USB3803 datasheet(14/99 Pages) MICROCHIP

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USB3803

DS00001691B-page 14

 2014-2015 Microchip Technology Inc.

3.3.4

INTERRUPT

The general interrupt pin (INT_N) is intended to communicate a condition change within the hub. The conditions which

may cause an interrupt are captured within a register mapped to the serial port (Register E8h: Serial Port Interrupt Status

- INT_STATUS.) The conditions which cause the interrupt to assert can be controlled through use of an interrupt mask

The general interrupt and all interrupt conditions are functionally latched and event driven. Once the interrupt or any of

the conditions have asserted, the status bit will remain asserted until the SOC negates the bit using the serial port. The

bits will then remain negated until a new event condition occurs. The latching nature of the register causes the status to

remain even if the condition that caused the interrupt ceases to be active. The event driven nature of the register causes

the interrupt to only occur when a new event occurs- when a condition is removed and then is applied again. (e.g. if the

battery charger detection routine has completed and the SOC negates the interrupt status, it will not cause an interrupt

just because the charger detection is still completed- a new charger detection routine has to run before its associated

interrupt will assert again.)

The function of the interrupt and the associated status and masking registers are illustrated in Figure 3-2, "INT_N Oper-

ation". Registers & Register bits shown in the figure are defined in Table 5-2, “Serial Interface Registers,” on page 21

and Section 5.3, "Serial Interface Register Definitions," on page 23.

Figure 3-2 also shows an alternate configuration option (CFGP.INTSUSP) for a suspend interrupt. This option allows

the user to change the behavior of the INT_N pin to become a direct level indication of configuration and suspend status.

When selected, the INT_N indicates that the entire hub has entered the USB suspend state and that VBUS current con-

sumption should be reduced in accordance with the USB specification. Selective suspend set by the host on down-

stream hub ports have no effect on this signal because there is no requirement to reduce current consumption from the

upstream VBUS. It can be used by the system to monitor INT_N to dynamically adjust how much current the PMIC

draws from VBUS to charge the battery in the system during a USB session. Because it is a level indication, it will assert

or negate to reflect the current status of suspend without any interaction through the serial port.

When negated high this means no level suspend interrupt and device has been configured by the USB Host. The full

configured current can be drawn from the USB VBUS pin on the USB connector for charging - up to 500mA depending

on descriptor setting. When asserted low, this indicates a suspend interrupt or device not yet configured by USB Host.

The current draw can be limited by the system according to the USB specification. The USB specification limits current

to 100mA before configuration, and up to 12.5mA in USB suspend mode.

FIGURE 3-2:

INT_N OPERATION

Note:

Because INT_N is driven low when active, care must be taken when selecting the external pullup resistor

value for this open drain output. A sufficiently large resistor must be selected to insure suspend current

requirements can be satisfied for the system.

Reserved

Serial Port

W rite Logic

INT_N

SET

CLR

INT_MASK

<1>

<2>

<3>

<4>

SET

CLR

INT_STATUS <7>

<0>

SET

CLR

SET

CLR

SET

CLR

SET

CLR

SET

CLR

INT_STATUS<4:0>

SCL/SDA

Hub Configured by USB Host

(HubConf)

Port Power Register Updated

(PrtPwr)

Hub in USB Suspend Mode

(SuspInd)

Suspended OR

NOT Configured

SET

CLR

CFGP.INTSUSP

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