Datasheet

ADSP-2184L/ADSP-2185L/ADSP-2186L/ADSP-2187L
Rev. C | Page 43 of 48 | January 2008
TEST CONDITIONS
Figure 44 shows voltage reference levels for all ac measurements
(except output disable/enable).
Output Disable Time
Output pins are considered to be disabled when they have
stopped driving and started a transition from the measured out-
put high or low voltage to a high impedance state. The output
disable time (t
DIS
) is the difference of t
MEASURED
and t
DECAY
, as
shown in Figure 45. The time is the interval from when a refer-
ence signal reaches a high or low voltage level to when the
output voltages have changed by 0.5 V from the measured out-
put high or low voltage.
The decay time, t
DECAY
, is dependent on the capacitive load, C
L
,
and the current load, i
L
, on the output pin. It can be approxi-
mated by the following equation:
from which
is calculated. If multiple pins (such as the data bus) are disabled,
the measurement value is that of the last pin to stop driving.
Output Enable Time
Output pins are considered to be enabled when they have made
a transition from a high-impedance state to when they start
driving. The output enable time (t
ENA
) is the interval from when
a reference signal reaches a high or low voltage level to when the
output has reached a specified high or low trip point, as shown
in Figure 45. If multiple pins (such as the data bus) are enabled,
the measurement value is that of the first pin to start driving.
ENVIRONMENTAL CONDITIONS
Figure 44. Voltage Reference Levels for AC Measurements (Except Output
Enable/Disable)
1.5V
INPU T
OR
OUTPUT
1.5V
t
DECAY
C
L
0.5V×
i
L
------------------------
=
t
DIS
t
MEASURED
t
DECAY
–=
Figure 45. Output Enable/Disable
Figure 46. Equivalent Loading for AC Measurements (Including All Fixtures)
Table 28. Thermal Resistance
Rating Description
1
1
Where the ambient temperature rating (T
AMB
) is:
T
AMB
= T
CASE
– (PD × θ
CA
)
T
CASE
= case temperature in °C
PD = power dissipation in W
Symbol
LQFP
(°C/W)
BGA
(°C/W)
Thermal Resistance (Case-
to-Ambient)
θ
CA
48 63.3
Thermal Resistance
(Junction-to-Ambient)
θ
JA
50 70.7
Thermal Resistance
(Junction-to-Case)
θ
JC
27.4
2.0V
1.0V
t
ENA
REFERENCE
SIGNAL
OUTPUT
t
DECAY
V
OH
(MEASURED)
OUTPUT STOPS
DRIVING
OUTPUT STARTS
DRIVING
t
DIS
t
MEASURE D
V
OL
(MEASURED)
V
OH
(MEASURED) – 0.5V
V
OL
(MEASURED) + 0.5V
HIGH-IMPEDANCE STATE. TEST CONDITIONS CAUSE
THIS VOLTAGE LEVEL TO BE APPROXIMATELY 1.5V.
V
OH
(MEASURED)
V
OL
(MEASURED)
TO
OUTPUT
PIN
50pF
1.5V
I
OH
I
OL