MIC2551A-2.5
Micrel, Inc.
Functional Diagram
To Internal
Circuitry
LDO
Regulator
VBUS
VTERM
VPU
VIF
CON
SPD
OE#
D+
D–
RCV
Level
Translator
VP
VM
SUS
GND
MIC2551A
Applications Information
The MIC2551A is designed to provide USB connectivity in
mobile systems where available system supply voltages are
not able to satisfy USB requirements. The MIC2551A can
operate interface supply voltages as low as 1.6V and still
meet the USB physical layer specifications. As shown in the
circuit above, the MIC2551A takes advantage of the USB
supply voltage, V
BUS
, to operate the transceiver. The system
voltage, V
IF
, is used to set the reference voltage used by the
digital I/O lines interfacing to the system controller. Internal
circuitry provides translation between the USB and system
voltage domains. V
IF
will typically be the main supply voltage
rail for the controller.
In addition, a 3.3V, 10% termination supply voltage, (V
PU
),
is provided to support speed selection. V
PU
can be disabled
or enabled under software control via the CON input. This
allows for software-controlled connect or disconnect states.
A 1.5k resistor is required to be connected between this pin
and the D+ or D– lines to respectively specify high speed or
low speed operation.
March 2010
7
M9999-030810
MICREL [ MICREL SEMICONDUCTOR ]
