ICS84326AM 데이터 시트보기 (PDF) - Integrated Circuit Systems

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ICS84326AM

CRYSTAL-TO-3.3V LVPECL SERIAL ATTACHED SCSI CLOCK SYNTHESIZER/FANOUT BUFFER

Integrated Circuit Systems 

Integrated

Circuit

Systems, Inc.

PRELIMINARY

ICS84326

CRYSTAL-TO-3.3V LVPECL

SERIAL ATTACHED SCSI CLOCK SYNTHESIZER/FANOUT BUFFER

POWER CONSIDERATIONS

This section provides information on power dissipation and junction temperature for the ICS84326.

Equations and example calculations are also provided.

1. Power Dissipation.

The total power dissipation for the ICS84326 is the sum of the core power plus the power dissipated in the load(s).

The following is the power dissipation for VCC = 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 = VCC_MAX * IEE_MAX = 3.465V * 140mA = 485mW

• Power (outputs)MAX = 30.2mW/Loaded Output pair

If all outputs are loaded, the total power is 6 * 30.2mW = 181mW

Total Power_MAX (3.465V, with all outputs switching) = 485mW + 181mW = 666mW

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 HiPerClockSTM devices is 125°C.

The equation for Tj is as follows: Tj = θJA * Pd_total + TA

Tj = Junction Temperature

θJA = Junction-to-Ambient Thermal Resistance

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

TA = Ambient Temperature

In order to calculate junction temperature, the appropriate junction-to-ambient thermal resistance θJA must be used. Assuming a

moderate air flow of 200 linear feet per minute and a multi-layer board, the appropriate value is 43°C/W per Table 6 below.

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

70°C + 0.666W * 43°C/W = 98.6°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 (single layer or multi-layer).

TABLE 6. THERMAL RESISTANCE qJA FOR 24-PIN SOIC, FORCED CONVECTION

qJA by Velocity (Linear Feet per Minute)

Multi-Layer PCB, JEDEC Standard Test Boards

0

50°C/W

200

43°C/W

500

38°C/W

NOTE: Most modern PCB designs use multi-layered boards. The data in the second row pertains to most designs.

84326AM

www.icst.com/products/hiperclocks.html

11

REV. A MARCH 10, 2003

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