MCP1703-2802ESLASHCD datasheet(14/24 Pages) MICROCHIP

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MCP1703

DS22049A-page 14

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 Ther-

mal 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 depend-

ing on many factors, such as copper area and thick-

ness. Refer to AN792, “A Method to Determine How

Much Power a SOT23 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 MCP1703 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 MCP1703 LDO. The low-cost, low quiescent

current and small ceramic output capacitor are all

advantages when using the MCP1703 as a voltage

reference.

FIGURE 6-2:

Using the MCP1703 as a

Voltage Reference.

6.5

Pulsed Load Applications

For some applications, there are pulsed load current

events that may exceed the specified 250 mA

maximum specification of the MCP1703. The internal

current limit of the MCP1703 will prevent high peak

load demands from causing non-recoverable damage.

The 250 mA rating is a maximum average continuous

rating. As long as the average current does not exceed

250 mA, pulsed higher load currents can be applied to

the MCP1703

. The typical current limit for the

MCP1703 is 500 mA (TA +25°C).

Package

Package Type = SOT-23A

Input Voltage

VIN = 2.7V to 4.8V

LDO Output Voltages and Currents

VOUT =1.8V

IOUT =50 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 = (4.8V - (0.97 x 1.8V)) x 50 mA

PLDO = 152.7 milli-Watts

TJ(RISE) =PTOTAL x RqJA

TJRISE = 152.7 milli-Watts x 336.0°C/Watt

TJRISE = 51.3°C

TJ =TJRISE + TA(MAX)

TJ = 91.3°C

SOT-23A (336.0°C/Watt = R

JA)

PD(MAX) = (125°C - 40°C) / 336°C/W

PD(MAX) = 253 milli-Watts

SOT-89 (75°C/Watt = R

JA)

PD(MAX) = (125°C - 40°C) / 75°C/W

PD(MAX) = 1.133 Watts

SOT-223 (62.9°C/Watt = R

JA)

PD(MAX) = (125°C - 40°C) / 62.9°C/W

PD(MAX) = 1.35 Watts

PIC®

MCP1703

GND

VIN

CIN

1µF

COUT

1µF

Bridge Sensor

VOUT

VREF

ADO

AD1

Ratio Metric Reference

2 µA Bias

Microcontroller

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