ADN2530

Rev. A | Page 13 of 20

LOAD MISTERMINATION

Due to its excellent S22 performance, the ADN2530 can drive

differential loads that range from 35 Ω to 140 Ω. In practice,

many TOSAs have differential resistance not equal to 100 Ω. In

this case, with 100 Ω differential transmission lines connecting

the ADN2530 to the load, the load end of the transmission lines

are misterminated. This mistermination leads to signal reflections

back to the driver. The excellent back-termination in the

ADN2530 absorbs these reflections, preventing their reflection

back to the load. This enables excellent optical eye quality to

be achieved even when the load end of the transmission lines is

significantly misterminated. The connection between the load

and the ADN2530 must be made with 100 Ω differential (50 Ω

single-ended) transmission lines so that the driver end of the

transmission lines is properly terminated.

CROSSPOINT ADJUST

The crossing level in the output electrical eye diagram can be

adjusted between 35% and 65% using the crosspoint adjust (CPA)

control input. This can be used to compensate for asymmetry in

the VCSEL response and optimizes the optical eye mask margin.

The CPA input is a voltage control input, and a plot of eye cross-

point vs. CPA control voltage is shown in Figure 15 and Figure 16

in the Typical Performance Characteristics section. The equivalent

circuit for the CPA pin is shown in Figure 36. To disable the

crosspoint adjust function and set the eye crossing to 50%, the

CPA pin should be tied to VCC.

100

Ω

VCC

CPA

Figure 36. Equivalent Circuit for CPA Pin

POWER CONSUMPTION

The power dissipated by the ADN2530 is given by

)

2

.

1

(

50

×

×

+

⎟

⎠

⎞

⎜

⎝

⎛

+

×

=

IBIAS

V

I

V

VCC

P

IBIAS

SUPPLY

MSET

where:

VCC is the power supply voltage.

IBIAS is the bias current generated by the ADN2530.

IMODP, and IMODN pins of the ADN2530 when IBIAS =

IMOD = 0 expressed in amps (see Table 1).

Considering VBSET/IBIAS = 50 as the conversion factor from

⎟

⎠

⎞

⎜

⎝

⎛

×

×

+

⎟

⎠

⎞

⎜

⎝

⎛

+

×

=

2

.

1

50

50

BSET

IBIAS

SUPPLY

MSET

V

V

I

V

VCC

P

To ensure long-term reliable operation, the junction tempera-

ture of the ADN2530 must not exceed 125°C, as specified in

Table 2. For improved heat dissipation, the module’s case can be

used as a heat sink, as shown in Figure 37.

TPAD

DIE

PACKAGE

THERMAL COMPOUND

MODULE CASE

PCB

VIAS

COPPER PLANE

THERMO-COUPLE

Figure 37. Typical Optical Module Structure