MIC2551A-2.5 datasheet(8/10 Pages) MICREL

8 / 10 page

MIC2551A-2.5

Micrel, Inc.

M9999-031306

March 2006

Power Supply Conﬁguration

The MIC2551A can be set up for different power supply

conﬁgurations which modify the behavior of the device. Both

VBUS and VIF have special thresholds that detect when they

are either removed or grounded. Table 1 depicts the behavior

under the different power supply conﬁguration scenarios that

are explained below.

Normal Mode

VBUS is connected to the 5.0V USB bus voltage and VIF is

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

thiscaseVTRMsuppliesa3.3Vvoltageforpoweringthespeed

select resistor via VPU depending on the state of CON pin.

Disconnect Mode

VIF is connected to a supply in a range of 1.6V to 3.6V and

VBUSisopenorgrounded.IfVBUSisopenedwhiletransmitting,

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 VBUS ground,

D+, D– sharing mode is not permitted.

Disable Mode

VBUS is connected to the 5.0V USB bus voltage and VIF is

open. All logic controlled inputs become high impedances,

thus minimal current will be supplied by VIF if the input pins

are 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 con-

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

components are required; however, the load on VTRM must

not exceed 10mA.

MIC2551A

VIF

VBUS

I/O

VBUS

VP/VM/

RCV/OE#

VTRM

USB

Controller

VDD

3.3V

Figure 7. I/O Interface Using 3.3V

Bypass Input

VBUS and VTRM are tied together to a supply voltage in the

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

and the internal circuitry is run from the VTRM input. See

Figure 8.

MIC2551A

VIF

3.3V

VBUS

VTRM

Figure 8. Powering MIC2551A

from External 3.3V

Signal Amplitude Respective to VIF

When operating the MIC2551A, it is necessary to provide

input signals which do not exceed VIF + 0.3V.

Suspend

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

reduced to a minimum. VTRM is not disabled. RCV, VP and

VM 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 in-

creasing 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 ar-

rived at their proper operating conditions. Failure to do so

can result in leading edge distortion on the ﬁrst few data bits

transmitted.

Non-Multiplexed Bus

InordertosavepincountfortheUSBlogiccontrollerinterface,

the MIC2551Awas designed with VPand VM as bi-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.

VPO

VMO

USB Logic

Controller

(SIE)

MIC2551A

10k

Figure 9. MIC2551A Interface to

Non-Multiplexed Data Bus

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