Table 3.

Recommended Minimum Iih for a chosen ILED pulse
amplitude.
ILED Pulse Amplitude (mA) Recommended Minimum Iih (mA)
400 3.2
500 4.0
600 4.8
660 5.3
Minimum Vih (V) R1 () CX2 (pF)
4.25 560 220
3.5 420 300
2.4 220 560
LED Current Amplitude Maximum Pin 10 (Case) Temperature
(25% duty cycle) (mA) for the HSDL-1100 (degrees C)
400 101.3
450 98.4
500 95.3
550 92.1
600 88.7
660 83.0
Table 4. Electrical Specifications.
Table 5. LED Current
HC241 and LS/HC244 are buffer
chips that can be used to drive the
TXD of the HSDL-1100.
Heat Dissipation for LEDA
The PC board must be designed to
dissipate heat from the HSDL-
1100’s LED. The junction temperature
of the LED should be kept
below 125C. The thermal resistance
of the PC board can be
minimized in order to keep
Tjunction of the LED below 125C
while operating up to 660 mA. For
typical applications, the LEDA pin
10 trace should be at least 38 mm2
in area and no narrower than 2.5
mm at any point. Such a trace
should provide a thermal resistance
of approximately 100C/
Watt. The HSDL-1100 evaluation
board presents a thermal resistance
of approximately 100C/Watt
for the LEDA pin 10 trace. An
opening in the solder mask for the
whole trace can be made to further
decrease the thermal resistance.
If you do not know your PC
board’s thermal resistance (deg C/
Watt), then the easiest way to
determine the maximum allowable
LED current is from maximum pin
10 = LEDA case temperature, see
Table 5. From the LED current
table you can see the maximum
pin10 lead temperature on the
HSDL-1100 for the #007 leadform.
A thermocouple can be placed on
pin 10 while operating the HSDL-
1100 transmitter in their PC board.
If the pin 10 temperature exceeds
the listed maximum temperature,
the PC board thermal resistance
must be reduced, or the LED
current must be reduced. The PC
board thermal resistance can be
reduced by increasing the metal
area of the pin 10 trace on the PC
board, and by leaving it bare (no
epoxy glass over a section of that
trace).
For Example: If ILED = 550 mA,
then the PC board should be
designed so that the pin 10 temperature
does not exceed 92.1C
when the PC board is enclosed in a
notebook or handy terminal box.