MIC2551A
Micrel
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 down to supply voltages of 1.6V and still meet 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.
The use of ESD transient protection devices is not required
for operation, but is recommended. The MIC2551A is ESD
rated for 11kV at the VBUS and D+, D– pins and 2kV for all
other pins.
May 2004
7
M9999-051004
MICREL [ MICREL SEMICONDUCTOR ]
