MIC2555_06 Datasheet, PDF (17/29 Pages) Micrel Semiconductor – USB – OTG Transceiver

Micrel, Inc.
Pin Descriptions
VBAT
This pin is an input, and supplies power to the
transceiver. Transceiver typical operational voltages are
between 3.0 V ≤ V_BAT ≤ 4.5V and 1.6V < V_{DD_LGC} < V_BAT.
VDD_LGC
This input is used to set the logic thresholds of the
following logic signals:
• DAT_VP_RX
• SE0_VM_TX
• RCV
• OE_INT/
• INT/
• ADR0
• RESET/
• GPIO
Important Note:
V_{DD_LGC} can be at a voltage less than or equal to V_BAT,
but never higher than V_BAT. Doing so will forward bias
internal pad protection diodes and current will flow from
V_{DD_LGC} to V_BAT. For this reason, systems should not
allow V_BAT to go to zero while V_{DD_LGC} remains powered.
This condition may damage the MIC2555, and could put
a severe load on V_{DD_LGC} as it attempts to power the
MIC2555 and all other circuits attached to the V_BAT line.
VBUS
This pin functions as both an input to, and output from,
the transceiver. Unlike standard USB transceivers,
however, the MIC2555 always derives its operating
power from V_BAT and never from V_BUS. The MIC2555 will
supply power to V_BUS when acting as a host device and
when petitioning another OTG, capable device to
become the host. To do so the vbus_chrg bit is asserted.
To power V_BUS, as a host device, the vbus_drv bit is
asserted. The difference between these two controls is
vbus_chg applies V_TRM (3.3V) to V_BUS, where as
vbus_driv uses the 5V charge pump output. While V_TRM
is sufficient for signaling purposes, it does not meet the
4.4V minimum for V_BUS.
VTRM
V_TRM supplies a regulated 3.3V to the D+, D- output
drivers, pull-up resistors and other circuitry internal to the
MIC2555. A small filter capacitor is required to insure the
regulator remains stable under all operating conditions.
A good quality 1µF capacitor is sufficient for this
purpose.
MIC2555
V_TRM can be used to supply small amounts of current to
other system functions, typically 3 mA or less. However,
trying to source more current can reduce output drive on
D+, D- by stealing current from the differential driver.
ID
ID detects the arrival or departure of a peripheral device,
and differentiates between USB and non-USB devices.
To accomplish this, ID is pulled-up by a resistance of
approximately 100 kΩ connected to V_BAT and the voltage
at ID monitored by a set of comparators. When no
device is present, ID is pulled high and NO DEVICE
condition is reported. When a Mini-A plug is inserted into
the system’s Mini-AB receptacle, ID is connected to
ground by the Mini-A plug, which triggers the MIC2555
to indicate a USB device is present.
Non-USB peripherals use a modified Mini-A plug or non-
standard cable assembly with a resistor connected
between ID and ground. When connected, this forms a
resistor divider such that a voltage of approximately ½
V_BAT appears at MIC2555’s ID pin, indicating a non-USB
device is present.
Additionally, ID can be used to signal non-USB devices.
This is accomplished by grounding ID through a low
value resistor (~ 1 kΩ), dropping the ID voltage from ½
V_BAT to nearly zero, which can be detected by the
attached device. This switch is activated by the
id_gnd_out bit in Control Register 2.
C-, C+, C++
C-, C+ and C++ are the capacitors required for charge
pump operation. C- and C+ are the connections to the
‘flying’ capacitor, which creates the pumping effect. C++
is the reservoir capacitor that stores the 5V supplied to
V_BUS when vbus_drv is asserted.
Because the input source is a low voltage and the
charge pump’s regulator is set to limit V_OUT to 5V, these
capacitors need only be rated at 6 VDC, which helps
reduce physical size and cost.
GND_A, GND_D
MIC2555 uses separate ground lines within the chip to
isolate digital noise from analog signals. Ultimately,
these two grounds need to be tied together. This is best
done by having both grounds return separately to the
power source and join at the bypass capacitor.
RESET/
System reset. Returns all control register bits to their
default settings. MIC2555 is not equipped with an
internal power-on reset generator, and thus relies upon
the system for its reset at power up.
December 2006
17
M9999-121406