Micrel, Inc.
MIC2555
Functional Description
The MIC2555 is designed to provide full USB On-The-
Go (OTG) connectivity in mobile systems where low
power and small size are key considerations. Intended
for use in self-powered systems, the MIC2555 draws no
current from VBUS for its operation, but will supply a
minimum of 10mA at 5V to VBUS, from an on-chip
charge pump, when operating as an A-device. The
MIC2555 meets USB physical layer specifications while
operating with logic supply voltages as low as 1.6V and
battery voltages down to 3.0V.
MIC2555 operation is controlled through an I2C bus by
reading and/or writing to registers within the MIC2555.
Control registers are used to set the operational mode to
USB, Audio or UART (‘RS232’ format). Other features
include VBUS comparators for SRP detection and ID pin
recognition of USB and non-USB peripherals.
The MIC2555 minimizes collateral components,
requiring only 4 external capacitors and two resistors. All
USB required pull-up/pull-down resistors are on-chip.
15KV ESD protection on all pins exposed to user contact
(VBUS, D+, D-, ID and GND) eliminates the need for
external ESD transient protection devices.
Definitions and Conventions
Car Kit
IC
NUT
OTG
SIE
SE0
SRP
USB
USB-IF
Serial
Controller
UPPER CASE
Lower case
(1)
2
System Description
Overview:
The MIC2555 OTG Transceiver provides the physical
interface for ASICs, uPs and SOCs having an On-The-
Go Serial Interface Engine (SIE) but lacking a physical
interface capable of driving cables, or generating and
detecting the necessary voltages to operate as a USB
host.
MIC2555 goes beyond the confines of the USB OTG
standard and provides flexible communication between
many kinds of digital devices. Point-to-point UART and
Audio communications can also be accomplished using
the MIC2555 and any and all of these formats can be
utilized by a single system.
All communications are accomplished via the D+ and D-
I/O pins. The information passed through D+ and D-,
such as USB, UART, or audio, depends upon the mode
of communication. The system controls the mode of
communication through the MIC2555’s control registers.
Modes of Operation
The MIC2555 OTG Transceiver has five distinct
operating modes:
•
•
•
USB mode:
Operates as a USB OTG transceiver.
UART mode:
Operates as a UART transceiver
Audio mode:
Operates as a passive device within
the audio path, but actively monitoring for digital
control signals.
=
=
=
=
=
=
=
=
=
=
=
=
A non-USB target device
Inter IC Bus (I C)
non-USB target device
On-The-Go
Serial Interface Engine
Single Ended Zero
Session Request Protocol
Universal Serial Bus
USB Implementers Forum
Means the I C control function within
MIC2555.
IC pins
Control Register Bits
2
2
USB mode
The two modes of USB operation involve the way data is
transferred between the SIE and the transceiver. These
modes are:
•
DAT-SE0 mode:
-
DAT_VP_RX .DAT: single ended data I/O
SEO: detects or sends the SE0
-
SE0_VM_TX
condition.
-
RCV is not used
•
VP-VM mode:
-
DAT_VP_RX
VP: D+ data to transceiver output.
-
SE0_VM_TX
VM: D- data to transceiver output.
-
RCV Output of the differential receiver.
Note:
1. An ‘OTG Controller’ is understood to be any integrated circuit, or
system, possessing a built-in USB OTG Host/Device control
function but lacking the USB physical layer interface.
Data flow direction:
Transmit
Receive
OE_INT/ = 0
OE_INT/ = 1
Conditions for USB mode:
uart_en = 0
Speed = Low speed =0
Full speed = 1
December 2006
10
M9999-121406
MICREL [ MICREL SEMICONDUCTOR ]
