LT1328 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LT1328' PDF : 12 Pages View PDF
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.
VCC (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).
VBIAS (Pin 8): A 1000pF capacitor from this pin to ground
is required.
BLOCK DIAGRAM
VCC
RFB
50k
D1
PHOTODIODE
TEMIC
BPV22NF
1 IN
PREAMP
RIN
2k
C4
330pF
FILTER
2 FILTER
C1
10nF 3 FILTER SWITCH
DC SERVO
+
gm
60k
–
4 GND
1.5V
VBIAS 8
BIAS
MODE 7
C6
1000pF
HIGH: SIR
LOW: FIR AND 4ppm
VCC 6
5V
C2
4.7µF
DATA 5
COMPARATOR
1328 BD
Figure 1. LT1328 Block Diagram
4
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