November 2008

7

M9999-112008

MIC2551

Micrel, Inc.

Functional Description

The MIC2551 is designed to provide USB connectivity in

mobile systems where available system supply voltages are

not able to satisfy USB requirements. The MIC2551 can

operate down to supply voltages of 1.6V and still meet USB

physical layer specifications. As shown in the circuit above,

the MIC2551 takes advantage of the USB supply voltage,

V

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

controller.

Functional Diagram

To Internal

Circuitry

VBUS

VTERM

VPU

D+

D–

LDO

Regulator

VIF

CON

SPD

OE#

RCV

VP

VM

SUS

GND

MIC2551 Block Diagram

In addition, a 3.3V, 10% termination supply voltage, V

provided to support speed selection. V

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 MIC2551 is ESD

rated for 11kV at the VBUS and D+, D– pins and 2kV for all

other pins.