FAN3988 Datasheet, PDF (7/9 Pages) Fairchild Semiconductor – USB/Charger and Over-Voltage Detection Device

Without USB Transceiver (Figure 8)
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 condition where a USB transceiver is not
incorporated or there is a switch between the USB port
and the FAN3988, external resistors must be used to
set the correct input logic states on the FAN3988 D+ D-
inputs. A 5MΩ pull-down on the D- line and a 1MΩ pull-
up to V_DD (system supply) on the D+ line are
recommended.
When a condition exists where a charger is plugged into
the USB port (D+ D- shorted), the voltage divider of 1M
and 5M puts a voltage of 2.75V on the D+ D- inputs and
flag1 is HIGH, indicating a charger is connected to port.
In a condition where the USB port is connected to a
standard USB device, the D+ input is pulled up to V_DD
(system supply) in parallel with the 1.5KΩ on a USB
transceiver with a parallel R value of 1.497KΩ. The D-
input is connected to a 15KΩ pull-down by the USB
device and in parallel with 5MΩ with a parallel R value
of 14.955KΩ. This condition makes flag1 LOW.
If D+ and D- are open (floating), D+ is pulled to V_DD
(system supply) and D- floats LOW, which makes
flag1 LOW.
Control
Battery
Rsense
Vbus
D-
D+
Gnd
USB
Vbus
Comparator
OVP
UVP
Logic
D-
D+
GND
5M 1M
Std USB/
Charger
Detect
Logic
Vdd
Figure 8. Typical System Application without USB Transceiver
Flag 2
Flag 1
© 2007 Fairchild Semiconductor Corporation
FAN3988 • Rev. 1.0.5
7
www.fairchildsemi.com