MCP1702 View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

MCP1702

250 mA Low Quiescent Current LDO Regulator

Microchip Technology 

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

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

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 more information

regarding this subject.

TJ(RISE) = PTOTAL x RqJA

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

TJRISE = 73.3°C

MCP1702

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.

TJ = TJRISE + TA(MAX)

TJ = 113.3°C

Maximum Package Power Dissipation at +40°C

Ambient Temperature Assuming Minimal Copper

Usage.

SOT-23 (336.0°C/Watt = RJA)

PD(MAX) = (+125°C - 40°C) / 336°C/W

PD(MAX) = 253 milli-Watts

SOT-89 (153.3°C/Watt = RJA)

PD(MAX) = (+125°C - 40°C) / 153.3°C/W

PD(MAX) = 0.554 Watts

TO92 (131.9°C/Watt = RJA)

PD(MAX) = (+125°C - 40°C) / 131.9°C/W

PD(MAX) = 644 milli-Watts

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.

Ratio Metric Reference

2 µA Bias

MCP1702

CIN

1 µF

VIN

VOUT

GND

COUT

1 µF

PIC®

Microcontroller

VREF

ADO

AD1

Bridge Sensor

FIGURE 6-2:

Using the MCP1702 as a

Voltage Reference.

 2010 Microchip Technology Inc.

DS22008E-page 15

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