7.3.4 Dynamic PDN Analysis
Three power net parameters derived from a PCB’s PDN dynamic analysis are the Loop Inductance (LL), Impedance (Z) and PCB Frequency of Interest (Fpcb).
- LL values shown are the recommended max PCB trace inductance between a decoupling capacitor’s power supply and ground reference terminals when viewed from the decoupling capacitor with a "theoretical shorted” applied across the Processor’s supply inputs to ground reference.
- Z values shown are the recommended max PCB trace impedances allowed between Fpmic up to Fpcb frequency range that limits transient noise drops to no more than 5% of min supply voltage during max transient current events.
- Fpcb (Frequency of Interest) is defined to be a power rail’s max frequency after which adding a reasonable number of decoupling capacitors no longer significantly reduces the power rail impedance below the desired impedance target (Zt2). This is due to the dominance of the PCB’s parasitic planar spreading and internal package inductances.
Table 7-3 Recommended PDN and Decoupling Characteristics (1)(2)(3)(4)(5)
PDN Analysis: |
Static |
Dynamic |
Number of Recommended Decoupling Capacitors per Supply |
Supply |
Max Reff(7)
[mΩ] |
Dec. Cap.
Max LL(8)(6)
[nH] |
Max Impedance
[mΩ] |
Frequency range
of Interest
[MHz] |
100 nF(6) |
220 nF |
470 nF |
1μF |
2.2 μF |
4.7 μF |
10 μF |
22 μF |
vdd_dspeve |
33 |
2.5 |
54 |
≤20 |
6 |
1 |
1 |
1 |
1 |
1 |
|
1 |
vdd |
83 |
2 |
87 |
≤50 |
6 |
1 |
1 |
1 |
1 |
1 |
|
|
vdds_ddr1, vdds_ddr2, vdds_ddr3 |
33 |
2.5 |
200 |
≤100 |
8 |
4 |
|
2 |
|
2 |
|
1 |
cap_vddram_core1 |
N/A |
6 |
N/A |
N/A |
|
|
|
1 |
|
|
|
|
cap_vddram_core2 |
N/A |
6 |
N/A |
N/A |
|
|
|
1 |
|
|
|
|
cap_vddram_dspeve |
N/A |
6 |
N/A |
N/A |
|
|
|
1 |
|
|
|
|
- For more information on peak-to-peak noise values, see the Recommended Operating Conditions table of the Electrical Characteristics chapter.
- ESL must be as low as possible and must not exceed 0.5 nH.
- The PDN (Power Delivery Network) impedance characteristics are defined versus the device activity (that runs at different frequency) based on the Recommended Operating Conditions table of the Electrical Characteristics chapter.
- The static drop requirement drives the maximum acceptable PCB resistance between the PMIC or the external SMPS and the processor power balls.
- Assuming that the external SMPS (power IC) feedback sense is taken close to processor power balls.
- High-frequency (30 to 70MHz) PCB decoupling capacitors
- Maximum Total Reff from PMIC output to remote sensing feedback point located as close to the Device's point of load as possible.
- Maximum Loop Inductance for decoupling capacitor.