HSDL-1100 Agilent(Hewlett-Packard), HSDL-1100 Datasheet - Page 4

• Manufacturer Part Number: HSDL-1100
• Description: General Application Guide for the HSDL-1100 4 Mb/s Infrared Transceiver
• Manufacturer: Agilent(Hewlett-Packard)

If any of the above aspects of
board layout are compromised,
and it is suspected that an EMI
shield over the HSDL-1100 may
be necessary, Hewlett-Packard
can provide EMI shields, or
shielded HSDL-1100s in produc-
tion volumes. The PC board
should be prepared with the
proper through holes, if it is
suspected that an EMI shield will
be necessary (see datasheets for
HP part numbers HSDL-810x, or
HSDL-1100#S07).
Application Specific
Transmitter Design:
Transmitter Drive
The infrared LED in the HSDL-
1100 is driven by signals present
at TXD. See Figure 3.
The IrDA physical layer specifica-
tion requires t
transmitted optical signal at
4 Mb/s to be 40 ns or less. The
HSDL-1100 budgets 30 ns of t
and t
for t
ILED pulse. In order to reach
< 30 ns t
• The ground plane for the
• The DC-DC converter should
rise
critical ground plane zone.
The board layer chosen as
the ground plane island
should be maximized in area
within the ground plane
zone, and should include all
resistor and capacitor
components recommended
for use with the HSDL-1100.
HSDL-1100 module should
be connected ONLY to the
least noisy ground node
available on the PC board.
be located as far away from
the HSDL-1100 on the PC
board as possible (at least
3 cm away). The board may
then look like Figure 2.
fall
and t
for the LED, and 10 ns
rise
and t
fall
rise
of the electrical
fall
and t
for the LED,
fall
of the
rise
a peaking circuit of R1 and CX2 is
recommended. The R1•CX2 time
constant provides overdrive for
both turn-on and turn-off of the
LED, shortening the optical t
and t
electrical ILED pulse t
to 5-10 ns, TXD must be driven
with a pulse current Iih of approxi-
mately ILED/125. See Figure 4.
The HSDL-1100 datasheet Electri-
cal Specifications show that at Vih
= 4.25 V, the required Iih 6.6 mA.
Using R1 = 560 ohms, Iih will be
sufficient for 5-10ns t
ILED, if Vih 4.25 V. If the chosen
Figure 2.
TXD
Figure 3.
Figure 4.
V
IH
CONVERTER
fall
TXD PULSE
DC - DC
. In order to limit the
CX2
R1
7
rise
rise
CX7
and t
and t
MAIN GROUND
rise
>3 cm
fall
fall
HSDL-1100 PIN 7
of
RLED
10
I/O chip, controller chip, or EnDec
chip does not support Vih
and CX2 can be chosen to allow for
a lower Vih at the required Iih value.
R1 can be lowered from 560 ohms
to allow for Vih < 4.25 V. CX2
should then be increased to pre-
serve the peaking characteristic.
If the I/O chip or controller chip
cannot provide the required Iih
even at Voh = 2.4 V, then a buffer
chip can be used to drive TXD of
the HSDL-1100. The output of
the buffer chip should be able
to source current of at least
4.25 V at the required Iih, then R1
HSDL-1100
OPTICAL ILED PULSE
CX5
PLANE ISLAND
GROUND
CX1