ZHCSH72I September   2011  – December 2017

PRODUCTION DATA.

1. 特性
2. 应用
3. 说明
1.     Device Images
4. 修订历史记录
5. Device Comparison Table
6. Pin Configuration and Functions
7. Specifications
8. Parameter Measurement Information
9. Detailed Description
1. 9.1 Overview
2. 9.2 Functional Block Diagram
3. 9.3 Feature Description
1. 9.3.1 VCC and VCCO Power Supplies
2. 9.3.2 Clock Inputs
3. 9.3.3 Clock Outputs
10. 10Application and Implementation
11. 11Power Supply Recommendations
12. 12器件和文档支持
1. 12.1 文档支持
2. 12.2 社区资源
3. 12.3 商标
4. 12.4 静电放电警告
5. 12.5 Glossary
13. 13机械、封装和可订购信息

• RHS|48
• RHS|48

#### 11.2.1 Power Dissipation Example #1: Separate Vcc and Vcco Supplies with Unused Outputs

This example shows how to calculate IC power dissipation for a configuration with separate VCC and VCCO supplies and unused outputs. Because some outputs are not used, the ICCO_PECL value specified in Electrical Characteristics cannot be used directly, and output bank current (ICCO_BANK) should be calculated to accurately estimate the IC power dissipation.

• VCC = 3.3 V, VCCOA = 3.3 V, VCCOB = 2.5 V. Typical ICC and ICCO values.
• CLKin0/CLKin0* input is selected.
• Bank A is configured for LVPECL: 4 pairs used with RT = 50 Ω to VT = Vcco - 2 V (1 pair unused).
• Bank B is configured for LVDS: 3 pairs used with RL = 100 Ω differential (2 pairs unused).
• REFout is disabled.
• TA = 85 °C

Using the current and power calculations from the previous section, we can compute PTOTAL and PDEVICE.

• From Equation 5: ICC_TOTAL = 8.5 mA + 20 mA + 26 mA + 0 mA = 54.5 mA
• From Table 6: IOUT_LOAD (LVPECL) = (1.6 V - 0.5 V)/50 Ω + (0.75 V - 0.5 V)/50 Ω = 27 mA
• From Equation 6: ICCO_BANK_A = 33 mA + (4 * 27 mA) = 141 mA
• From Equation 7: PTOTAL = (3.3 V * 54.5 mA) + (3.3 V * 141 mA) + (2.5 V * 34 mA)] = 730 mW
• From Equation 8: PRT_PECL = ((2.4 V - 1.3 V)2/50 Ω) + ((1.55 V - 1.3 V)2/50 Ω) = 25.5 mW (per output pair)
• From Equation 9: PVTT_PECL = 0.5 V * [ ((2.4 V - 1.3 V) / 50 Ω) + ((1.55 V - 1.3 V) / 50 Ω) ] = 13.5 mW (per output pair)
• From Equation 10: PRT_HCSL = 0 mW (no HCSL outputs)
• From Equation 11: PDEVICE = 730 mW - (4 * (25.5 mW + 13.5 mW)) - 0 mW = 574 mW

In this example, the IC device will dissipate about 574 mW or 79% of the total power (730 mW), while the remaining 21% will be dissipated in the emitter resistors (102 mW for 4 pairs) and termination voltage (54 mW into Vcco - 2 V).

Based on the thermal resistance junction-to-case (RθJA) of 28.5 °C/W, the estimated die junction temperature would be about 16.4 °C above ambient, or 101.4 °C when TA = 85 °C.