Rainbow Electronics MAX3301E - Manual (Page 14)

MAX3301E
USB On-the-Go Transceiver and Charge Pump
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MODE I 2 C ID_IN
sess_end
COMP
sess _vld
COMP
vbus_ vld
COMP
cr_int
COMP
dp_hi
COMP
dm_hi
COMP
TRM TX
DIFF
RX
SE
RX
Shutdown 1 ✓ X X X X X X X X X X X
Interrupt
Shutdown 2
✓ ✓ X ✓ X X ✓ ✓ X X X X
Suspend 3 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ X ✓
Normal
Operating
✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
Table 1. Functional Blocks Enabled During Specific Operating Modes
✓ = Enabled.
X = Disabled.
1. Enter shutdown mode by writing a 1 to sdwn (bit 0 of special-function register 2).
2. Enter interrupt shutdown mode by writing a 1 to int_sdwn (bit 0 of special-function register 1).
3. Enter suspend mode by writing a 1 to spd_susp_ctl (bit 1 of special-function register 1) and suspend (bit 1 of control register 1), or
by writing a 0 to spd_susp_ctl (bit 1 of special-function register 1) and driving SUS high.
ID_IN
The USB OTG specification defines an ID input that
determines which dual-role device is the default host.
An OTG cable connects ID to ground in the connector
of one end and is left unconnected in the other end.
Whichever dual-role device receives the grounded end
becomes the A device. The MAX3301E provides an
internal pullup resistor on ID_IN. Internal comparators
detect if ID_IN is grounded or left floating.
Interrupt Logic
When OTG events require action, the MAX3301E pro-
vides an interrupt output signal on INT. Alternatively,
OE/INT can be configured to act as an interrupt output
while the device operates in USB suspend mode.
Program INT and OE/INT as open-drain or push-pull
interrupts with irq_mode (bit 1 of special-function regis-
ter 2, see Table 15).
V BUS Power Control
V BUS is a dual-function port that powers the USB bus
and/or provides a power source for the internal linear reg-
ulator. The V
BUS power-control block performs the various
switching functions required by an OTG dual-role device.
These actions are programmed by the system logic using
bits 5 to 7 of control register 2 (see Table 8) to:
• Discharge V BUS through a resistor
• Provide power-on or receive power from V BUS
• Charge V BUS through a resistor
The OTG supplement allows an A device to turn V BUS
off when the bus is not being used to conserve power.
The B device can issue a request that a new session be
started using SRP. The B device must discharge V
BUS
to a level below the session-end threshold (0.8V) to
ensure that no session is in progress before initiating
SRP. Setting bit 6 of control register 2 to a 1, discharges
V
BUS to GND through a 5k
Ω current-limiting resistor.
When V BUS has discharged, the resistor is removed
from the circuit by resetting bit 6 of control register 2.
An OTG A device is required to supply power on V BUS .
The MAX3301E provides power to V BUS from V CC or
from the internal charge pump. Set bit 5 in control regis-
ter 2 to a 1 in both cases. Bit 5 in control register 2 con-
trols a current-limited switch, preventing damage to the
device in the event of a V
BUS short circuit.
An OTG B device (peripheral mode) can request a ses-
sion using SRP. One of the steps in implementing SRP
requires pulsing V
BUS high for a controlled time. A 930 Ω
resistor limits the current according to the OTG specifi-
cation. Pulse V
BUS through the pullup resistor by assert-
ing bit 7 of control register 2. Prior to pulsing V BUS (bit
7), a B device first connects an internal pulldown resis-
tor to discharge V
BUS below the session-end threshold.
The discharge current is limited by the 5k Ω resistor and
set by bit 6 of control register 2. An OTG A device must
supply 5V power and at least 8mA on V
BUS . Setting bit
5 of control register 2 turns on the V BUS charge pump.
Operating Modes
The MAX3301E has four operating modes to optimize
power consumption. Only the I
2 C interface remains active
in shutdown mode, reducing supply current to 1µA. The
I
2 C interface, the ID_IN port, and the session-valid com-
parator all remain active in interrupt shutdown mode. RCV
asserts low in suspend mode; however, all other circuitry
remains active. Table 1 lists the active blocks’ power in
each of the operating modes.