AAT3670 View Datasheet(PDF) - Analog Technology Inc
Part Name
Description
MFG CO.
'AAT3670' PDF : 32 Pages View PDF
If the desired current charge current level is not list-
ed in Table 2, the ADPSET and USBSET resistor
values may be calculated by the following equations:
For the Adapter input mode:
Where:
RADPSET
=
K
·
⎛
⎝
VADPSET⎞
ICC ⎠
K
= KI_CCADP = 29300
VADPSET = 2V
ICC
= Fast Charge Constant Current
For the USB input mode:
Where:
RUSBSET
=
K
·
⎛
⎝
VUSBSET⎞
ICC ⎠
K
= KI_CCUSBH = 17900 (USBH)
K
= KI_CCUSBL = 3600 (USBL)
VUSBSET = 2V
ICC
= Fast Charge Constant Current
All constants K and VADP/USBSET are specified in the
Typical Characteristics section of this datasheet.
Protection Circuitry
Thermal Loop Control
Due to the integrated nature of the linear charging
control pass devices for both the adapter and USB
modes, a special thermal loop control system has
been employed to maximize charging current under
all operating conditions. The thermal management
system measures the internal circuit die temperature
and reduces the charge current when the device
exceeds a preset internal temperature control
threshold. Once the thermal loop control becomes
active, the constant charge current is initially
reduced by a factor of 0.44.
AAT3670
1.6A Dynamic Battery Charger
and Power Manager
The initial thermal loop current can be estimated by
the following equations:
In ADP mode: ITLOOP = ICCADP · 0.44
In USB mode: ITLOOP = ICCUSBH · 0.44
The thermal loop control re-evaluates the internal
die temperature every three seconds and adjusts
the fast charge current back up in small steps up
to the full fast charge current level or until an equi-
librium current is discovered and maximized for
the given ambient temperature condition. In this
manner, the thermal loop controls the system
charge level. The AAT3670 will always provide the
highest possible level of constant current in the
fast charge mode for any given ambient tempera-
ture condition.
Programmable Watchdog Timer
The AAT3670 contains a watchdog timing circuit
which operates only in adapter charging mode.
Typically a 0.1µF ceramic capacitor is connected
between the CT pin and ground. When a 0.1µF
ceramic capacitor is used, the device will time a
shutdown condition if the trickle charge mode
exceeds 45 minutes. When the device transitions
to the trickle charge to the fast charge constant cur-
rent mode and then to the constant voltage mode,
the timing counter is reset and will time out after 3
hours for each mode.
Summary for a 0.1µF used for the timing capacitor:
Trickle Charge (TC) time out = 45 minutes
Fast Charge Constant Current (CC) time out =
3 hours
Constant Voltage (VC) mode time out = 3 hours
The CT pin is driven by a constant current source
and will provide a linear response to increases in
the timing capacitor value. Thus, if the timing
capacitor were to be doubled from the nominal
0.1µF value, the time out time of the CC + CV
modes would be doubled. The corresponding trick-
le charge time out time would be the combined CC
+ VC time divided by 8.
3670.2007.02.1.1
25
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