FT121Q-R datasheet(9/46 Pages) FTDI

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Document No.: FT_000648

FT121 ENHANCED USB DEVICE CONTROLLER WITH SPI SLAVE IC

Datasheet Version 1.2

Clearance No.: FTDI#

312

4 Function Description

The FT121 is a USB device controller which interfaces with microcontrollers via an SPI slave interface.

4.1 Functional Block Descriptions

The following sections describe the function of each block. Please refer to the block diagram shown in

Figure 2-1.

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

core of the IC with input capabilities from 3.3V or 5V.

+3.3V LDO Regulator. The +3.3V LDO regulator generates the +3.3V supply voltage for the USB

transceiver. An external decoupling capacitor needs to be attached to the VOUT3V3 regulator output pin.

The regulator also provides +3.3V power to the 1.5kΩ internal pull up resistor on DP pin. The allowable

input voltages are 5V or 3.3V. When using 3.3V as the input voltage, the VCC and VOUT3V3 pins should

be tied together. This will result in the regulator being by-passed.

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

Output drivers provide +3.3V level slew rate control, while a differential input and two single ended input

receivers provide data in, Single-Ended-0 (SE0) and USB reset detection conditions respectfully. A 1.5kΩ

pull up resistor on DP is incorporated.

DPLL. The DPLL cell locks on to the incoming NRZI USB data and generates recovered clock and data

signals.

Internal Oscillator. The Internal Oscillator cell generates a reference clock. This provides an input to

the Clock Multiplier function.

Clock Multiplier. The 12MHz and 48MHz reference clock signals for various internal blocks can be

generated from the reference clock via the oscillator functions and clock multiplier circuitry.

Serial Interface Engine (SIE). The Serial Interface Engine (SIE) block performs the parallel to serial

and serial to parallel conversion of the USB data. In accordance with the USB 2.0 specification, it

performs bit stuffing/un-stuffing and CRC5/CRC16 generation. It also checks the CRC on the USB data

stream.

USB Protocol Engine. The USB Protocol Engine manages the data stream from the device USB control

endpoint. It handles the low level USB protocol requests generated by the USB host controller. The

Protocol Engine also includes a memory management unit which handles endpoint buffers.

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