Datasheet

Analog Integrated Circuit Device Data
Freescale Semiconductor 88
MC34708
Functional Block Description
Figure 20. USB Interface
7.8.4.1 Supplies
The MC34708 provides the regulators required to power the PHY in the i.MX50, i.MX51, and i.MX53 processors, which are
VUSB2 (detailed
Linear Regulators (LDOs)), and VUSB. The IC also provides the 5.0 V supply for USB OTG operation.
The VUSB regulator is used to supply 3.3 V to the external USB PHY. The input to the VUSB regulator can be supplied from the
VBUS wire of the cable when supplied by a host (PC or Hub), or by the SWBST voltage via the VINUSB pin. The VUSB regulator
is powered from the SWBST boost supply to ensure OTG current sourcing compliance through the normal discharge range of
the main battery. The VUSBSEL SPI bit is used to make the selection between a host or OTG mode operation.
The VUSB regulator defaults to ON when PUMS4:1 = [0100], and is supplied by the SWBST output. As shown in Figure 20, this
means 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 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 1 on power up and
Table 86. VUSB Input Source Control
(68)
Parameter Value Function
V
USBSEL
0
Powered by Host: VBUS powers VUSB regulator (switch M0 closed and M1 open)
1
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
68. 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)
ID
VBUS
VUSB
VUSB2
UART
USB
Audio
GND
ID
VBUS
VINUSB
VUSB
VINUSB2
VUSB2
DP
DM
TXD
RXD
D+
D-
SPKR
SPKRL
MIC
VBUS
M0
M1
MOTG
Switches
Switches
Switches
Regulator
Regulator
Detect
Detect
To/From
Application
Processor
To/From
Audio IC
To/From
Mini-USB
Connector
SWBST (5.0 V boosted supply)
3.3 V USB Analog supply
BP
2.5V USB Analog supply
To/from
Mini-USB
Connector