MC68EC040FE20A Freescale Semiconductor, MC68EC040FE20A Datasheet - Page 343

• Manufacturer Part Number: MC68EC040FE20A
• Description: IC MPU 32BIT 20MHZ 184-CQFP
• Manufacturer: Freescale Semiconductor

Specifications of MC68EC040FE20A

• Processor Type: M680x0 32-Bit
• Speed: 20MHz
• Voltage: 5V
• Mounting Type: Surface Mount
• Package / Case: 184-CQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -

If a designer uses alternative standard termination methods, such as RC termination
network (see Figure 11-9), Thévenin termination network (not illustrated), or no
termination method at all, which is not recommended, then the power dissipation of the
MC68040 will be significantly less than the large buffer terminated values. For termination
networks other than that illustrated in Figure 11-31, the designer must calculate the
component of power dissipated in the output buffer and add this value to the small buffer
unterminated value.
The following paragraphs describe how the large buffer terminated values were
calculated. The MC68040 termination network causes current flow through the output
buffer of the MC68040, regardless of whether the MC68040 is driving a logic one or a
logic zero. The following equation gives the large buffer termination network power
dissipation for a given pin:
R
pulldown resistance, and a duty cycle average of how often the pin is high, low, or three-
stated. Typical values for Z
output, and 25
based on sequential burst write cycles, R
buffer mode and 25
Maximum termination current in the large buffer mode occurs for output:
MOTOROLA
eff
I = (V
P = I
Low:
High:
is the effective average output resistance, including typical pullup resistance, typical
2
R
eff
I
I
tl
Figure 11-9. Typical Configuration for RC Termination Network
th
(R + Z
= (2.5 V
= (2.75 V
for small buffer output. Using these values and duty cycle assumptions
o
)) + 5 mA
Figure 11-8. MC68040 Termination Network
for the small buffer mode.
MC68040 OUTPUT
TYPICAL Z = 4–12
TYPICAL Z = 25
Freescale Semiconductor, Inc.
MC68040 OUTPUT
TYPICAL Z = 4–12
TYPICAL Z = 25
(50 + 6 )) + 5 mA = 49.6 mA
BUFFER
(50 + 12 )) + 5 mA = 50.8 mA
For More Information On This Product,
BUFFER
o
are 6
0
0
0
0
Go to: www.freescale.com
M68040 USER’S MANUAL
(SMALL)
(SMALL)
(LARGE)
(LARGE)
for large buffer low output, 12
50
50
T.L
eff
T.L
calculates to 7.7
R = 50
R = 50
C = 300 pF
2.5 V
for the MC68040 large
for large buffer high
11-15