73M1903C-IM/F Maxim Integrated Products, 73M1903C-IM/F Datasheet - Page 39

• Manufacturer Part Number: 73M1903C-IM/F
• Description: IC MODEM AFE MULTIREGIONAL 32QFN
• Manufacturer: Maxim Integrated Products

Specifications of 73M1903C-IM/F

• Number Of Channels: 2
• Voltage - Supply, Analog: 3 V ~ 3.6 V
• Voltage - Supply, Digital: 3 V ~ 3.6 V
• Package / Case: 32-VFQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power (watts): -
• Number Of Bits: -

DS_1903C_033
Appendix A
73M1903C DAA Resistor Calculation Guide
The following procedure can be used to approximate the component values for the DAA with a 600 Ohm
termination. With other terminations the values will be different. The optimal values will be somewhat
different due to the effects of the reactive components in the DAA (this is a resistive approximation).
Simulations with the reactive components accurately modeled will yield optimal values. The procedures
for calculating the component values in the DAA are as follows. First determine R1. For a differential
transmitter R1 is composed of 2 resistors that represent the difference in resistance between the total
winding resistance of the transformer and the reflected impedance, 600 Ω. This value is usually supplied
by the transformer vendor. The DAA should be designed to reflect 600 Ω when looking in at TIP/RING.
The transformer is normally a 1 to 1 turns ratio, the holding coil and ring detect circuit are high
impedance, and Cblock is a high value so in the frequency band of interest it is negligible. The sum of R2
and R3 is much greater than R1, and the output impedance of the drivers driving TXAP/TXAN are low,
therefore:
RW is the sum of the winding resistance of both sides of the transformer. Measure each side of the
transformer with an Ohmmeter and sum them.
Rohswitch is the on resistance of the Off Hook Switch. Mechanical Relay switches are ignored, but Solid
State Relays sometimes have an appreciable on resistance.
Rbead is the DC resistance of whatever series RF blocking devices may be in the design.
For Rin equal to 600 Ω:
To maximize THL (Trans-Hybrid Loss), or to minimize the amount of transmit signal that shows up back
on the Receive pins. The RXAP/RXAN pins get their DC bias from the TXAP/TXAN pins. By capacitively
coupling the R3 resistors with the C1 caps, the DC offset is minimized from the TXAP/TXAN to the
RXAP/RXAN because the DC offset will be divided by the ratio of the R1 resistors to the winding
resistance on the modem side of the transformer.
Rev. 5.0
Rin 2 R1
R1
RXAP
TXAP1
TXAN1
RXAN
600 RW
.
RW
Rohswitch
Rohswitch
C1
R2
R3
R3
R2
2
C1
R1
R1
2 Rbead
.
2 Rbead
.
Figure 17: Typical DAA Block Diagram
RW
CBlock
INDUCTOR
ACTIVE
Bridge
Diode
73M1903C Data Sheet
Switch
Hook
DETECTOR
RING
Bead
Bead
TIP
RING
39