LTC2847CUHF Linear Technology, LTC2847CUHF Datasheet - Page 14

• Manufacturer Part Number: LTC2847CUHF
• Description: IC TXRX MULTIPROTOCOL 38-QFN
• Manufacturer: Linear Technology
• Type: Transceiverr

Specifications of LTC2847CUHF

• Number Of Drivers/receivers: 3/3
• Protocol: Multiprotocol
• Voltage - Supply: 5V
• Mounting Type: Surface Mount
• Package / Case: 38-QFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
LTC2847
In V.28 mode, S3 is closed inside the LTC2847/LTC2845
which connects a 6k (R8) impedance to ground in parallel
with 20k (R5) plus 10k (R6) for a combined impedance of
5k as shown in Figure 25. Proper termination is only pro-
vided when the B input of the receivers is floating, since S1
of the LTC2847’s R2 and R3 receivers remains on in V.28
mode
LTC2847/LTC2845 receiver and connected to a TTL level
reference voltage to give a 1.4V receiver trip point.
V.35 Interface
A typical V.35 balanced interface is shown in Figure 26. A
V.35 differential generator with outputs A and B and
ground C is connected to a differential receiver with input
A
connected via the signal return to ground C. The V.35
interface requires a T or delta network termination at the
receiver end and the generator end. The receiver differen-
tial impedance measured at the connector must be
100
nals (A
14
'
connected to A, input B
1
GENERATOR
50
50
. The noninverting input is disconnected inside the
'
A
B
C
10 , and the impedance between shorted termi-
'
'
and B
'
Figure 27. V.35 Receiver Configuration
125
R1
51.5
S1
R2
51.5
'
Figure 26. Typical V.35 Interface
S2
) and ground (C
A
B
C
124
U
R3
INTERCONNECTING
BALANCED
CABLE
GND
R8
6k
S3
'
U
connected to B, and ground C
20k
20k
R5
R4
')
must be 150
C
B
A
'
W
'
'
TERMINATION
R6
10k
R7
10k
125
CABLE
RECEIVER
LTC2847
LOAD
50
50
2847 F27
U
RECEIVER
15 .
2847 F26
'
In V.35 mode, both switches S1 and S2 inside the LTC2847
are on, connecting a T network impedance as shown in
Figure 27. The 30k input impedance of the receiver is
placed in parallel with the T network termination, but does
not affect the overall input impedance significantly.
The generator differential impedance must be 50
150 and the impedance between shorted terminals (A
and B) and ground (C) must be 150
No-Cable Mode
The no-cable mode (M0 = M1 = M2 = 1) is intended for
the case when the cable is disconnected from the con-
nector. The charge pump, bias circuitry, drivers and
receivers are turned off, the driver outputs are forced into
a high impedance state, and the V
transceiver drops to less than 300 A while its V
current drops to less than 10 A. Note that the LTC2847’s
R2 and R3 receivers continue to be terminated by a 103
differential impedance.
Charge Pump
The LTC2847 uses an internal capacitive charge pump to
generate V
doubler generates about 8V on V
generates about – 7.5V on V
tantalum or ceramic capacitors are required for C1, C2, C3
and C5. The V
3.3 F. All capacitors are 16V and should be placed as close
as possible to the LTC2847 to reduce EMI.
Receiver Fail-Safe
All LTC2847/LTC2845 receivers feature fail-safe opera-
tion in all modes. If the receiver inputs are left floating or
are shorted together by a termination resistor, the receiver
output will always be forced to a logic high.
5V
C3
1 F
DD
and V
EE
C1
1 F
C5
1 F
capacitor C4 should be a minimum of
Figure 28. Charge Pump
EE
V
C1
C1
V
DD
CC
+
–
as shown in Figure 28. A voltage
LTC2847
EE
. Four 1 F surface mounted
GND
DD
C2
C2
V
CC
EE
+
–
and a voltage inverter
supply current to the
15 .
+
2847 F28
C2
1 F
C4
3.3 F
IN
sn2847 2847fs
supply
to