Datasheet

SCEA019 - January 2001
Texas Instruments GTLP Frequently Asked Questions 7–107
I
CC
= 50 mA, V
TT
= 1.5 V, V
OL
= 0.55 V, and R
TT
= 38
P
STAT
= V
CC
(0.75 × I
CCL
+ 0.25 × I
CCH
) = 3.3 V (0.75 × 50 mA + 0.25 × 50 mA) = 165 mW
I
OL
= (V
TT
V
OL
) / (R
TT
/ 2) = (1.5 V 0.55 V) / (38 / 2) = 50 mA
P
OUT
switching = I
OL
× V
OL
× (1 output duty cycle) = 50 mA × 0.55 V × (1 0.5) = 13.75
mW/bit
P
OUT
static low = I
OL
× V
OL
× (1 output duty cycle) = 50 mA × 0.55 V × (1 0) = 27.5 mW/bit
There are nine switching outputs and nine static low outputs, therefore:
P
OUT
= 13.75 mW × 9 bits + 27.5 mw × 9 bits = 123.75 mW + 247.5 mW = 371.25 mW
The total power consumption is:
P
TOT
= P
STAT
+ P
DYN
+ P
OUT
= 165 mW + 0 mW + 371.25 mW = 536.25 mW
The junction temperature of the device never must exceed 150
o
C. To determine if the total
power consumption exceeds the maximum junction temperature for a certain package,
calculate junction temperature using the following equation:
T
J
= R
Θ
JA
× P
TOT
+ T
A
In the previous example, assuming a 56-pin TSSOP (DGG) package with high-K board and no
airflow, the junction temperature is:
T
J
= R
Θ
JA
× P
TOT
+ T
A
= 64
o
C/W × 0.53625 W + 25
o
C = 34.32
o
C + 25
o
C = 59.32
o
C
The R
Θ
JA
for all packages can be found at www.ti.com/sc/package