ADN2526

Rev. A | Page 13 of 16

CROSSPOINT ADJUSTMENT

The optical eye cross point is adjustable between 35% and 65%

using the cross point adjust (CPA) control input. The equivalent

circuit for the CPA pin is shown in Figure 31. In a default CPA

setting, leave CPA unconnected (maintain pin-to-pin compatibil-

ity with the ADN2525). The internal bias circuit presents about

1.9 V at the CPA pin and the eye cross point is set to 50%. To set

the cross point at various points, apply an external voltage to the

CPA pin.

7kΩ

7kΩ

7kΩ

VCC

CPA

Figure 31. Equivalent Circuit for CPA Pin

POWER SEQUENCE

To ensure reliable operation, the recommended power-up

sequence is: the supply rail to ADN2526 first, then the BSET

pin, followed by the MSET pin, and, finally, the CPA pin.

To turn off the ADN2526, the operation is reversed: shut down

CPA first, then MSET, followed by BSET, and, last, the supply rail.

POWER CONSUMPTION

The power dissipated by the ADN2526 is given by

IBIAS

V

I

V

VCC

P

IBIAS

SUPPLY

MSET

×

+

⎟

⎠

⎞

⎜

⎝

⎛

+

×

=

13.5

where:

VCC is the power supply voltage.

IBIAS is the bias current sank by the ADN2526.

IBIAS

BSET

SUPPLY

MSET

V

V

I

V

VCC

P

×

+

⎟

⎠

⎞

⎜

⎝

⎛

+

×

=

10

5

.

13

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

ture of the ADN2526 must not exceed 125°C, as specified in

Table 2. For improved heat dissipation, the SFP+ module case

can work as a heat sink, as shown in Figure 32. A compact

optical module is a complex thermal environment, and

calculations of device junction temperature using the package

accurate results.

TPAD

DIE

PACKAGE

THERMAL COMPOUND

MODULE CASE

PCB

VIAS

COPPER PLANE

THERMOCOUPLE

Figure 32. Typical Optical Module Structure

The parameters in Table 6 can be used to estimate the IC

junction temperature.

Table 6. Definitions

Parameter

Description

Unit

Temperature at the top of the package

°C

Temperature at the package exposed paddle

°C

IC junction temperature

°C

P

Power dissipation

W

Thermal resistance from the IC junction to

the package top

°C/W

Thermal resistance from the IC junction to

the package exposed paddle

°C/W

at points inside the module, as shown in Figure 32. The thermo-

couples should be positioned to obtain an accurate measurement

of the package top and paddle temperatures. Using the model

shown in Figure 33, the junction temperature can be calculated by

(

)

TOP

J

PAD

J

TOP

J

PAD

PAD

J

TOP

TOP

J

PAD

J

T

T

P

−

−

−

−

−

−

+

×

+

×

+

×

×

θ

θ

θ

θ

θ

θ

where:

P is the power dissipated by the ADN2526.

P

Figure 33. Electrical Model for Thermal Calculations