AAT3688AIWP-4.2-4-T1 AnalogicTech, AAT3688AIWP-4.2-4-T1 Datasheet - Page 13

• Manufacturer Part Number: AAT3688AIWP-4.2-4-T1
• Description: USB Port Lithium-Ion/Polymer Battery Charger
• Manufacturer: AnalogicTech

BatteryManager
Application Information
USB System Power Charging
The USB charge mode provides two programmable fast
charge levels up to 500mA for each, USB high and USB
low, USBH and USBL, respectively. The USBH or USBL
modes may be externally selected by the USB select pin
(USBSEL). When the USBSEL pin is connected to a logic
high level, the USBH level will be active. Conversely,
when USBSEL is pulled to a logic low level (ground), the
USBL level will be used for fast charging. Typically USBH
is set for 500mA and USBL is set for 100mA. However,
these two USB charge levels may be user programmed
to any level between 50mA and 500mA by selecting the
appropriate resistor values for R
Table 1 for recommended R
desired USB input constant current charge levels.
USB Charge Reduction
In many instances, product system designers do not
know the real properties of a potential USB port to be
used to supply power to the battery charger.
powered USB ports commonly found on desktop and
notebook PCs should supply up to 500mA. In the event
a USB port being used to supply the charger is unable to
provide the programmed fast charge current, or if the
system under charge must also share supply current
with other functions, the AAT3688 will automatically
reduce USB fast charge current to maintain port integ-
rity and protect the host system.
The USB charge reduction system becomes active when
the voltage on the USB input falls below the USB charge
reduction threshold (V
Regardless of which USB charge function is selected
(USBH or USBL), the charge reduction system will
reduce the fast charge current level in a linear fashion
until the voltage sensed on the USB input recovers
above the charge reduction threshold voltage. The USB
charge reduction threshold (V
set to a value lower than 4.5V by placing a resistor
divider network between V
connected to the CHR pin. The USB charge reduction
feature may be disabled by connecting a 10kΩ resistor
from the CHR pin directly to the USB input pin.
The following equation may be used to approximate a
USB charge reduction threshold below 4.5V:
3688.2007.12.1.6
TM
USBCHR
USB
SETH
), which is typically 4.5V.
and ground with the center
USBCHR
and R
SETH
) may be externally
and R
SETL
values for the
SETL
. Refer to
w w w . a n a l o g i c t e c h . c o m
Typical
USB Port Lithium-Ion/Polymer Battery Charger
where R11/R12 << 1MΩ.
USB Input Charge Inhibit and Resume
The AAT3688 UVLO and power on reset feature will func-
tion when the USB input pin voltage level drops below
the UVLO threshold. At this point, the charger will sus-
pend charging and shut down. When power is re-applied
to the USB pin or the UVLO condition recovers, the sys-
tem charge control 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.
Enable / Disable
The AAT3688 provides an enable function to control 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 charg-
ing state. When the device is re-enabled, the charge
100
200
300
400
500
Figure 2: Internal Equivalent Circuit
I
Table 1: Recommended R
50
75
CC
Eq. 1:
R11
R12
V
V
USB
for the CHR Pin.
USBCHR
CHR
PRODUCT DATASHEET
R
SET
USBH
= 2.0V ÷
86.6
57.6
42.2
21.0
13.7
10.2
8.06
(kΩ)
USB
AAT3688
825k
1.025M
V
CHR
R12 + R11
= 2.0V
SET
R12
Values.
R
SET
USBL
86.6
57.6
42.2
20.5
13.7
10.2
8.06
(kΩ)
13