Intel 1.70 GHz RH80532NC029256 Data Sheet

98 Datasheet

 

298517-006 

R1 Various 

1

Ω 

10% 1/16W 

To satisfy damping requirements, total series resistance in the filter (from V

CCT

 to the top plate of the 

capacitor) must be at least 0.35 

Ω.  This resistor can be in the form of a discrete component, or routing, 

or both.  For example, if the picked inductor has minimum DCR of 0.25 

Ω, then a routing resistance of 

at least 0.10 

Ω is required.  Be careful not to exceed the maximum resistance rule (2 Ω).  For example, if 

using discrete R1, the maximum DCR of the L should be less than 2.0 - 1.1 = 0.9 

Ω, which precludes 

using L2 and possibly L1. 

Other routing requirements include: 

•  The capacitor should be close to the PLL1 and PLL2 pins, with less than 0.1 Ω per route (These 

routes do not count towards the minimum damping resistance requirement). 

•  The PLL2 route should be parallel and next to the PLL1 route (minimize loop area). 
•  The inductor should be close to the capacitor; any routing resistance should be inserted between 

VCCT and the inductor. 

•  Any discrete resistor should be inserted between V

CCT

 and the inductor. 

•  A magnetically shielded inductor protects the circuit from picking up external flux noise.  This 

should provide better timing margins than with an unshielded inductor.   

•  A discrete or routed resistor is required because the LC filter by nature has an under-damped 

response, which can cause resonance at the LC pole.  Noise amplification at this band, although 
not in the PLL-sensitive spectrum, could cause a fatal headroom reduction for analog circuitry.  
The resistor serves to dampen the response. Systems with tight space constraints should consider a 
discrete resistor to provide the required damping resistance. Too large of a damping resistance can 
cause a large IR drop, which means less analog headroom and lower frequency. 

•  Ceramic capacitors have very high self-resonance frequencies, but they are not available in large 

capacitance values.  A high self-resonant frequency coupled with low ESL/ESR is crucial for 
sufficient rejection in the PLL and high frequency band.  The recommended tantalum capacitors 
have acceptably low ESR and ESL. 

•  The capacitor must be close to the PLL1 and PLL2 pins; otherwise the value of the low ESR 

tantalum capacitor is wasted.  Note the distance constraint should be translated from the 0.1-

Ω 

requirement.