MCP1801 datasheet(18/26 Pages) MICROCHIP

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MCP1801

DS22051C-page 18

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 in the following table.

Maximum Package Power Dissipation at +25°C

Ambient Temperature

6.4

Voltage Reference

The MCP1801 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 MCP1801 LDO. The low cost, low quiescent

current, and small ceramic output capacitor are all

advantages when using the MCP1801 as a voltage

reference.

FIGURE 6-2:

Using the MCP1801 as a

Voltage Reference.

6.5

Pulsed Load Applications

For some applications, there are pulsed load current

events that may exceed the specified 150 mA

maximum specification of the MCP1801. The internal

current limit of the MCP1801 will prevent high peak

load demands from causing non-recoverable damage.

The 150 mA rating is a maximum average continuous

rating. As long as the average current does not exceed

150 mA nor the maximum power dissipation of the

packaged device, pulsed higher load currents can be

applied to the MCP1801

. The typical current limit for

the MCP1801 is 300 mA (TA +25°C).

Package

Package Type:

SOT-23-5

Input Voltage

VIN = 2.4V to 5.0V

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 = (5.0V - (0.98 x 1.8V)) x 50 mA

PLDO = 161.8 milli-Watts

TJ(RISE) =PTOTAL x RqJA

TJRISE = 161.8 milli-Watts x 256.0°C/Watt

TJRISE = 41.42°C

TJ =TJRISE + TA(MAX)

TJ = 81.42°C

SOT-23-5 (256°C/Watt = R

JA)

PD(MAX) = (85°C - 25°C) / 256°C/W

PD(MAX) = 234 milli-Watts

PIC®

MCP1801

GND

VIN

CIN

1µF

COUT

1µF

Bridge Sensor

VOUT

VREF

ADO

AD1

Ratio Metric Reference

25 µA Bias

Microcontroller

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