FT221XS-R datasheet(12/45 Pages) FTDI

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FT221X USB 8-BIT SPI/FT1248 IC Datasheet

Version 1.3

Document No.: FT_000630 Clearance No.: FTDI# 263

4 Function Description

The FT221X is a USB to FTDI Proprietary FT1248 interface device which simplifies USB implementations

and reduces external component count by fully integrating into the device an MTP memory, and an

integrated clock circuit which requires no external crystal. It has been designed to operate efficiently

with USB host controllers by using as little bandwidth as possible when compared to the total USB

bandwidth available.

4.1 Key Features

Functional Integration. Fully integrated MTP memory, USB termination resistors, clock generation,

AVCC filtering, Power-On-Reset and LDO regulator.

Configurable CBUS I/O Pin Options. The fully integrated MTP memory allows configuration of the

Control Bus (CBUS) functionality and drive strength selection. There is 1 configurable CBUS I/O pin.

These configurable options are defined in section 3.3

The CBUS line can be configured with any one of these output options by setting bits in the internal MTP

memory. The device is shipped with the most commonly used pin definitions pre-programmed - see

Section 9 for details.

Asynchronous Bit Bang Mode with RD# and WR# Strobes. The FT221X supports FTDI’s previous

chip generation bit-bang mode. In bit-bang mode, the eight data lines can be switched from the regular

interface mode to an 8-bit general purpose I/O port. Data packets can be sent to the device and they will

be sequentially sent to the interface at a rate controlled by an internal timer (equivalent to the baud rate

pre-scalar).

Synchronous Bit Bang Mode. The FT221X supports synchronous bit bang mode. This mode differs from

asynchronous bit bang mode in that the interface pins are only read when the device is written to. This

makes it easier for the controlling program to measure the response to an output stimulus as the data

returned is synchronous to the output data. An application note, AN232R-01, available from FTDI website

(www.ftdichip.com) describes this feature.

Source Power and Power Consumption. The FT221X is capable of operating at a voltage supply

between +3.3V and +5.25V with a nominal operational mode current of 8mA and a nominal USB suspend

mode current of 125µA. This allows greater margin for peripheral designs to meet the USB suspend mode

current limit of 2.5mA. An integrated level converter within the device allows the FT221X to interface to

logic running at +1.8V to +3.3V (5V tolerant).

4.2 Functional Block Descriptions

The following paragraphs detail each function within the FT221X. Please refer to the block diagram shown

in Figure 2.1

Internal MTP Memory. The internal MTP memory in the FT221X is used to store USB Vendor ID (VID),

Product ID (PID), device serial number, product description string and various other USB configuration

descriptors. The internal MTP memory is also used to configure the CBUS pin functions. The FT221X is

supplied with the internal MTP memory pre-programmed as described in Section 9. A user area of the

internal MTP memory is available to system designers to allow storing additional data from the user

application over USB. The internal MTP memory descriptors can be programmed in circuit, over USB

without any additional voltage requirement. The descriptors can be programmed using the FTDI utility

software called FT_PROG, which can be downloaded from FTDI Utilities on the FTDI website

(www.ftdichip.com).

+1.8V LDO Regulator. The +1.8V LDO regulator generates the +1.8V reference voltage for driving the

internal core of the IC.

+3.3V LDO Regulator. The +3.3V LDO regulator generates the +3.3V reference voltage for driving the

USB transceiver cell output buffers. It requires an external decoupling capacitor to be attached to the

3V3OUT regulator output pin. It also provides +3.3V power to the 1.5kΩ internal pull up resistor on

USBDP. The main function of the LDO is to power the USB Transceiver and the Reset Generator Cells

rather than to power external logic. However, it can be used to supply external circuitry requiring a

+3.3V nominal supply with a maximum current of 50mA.

USB Transceiver. The USB Transceiver Cell provides the USB 1.1 / USB 2.0 full-speed physical interface

to the USB cable. The output drivers provide +3.3V level slew rate control signalling, whilst a differential

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