AAT3688 Просмотр технического описания (PDF) - Advanced Analogic Technologies

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производитель

AAT3688

USB Port Lithium-Ion/Polymer Battery Charger

Advanced Analogic Technologies 

BatteryManagerTM

Timing Diagram

PRODUCT DATASHEET

AAT3688

USB Port 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

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, VUSB

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.

Where:

Eq. 5: TA = TJ - (θJA · PD)

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:

VADP = 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

The maximum ambient temperature before the AAT3688

thermal limit protection will shut down charging can now

be calculated using Equation 5:

Eq. 7: TA = 140°C - (50°C/W · 1.00375W)

= 89.81°C

Therefore, under the stated conditions for this worst

case power dissipation example, the AAT3688 will sus-

pend charging operations when the ambient operating

temperature rises above 89.81°C.

3688.2007.12.1.6

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