USB3370 datasheet(24/75 Pages) MICROCHIP

24 / 75 page

USB3370

DS00001915B-page 24

 2012 - 2015 Microchip Technology Inc.

5.7

USB On-The-Go (OTG)

The USB3370 provides support for the USB OTG protocol. OTG allows the USB3370 to be dynamically configured as

a host or peripheral depending on the type of cable inserted into the Micro-AB receptacle. When the Micro-A plug of a

cable is inserted into the Micro-AB receptacle, the USB device becomes the A-device. When a Micro-B plug is inserted,

the device becomes the B-device. The OTG A-device behaves similar to a Host while the B-device behaves similar to

a peripheral. The differences are covered in the “On-The-Go Supplement to the USB 2.0 Specification”. In applications

where only USB Host or USB Peripheral is required, the OTG Module is unused.

5.7.1

ID RESISTOR DETECTION

The ID pin of the USB connector is monitored by the ID pin of the USB3370 to detect the attachment of different types

of USB devices and cables. For device only applications that do not use the ID signal the ID pin should be connected

to VDD33. The block diagram of the ID detection circuitry is shown in Figure 5-6 and the related parameters are given

in Table 4-8.

5.7.1.1

USB OTG Operation

The USB3370 can detect ID grounded and ID floating to determine if an A or B cable has been inserted. The A plug will

ground the ID pin while the B plug will float the ID pin. These are the only two valid states allowed in the OTG Protocol.

To monitor the status of the ID pin, the Link activates the IdPullup bit in the OTG Control register, waits 50mS and then

reads the status of the IdGnd bit in the USB Interrupt Status register. If an A cable has been inserted the IdGnd bit will

read 0. If a B cable is inserted, the ID pin is floating and the IdGnd bit will read 1.

The USB3370 provides an integrated weak pull-up resistor on the ID pin, RIDW. This resistor is present to keep the ID

pin in a known state when the IdPullup bit is disabled and the ID pin is floated. In addition to keeping the ID pin in a

known state, it enables the USB3370 to generate an interrupt to inform the link when a cable with a resistor to ground

has been attached to the ID pin. The weak pull-up is small enough that the largest valid RID resistor pulls the ID pin low

and causes the IdGnd comparator to go low.

After the link has detected an ID pin state change, the RID converter can be used to determine the resistor value as

described in Section 5.7.1.2.

FIGURE 5-6:

USB3370 ID RESISTOR DETECTION CIRCUITRY

IdPullup

IdGnd

Vref IdGnd

IdFloat

OTG Module

VDD33

To USB Con.

RidValue

Vref IdFloat

IdGnd Rise

IdGnd Fall

IdFloatRise

IdFloatFall

Rid ADC

IdGndDrv

USB3370 数据表(PDF) 24 Page - Microchip Technology

USB3370 数据表(HTML) 24 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75

数据表下载