

Package Type

SOT-23A

Input Voltage

VIN = 2.8V to 3.2V

LDO Output Voltages and Currents

VOUT =1.8V

IOUT =150 mA

Maximum Ambient Temperature

TA(MAX) = +40°C

Internal Power Dissipation

Internal Power dissipation is the product of the LDO

output current times the voltage across the LDO

(VIN to VOUT).

PLDO(MAX) =(VIN(MAX) - VOUT(MIN)) x

IOUT(MAX)

PLDO = (3.2V - (0.97 x 1.8V)) x 150 mA

PLDO = 218.1 milli-Watts

TJ(RISE) =PTOTAL x RqJA

TJRISE = 218.1 milli-Watts x 336.0°C/Watt

TJRISE = 73.3°C

TJ =TJRISE + TA(MAX)

TJ =113.3°C

SOT-23 (336.0°C/Watt = R

JA)

PD(MAX)

(+125°C - 40°C) / 336°C/W

PD(MAX)

253 milli-Watts

SOT-89 (52°C/Watt = R

JA)

PD(MAX)

(+125°C - 40°C) / 52°C/W

PD(MAX)

1.635 Watts

TO92 (131.9°C/Watt = R

JA)

PD(MAX)

(+125°C - 40°C) / 131.9°C/W

PD(MAX)

644 milli-Watts

PIC®

MCP1702

GND

VIN

CIN

1µF

COUT

1µF

Bridge Sensor

VOUT

VREF

ADO

AD1

Ratio Metric Reference

2 µA Bias

Microcontroller

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