AAT3688AIWP-4.2-4-T1 AnalogicTech, AAT3688AIWP-4.2-4-T1 Datasheet - Page 17

• Manufacturer Part Number: AAT3688AIWP-4.2-4-T1
• Description: USB Port Lithium-Ion/Polymer Battery Charger
• Manufacturer: AnalogicTech

Timing Diagram
BatteryManager
First, the maximum power dissipation for a given situa-
tion should be calculated:
Where:
P
V
V
I
I
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:
T
T
P
θ
3688.2007.12.1.6
CC
OP
A
JA
D
J
D
IN
BAT
= Ambient Temperature in Degrees C
= Maximum Device Junction Temperature Protected
= Total Power Dissipation by the Device
= Package Thermal Resistance in °C/W
= Total Power Dissipation by the Device
= Input Voltage Level, V
= Battery Voltage as Seen at the BAT Pin
= Maximum
= Quiescent Current Consumed by the Charger IC
by the Thermal Limit Control
Programmed for the Application
for Normal Operation
Eq. 4:
SQ
CK
Data
P
Eq. 5:
D
= [(V
Constant
TM
T
T
T
IN
DATA(RPT)
OFF
A
- V
= T
> 2 P
BAT
USB
J
- (θ
= T
) · I
DATA
T
Fast
System Reset
System Start
SQ
SYNC
SYNC
JA
CC
PULSE
· P
+ T
+ (V
Charge
D
LAT
)
IN
< 2.5 P
· I
T
LAT
OP
)]
w w w . a n a l o g i c t e c h . c o m
DATA
Current
USB Port Lithium-Ion/Polymer Battery Charger
P
DATA
N=1
Example:
For an application where the fast charge current is set to
500mA, V
at 3.0V, what is the maximum ambient temperature at
which the thermal limiting will become active?
Given:
Using Equation 4, calculate the device power dissipation
for the stated condition:
The maximum ambient temperature before the AAT3688
thermal limit protection will shut down charging can now
be calculated using Equation 5:
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.
V
V
I
I
T
θ
CC
OP
JA
J
ADP
BAT
Eq. 6:
= 5.0V
= 3.0V
= 500mA
= 0.75mA
= 140°C
= 50°C/W
Eq. 7:
N=2
P
USB
D
= (5.0V - 3.0V) (500mA) + (5.0V · 0.75mA)
= 1.00375W
= 5.0V and the worst case battery voltage
T
A
= 140°C - ( 50°C/W · 1.00375W)
= 89.81°C
N=3
PRODUCT DATASHEET
T
OFF
AAT3688
17