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FAN3988

USB/Charger and Over-Voltage Detection Device

ON Semiconductor 

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 VBUS for

over- or under-voltage conditions. The FLAG2 pin is set

LOW if VBUS is less than 3.3 V or greater than 6.0 V.

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 D+ D- inputs. A

5 MΩ pull-down on the D- line and a 1 MΩ pull-up to

VDD (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

1 MΩ and 5 MΩ puts a voltage of 2.75 V 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 VDD

(system supply) in parallel with the 1.5 kΩ on a USB

transceiver with a parallel R value of 1.497 kΩ. The D-

input is connected to a 15 kΩ pull-down by the USB

device and in parallel with 5 MΩ with a parallel R value

of 14.955 kΩ. This condition makes flag1 LOW.

If D+ and D- are open (floating), D+ is pulled to VDD

(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

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