IDT™ / ICS™ SAS/SATA CLOCK GENERATOR

13

ICS843241BG REV. A AUGUST 20, 2008

ICS843241

FEMTOCLOCKS™ SAS/SATA CLOCK GENERATOR

POWER CONSIDERATIONS

This section provides information on power dissipation and junction temperature for the ICS843241.

Equations and example calculations are also provided.

1. Power Dissipation.

The total power dissipation for the ICS843241 is the sum of the core power plus the power dissipated in the load(s).

The following is the power dissipation for V

CC

= 3.3V + 5% = 3.465V, which gives worst case results.

NOTE: Please refer to Section 3 for details on calculating power dissipated in the load.

• Power (core)

MAX

= V

CC_MAX

* I

EE_MAX

= 3.465V * 77mA = 266.8mW

• Power (outputs)

MAX

= 30mW/Loaded Output pair

Total Power

_MAX

(3.465V, with all outputs switching) = 266.8mW + 30mW = 296.8mW

2.

Junction Temperature.

Junction temperature, Tj, is the temperature at the junction of the bond wire and bond pad and directly affects the reliability of the

device. The maximum recommended junction temperature for HiPerClockS

TM devices is 125°C.

The equation for Tj is as follows: Tj =

θ

JA * Pd_total + TA

Tj = Junction Temperature

θ

JA = Junction-to-Ambient Thermal Resistance

Pd_total = Total Device Power Dissipation (example calculation is in section 1 above)

T

A = Ambient Temperature

In order to calculate junction temperature, the appropriate junction-to-ambient thermal resistance

θ

JA must be used. Assuming no air

flow and a multi-layer board, the appropriate value is 96°C/W per Table 7B below.

Therefore, Tj for an ambient temperature of 70°C with all outputs switching is:

70°C + 0.297W * 96°C/W = 97.6°C. This is well below the limit of 125°C.

This calculation is only an example. Tj will obviously vary depending on the number of loaded outputs, supply voltage, air flow,

and the type of board.

TABLE 7B.

θ

JA

VS

. AIR FLOW TABLE FOR 8 LEAD SOIC

TABLE 7A.

θ

JA

VS

. AIR FLOW TABLE FOR 16 LEAD TSSOP

θθθθθ

JA

by Velocity (Meters per Second)

0

1

2.5

Multi-Layer PCB, JEDEC Standard Test Boards

92.4°C/W

88.0°C/W

85.9°C/W

θθθθθ

JA

by Velocity (Linear Feet per Minute)

0

200

500

Multi-Layer PCB, JEDEC Standard Test Boards

96°C/W

87°C/W

82°C/W