SPRS968F August 2016 – November 2019 DRA790 , DRA791 , DRA793 , DRA797
PRODUCTION DATA.
Refer to the PDF data sheet for device specific package drawings
Maximum acceptable PCB resistance (Reff) between the PMIC and Processor input power balls should not exceed 10mΩ.
Maximum decoupling capacitance loop inductance (LL) between Processor input power balls and decoupling capacitances should not exceed 2.0nH (ESL NOT included)
Impedance target for key frequency of interest between Processor input power balls and PMIC’s SMPS output power balls should not exceed 57mΩ at 20MHz.
Parameter | Recommendation | Example PCB |
---|---|---|
OPP | OPP_NOM | |
Clocking Rate | 266 MHz | |
Voltage Level | 1 V | 1 V |
Max Current Draw | 1 A | 1 A |
Max Effective Resistance: Power Inductor Segment Total Reff | 10mΩ | 9.7 mΩ |
Max Loop Inductance | 2.0nH | 0.97 –1.75nH |
Impedance Target | 57mΩ F<20Mhz | 57mΩ F<20Mhz |
Figure 7-15 show a PCB layout example and the resulting PI analysis results.
NOTE
PCB Etch Resistance Breakdown, PDN Effective Resistance, and vdd routings are UNDER DEVELOPMENT!
IR Drop: vdd (PCB Rev Oct25, CAD sPSI v13.1.1)
Dynamic analysis of this PCB design for the CORE power domain determined the vdd decoupling capacitor loop inductance and impedance vs frequency analysis shown below. As you can see, the loop inductance values ranged from 0.97 –1.75nH and were less than maximum 2.0nH recommended.
NOTE
Comparing loop inductances for capacitors at different distances from the SoC’s input power balls shows an 18% reduction for caps placed closer. This was derived by averaging the inductances for the 3 caps with distances over 800mils (Avg LL = 1.33nH) vs the 3 caps with distances less than 600mils (Avg LL = 1.096nH).
Cap Ref Des | Model Port # | Loop Inductacne [nH] | Footprint Types | PCB Side | Distance to Ball-Field [mils] | Value [μF] | Size |
---|---|---|---|---|---|---|---|
C487 | 10 | 0.97 | 4vWSE | Top | 521 | 4.7 | 0805 |
C393 | 6 | 1.11 | 4vWSE | Bottom | 358 | 1.0 | 0603 |
C394 | 7 | 1.12 | 4vWSE | Bottom | 357 | 0.47 | 0603 |
C456 | 9 | 1.13 | 4vWSE | Bottom | 403 | 2.2 | 0603 |
C386 | 3 | 1.16 | 2vWSE | Bottom | 40 | 0.1 | 0402 |
C395 | 8 | 1.18 | 4vWSE | Bottom | 460 | 0.22 | 0603 |
C363 | 1 | 1.46 | 2vWSE | Bottom | 40 | 0.1 | 0402 |
C390 | 5 | 1.48 | 2vWSE | Bottom | 40 | 0.1 | 0402 |
C364 | 2 | 1.74 | 2vWSE | Bottom | 40 | 0.1 | 0402 |
C498 | 11 | 1.74 | 2vWSE | Bottom | 40 | 0.1 | 0402 |
C388 | 4 | 1.75 | 2vWSE | Bottom | 40 | 0.1 | 0402 |
Loop Inductance range: 0.97 –1.75nH
Figure 7-18 shows vdd Impedance vs Frequency characteristics.