AAT3670 View Datasheet(PDF) - Analog Technology Inc
Part Name
Description
MFG CO.
'AAT3670' PDF : 32 Pages View PDF
All constants K and VADP/USBLIM are specified in the
Typical Characteristics section of this datasheet.
Over-Voltage Protection
An over-voltage event is defined as a condition
where the voltage on the BATS pin exceeds the
maximum battery charge voltage and is set by the
over-voltage protection threshold (VOVP). If an
over-voltage condition occurs, the AAT3670 charge
control will shutdown the device until voltage on the
BATS pin drops below the over-voltage protection
threshold (VOVP). The AAT3670 will resume normal
charging operation once the battery over-voltage
condition is removed. During an over-voltage
event, the STAT2 LED will report a system fault.
Over-Temperature Shutdown
The AAT3670 has a thermal protection control cir-
cuit which will shut down charging functions should
the internal die temperature exceed the preset
thermal limit threshold.
Battery Temperature Fault Monitoring
In the event of a battery over-temperature condition,
the charge control will turn off the internal charge
path regulation device and report the fault condition
via the STAT2 display LED. After the system recov-
ers from a temperature fault, the device will resume
charging operation. The AAT3670 checks battery
temperature before starting the charge cycle, as
well as during all stages of charging.
Typically, batteries employ the use of a negative
temperature coefficient (NTC) thermistor that is
integrated into the battery package. Most com-
monly used NTC thermistors used in battery packs
are approximately 10kΩ at room temperature
(25°C). However, the AAT3670 TS pin, in conjunc-
tion with the VTS pin, permits the use of almost any
value of NTC thermistor.
There are two pins associated with the battery tem-
perature sensing function, TS and VTS. The battery
pack thermistor should be connected between the
TS pin and ground. The VTS pin is provided to allow
the user to program battery temperature sense
thresholds depending upon the value of the NTC
thermistor used in a given battery pack. A resistor
(RT) connected between the VTS pin and the TS pin
will set a bias for the NTC thermistor function. The
TS function has been designed such that a default
NTC thermistor value of 10kΩ will then require a 10k
3670.2007.02.1.1
AAT3670
1.6A Dynamic Battery Charger
and Power Manager
resistor for RT. To determine the actual operating
temperature window for the the NTC thermistor and
the TS pin, one must first specify the NTC thermis-
tor to be used, then refer to the thermistor datasheet
to determine its characteristics.
The internal battery temperature sensing system is
comprised of two comparators which establish a
voltage window for safe operation. The thresholds
for the TS operating window are bounded by the
TS1 and TS2 specifications. Referring to the elec-
trical characteristics table in this datasheet, the TS1
threshold = 0.30 · VVTS and the TS2 threshold =
0.72 · VVTS. The VTS pin is capable of sourcing up
to 2mA.
VTS
RT
0.72 · VVTS
-
TS
+
RNTC
T
-
+
0.30 · VVTS
Battery Cold Fault
Battery Hot Fault
Figure 5: Battery Temperature Sense Circuit.
VTS
RT
TS
RADJ
RNTC
T
0.72V
-
+
-
0.30V +
Battery Cold Fault
Battery Hot Fault
Figure 6: Battery Temperature Sense Circuit
with Externally Adjusted Window Threshold.
27
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