EL5281CS ELANTEC [Elantec Semiconductor], EL5281CS Datasheet - Page 9

• Manufacturer Part Number: EL5281CS
• Description: Dual 8ns High-Speed Comparator
• Manufacturer: ELANTEC [Elantec Semiconductor]

R
and R
follows:
Select the threshold voltage V
R
times greater than the input bias current of the
comparator:
Let the hysteresis be V
where:
Recalculate R
Non inverting comparator with hysteresis:
R
Note that the current through R
than the input bias current in order to minimize errors.
The calculation of the resistor values as follows:
Pick the value of R
in order to minimize the propagation delay time.
Choose the hysteresis V
3
2
3
. The current through R
V
adds a portion of the output to the threshold set by R
adds a portion of the output to the positive input.
O
=V
2
. The calculation of the resistor values are as
SD
R
2
1
-0.8V (swing of the output)
=
2
to maintain the same value of V
V
REF
V
IN
V
R
1
R
T H
3
. R
–
3
=
V
=
H
=
1
TH
R
H
, and calculate R
V
V
--------
V
should be small (less than 1k )
1
V
O
H
S D
V
1
and calculate R
R E F
REF
/R
–
V
-----------
2
R
0.8
R
T H
1
bias string must be many
1
TH
-------------------
R
3
1
+
-
should be much greater
R
+
R
+
R
1
and calculate R
2
V
-------------------------------------
--------
V
3
R
R
T H
1
H
2
–
R
0.5V
3
3
3
:
:
SD
TH
:
1
and
1
9
Check the current through R
much greater than the input bias current as follows:
The above two methods will generate hysteresis of up to
a few hundred millivolts. Beyond that, the impedance of
R
of R
Power Dissipation
When switching at high speeds, the comparator's drive
capability is limited by the rise in junction temperature
caused by the internal power dissipation. For reliable
operation, the junction temperature must be kept below
T
An approximate equation for the device power dissipa-
tion is as follows. Assume the power dissipation in the
load is very small:
where:
I
Please refer to the performance curve to choose the input
driving frequency. Having obtained the power dissipa-
tion, the maximum junction temperature can be
determined as follows:
where:
SD
JMAX
3
V
I
V
I
N is the number of comparators in the package
T
is low enough to affect the bias string and adjustment
S
SD
JA
MAX
S
SD
strongly depends on the input switching frequency.
1
is the analog quiescent supply current per comparator
is the analog supply voltage from V
may be required.
is the digital supply current per comparator
is the thermal resistance of the package
is the digital supply voltage from V
(125°C).
is the maximum ambient temperature
Dual 8ns High-Speed Comparator
P
DISS
T
J M A X
=
I
=
=
V
S
0.5V
--------------------------------------- -
T
M A X
I
S
S D
+
R
+
V
3
–
3
SD
V
and make sure that it is
J A
R E F
EL5281C
I
S D
P
D I S S
S
N
+ to V
SD
to ground
S
-