AN2148 - APPLICATION NOTE

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3 - STOTG04 APPLICATION

The STOTG04 transceiver supports carkit signaling on both D+ and ID lines. Therefore, it is able to

operate with both four-wire and five-wire protocol. It is up to the carkit accessory which protocol will be

used. Figure 4 shows connection of the STOTG04 full-speed USB-OTG transceiver in an application

requiring even audio mode operation.

operation in audio mode it is necessary to release internal drivers to force the D+ and D- lines into high

impedance state. The UART mode is also needed for carkit. To use the transceiver in the UART mode it

is necessary to properly set the direction of UART drivers. The correct setup of control registers of the

transceiver is described in Table 2 for both audio and UART modes.

In the UART mode after a proper setup it is possible to transmit data from the SE0_VM pin to the D- line

and to receive data from the D+ line on the DAT_VP pin.

Figure 4 : Carkit Five-Wire Interface

Table 2 : Alternate Functions of a USB Signal Lines

Register

UART Mode

Audio Mode

Control 1

x 1 x x 0 x x x

(transp_en = 0, uart_en = 1)

x 0 x x 0 x x x

(transp_en = 0, uart_en = 0)

Control 2

0 0 0 0 0 0 0 0

(release all PU/PD resistors)

0 0 0 0 0 0 0 0

(release all PU/PD resistors)

Control 3

x x x 1 0 x x x

(bdir[0] = 0, bdir[1] = 1)

x x 1 x x x x x

(audio_en = 1)

VIF

SDA

SCL

ADR_PSW

RESET/

INT/

SPEED

SUSPEND

VM

VP

RCV

OE_TP_INT/

SE0_VM

DAT_VP

GND

VBAT

CAP1

CAP2

ID

VBUS

D+

D-

VTRM

CGND

ID

D+

D-

VBUS

GND

2.7–5.0 V

1.6–3.6 V

STOTG04E

Mini-AB

20

Ω±5%

220nF

4.7

µF

1

µF

TXD

RXD

SPKR_MIC

SPKR_L

VCC

VCC

Phone Processor

USB-OTG Controller

SDA

SCL

RESET/

INT/

VM

VP

RCV

OE_TP_INT/

SE0_VM

DAT_VP