FAN3988 Datasheet, PDF (6/9 Pages) Fairchild Semiconductor – USB/Charger and Over-Voltage Detection Device

Application Information
Std 15K pull-down on D-
input and 1.5K pull-up
on D+ by USB
transceiver.
1.5K
Vdd
15K
USB Transceiver
Control
Battery
Rsense
Vout
Vbus
STD USB
Device
(ie USB
Headphones)
Vbus
D-
D+
Gnd
USB
D-
D+
GND
Comparator
OVP
UVP
Std USB/
Charger
Detect
Logic
Logic
Figure 7. Typical Application System with USB Transceiver
Flag 2
Flag 1
With USB Transceiver (Figure 7)
The FAN3988 sets the FLAG1 pin to logic HIGH or
LOW as an indicator to the system controller that a
standard USB device or a charger is connected to the
USB port. The FAN3988 also monitors the V_BUS for
over- or under-voltage conditions. The FLAG2 pin is set
LOW if V_BUS is less than 3.3V or greater than 6.0V.
In a standard USB configuration, there is a switch in the
USB transceiver that is always ON in the full-speed
mode. It is ON during the transition from full-speed
mode to high-speed mode and is turned off after
enumeration is complete.
In a condition where D+ and D- are shorted when a
charger is plugged into the USB port, the USB switch is
ON and pulled to V_DD, which is about 3.3V, making both
D+ and D- HIGH and flag1 set HIGH – indicating that a
charging device is connected to the port.
In a condition where D+ and D- are connected to a
standard USB device, the D+ is pulled to V_DD and D- is
set LOW (due to the 15KΩ pull-down in the USB
tranceiver) and flag1 is LOW.
If D+ and D- are open (floating), D+ is pulled to V_DD and
D- floats LOW, which makes flag1 LOW.
© 2007 Fairchild Semiconductor Corporation
FAN3988 • Rev. 1.0.10
6
www.fairchildsemi.com