USB3320 datasheet(32/70 Pages) MICROCHIP

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USB3320

DS00001792B-page 32

 2014-2015 Microchip Technology Inc.

During normal USB operation the switches are off. When USB Audio is desired the switches can be turned “on” by

enabling the SpkLeftEn, SpkRightEn, or MicEn bits in the Carkit Control register as described in Section 6.5.2. These

bits are disabled by default. The USB Audio Switches can also be enabled by asserting the RESETB pin or removing

the voltage at VDD18 as shown in Table 5-9. While using the USB switches, VDD18 is not required, but 3.3V must be

present at VDD33. The integrated 3.3V LDO regulator may be used to generate VDD33 from power applied at the VBAT

pin.

In addition to USB Audio support the switches can also be used to multiplexed a second FS USB transceiver to the USB

connector. The signal quality will be degraded slightly due to the “on” resistance of the switches. The USB3320 single-

ended receivers described in Section 5.2.1 are disabled when either USB Audio switch is enabled.

The USB3320 does not provide the DC bias for the audio signals. The SPK_R and SPK_L pins should be biased to

1.65V when audio signals are routed through the USB3320. This DC bias is necessary to prevent the audio signal from

swinging below ground and being clipped by ESD Diodes.

When the system is not using the USB Audio switches, the SPK_R and SPK_L pins should not be connected.

5.10

Reference Frequency Selection

The USB3320 is configured for the desired reference frequency by the REFSEL[2], REFSEL[1] and REFSEL[0] pins.

If a pin is connected to VDDIO, the value of “1” is assigned. Connect the pin to ground to assign a “0.” When using the

ULPI Input Clock Mode (60MHz REFCLK Mode), the reference frequency is always fixed at 60 MHz. Eight reference

clock frequencies are available as described in Table 5-10.

TABLE 5-9:

USB AUDIO SWITCH ENABLE

RESETB

VDD18

DP Switch Enable

DM Switch Enable

011

0111

SpkLeftEn

SpkRightEn

or MicEn

Note:

SpkLeftEn, SpkRightEn,

and MicEn are enabled in the Carkit Control register.

TABLE 5-10:

CONFIGURATION TO SELECT REFERENCE CLOCK FREQUENCY

Configuration Pins

Description

REFSEL[2]

REFSEL[1]

REFSEL[0]

Reference Frequency

52 MHz

38.4 MHz

12 MHz

27 MHz

13 MHz

19.2 MHz

26 MHz

24 MHz

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