LT1328CS8#TRPBF Linear Technology, LT1328CS8#TRPBF Datasheet - Page 5

• Manufacturer Part Number: LT1328CS8#TRPBF
• Description: IC RECEIVER 4MBPS IRDA IR 8-SOIC
• Manufacturer: Linear Technology
• Type: Receiverr

Specifications of LT1328CS8#TRPBF

• Number Of Drivers/receivers: 0/1
• Protocol: Infrared (IRDA)
• Voltage - Supply: 4.5 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS
The LT1328 is a low noise, high speed, high gain infrared
receiver designed to easily provide IR communications with
portable computers, PDAs, desktop computers and periph-
erals. The receiver takes the photodiode current from an
infrared photodiode (typically Temic BPV22NF) and per-
forms a current-to-voltage conversion. Figure 1 is a block
diagram of the LT1328. Photodiode current is transformed
into a voltage by feedback resistor R
preamp is held at V
transconductance amplifier g
presses frequencies below the R
This highpass filtering attenuates interfering signals such
as sunlight, incandescent and fluorescent lamps. For
higher data rates, the rejection band can be increased to
include higher frequencies (Pin 7 LOW). If this option is
not used, Pin 7 is grounded and Pin 3 is open. The rejection
band of the filter is then determined by the lowest data rate;
C4 equals 10nF for IrDA (SIR, FIR and 4ppm). The high-
pass filter break point is set by the capacitor from Pin 2 to
ground at f(Hz) = 25/(2 • R
330pF capacitor in Figure 1 sets a 200kHz corner fre-
quency and is used for data rates above 115kbps. For low
TRANSMITTER
RECEIVER
OUTPUT
INPUT
IrDA-SIR (1m)
U
BIAS
INFORMATION
due to the servo action of the
U
gm
m
. The servo action only sup-
• C) where R
gm
DATA RATES: 2400BAUD TO 115kbps
BIT INTERVAL: 417 s TO 8.7 s
PULSE WIDTH: 3/16 OF INTERVAL OR 1.63 s
, C
W
FB
0
. The DC level of the
FILT
1
pole.
gm
0
Figure 2. IrDA-SIR Modulation
= 60k. The
U
0
1
data rates (115kbps and below) Pin 7 should be set to TTL
HIGH which grounds Pin 3 and reduces the break fre-
quency with the addition of the capacitor between Pins 2
and 3. A 10nF capacitor produces a 6.6kHz corner.
Signals passed by the preamp/g
cause the comparator output to swing low.
Performance of the LT1328 circuit in Figure 1 extends
over the full 1cm to 1 meter range of the IrDA standard at
the stipulated light levels. For IrDA data rates of 115kbps
and below, a 1.6 s pulse width is used for a logic zero and
no pulse for a logic one. Light levels are 40mW/SR to
500mW/SR.
Figure 2 shows a scope photo for a transmitter input
(bottom trace) and the LT1328 output (top trace). Note
that the input to the transmitter is inverted, i.e., a high at
the input is light transmitted, which is a zero at the output
of the transmitter (Pin 5). The MODE pin (Pin 7) should be
high for these data rates.
The second fastest tier of the IrDA standard addresses
576kbps and 1.152Mbps data rates with pulse widths of
1/4 of the bit interval for zero and no pulse for one. The
1
TRANSMITTER
RECEIVER
OUTPUT
0
INPUT
1
IrDA-SIR (1cm)
0
1328 F02a
NRZ DATA
IrDA-SIR HIGH = LIGHT TRANSMITTED
m
amplifier combination
LT1328
5