MCP1700T-1802ETO 查看數據表（PDF） - Microchip Technology

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MCP1700T-1802ETO

Low Quiescent Current LDO

Microchip Technology 

MCP1700

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-23

Input Voltage

VIN = 2.3V 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 (RθJA) 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 230.0°C/Watt

TJRISE = 50.2°C

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.

DS21826B-page 14

TJ = TJRISE + TA(MAX)

TJ = 90.2°C

Maximum Package Power Dissipation at +40°C

Ambient Temperature

SOT-23 (230.0°C/Watt = RθJA)

PD(MAX) = (125°C - 40°C) / 230°C/W

PD(MAX) = 369.6 milli-Watts

SOT-89 (52°C/Watt = RθJA)

PD(MAX) = (125°C - 40°C) / 52°C/W

PD(MAX) = 1.635 Watts

TO-92 (131.9°C/Watt = RθJA)

PD(MAX) = (125°C - 40°C) / 131.9°C/W

PD(MAX) = 644 milli-Watts

6.4 Voltage Reference

The MCP1700 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 MCP1700 LDO. The low cost, low quiescent

current and small ceramic output capacitor are all

advantages when using the MCP1700 as a voltage

reference.

Ratio Metric Reference

1 µA Bias

MCP1700

CIN

1 µF

VIN

VOUT

GND

COUT

1 µF

PIC®

Microcontroller

VREF

ADO

AD1

Bridge Sensor

FIGURE 6-2:

Using the MCP1700 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 MCP1700. The internal

current limit of the MCP1700 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 MCP1700. The typical current limit for the

MCP1700 is 550 mA (TA +25°C).

© 2007 Microchip Technology Inc.

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