FSA9280A Просмотр технического описания (PDF) - Fairchild Semiconductor

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FSA9280A

USB Port Multimedia Switch Featuring Automatic Select and Accessory Detection

Fairchild Semiconductor 

5.3. OCP and OVP Detection

With VBUS_IN greater than 6.8V, VBUS_IN is disconnected,

protecting the FSA9280A and all application circuitry from

excess voltage. This block is capable of withstanding

continuous 28V in Shutdown Mode. Upon entering

Shutdown Mode, the OVP_EN bit in the Interrupt 1 register

is set HIGH and an interrupt is sent to the baseband. The

Over-Current Protection (OCP) feature limits current through

the charger FET to ≤ 1.5A. The FSA9280A automatically

senses an over-current event, shuts down VBUSOUT, and

reports this to the baseband by asserting OCP_EN in the

Interrupt 1 register. OCP Mode is only implemented when

VBUS_IN is provided by the attached accessory. Removal of

an OVP or OCP condition triggers another interrupt sent to

the processor clearing the OCP_EN and/or the OVP_EN bits

and setting the OCP_OVP_DIS bit in the Interrupt 1 register.

6. Processor Communication

Typical communication steps between the processor and the

FSA9280A during accessory detection are:

1. INTB asserted LOW, indicating change in accessory

detection.

a) CHG_DET asserted LOW if USB charger detected.

2. Processor reads Interrupt registers to determine which

event occurred.

a) Interrupt 1 (03h): Indicates if an attach, detach, key

press, long key press, long key release, OVP / OCP

event, or OVP / OCP event recovery was detected.

Each bit can be masked by setting the corresponding

bit in the Interrupt Mask 1 (05h) register.

b) Interrupt 2 (04h): Indicates if a reserved

accessory, ADC change, stuck key, or stuck key

recovery was detected. Each bit can be masked

by setting the corresponding bit in the Interrupt

Mask 2 (06h) register.

3. Processor reads Status registers to determine exact

accessory detected.

a) Device Type 1 (0Ah): Indicates which USB, Car Kit

UART, or audio accessory was detected.

b) Device Type 2 (0Bh): Indicates which factory mode

was detected or if a TTY cable was detected.

c) Button 1 (0Ch & ODh): Indicates which button press

was detected with Audio Type 1 accessories.

d) Car Kit Status (0Eh): Indicates which type of car kit

charger was detected.

6.1. Interrupts

The baseband processor recognizes interrupt signals by

observing the INTB signal, which is active LOW. Interrupts

are masked upon reset or power up via the INT Mask

register bit (bit 0 of Control register, address 02h in Table 7.

Register Map) and INTB pin defaults LOW right after this

reset or power up. After the INT Mask bit is cleared by the

baseband processor, the INTB pin is driven HIGH in

preparation for a future interrupt. When an interruptible event

occurs, INTB transitions LOW and returns HIGH when the

processor reads the Interrupt register at address 03h.

Subsequent to the initial power up or reset; if the processor

writes a “1” to INT Mask bit when the system is already

powered up, the INTB pin stays HIGH and ignores all

interrupts until the INT Mask bit is cleared. If an event

happens that would ordinarily cause an interrupt when the

INT Mask bit is set, the INTB pin is LOW for tINT_MASK after

the INT Mask bit is cleared.

VBAT

VDDIO

Internal Reset

INTB Mask bit

INTB

Figure 16.

Standby Mode

100µs

INTB event

TINT_MASK

Switch Wait Time

Interrupt

registers read

Power-up Interrupt Timing Diagram

VBAT

VDDIO Reset

VDDIO

Internal Reset

INTB Mask bit

INTB

Standby Mode

100µs

INTB event

TINT_MASK

Switch Wait Time

Interrupt

registers read

Figure 17. VDDIO Reset Interrupt Timing Diagram

VBAT

VDDIO

INTB event

INTB Mask bit

INTB event

INTB Don‟t Care (High or Low)

TINT_MASK

Figure 18. INT Mask to INTB Interrupt Timing Diagram

7. Switch Configuration

FSA9280A devices have two modes of operation when

configuring the internal switches. The FSA9280A can auto-

configure the switches or the switches can be configured

manually by the processor. Typical applications can use the

Auto-Configuration Mode and do not require interaction with

the baseband to configure the switches correctly.

© 2009 Fairchild Semiconductor Corporation

FSA9280A • Rev 1.1.0

13

www.fairchildsemi.com

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