MIC2551A

Micrel

M9999-051004

8

May 2004

Power Supply Configuration

The MIC2551A can be set up for different power supply

configurations which modify the behavior of the device. Both

V

are either removed or grounded. Table 3 depicts the behavior

under the different power supply configuration scenarios that

are explained below.

Normal Mode

V

connected to a supply voltage in the range of 1.6V to 3.6V. In

this case V

speed select resistor via V

pin.

Disconnect Mode

V

V

ting, the data lines (D+, D–) have sharing capability and may

be driven with external devices up to approximately 3.6V if

and only if SUSPEND is enabled (SUS = 1). With V

BUS

ground, D+, D– sharing mode is not permitted.

Disable Mode

V

open. All logic controlled inputs become high impedances,

thus minimal current will be supplied by V

pulled up to an external source.

Alternate Power Supply Configuration Options

I/O Interface Using 3.3V

In systems where the I/O interface utilizes a 3.3V USB

controller, an alternate solution is shown in Figure 7. No extra

components are required; however, the load on V

not exceed 10mA.

MIC2551A

VIF

VBUS

I/O

VBUS

RCV/OE#

VTRM

USB

Controller

3.3V

Figure 7. I/O Interface Using 3.3V

Bypass Input

V

range of 3.0V to 3.6V. The internal regulator is bypassed and

the internal circuitry is run from the V

MIC2551A

VIF

3.3V

VBUS

VTRM

Figure 8. Powering MIC2551A

from External 3.3V

Signal Amplitude Respective to V

IF

When operating the MIC2551A, it is necessary to provide

input signals which do not exceed V

Suspend

When the suspend pin (SUS) is high, power consumption is

reduced to a minimum. V

are still functional to enable the device to detect USB activity.

For minimal current consumption in suspend mode, it is

recommended that OE# = 1, and SPD = 0.

Speed

The speed pin (SPD) sets D+/D– output edge rates by increas-

ing or decreasing biasing current sources within the output

drivers. For low speed, SPD = 0. For full speed, SPD = 1. By

setting SPD = 0 during idle periods, in conjunction with suspend

(SUS), the lowest quiescent current can be obtained. However,

designers must provide a 300ns delay between changing SPD

from 0 to 1 and transmission of data at full speed. This delay

ensures the output drivers have arrived at their proper operating

conditions. Failure to do so can result in leading edge distortion

on the first few data bits transmitted.

External ESD Protection

The use of ESD transient protection devices is not required

for operation, but is recommended. We recommend the

following devices or the equivalent:

Cooper Electronic Technologies (www.cooperet.com)

Littelfuse (www.littelfuse.com)

V0402MHS05

SP0503BAHT

Non-Multiplexed Bus

In order to save pin count for the USB logic controller

interface, the MIC2551A was designed with V

directional pins. To interface the MIC2551A with a non-

multiplexed data bus, resistors can be used for low cost

isolation as shown in Figure 9.

USB Logic

Controller

(SIE)

MIC2551A

10k

10k

Figure 9. MIC2551A Interface to

Non-Multiplexed Data Bus