AAT3670 View Datasheet(PDF) - Analog Technology Inc
Part Name
Description
MFG CO.
'AAT3670' PDF : 32 Pages View PDF
No Battery Present Indication
If the AAT3670 charger IC is powered and enabled
from either the ADP or USB input, yet no battery is
connected to the BAT and BATS pins, the STAT1
LED will flash at a 1Hz rate with an approximate
40% duty cycle when a 10µF capacitor is connect-
ed between the BAT pin and ground. The flash rate
of the STAT1 LED can be adjusted by changing the
value of the battery output (BAT pin) capacitor. If
the capacitor value is increased above 20µF, the
no battery detect flashing function will be defeated.
The flash rate of the no battery detect function may
be approximated by the following equation:
Eq.
6:
C
=
I
·T
V
Where:
C = Capacitor value
I = Start up source current from the BAT pin = 5µA
V = Difference voltage between the end of charge
voltage and the battery recharge threshold =
0.2V
T = Rate of LED flashing in seconds
Thermal Considerations
The AAT3670 is available in a 4x4mm 24-pin QFN
package which can provide up to 2.0W of power
dissipation when it is properly bonded to a printed
circuit board, but can achieve a maximum thermal
resistance of 37°C/W with printed circuit board
enhancement. Many considerations should be
taken into account when designing the printed cir-
cuit board layout as well as the placement of the
charger IC package in proximity to other heat gen-
erating devices in a given application design. The
ambient temperature around the charger IC will
also have an effect on the thermal limits of a bat-
tery charging application. The maximum limits that
can be expected for a given ambient condition can
be estimated by the following discussion:
AAT3670
1.6A Dynamic Battery Charger
and Power Manager
First, the maximum power dissipation for a given
situation should the calculated:
Eq. 7: PD = [(VIN - VBAT) · ICC + (VIN · IOP) + (IOUT2 · RDS(ON))
Where:
PD = Total power dissipation by the device
VIN = either VADP or VUSB, depending on which
mode is selected
VBAT
ICC
= Battery voltage as seen at the BAT pin
= Maximum constant fast charge current
programmed for the application
IOP = Quiescent current consumed by the
charger IC for normal operation
IOUT = Load current to system from the OUT pin
RDS(ON) = On-resistance of load switch between
ADP or USB and OUT
Next, the maximum operating ambient temperature
for a given application can be estimated based on
the thermal resistance of the 4x4 QFN package
when sufficiently mounted to a PCB layout and the
internal thermal loop temperature threshold.
Eq. 8: TA = TJ - (θJA · PD)
Where:
TA = Ambient temperature in °C
TJ = Maximum device junction temperature below
the thermal loop threshold
PD = Total power dissipation by the device
θJA = Package thermal resistance in °C/W
3670.2007.02.1.1
29
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