DM3730_17 Datasheet, PDF (135/280 Pages) Texas Instruments – Digital Media Processors

DM3730, DM3725
www.ti.com
SPRS685D – AUGUST 2010 – REVISED JULY 2011
Table 4-3 details the switching characteristics of the oscillator and the requirements of the input clock.
Table 4-3. Oscillator Switching Characteristics—Crystal Mode
NAME
DESCRIPTION
MIN
TYP
MAX
UNIT
f_p
Oscillation frequency
t_sX
Start-up time^{(1) (2)}
12, 13, 16.8, or 19.2
3
MHz
ms
(1) Start-up time is defined as the time the oscillator takes to gain sys_xtalin amplitude enough to have 45% to 55% duty cycle at the core
input from the time power down (PWRDN) is released. Start-up time is a strong function of crystal parameters. At power-on reset, the
time is adjustable using the pin itself. The reset must be released when the oscillator or clock source is stable. To switch from bypass
mode to crystal or from crystal mode to bypass mode, there is a waiting time about 100 μs; however, if the chip comes from bypass
mode to crystal mode then the crystal will start-up after time mentioned in the t_sX parameter.
(2) Before the processor boots up and the oscillator is set to bypass mode, there is a waiting time when the internal oscillator is in
application mode and receives a square wave. The switching time in this case is about 100 μs.
4.1.3 sys_xtalin Squarer Input Clock
Table 4-4 summarizes the base oscillator electrical characteristics.
Table 4-4. Oscillator Electrical Characteristics—Bypass Mode
NAME
DESCRIPTION
MIN
TYP
MAX
UNIT
f
Frequency
12, 13, 16.8, 19.2, 26, or 38.4
MHz
C_i
Input Capacitance
R_i
Input Resistance
t_sX
Start-up time⁽¹⁾
1.00
1.15
1.35
pF
160
216
280
Ω
See⁽²⁾
ms
(1) To switch from bypass mode to crystal mode or from crystal mode to bypass mode, there is a waiting time about 100 μs; however, if the
chip comes from bypass mode to crystal mode then the crystal will start-up after time mentioned in Table 4-3, t_sX parameter above.
(2) Before the processor boots up and the oscillator is set to bypass mode, there is a waiting time when the internal oscillator is in
application mode and receives a square wave. The switching time in this case is about 100 μs.
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Clock Specifications 135