Datasheet
SCEA019 - January 2001
Texas Instruments GTLP Frequently Asked Questions 7–105
22 What is the total power consumption of an 18-bit GTLP driver?
When you look at backplane performance, you must take into consideration static drive and
dynamic drive. The static output drive is the current needed to maintain a steady-state dc
voltage level on an output. Dynamic output drive is the current available when an output
switches output states. This drive is necessary to overcome reactive loading effects and can
determine the switching speeds in your applications.
Total power consumption is defined as the sum of the static (measured by the device I
CC
),
dynamic (measured by the device internal transistor switching), and output (measured by the
external capacitive load) power of the device.
Static Power
P
STAT
= ∑ {V
CC
[share
L
(k) × I
CCL
+ share
H
(k) × I
CCH
+ share
Z
(k) × I
CCZ
]} / n
Where:
∑ = Sum of k = 1 to n
V
CC
= Supply voltage
share
L
(k) = Average percentage share of the k
th
output in a low state
share
H
(k) = Average percentage share of the k
th
output in a high state
share
Z
(K) = Average percentage share of the k
th
output in a high-impedance state
I
CCL
= Device current consumption for static low at output
I
CCH
= Device current consumption for static high at output
I
CCH
= Device current consumption for high-impedance state at output
n = Total number of outputs in the device
Example 1:
A 50% duty cycle output waveform on all outputs force share
L
(k) and share
H
(k) to be 0.5
each. Share
Z
(k) is zero. Therefore, for an 18-bit device, sum k = 1 to 18, static power is:
P
STAT
= ∑ [V
CC
(0.5 × I
CCL
+ 0.5 × I
CCH
+ 0 × I
CCZ
)]/18 = 0.5 V
CC
(I
CCL
+ I
CCH
)
Example 2:
A 50% duty cycle output waveform on nine outputs and nine outputs at a fixed static low.
share
Z
(k) is zero. Therefore, for an 18-bit device, sum k = 1 to 9, the static power is:
P
STAT
= ∑ [V
CC
(0.5 × I
CCL
+ 0.5 × I
CCH
+ 0 × I
CCZ
)] / 18 + ∑ [V
CC
(1 × I
CCL
+ 0 × I
CCH
+
0 × I
CCZ
)] / 18