SM320LF2407-EP Datasheet, PDF (44/112 Pages) Texas Instruments – 
DSP CONTROLLERS

SM320LF2407AĆEP
DSP CONTROLLERS
SGUS036B − JULY 2003 − REVISED OCTOBER 2003
external reference crystal clock option
The internal oscillator is enabled by connecting a crystal across the XTAL1/CLKIN and XTAL2 pins as shown
in Figure 10a. The crystal should be in fundamental operation and parallel resonant, with an effective series
resistance of 30 Ω−150 Ω and a maximum power dissipation of 1 mW; it should be specified at a load
capacitance of 20 pF.
external reference oscillator clock option
The internal oscillator is disabled by connecting a clock signal to XTAL1/CLKIN and leaving the XTAL2 input
pin unconnected as shown in Figure 10b.
XTAL1/CLKIN
XTAL2
XTAL1/CLKIN
XTAL2
Cb1
(see Note A)
Crystal
Cb2
External Clock Signal
(see Note A)
(Toggling 0 −3.3 V)
NC
(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 10. 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 9). 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)
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
R1 (Ω) (± 5% TOLERANCE)
4.7
5.6
6.8
8.2
9.1
10
11
12
13
15
15
16
18
18
20
22
24
C1 (µF) (± 20% TOLERANCE)
3.9
2.7
1.8
1.5
1
0.82
0.68
0.56
0.47
0.39
0.33
0.33
0.27
0.22
0.22
0.18
0.15
C2 (µF) (± 20% TOLERANCE)
0.082
0.056
0.039
0.033
0.022
0.015
0.015
0.012
0.01
0.0082
0.0068
0.0068
0.0056
0.0047
0.0047
0.0039
0.0033
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