AAT3688
USB Port Lithium-Ion/Polymer Battery Charger
USB Input Charge Inhibit and Resume
for 500mA and 100mA USB fast charge levels.
The AAT3688 UVLO and power on reset feature
will function when the USB input pin voltage level
drops below the UVLO threshold. At this point, the
charger will suspend charging and shut down.
When power is re-applied to the USB pin or the
UVLO condition recovers, the system charge con-
trol will assess the state of charge on the battery
cell and will automatically resume charging in the
appropriate mode for the condition of the battery.
However, these two charge levels may be set to any
level between 50mA and 500mA, depending upon
the system design requirements for a given USB
charge application. Refer to Table 1 and Figure 3
for recommended RSETH and RSETL values.
1000
USBL
100
Enable / Disable
USBH
The AAT3688 provides an enable function to con-
trol the charger IC on and off. The enable (EN) pin
is an active high. When pulled to a logic low level,
the AAT3688 will be shut down and forced into the
sleep state. Charging will be halted regardless of
the battery voltage or charging state. When the
device is re-enabled, the charge control circuit will
automatically reset and resume charging functions
with the appropriate charging mode based on the
battery charge state and measured cell voltage.
10
1
10
100
1000
RSET (kΩ)
Figure 3: IFASTCHARGE vs. RSET
.
Protection Circuitry
Over-Voltage Protection
Programming Charge Current
An over-voltage event is defined as a condition
where the voltage on the BAT pin exceeds the
maximum battery charge voltage and is set by the
over-voltage protection threshold (VOVP). If an
over-voltage condition occurs, the AAT3688 charge
control will shut down the device until voltage on
the BAT pin drops below the over-voltage protec-
tion threshold (VOVP). The AAT3688 will resume
normal charging operation after the over-voltage
condition is removed. During an over-voltage
event, the STAT LEDs will report a system fault; the
actual fault condition may also be read via the
DATA pin signal.
The fast charge constant current charge level for the
USB input is programmed with set resistors placed
between the USBH and USBL pins and ground. The
accuracy of the fast charge, as well as the precondi-
tioning trickle charge current, is dominated by the
tolerance of the set resistors used. For this reason,
1% tolerance metal film resistors are recommended
for programming the desired constant current level.
The USB input fast charge constant current charge
control provides for two current set levels, USBH
and USBL. The USBSEL pin is used to select the
high or low charge current levels in the USB charge
mode. When the USBSEL pin is pulled to a voltage
level above the VUSBSEL(H) threshold, the USBH cur-
rent level will be selected. Conversely, this pin
should be pulled below the VUSBSEL(L) to enable the
USBL charge level. Typically, the two RSETH and
RSETL for the USBH and USBL functions are fixed
Over-Temperature Shutdown
The AAT3688 has a thermal protection control cir-
cuit which will shut down charging functions should
the internal die temperature exceed the preset
thermal limit threshold.
14
3688.2006.10.1.5
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
