MAX3420E Просмотр технического описания (PDF) - Maxim Integrated

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MAX3420E

USB Peripheral Controller with SPI Interface

Maxim Integrated 

MAX3420E

USB Peripheral Controller with SPI Interface

3.3V

REGULATOR

MAX6349TL

4.7µF

10kΩ

1.0µF

CERAMIC

0.1µF

12MHz

CXI

CXO

VCC VL

XI XO

RES

VBUS

INT

33Ω

MOSI

D+

D+

USB

"B" CONNECTOR

33Ω

MAX3420E

MISO

SCLK

µP

D-

D-

SS

GND

VBCOMP

GPI

GND

GPIN GPOUT

4

4

Figure 16. MAX3420E in a Bus-Powered Application

MAX3420E in a Bus-Powered Application

Figure 16 depicts the MAX3420E in a peripheral

device that is powered by VBUS. This configuration is

advantageous because it requires no external power

supply. VBUS is specified from 4.75V to 5.25V, so a 3.3V

regulator is required to power the MAX3420E. This

diagram assumes that the microprocessor is powered by

3.3V as well, so the VL pin (logic-level reference voltage)

is connected to VCC. Therefore, the GPIO (general-

purpose inputs/outputs) are referenced to 3.3V.

USB is a hot-plug system (VBUS is hot when the device

is plugged in), so it is good design practice to use a

power-on reset circuit to provide a clean reset to the

system when the device is plugged in. The MAX6349TL

serves as an excellent USB regulator, since it has very

low quiescent current and a POR circuit built in.

Because this design is bus powered, it is not necessary

to test for the presence of VBUS. In this case, the bus

voltage-detection input (VBCOMP) makes an excel-

lent general-purpose input when pulled up to VL. The

VBCOMP input has two interrupts associated with it,

VBUSIRQ and NOVBUSIRQ. These interrupts can detect

both edges of any transitions on the VBCOMP input.

The configuration in Figure 16 shows the SPI

interface using the maximum number of SPI interface

pins. The data pins, MOSI and MISO, are separate, and

the MAX3420E supplies an interrupt signal through the

INT output pin to the µP to notify the µP when its attention

is required.

MAX3420E in a Self-Powered Application

Figure 17 shows a self-powered design in which the µP

has its own power source. This is a common configuration

in battery-powered handheld devices. Figure 17 also

illustrates the SPI interfacing with the minimum number

of pins. This is achieved by using a single bidirectional

data line and no interrupt pin connection. The MAX3420E

register bit, FDUPSPI, configures the SPI interface for

bidirectional operation.

Although Figure 17 shows VL = VCC, if the microcontroller

uses a different interface voltage (1.71V to 3.6V) this

reference voltage can be connected to VL. Figure 17

shows a connection from the MAX3420E GPX output to

the microcontroller. GPX can be programmed (see Table

3) to connect the output of the internal VBUS comparator

to the GPX output. This enables the microprocessor to

detect a USB plug-in event even if the MAX3420E is put

into its power-down state.

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