MC34708 datasheet(90/159 Pages) FREESCALE

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Analog Integrated Circuit Device Data



Freescale Semiconductor

MC34708

Functional Block Description

The VUSB regulator defaults to ON when PUMS4:1 = [0100], and is supplied by the SWBST output. As shown in Figure 20, this

means that the M0 and MOTG switches are open, while the M1 switch is closed.

When PUMS4:1 is not equal to [0100], the VUSB regulator can not be enabled unless 5.0 V is present on the VBUS pin. If VBUS

is detected during a cold start, then the VUSB regulator will be enabled and powered ON in the sequence shown in Startup

Requirements, and it will default to be supplied by the VBUS pin. This means that switch M0 is closed and switch M1 and MOTG

in Figure 20 are open. If VBUS is not detected at cold start, then the VUSB regulator cannot be enabled. If VBUS is detected

later, the VUSB regulator will be enabled automatically and supplied from the VBUS pin. The VUSBEN SPI bit is initialized at

startup, based on the PUMS4:1 configuration. With PUMS4:1 not equal to [0100], the VUSBEN SPI bit will default to a one on

power up and will reset to a 1, when either RESETB is valid or VBUS is invalid. This allows the VUSBEN regulator to be enabled

automatically if the VUSB regulator was disabled by software. With PUMS4:1 equal to [0100], the VUSBEN bit will be enabled in

the power up sequence.

The MC34708 also supports USB OTG mode by supplying 5.0 V to the VBUS pin. The OTGEN SPI bit along with the VUSBSEL

SPI bit, control switching the SWBST to drive VBUS in OTG mode. When OTGEN = 1 and VUSBSEL = 1, SWBST will be driving

the VBUS (switch M1 and MOTG are closed, and the M0 switch is open). When OTG mode is disabled, the switch (MOTG) from

VINUSB to VBUS will be open.

In OTG mode, the VUSB regulator is enabled by setting the VUSBEN SPI bit to a one. When SWBST is supplying the VBUS pin

(OTG Mode), it will generate a USBDET interrupt. The USBDET interrupt while in OTG mode should not be interpreted as being

Table 86. VUSB Input Source Control (66)

Parameter

Value

Function

VUSBSEL

OTG mode: SWBST internally switched to supply the VUSB regulator (switch M1 closed, M0 open), and

SWBST will drive VBUS from the VINUSB pin as long as SPI bit OTGEN is set = 1.

Notes

66.

VUSBSEL = 1 and OTGEN = 1 only close the switch between the VINUSB and VBUS pins, but do not enable the SWBST boost

regulator (which should be enabled with SWBSTEN = 1)

Table 87. VUSB/OTG Switch Configuration

Mode

OTGEN VUSBSEL Switches Enabled (Closed) Switches Disabled (Open)

VUSB powered from VBUS pin

M1, MOTG

VUSB powered from VINUSB pin

M0, MOTG

Invalid option

OTG Mode (VUSB powered from VINUSB pin and SWBST

M1, MOTG

Table 88. VUSB Electrical Characteristics

Characteristics noted under conditions BP = 3.6 V, VBUS = 5.0 V, -40 C  TA  85 C, unless otherwise noted. Typical values

at BP = 3.6 V and TA = 25 °C under nominal conditions, unless otherwise noted.

Symbol

Characteristic

Min

Typ

Max

Unit

Notes

VUSB REGULATOR

VUSBIN

Operating Input Voltage Range VINMIN to VINMAX

• Supplied by VBUS

• Supplied by SWBST

4.4

5.0

5.25

5.75

IUSB

Operating Current Load Range ILMIN to ILMAX

0.0

100

COVUSB

Bypass Capacitor Value Range

0.65

2.2

F

ESRVUSB Bypass Capacitor ESR

•10 kHz - 1.0 MHz

0.0

0.1



MC34708 数据表(PDF) 90 Page - Freescale Semiconductor, Inc

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