AAT3670 View Datasheet(PDF) - Analog Technology Inc
Part Name
Description
MFG CO.
'AAT3670' PDF : 32 Pages View PDF
Applications Information
AC Adapter/USB System Power
Charging
Adapter Input Mode
In the adapter mode, constant current charge lev-
els up to 1.6A may be programmed by the user.
The AAT3670 system control will always select the
adapter input over the USB supply input when ever
voltage is present on the ADP pin. The ADP input
will operate over a range from 4.35V to 5.5V.
The constant fast charge current for the adapter
input mode is set by the RADPSET resistor connected
between the ADPSET pin and ground. The battery
preconditioning or trickle charge current is fixed at
10% of the programmed fast charge constant current
level. Refer to Table 2 for recommended RADPSET
values for a desired constant current charge level.
Battery charging states will be indicated via the
STAT1 and STAT2 display LEDs. Please refer to the
Battery Charge Status Indication discussion for fur-
ther details on data reporting.
ADP Charge Reduction
Under normal operation, the AAT3670 should be
operated from an adapter power source with a suffi-
cient capacity to supply the desired constant charge
current plus any additional load which may be
placed on the source by the operating system. In the
event that the power source to the ADP pin is unable
to provide the programmed fast charge constant cur-
rent, or if the system under charge must also share
supply current with other functions, the AAT3670 will
automatically reduce the ADP fast charge current
level to maintain the integrity of the source supply,
power the operating system, and charge the battery
cell with the remaining available current.
The ADP charge reduction system becomes active
when the voltage on the ADP input falls below the
ADP charge reduction threshold (VCHRADP), which is
preset to 4.6V. Should the input supply drop below
the VCHRADP threshold, the charge reduction system
will reduce the fast charge current level in a linear
fashion until the voltage sensed on the ADP input
recovers to a point above the charge reduction
threshold voltage. The ADP charge reduction
threshold (VCHRADP) may be externally set to a value
other than 4.6V by placing a resistor divider network
between the ADP pin and ground with the center
3670.2007.02.1.1
AAT3670
1.6A Dynamic Battery Charger
and Power Manager
connected to the CHRADP pin. The ADP charge
reduction feature may be disabled by shorting the
CHRADP pin directly to the ADP input pin.
The following equation may be used to approxi-
mate the ADP charge reduction threshold above or
below 4.5V:
Eq.
1:
VADPCHR
=
2.0V
(R12/[R12 +
R11])
where R11and R12 < 500kΩ.
VADP
ADP
R11
CHRADP
R12
850k
VCHR = 2.0V
650k
Figure 2: Internal Equivalent Circuit for the
CHRADP Pin.
Adapter Input Charge Inhibit and Resume
The AAT3670 has an under-voltage lockout
(UVLO) and power on reset feature to protect the
charger IC in the event the input supply to the
adapter pin drops below the UVLO threshold.
Under a UVLO condition, the charger will suspend
the charging process. When power is re-applied to
the adapter pin or the UVLO condition recovers,
the system charge control will asses the state of
charge on the battery cell and will automatically
resume charging in the appropriate mode for the
condition of the battery.
USB Input Mode
The AAT3670 provides an input for intelligent USB
charging. When no voltage is present on the
adapter input pin, the charge controller will auto-
matically switch to accepting power from the USB
input. The USB charge mode provides two pro-
grammable fast charge levels, USB high (USBH)
21
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