TMS320VC5504 datasheet(65/128 Pages) TI

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RTC_XI

RTC_XO

Crystal

32.768kHz

VSSRTC

CVDDRTC

0.998-1.43V

1.05/1.3V

CVDD

VSS

(

)

C C

1 2

6.4.2

CLKIN Pin With LVCMOS-Compatible Clock Input (Optional)

TMS320VC5504

Fixed-Point Digital Signal Processor

www.ti.com

SPRS609A – JUNE 2009 – REVISED JULY 2009

Figure 6-3. 32.768-kHz RTC Oscillator

The crystal should be in fundamental-mode function, and parallel resonant, with a maximum effective

series resistance (ESR) specified in Table 6-1. The load capacitors, C1 and C2, are the total capacitance

of the circuit board and components, excluding the IC and crystal. The load capacitors values are usually

approximately twice the value of the crystal's load capacitance, CL, which is specified in the crystal

manufacturer's datasheet and should be chosen such that the equation is satisfied. All discrete

components used to implement the oscillator circuit should be placed as close as possible to the

associated oscillator pins (RTC_XI and RTC_XO) and to the VSSRTC pin.

Table 6-1. Input Requirements for Crystal on the 32.768-kHz RTC Oscillator

PARAMETER

MIN

NOM

MAX

UNIT

Start-up time (from power up until oscillating at stable frequency of

0.2

sec

32.768-kHz)(1)

Oscillation frequency

32.768

kHz

ESR

100

Ω

Maximum shunt capacitance

1.6

Maximum crystal drive

1.0

µW

(1)

The startup time is highly dependent on the ESR and the capacitive load of the crystal.

Note: If CLKIN is not used, the pin must be tied low.

A LVCMOS-compatible clock input of a frequency less than 24 MHz can be fed into the CLKIN pin for use

by the DSP system clock generator. The external connections are shown in Figure 6-4 and Figure 6-5.

The bootloader assumes that the CLKIN pin is connected to the LVCMOS-compatible clock source with a

frequency of 11.2896-, 12.0-, or 12.288-MHz. These frequencies were selected to support boot mode

peripheral speeds of 500 KHz for SPI, 400 KHz for I2C, and 57600 baud for UART (UART is currently not

supported on this device). These clock frequencies are achieved by dividing the CLKIN value by 25 for

SPI, by 32 for I2C, and by 208 for UART. If a faster external clock is input, then these boot modes will run

at faster clock speeds. If the system design utilizes faster peripherals or these boot modes are not used,

CLKIN values higher than 12.288 MHz can be used. Note: the CLKIN pin operates at the same voltage as

the DVDDIO supply (1.8-, 2.5-, 2.8-, or 3.3-V).

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TMS320VC5504 Datasheet(PDF) 65 Page - Texas Instruments

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