TMS320LC2401AVFS datasheet(59/134 Pages) TI

59 / 134 page

TMS320LF2407A,TMS320LF2406A,TMS320LF2403A,TMS320LF2402A

TMS320LC2406A,TMS320LC2404A,TMS320LC2403A,TMS320LC2402A

DSP CONTROLLERS

SPRS145K − JULY 2000 − REVISED AUGUST 2005

POST OFFICE BOX 1443

• HOUSTON, TEXAS 77251−1443

external reference oscillator clock option (continued)

External Clock Signal

(Toggling 0 −3.3 V)

Cb1

(see Note A)

XTAL2

XTAL1/CLKIN

XTAL2

Crystal

Cb2

(see Note A)

(a)

(b)

NOTE A: TI recommends that customers have the resonator/crystal vendor characterize the operation of their device with the DSP chip. The

resonator/crystal vendor has the equipment and expertise to tune the tank circuit. The vendor can also advise the customer regarding

the proper tank component values that will ensure start-up and stability over the entire operating range.

Figure 17. Recommended Crystal/Clock Connection

loop filter

The PLL module uses an external loop filter circuit for jitter minimization. The components for the loop filter

circuit are R1, C1, and C2. The capacitors (C1 and C2) must be non-polarized. This loop filter circuit is connected

between the PLLF and PLLF2 pins (see Figure 16). For examples of component values of R1, C1, and C2 at

a specified oscillator frequency (XTAL1), see Table 10.

Table 10. Loop Filter Component Values With Damping Factor = 2.0

XTAL1/CLKIN FREQUENCY

(MHz)

R1 (

Ω) (±5% TOLERANCE)

C1 (

µF) (±20% TOLERANCE)

C2 (

µF) (±20% TOLERANCE)

4.7

3.9

0.082

5.6

2.7

0.056

6.8

1.8

0.039

8.2

1.5

0.033

9.1

0.022

0.82

0.015

0.68

0.015

0.56

0.012

0.47

0.01

0.39

0.0082

0.33

0.0068

0.33

0.0068

0.27

0.0056

0.22

0.0047

0.22

0.0047

0.18

0.0039

0.15

0.0033

low-power modes

The 240xA has an IDLE instruction. When executed, the IDLE instruction stops the clocks to all circuits in the

CPU, but the clock output from the CPU continues to run. With this instruction, the CPU clocks can be shut down

to save power while the peripherals (clocked with CLKOUT) continue to run. The CPU exits the IDLE state if

it is reset, or, if it receives an interrupt request.

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