FAN3988 Просмотр технического описания (PDF) - ON Semiconductor

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FAN3988

USB/Charger and Over-Voltage Detection Device

ON Semiconductor 

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

STD USB

Device

(ie USB

Headphones)

Vbus

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 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 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 VDD, which is about 3.3 V, 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 VDD and D- is

set LOW (due to the 15 kΩ pull-down in the USB

transceiver) and flag1 is LOW.

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

D- floats LOW, which makes flag1 LOW.

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