TDA3MV Datasheet, PDF (180/256 Pages) Texas Instruments – TDA3x SoC for Advanced Driver Assistance Systems (ADAS) 15mm Package (ABF) Silicon Revision 2.0

TDA3MV, TDA3MA
TDA3LX, TDA3LA
SPRS964C – JUNE 2016 – REVISED JULY 2017
www.ti.com
The resistance Rs of a plane conductor
for a unit length and unit width is called
the surface resistivity (ohms per square).
L
t
W
1^r
Rs = =
σ×t t
l
R = Rs ×
w
SPRS91v_PCB_STATIC_01
Figure 8-4. Static IR Drop Budget for PCB Only
The system-level IR drop budget is made up of three portions: on-chip, package, and PCB board. Static IR
or dc analysis/design methodology consists of designing the PDN such that the voltage drop (under dc
operating conditions) across power and ground pads of the transistors of the application processor device
is within a specified value of the nominal voltage for proper functionality of the device.
A PCB system-level voltage drop budget for proper device functionality is typically 1.5% of nominal
voltage. For a 1.35-V supply, this would be ≤20 mV.
To accurately analyze PCB static IR drop, the actual geometry of the PDN must be modeled properly and
simulated to accurately characterize long distribution paths, copper weight impacts, electro-migration
violations of current-carrying vias, and "Swiss-cheese” effects via placement has on power rails. It is
recommended to perform the following analyses:
• Lumped resistance/IR drop analysis
• Distributed resistance/IR drop analysis
NOTE
The PMIC companion device supporting Processor has been designed with voltage sensing
feedback loop capabilities that enable a remote sense of the SMPS output voltage at the
point of use.
The NOTE above means the SMPS feedback signals and returns must be routed across PCB and
connected to the Device input power ball for which a particular SMPS is supplying power. This feedback
loop provides compensation for some of the voltage drop encountered across the PDN within limits. As
such, the effective resistance of the PDN within this loop should be determined in order to optimize
voltage compensation loop performance. The resistance of two PDN segments are of interest: one from
the power inductor/bulk power filtering capacitor node to the Processor’s input power and second is the
entire PDN route from SMPS output pin/ball to the Processor input power.
In the following sections each methodology is described in detail and an example has been provided of
analysis flow that can be used by the PCB designer to validate compliance to the requirements on their
PCB PDN design.
8.2.3.1 PDN Resistance and IR Drop
Lumped methodology consists of grouping all of the power pins on both the PMIC (voltage source) and
processor (current sink) devices. Then the PMIC source is set to an expected Use Case voltage level and
the processor load has its Use Case current sink value set as well. Now the lumped/effective resistance
for the power rail trace/plane routes can be determine based upon the actual layout’s power rail etch wide,
shape, length, via count and placement Figure 8-5 illustrates the pin-grouping/lumped concept.
The lumped methodology consists of importing the PCB layout database (from Cadence Allegro tool or
any other layout design tool) into the static IR drop modeling and simulation tool of preference for the PCB
designer. This is followed by applying the correct PCB stack-up information (thickness, material
properties) of the PCB dielectric and metallization layers. The material properties of dielectric consist of
permittivity (Dk) and loss tangent (Df).
180 Applications, Implementation, and Layout
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