CYUSB3035-BZXC datasheet(13/54 Pages) CYPRESS

13 / 54 page

CYUSB303X

Document Number: 001-84160 Rev. *G

Page 13 of 54

Clocking

FX3S allows either a crystal to be connected between the

XTALIN and XTALOUT pins or an external clock to be connected

at the CLKIN pin. The XTALIN, XTALOUT, CLKIN, and

CLKIN_32 pins can be left unconnected if they are not used.

Crystal frequency supported is 19.2 MHz, while the external

clock frequencies supported are 19.2, 26, 38.4, and 52 MHz.

FX3S has an on-chip oscillator circuit that uses an external

19.2-MHz (±100 ppm) crystal (when the crystal option is used).

An appropriate load capacitance is required with a crystal. Refer

to the specification of the crystal used to determine the

appropriate load capacitance. The FSLC[2:0] pins must be

configured appropriately to select the crystal- or clock-frequency

option. The configuration options are shown in Table 3.

Clock inputs to FX3S must meet the phase noise and jitter

requirements specified in Table 4.

The input clock frequency is independent of the clock and data

rate of the FX3S core or any of the device interfaces (including

P-Port and S-Port). The internal PLL applies the appropriate

clock multiply option depending on the input frequency.

32-kHz Watchdog Timer Clock Input

FX3S includes a watchdog timer. The watchdog timer can be

used to interrupt the ARM926EJ-S core, automatically wake up

the FX3S in Standby mode, and reset the ARM926EJ-S core.

The watchdog timer runs a 32-kHz clock, which may be

optionally supplied from an external source on a dedicated FX3S

pin.

The firmware can disable the watchdog timer.

Requirements for the optional 32-kHz clock input are listed in

Table 5.

Table 3. Crystal/Clock Frequency Selection

FSLC[2]

FSLC[1]

FSLC[0]

Crystal/Clock

Frequency

19.2-MHz crystal

19.2-MHz input CLK

26-MHz input CLK

38.4-MHz input CLK

52-MHz input CLK

Table 4. FX3S Input Clock Specifications

Parameter

Description

Specification

Units

Min

Max

Phase noise

100-Hz offset

–

–75

1- kHz offset

–

–104

10-kHz offset

–

–120

100-kHz offset

–

–128

1-MHz offset

–

–130

Maximum frequency deviation

–

150

ppm

Duty cycle

Overshoot

–

Undershoot

–

–3

Rise time/fall time

–

Table 5. 32-kHz Clock Input Requirements

Parameter

Min

Max

Units

Duty cycle

Frequency deviation

–

±200

ppm

Rise time/fall time

–

200

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