DRA790 Datasheet, PDF (369/436 Pages) Texas Instruments – Infotainment Applications Processor

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DRA790, DRA791
DRA793, DRA797
SPRS968A – AUGUST 2016 – REVISED FEBRUARY 2017
1. Use lowest inductance footprint and trace connection scheme possible for given PCB technology and
layout area in order to minimize Dcap loop inductance to power pin as much as possible (see Figure 7-
9).
2. Place Dcaps on “same-side” as component within their power plane outline to minimize “decoupling
loop inductance”. Target distance to power pin should be less than ~500mils depending upon PCB
layout characteristics (plane's layer assignment and solid nature). Use PI modeling CAD tool to verify
minimum inductance for top vs bottom-side placement.
3. Place Dcaps on “opposite-side” as component within their power plane outline if “same-side” is not
feasible or if distance to power pin is greater than ~500mils for top-side location. Use PI modeling CAD
tool to verify minimum inductance for top vs bottom-side placement.
4. Use minimum 10mil trace width for all voltage and gnd planes connections (i.e. Dcap pads, component
power pins, etc.).
5. Place all voltage and gnd plane vias “as close as possible” to point of use (i.e. Dcap pads, component
power pins, etc.).
6. Use a “Power/Gnd pad/pin to via” ratio of 1:1 whenever possible. Do not exceed 2:1 ratio for small
number of vias within restricted PCB areas (i.e. underneath BGA components).
Frequency analysis for the CORE power domain has yielded the vdd Impedance vs Frequency response
shown in Section 7.3.7.2, vdd Example Analysis. As the example shows the overall CORE PDN R_eff meets
the maximum recommended PDN resistance of 10mΩ.
7.2.5 System ESD Generic Guidelines
7.2.5.1 System ESD Generic PCB Guideline
Protection devices must be placed close to the ESD source which means close to the connector. This
allows the device to subtract the energy associated with an ESD strike before it reaches the internal
circuitry of the application board.
To help minimize the residual voltage pulse that will be built-up at the protection device due to its nonzero
turn-on impedance, it is mandatory to route the ESD device with minimum stub length so that the low-
resistive, low-inductive path from the signal to the ground is granted and not increasing the impedance
between signal and ground.
For ESD protection array being railed to a power supply when no decoupling capacitor is available in close
vicinity, consider using a decoupling capacitor (≥ 0.1 µF) tight to the VCC pin of the ESD protection. A
positive strike will be partially diverted to this capacitance resulting in a lower residual voltage pulse.
Ensure that there is sufficient metallization for the supply of signals at the interconnect side (VCC and
GND in Figure 7-10) from connector to external protection because the interconnect may see between 15-
A to 30-A current in a short period of time during the ESD event.
Copyright © 2016–2017, Texas Instruments Incorporated
Applications, Implementation, and Layout 369
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