AAT3685IWP-4.2-1-T1 Ver la hoja de datos (PDF) - Analog Technology Inc

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componentes Descripción

Fabricante

AAT3685IWP-4.2-1-T1

Lithium-Ion/Polymer Battery Charger

Analog Technology Inc 

BatteryManagerTM

Timing Diagram

PRODUCT DATASHEET

AAT3685

Lithium-Ion/Polymer Battery Charger

SQ

CK

Data

SQPULSE

System Reset

System Start

TSYNC

TLAT

TDATA(RPT) = TSYNC + TLAT < 2.5 PDATA

TOFF > 2 PDATA

PDATA

N=1

N=2

TOFF

N=3

Thermal Considerations

The AAT3685 is packaged in a Pb-free, 3x3mm TDFN

package which can provide up to 2.0W of power dissipa-

tion when it is properly bonded to a printed circuit board

and has a maximum thermal resistance of 50°C/W.

Many considerations should be taken into account when

designing the printed circuit board layout, as well as the

placement of the charger IC package in proximity to

other heat generating devices in a given application

design. The ambient temperature around the charger IC

will also have an affect on the thermal limits of a battery

charging application. The maximum limits that can be

expected for a given ambient condition can be estimated

by the following discussion.

First, the maximum power dissipation for a given situa-

tion should be calculated:

Eq. 4: PD = [(VIN - VBAT) · ICC + (VIN · IOP)]

Where:

PD = Total Power Dissipation by the Device

VIN = Input Voltage Level, VADP/USB

VBAT = Battery Voltage as Seen at the BAT Pin

ICC = Maximum Constant Fast Charge Current

Programmed for the Application

IOP = Quiescent Current Consumed by the Charger IC

for Normal Operation

Next, the maximum operating ambient temperature for

a given application can be estimated based on the ther-

mal resistance of the 3x3mm TDFN package when suf-

ficiently mounted to a PCB layout and the internal ther-

mal loop temperature threshold.

Eq. 5: TA = TJ - (θJA · PD)

Where:

TA = Ambient Temperature in Degrees C

TJ = Maximum Device Junction Temperature Protected

by the Thermal Limit Control

PD = Total Power Dissipation by the Device

θJA = Package Thermal Resistance in °C/W

Example:

For an application where the fast charge current is set to

500mA, VUSB = 5.0V and the worst case battery voltage

at 3.0V, what is the maximum ambient temperature at

which the thermal limiting will become active?

Given:

VUSB = 5.0V

VBAT = 3.0V

ICC = 500mA

IOP = 0.75mA

TJ = 140°C

θJA = 50°C/W

Using Equation 4, calculate the device power dissipation

for the stated condition:

Eq. 6: PD = (5.0V - 3.0V)(500mA) + (5.0V · 0.75mA)

= 1.00375W

3685.2007.12.1.4

www.analogictech.com

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