LM1893N National Semiconductor, LM1893N Datasheet - Page 13

• Manufacturer Part Number: LM1893N
• Description: IC TXRX CARRIER CURRENT
• Manufacturer: National Semiconductor
• Type: Transceiverr

Specifications of LM1893N

• Number Of Drivers/receivers: 1/1
• Voltage - Supply: 18V
• Mounting Type: Through Hole
• Package / Case: *
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Protocol: -
• Other names: *LM1893N; LM1893

Figure 21 gives C
Component Selection
C
The impulse noise filter integrator capacitor C
disallow the passage of any pulse shorter than the integra-
tor charge time That charge time set to a nominal
time is the time required for a
swing C
conditions must never be greater than a bit time since no
signal could then pass Using a
tion temperature range and full specified current range a
maximum nominal charge time of
R
The collector pull-up resistor is sized to supply adequate
pull-up current drive and speed while preserving adequate
output low current drive
I
C
FIGURE 21 Impulse noise filter cap C
FIGURE 22 Circuit to view the differential demodulated data signal minus the noise and 2F
FIGURE 20 Size C
I
over a 2 V
where the charge time is
I
versus data rate under those conditions
BE
receive bias time
range Charge time under worst case
M
assuming a 2 bit-time
g
g
50
10% capacitor full junc-
conveniently with a single-ended gain-of-one output
(Continued)
bit is recommended
A charge current to
bit time
I
versus F
I
TL H 6750– 22
TL H 6750– 24
is used to
DATA
bit
13
Z
The 5 1V silicon zener diode Z
RX-to-TX switch-over time is needed at the same time that
the chip is operating in the RX mode with a pin 10 input
signal swing approaching or exceeding twice the supply
voltage Predominant causes of these large swings imping-
ing on the RX input are 1) a transmitter’s supply voltage
higher than the receiver’s supply voltage 2) a TX and RX
pair that are electrically close or 3) a higher RX T
turns ratio than the TX T
Normally when in the RX mode with small incoming signal
on pin 10 the ALC remains off with pin 7 at a 6V
(V
mode may then be selected with 6V on C
TX power to pump T
quickly for fast RX-to-TX switch time As TX output swing
increases so that pin 10 swings below V
that ALC activates to charge C
output drive However if in the RX mode pin 10 ever swings
below V
TX mode is selected with C
100% TX output drive is available to pump T
resulting in a slower rising line signal - effectively reducing
the RX-to-TX switch time
Use a 5 1V Z
guarantee over-temp operation R
Z
R
Z
into pin 7 that must be limited to 1 mA (with R
series R)
Breadboarding Tips
During CCT system evaluation some techniques listed be-
low will simplify certain measurements
A
A
A
A
Z
b
to limit current flow and should never fall below 1 k
Use caution when working on this circuit - dangerous
line voltages may be present
When evaluating PLL operation offset cancel circuit op-
eration and loop filter values use the filter of Figure 22
to view the demodulated signal minus the 2F
components This filter models the RC lowpass filter on
chip
is less than 1 k
Logic high voltages above 10V will cause current flow
2V
ALC
BE
) bias voltage C
C
A
A
driven by a 0 to 0 8V logic low signal to
will charge to above 6 6V Now when the
1
then put a 2 k
’s tuned circuit and so the AC line
1
step-down ratio
A
A
at 6 6V somewhere from 0 to
A
is then charged to 6V TX
A
to about 6 6V to reduce TX
is required when a short
A
O
must be in series with
resistor in series with
components
ALC
TL H 6750 – 25
A
1
(4 7V typically)
allowing 100%
’s tuned circuit
O
and noise
1
step-up
A
or a
If