NS32CG16-10 Datasheet, PDF (36/82 Pages) National Semiconductor (TI) – High-Performance Printer / Display Processor

3 0 Functional Description (Continued)
During prototype using wire-wrap or similar methods the
capacitors should be soldered directly to the power pins of
the NS32CG16 socket or as close as possible with very
short leads
Recommended bypass for production in printed circuit
boards
a5
Ground
Capacitors
VCCL
VSSL
0 1 mF Disk Ceramic
1 0 mF Tantalum
VCCIO
VSSIO
0 1 mF
VCCCTTL
VSSNTSO
0 1 mF
VCCAD
VSSLAD
0 1 mF
VCCAD
VSSHAD
None
VCCFCLK
VSSFCLK
0 1 mF
VCCL – VSSL bypass requires a very short lead length and
low inductance on the 0 1 mF capacitor
Design Notes
When constructing a board using high frequency clocks with
multiple lines switching special care should be taken to
avoid resonances on signal lines A separate power and
ground layer is recommended This is true when designing
boards for the NS32CG16 Switching times of under 5 ns on
some lines are possible Resonant frequencies should be
maintained well above the 200 MHz frequency range on
signal paths by keeping traces short and inductance low
Loading capacitance at the end of a transmission line con-
tributes to the resonant frequency and should be minimized
if possible Capacitors should be located as close as possi-
ble across each power and ground pair near the
NS32CG16
Power and ground connections are shown in Figure 3-12
3 4 2 Clocking
The NS32CG16 provides an internal oscillator that interacts
with an external clock source through two signals
OSCIN and OSCOUT
Either an external single-phase clock signal or a crystal can
be used as the clock source If a single-phase clock source
is used only the connection on OSCIN is required OSC-
OUT should be left unconnected or loaded with no more
than 5 pF of stray capacitance The voltage level require-
ments specified in Section 4 3 must also be met for proper
operation
When operation with a crystal is desired special care
should be taken to minimize stray capacitances and induc-
tances The crystal as well as the external components
should be placed in close proximity to the OSCIN and
OSCOUT pins to keep the printed circuit trace lengths to an
absolute minimum Figure 3-13a and 3-13b show the exter-
nal crystal interconnections Table 3-3 provides the crystal
characteristics and the values of the R C and L compo-
nents including stray capacitance required for various fre-
quencies
TL EE 9424 – 21
FIGURE 3-13a Crystal Interconnections
20 MHz 30 MHz
TL EE 9424 – 22
FIGURE 3-13b Crystal Interconnections 30 MHz
TL EE 9424–7
FIGURE 3-12 Power and Ground Connections
36