DM3725CBC datasheet(135/280 Pages) TI

135 / 280 page

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

Oscillation frequency

12, 13, 16.8, or 19.2

MHz

tsX

Start-up time(1) (2)

(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 tsX 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

Frequency

12, 13, 16.8, 19.2, 26, or 38.4

MHz

Input Capacitance

1.00

1.15

1.35

Input Resistance

160

216

280

Ω

tsX

Start-up time(1)

See(2)

(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, tsX 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.

Clock Specifications

135

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