XRT5794ES-PLCC Exar, XRT5794ES-PLCC Datasheet - Page 13

• Manufacturer Part Number: XRT5794ES-PLCC
• Description: Peripheral Drivers & Components - PCIs 4 CH E1 AFE
• Manufacturer: Exar

Specifications of XRT5794ES-PLCC

• Product Category: Peripheral Drivers & Components - PCIs
• Rohs: yes

Output Transformer Selection
The 1:1.265 ratio output transformer is recommended for
the XR-T5794 because this ratio gives the best possible
transmitter output return loss for 120
service. However, other transformers may provide an
adequate return loss for many applications. The two
characteristics that determine series build-out resistor
requirements are:
The following method may be used to determine
transformer suitability for a given use.
1. List the application requirements.
2. Calculate equivalent output voltage and load
Driver output impedance is less than 5 .
V
4.5V peak.
Figure 6. Equivalent Impedance Schematic
Vs
Transformer Ratio = 1:n
Vo = Peak Output Pulse Amplitude
R
resistance without the transformer.
Rev. 2.01
s
Vs
Figure 7. Equivalent Simplified Schematic
, which is the driver open circuit output voltage, is
L
= Load Resistance
Req
R
Rs
n
Rs
2
L
Req
3
4
1:n
Veq
1
2
V
eq
V
n
V
o
O
balanced E1
R
L
13
3. Calculate the source resistance, R
4. Now calculate the theoretical return loss.
The calculation given below uses the recommended
1:1.265 ratio transformer as an example:
Transformer Ratio = 1 :1.265
V
R
(Datasheet specifies standard value of 68 )
Calculate the theoretical return loss to determine if the
transformer is acceptable.
O
L
= 120
= 3.0V Peak
Req
Veq
Rs
Return Loss
Rs
Return Loss
Req
Req
V
R
n
n
o
2
L
Veq
1.265
120
Vs
Veq
1.6
Vs
3.0
20 log
20 log 75
1
75
1
2.37 V
Req
Req
75
XR-T5794
75
2.37
67.4
67.4
4.5
Rs
Rs
S
.
1
25.5 dB
67.4