Micrel, Inc.
MIC2555
plug can produce multiple rail-to-rail transitions. These
will trigger both comparators and produce a conflicting
result: ID = GND and ID = Float. The Interrupt source
register contains the debounced steady state value of
ID.
Interrupt Detector
When in Audio mode, the MIC2555 does not participate
in the audio transmissions, but monitors the D+ line for
interrupt pulses. If the Serial Controller is configured to
flag interrupt pulses, the system controller can exchange
both audio signals and digital information with the target
device.
After the nature of the newly connected device has been
determined, activating a current source in series with the
internal ID pull-up resistor can reduce power
consumption caused by ID sensing. This is
accomplished by clearing rcs_dis in Control Register 3.
MIC2555 is designed to detect two different interrupt
pulses, those exceeding 3.0V and those crossing the
0.5V level. Under normal circumstances, the audio
signal seen on D+ is transposed on a DC level and
limited to voltage excursions between the 0.5V and 3.0V
levels, so only interrupt pulses should cross these
thresholds. Signaling is typically done with only one
polarity pulse so MIC2555 is designed to monitor only
one threshold at a time. Threshold selection is done with
the cr_int_sel bit, and the interrupt (cr_int) can be set to
trigger on pulses of either polarity.
When the connected device is removed, and the ID pin
is pulled HIGH by the current source (ID=GND is no
longer true), MIC2555 automatically resets rcs_dis,
disabling the current source.
VBAT
Open = Reduced
ID sensing current
4 µA
UART Mux
System controllers with UART communication ability
may or may not be able to route their UART signals
through the VP, VM or DAT, SE0 pins. For those with
independent UART connectivity, MIC2555 provides a
secondary UART I/O port. The MUX, under direction of
the Serial Controller, selects which UART I/O is used by
the OTG controller.
100 k
ID High
0.85x
VBAT
ID
Condition:
0.15x
VBAT
ID Low
uart_io = 0
SEO_VM_TX = transmit
DAT_VP_RX = receive
GPIO_1_TX = transmit
GPIO_0_RX = receive
uart_io = 1
Closes to
signal
Peripheral
1 k
Differential Driver / Differential Receiver
Operation of the Differential Driver and Differential
Receiver is described in the tables below and on the
following page. The register bits used in the column
headings are described in the Serial Controller section of
this data sheet.
ID Pin – Operational Diagram
VTRM
VBAT powers VTRM, which supplies 3.3V power to the
differential USB transmitter and the UART drivers and
receivers. As VBAT drops below 3.4V, VTRM is no
longer able to regulate and follows VBAT at about 0.1V
less than VBAT. When this occurs, output drive levels for
USB and UART are reduced accordingly.
M9999-121406
December 2006
14
MICREL [ MICREL SEMICONDUCTOR ]
