TMS320C5505_15 Datasheet, PDF (75/157 Pages) Texas Instruments – TMS320C5505 Fixed-Point Digital Signal Processor

TMS320C5505
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SPRS660F – AUGUST 2010 – REVISED SEPTEMBER 2013
The crystal should be in fundamental-mode function, and parallel resonant, with a maximum effective
series resistance (ESR) specified in Table 5-1. 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 V_SSRTC pin.
CL
=
C1C2
(C1 + C2 )
Table 5-1. Input Requirements for Crystal on the 32.768-kHz RTC Oscillator
PARAMETER
Start-up time (from power up until oscillating at stable frequency of 32.768-kHz)⁽¹⁾
Oscillation frequency
ESR
Maximum shunt capacitance
Maximum crystal drive
MIN
NOM
0.2
32.768
MAX
2
100
1.6
1.0
(1) The startup time is highly dependent on the ESR and the capacitive load of the crystal.
UNIT
sec
kHz
kΩ
pF
μW
5.4.2 CLKIN Pin With LVCMOS-Compatible Clock Input (Optional)
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 5-5 and Figure 5-6.
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 and 400 KHz for I2C. These clock frequencies are achieved by
dividing the CLKIN value by 25 for SPI and by 32 for I2C. 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 DV_DDIO supply (1.8-, 2.5-, 2.75-, or 3.3-V).
In this configuration the RTC oscillator can be optionally disabled by connecting RTC_XI to CV_DDRTC and
RTC_XO to ground (V_SS). However, when the RTC oscillator is disabled the RTC registers starting at I/O
address 1900h will not be accessible. This includes the RTC Power Management Register which provides
control to WAKEUP and RTC_CLKOUT pins. Note: the RTC must still be powered by an external power
source even if the RTC oscillator is disabled. None of the on-chip LDOs can power CV_DDRTC.
For more details on the RTC on-chip oscillator, see Section 5.4.1, Real-Time Clock (RTC) On-Chip
Oscillator With External Crystal.
CLKIN
RTC_XI
RTC_XO
V_SSRTC
CV_DDRTC
V_SS
Crystal
32.768 kHz
CV_DD
C1
C2
0.998-1.43 V
1.05/1.3/1.4 V
Figure 5-5. LVCMOS-Compatible Clock Input With RTC Oscillator Enabled
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Peripheral Information and Electrical Specifications
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