68HC705JB4 datasheet(77/134 Pages) FREESCALE

77 / 134 page

February 24, 1999

GENERAL RELEASE SPECIFICATION

MC68HC05JB4

UNIVERSAL SERIAL BUS MODULE

MOTOROLA

REV 2

10-11

USB registers. The following will detail the function of the regulator, transceiver

and control logic. See Section 10.5 for the register discussion.

10.4.1 Voltage Regulator

The USB data lines are required by the USB Speciﬁcation to have a maximum

output voltage between 2.8V and 3.6V. The data lines are also required to have an

external 1.5K

Ω pullup resistor connected between a data line and a voltage

source between 3.0V and 3.6V. Since the power provided by the USB cable is

speciﬁed to be between 4.4V and 5.0V, an on-chip regulator is used to drop the

voltage to the appropriate level for sourcing the USB transceiver and external

pullup resistor. An output pin driven by the regulator voltage is provided to source

the 1.5K

Ω external resistor. Figure 10-11 shows the worst case electrical

connection for the voltage regulator.

Figure 10-11. Regulator Electrical Connections

10.4.2 USB Transceiver

The USB transceiver provides the physical interface to the USB D+ and D– data

lines. The transceiver is composed of two parts: an output drive circuit and a

differential receiver.

10.4.2.1 Output Driver Characteristics

The USB transceiver uses a differential output driver to drive the USB data signal

onto the USB cable. The static output swing of the driver in its low state is below

the VOL of 0.3 V with a 1.5 kΩ load to 3.6 V and in its high state is above the VOH

of 2.8 V with a 15 k

Ω load to ground. The output swings between the differential

high and low state are well balanced to minimize signal skew. Slew rate control on

the driver is used to minimize the radiated noise and cross talk. The driver’s

outputs support three-state operation to achieve bi-directional half duplex

operation. The driver can tolerate a voltage on the signal pins of –0.5 V to 3.8 V

Transceiver

3.3V

R1 = 1.5K

Ω ±5%

R2 = 15K

Ω ±5%

Regulator

USB Data Lines

Host

Hub

USB Cable

4.4V

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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