AAT2557 AnalogicTech, AAT2557 Datasheet - Page 17

• Manufacturer Part Number: AAT2557
• Description: 500mA Battery Charger and 300mA LDO Regulator for Portable Systems
• Manufacturer: AnalogicTech

The LED should be biased with as little current as
necessary to create reasonable illumination; there-
fore, a ballast resistor should be placed between
the LED cathode and the STAT pin. LED current
consumption will add to the overall thermal power
budget for the device package, hence it is good to
keep the LED drive current to a minimum. 2mA
should be sufficient to drive most low-cost green or
red LEDs. It is not recommended to exceed 8mA
for driving an individual status LED.
The required ballast resistor values can be esti-
mated using the following formulas:
Example:
Note: Red LED forward voltage (V
2.0V @ 2mA.
Thermal Considerations
The AAT2557 is offered in a TSOPJW-14 package
which can provide up to 625mW of power dissipation
when it is properly bonded to a printed circuit board
and has a maximum thermal resistance of 160°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
2557.2007.06.1.0
Battery charging via adapter
No battery charging activity
Event Description
Charging completed
Table 2: LED Status Indicator.
R
or USB port
1
=
R
(5.5V - 2.0 V)
1
=
(V
2mA
ADP
I
- V
LED
F(LED)
= 1.75kΩ
)
F
) is typically
Status
OFF
OFF
ON
LDO Regulator for Portable Systems
500mA Battery Charger and 300mA
proximity to other heat generating devices in a given
application design. The ambient temperature around
the IC will also have an effect 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
situation should be calculated:
Where:
P
θ
T
T
Where:
P
V
V
I
I
V
V
I
I
P
CH
OP
LDOLOAD
QLDO
JA
J(MAX)
A
D(MAX)
D
D
ADP
BAT
INLDO
OUTLDO
= [(V
ADP
- V
= Maximum Power Dissipation (W)
= Package Thermal Resistance (°C/W)
= Maximum Device Junction Temperature
= Ambient Temperature (°C)
= Total Power Dissipation by the Device
= ADP/USB Voltage
= Battery Voltage as Seen at the BAT Pin
= Constant Charge Current Programmed
= Quiescent Current Consumed by the
= Input Voltage as Seen at the INLDO Pin
= Output Voltage as Seen at the OUTLDO
= LDO Load Current
= LDO Quiescent Current
BAT
(°C) [135°C]
for the Application
Charger IC for Normal Operation [0.5mA]
Pin
) · I
CH
P
+ (V
D(MAX)
ADP
· I
=
OP
)] + (V
(T
J(MAX)
INLDO
θ
- V
JA
- T
OUTLDO
AAT2557
A
)
) I
LDOLOAD
+ V
INLDO
· I
QLDO
17