Device Control

OE

OE controls the direction of communication. Drive OE

low to transfer data from the logic side to the USB side.

For

OE = low, VP and VM serve as differential driver

inputs to the USB transmitter.

Drive

OE high to transfer data from the USB side to the

logic side. For

OE = high, VP and VM serve as single-

ended receiver outputs from the USB inputs

(D+ and D-). RCV serves as a differential receiver out-

put, regardless of the state of

OE.

ENUM (MAX3451E)

The MAX3451E features an enumerate function that

allows software control of USB enumeration. USB proto-

col requires a 1.5kΩ pullup resistor to D+ or D- to indi-

cate the transmission speed to the host (see the

SPD

section). The MAX3451E provides an internal 1.5kΩ

pullup resistor. Remove the pullup resistor from the cir-

cuit to simulate a device disconnect from the USB. Drive

ENUM low to disconnect the internal pullup resistor.

Drive ENUM high to connect the internal pullup resistor.

The SPD state determines whether the pullup resistor

connects to D+ or D-. For ENUM = high, the internal

(full speed) or to D- when SPD = GND (low speed).

SPD

SPD sets the transceiver speed. Connect SPD to GND to

select the low-speed data rate (1.5Mbps). Connect SPD

MAX3451E provides an internal pullup resistor for

selecting the bus speed. The MAX3450E and

MAX3452E require an external pullup resistor to D+ or

D- to set the bus speed. Connect the 1.5kΩ resistor

data rate, or connect the 1.5kΩ resistor between D- and

SUS

The SUS state determines whether the MAX3450E/

MAX3451E/MAX3452E operate in normal mode or in

suspend mode. Connect SUS to GND to enable normal

operation. Drive SUS high to enable suspend mode.

RCV asserts low and VP and VM remain active in sus-

pend mode (Tables 3 and 4). Supply current decreases

in suspend mode (see the

Electrical Characteristics).

±15kV ESD-Protected USB Transceivers

_______________________________________________________________________________________

9

Figure 1. Rise and Fall Times

90%

10%

90%

10%

Table 3a. Transmit Truth Table

(

OE = 0, SUS = 0)

INPUTS

OUTPUTS

VP

VM

D+

D-

RCV

OUTPUT STATE

00

00X

SE0

01

01

0

Logic 0

10

10

1

Logic 1

1

1

1

1

X

Undefined

X = Undefined.

Table 3b. Transmit Truth Table

(OE = 0, SUS = 1)

INPUTS

OUTPUTS

VP

VM

D+

D-

RCV

OUTPUT STATE

00

00

0

SE0

01

01

0

Logic 0

10

10

0

Logic 1

1

1

1

1

0

Undefined

Table 4a. Receive Truth Table

(OE = 1 and SUS = 0)

INPUTS

OUTPUTS

D+

D-

VP

VM

RCV

OUTPUT STATE

0

000

X

SE0

0

1010

Logic 0

1

0101

Logic 1

1

1

1

1

X

Undefined

X = Undefined.