LT1328
4Mbps IrDA
Infrared Receiver
FEATURES
s
s
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s
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DESCRIPTION
The LT
®
1328 is a photodiode receiver that supports IrDA
®
data rates up to 4Mbps as well as other modulation
methods such as Sharp ASK and TV remote control. The
LT1328 MSOP contains all the necessary circuitry to
convert current pulses from an external photodiode to a
digital TTL output while rejecting unwanted lower fre-
quency interference. The LT1328 plus five external com-
ponents is all that is required to make an IrDA compatible
receiver.
Power requirements for the LT1328 are minimal—a single
5V supply and 2mA of quiescent current. Internal high-
pass filtering attenuates interfering signals such as sunlight,
incandescent and fluorescent lamps and is selectable at
Pin 7 for low or high data rates. The LT1328’s ease of use
and flexibility make it an ideal solution for numerous other
photodiode receiver applications. The LT1328 is available
in the SO-8 as well as the tiny MSOP for size-critical
applications.
, LTC and LT are registered trademarks of Linear Technology Corporation.
IrDA is a registered trademark of the Infrared Data Association.
SIR, FIR and 4ppm Compatible
Low Frequency Ambient Rejection Loop
Supply Current: 2mA
8-Lead MSOP and SO Packages
5V Single Supply Operation
Optional High Frequency Noise Rejection
APPLICATIONS
s
s
s
s
s
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IrDA Applications
Sharp/Newton
TV Remote
Noncontact Telemetry
Wireless Slave for Photographic Flash
Keyless Entry
Optical Data Transfer
Infrared Home Control Systems
TYPICAL APPLICATIONS
N
IrDA Receiver
C6
1000pF
8
7
5V
C2
4.7µF
ENABLE
*SILICONIX
1328 TA01
LT1328
1
LIGHT IN
TEMIC
BPV22NF
D1
C1
10nF
C4
330pF
2
IN
V
BIAS
HIGH: SIR
LOW: FIR AND 4ppm
(OPTIONAL)
OPTIONAL
SHUTDOWN
CIRCUIT
TP0610L*
5V
FILTER MODE
3 FILTER
6
V
CC
SWITCH
4
5
DATA
GND
TTL
DATA OUT
TRANSMIT
INPUT
U
U
U
IrDA Transmitter
V
CC
C5
4.7µF
D2
HSDL-4220*
R3
3.9Ω
1/2W
Q3
2N7002
R1
100Ω
R2
10k
*HEWLETT PACKARD
1328 TA02
1
LT1328
ABSOLUTE
MAXIMUM
RATINGS
Total Supply Voltage (V
CC
to GND) ........................... 6V
Differential Voltage (Any Two Pins) .......................... 6V
Operating Temperature Range .................... 0°C to 70°C
Specified Temperature Range ..................... 0°C to 70°C
Maximum Junction Temperature ......................... 150°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
PACKAGE/ORDER INFORMATION
ORDER PART
NUMBER
TOP VIEW
IN
FILTER
FILTER SWITCH
GND
1
2
3
4
8
7
6
5
V
BIAS
MODE
V
CC
DATA
IN 1
TOP VIEW
8 V
BIAS
7 MODE
6 V
CC
5 DATA
LT1328CMS8
MS8 PART MARKING
LTBG
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 150°C,
θ
JA
= 250°C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER
I
TH(MIN)
Minimum Input Current Pulse
CONDITIONS
V
CC
= 5V, V
GND
= 0V, V
MODE
= 2V unless otherwise specified. (Note 1)
MIN
TYP
200
600
q
Current Out of Pin 1 (SIR), Pulse Width 1.6µs,
Period 8.7µs
Current Out of Pin 1 (FIR, 4ppm), Pulse Width 125ns,
Period 500ns
Current Out of Pin 1
DC to 120Hz, Current Out of Pin 1
No Input Signal
No Input Signal
No Input Signal
No Input Signal
q
q
q
q
q
q
q
I
PD
I
REJECT
I
S
V
S
V
IN
V
BIAS
V
LT
V
THL
V
THH
V
OL
V
OH
Maximum Input Current
Maximum Low Frequency
Input Current
Supply Current
Operating Supply Voltage
Bias Voltage on Pin 1
Bias Voltage on Pin 8
Quiescent Voltage on Pin 2
Switch Logic Level Low Pin 7
Switch Logic Level High Pin 7
Comparator Output Low
Comparator Output High
Voltage On Pin 5, 800µA Sink Current
Voltage On Pin 5, 50µA Source Current
The
q
denotes specifications which apply over the full operating tempera-
ture range of 0°C
≤
T
A
≤
70°C.
2
U
U
W
W W
U
W
ORDER PART
NUMBER
LT1328CS8
S8 PART MARKING
1328
FILTER 2
FILTER
3
SWITCH
GND 4
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 190°C/ W
MAX
UNITS
nA
nA
mA
µA
15
30
1000
2
3
5.5
1.5
1.5
1.5
2.0
2.0
2.0
0.8
mA
V
V
V
V
V
V
V
V
4.5
1.0
1.0
1.0
2.0
0.4
4.0
4.3
q
q
0.5
Note 1:
MS8 package devices are designed for and intended to meet
commercial temperature range specifications but are not tested at 0°C.
LT1328
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Supply Voltage
4
4
CHANGE IN VOLTAGE ON PIN 1 (mV)
SUPPLY CURRENT (mA)
3
OUTPUT PULSE WIDTH
100 (%)
INPUT PULSE WIDTH
I
PIN1
= 0nA
V
PIN7
= 0V
T
A
= 25°C
2
1
0
0
1
2
3 4 5 6 7 8
SUPPLY VOLTAGE (V)
Change in Output Pulse Width
vs Input Duty Cycle
250
10
200
CHANGE IN VOLTAGE ON PIN 1 (mV)
OUTPUT PULSE WIDTH
100 (%)
INPUT PULSE WIDTH
V
S
= 5V
V
FILT
= 10nF
V
BIAS
= 1000pF
PULSE PERIOD = 8.7µs
150
I
PIN1
= 150nA TO 3mA
100
I
PIN1
> 3mA TO 10mA
50
0
1
Change in Voltage on Pin 2
vs Current
2.0
1000
1.5
PEAK INPUT CURRENT AMPLITUDE (µA)
CHANGE IN VOLTAGE ON PIN 2 (V)
V
S
= 5V
T
A
= 25°C
1.0
SOURCING
CURRENT
0.5
0
SINKING
CURRENT
– 0.5
0.1
1
10
100 1000 10000 100000
CURRENT (PIN 1) (µA)
1328 G06
U W
9
1328 G01
Change in Voltage on Pin 1
vs Supply Voltage
200
I
PIN1
= 0nA
T
A
= 25°C
2
Change in Output Pulse Width
vs Input Current Amplitude
V
S
= 5V
V
FILT
= 10nF
V
BIAS
= 1000pF
FOR INPUT PULSE WIDTHS
OF 8.6µs TO 0.22µs
PULSE PERIOD = 8.7µs
150
0
100
–2
50
10
–4
0
1
2
3 4 5 6 7 8
SUPPLY VOLTAGE (V)
9
10
0
0.1
1
100
1000
10
INPUT CURRENT (µA)
10000
1328 G03
1328 G02
Change in Voltage on Pin 1
vs Current
CURRENT SINKING
FROM PIN 1
0
V
S
= 5V
T
A
= 25°C
–10
CURRENT SOURCING
FROM PIN 1
–20
–30
– 40
3
30
10
INPUT DUTY CYCLE (%)
100
1328 G04
0.1
1
10
100 1000 10000 100000
CURRENT (PIN 1) (µA)
1328 G05
Peak Interfering Current
vs Frequency
V
S
= 5V
C
BIAS
= 1000pF
CURRENT IS
SOURCED
OUT OF PIN 1
C
FILT
= 330pF
C
FILT
= 10nF
1
AREA OF
SIGNAL
REJECTION
100
10
0.1
0.01
0.1
10
1
FREQUENCY (kHz)
100
1000
1328 G07
3
LT1328
PIN FUNCTIONS
IN (Pin 1):
Connect this pin to the photodiode cathode.
This is the input to the preamplifier and is held at 1.5V by
the output of the DC servo. To maintain the 1.5V on this
pin, the DC servo can source up to 2mA or sink 40µA to this
pin.
FILTER (Pin 2):
Connect a capacitor from this pin to
ground. The value of the capacitor will set the band of
frequencies that will be attenuated by the servo. The pole
is set by the formula f = 25/(2π • 60k • C). A 330pF
capacitor will attenuate photodiode signals below 200kHz
when operating at high data rates (FIR and 4ppm).
FILTER SWITCH (Pin 3):
Collector of a Transistor Switch.
When the MODE switch (Pin 7) is TTL HIGH this pin will be
switched to ground. This pin is used to increase the filter
capacitor for slower data rates (SIR). A 10nF capacitor
from Pin 2 to Pin 3 will bring the highpass frequency down
to 6.6kHz for SIR.
GND (Pin 4):
Ground.
DATA (Pin 5):
TTL Output of the Comparator. A TTL LOW
at this pin indicates that the photodiode has received a
pulse of light. This pin will remain HIGH when the light
signal and noise are below the attenuation band of the DC
servo.
V
CC
(Pin 6):
5V Supply. A bypass capacitor, connected as
close as possible from Pin 6 to ground is recommended
(4.7µF).
MODE (Pin 7):
A TTL HIGH on this pin will cause the open
collector at Pin 3 to switch to ground. This is an option that
switches in extra capacitance for lower frequency data
rates. If this pin is not used, select a capacitor (C4) to
accommodate the lowest data rate (for IrDA C4 = 10nF).
V
BIAS
(Pin 8):
A 1000pF capacitor from this pin to ground
is required.
BLOCK DIAGRAM
D1
PHOTODIODE
TEMIC
BPV22NF
C4
330pF
C1
10nF 3
4
W
U
U
U
V
CC
R
FB
50k
1.5V
V
BIAS
8
C6
1000pF
1
IN
R
IN
2k
PREAMP
BIAS
MODE
FILTER
DC SERVO
7
HIGH: SIR
LOW: FIR AND 4ppm
+
2
FILTER
FILTER SWITCH
g
m
60k
5V
–
V
CC
6
C2
4.7µF
4
GND
–
COMPARATOR
DATA
5
+
1328 BD
Figure 1. LT1328 Block Diagram
LT1328
APPLICATIONS INFORMATION
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
FB
. The DC level of the
preamp is held at V
BIAS
due to the servo action of the
transconductance amplifier g
m
. The servo action only sup-
presses frequencies below the R
gm
, C
FILT
pole.
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/(2π • R
gm
• C) where R
gm
= 60k. The
330pF capacitor in Figure 1 sets a 200kHz corner fre-
quency and is used for data rates above 115kbps. For low
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
m
amplifier combination
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 1.6µs 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
0
1
0
DATA RATES: 2400BAUD TO 115kbps
BIT INTERVAL: 417µs TO 8.7µs
PULSE WIDTH: 3/16 OF INTERVAL OR 1.63µs
IrDA-SIR (1m)
RECEIVER
OUTPUT
TRANSMITTER
INPUT
Figure 2. IrDA-SIR Modulation
U
W
U
U
NRZ DATA
0
1
1
0
1
0
IrDA-SIR HIGH = LIGHT TRANSMITTED
1328 F02a
IrDA-SIR (1cm)
RECEIVER
OUTPUT
TRANSMITTER
INPUT
5
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