DRA790 Datasheet, PDF (374/436 Pages) Texas Instruments – Infotainment Applications Processor

DRA790, DRA791
DRA793, DRA797
SPRS968A – AUGUST 2016 – REVISED FEBRUARY 2017
www.ti.com
• PMIC component DM and guidelines should be referenced for the following:
– Routing remote feedback sensing to optimize per each SMPS’s implementation
– Selecting power filtering capacitor values and PCB placement.
• Max Effective Resistance (Reff) budget can range from 4 – 100mΩ for key Device power rails not
including ground returns depending upon maximum load currents and maximum DC voltage drop
budget (as discussed above).
• Max Device supply input voltage difference budget of 5mV under max current loading shall be
maintained across all balls connected to a common power rail. This represents any voltage difference
that may exist between a remote sense point to any power input.
• Max PCB Loop Inductance (LL) budget between Device’s power inputs and local bulk and high
frequency decoupling capacitors including ground returns should range from 0.4 – 2.5nH depending
upon maximum transient load currents.
• Max PCB dynamic/AC peak-to-peak transient noise voltage budgets between PMIC and Device
including ground returns are as follows:
– +/-3% of nominal supply voltage for frequencies below the PMIC bandwidth (typ Fpmic ~
200kHz)
– +/-5% of nominal supply voltage for frequencies between Fpmic to Fpcb (typ 20 – 100MHz)
• Max PCB Impedance (Z) vs Frequency (F) budget between Device’s power inputs and PMIC’s output
power filter node including ground return is determined by applying the Frequency Domain Target
Impedance Method to determine the PCB’s maximum frequency of interest (Fpcb). Ideally a properly
designed and decoupled PDN will exhibit smoothly increasing Z vs. F curve. There are 2 general
regions of interest as can be seen in Figure 7-14.
– 1^st area is from DC (0Hz) up to Fpmic (typ a few 100 kHz) where a PMIC’s transient response
characteristic (i.e. Switching Freq, Compensation Loop BW) dominate. A PDN’s Z is typically very
low due to power filtering & bulk capacitor values when PDN has very low trace resistance (i.e.
good Reff performance). The goal is to maintain a smoothly increasing Z that is less than Zt1 over
this low frequency range. This will ensure that a max transient current event will not cause a
voltage drop more than the PMIC’s current step response can support (typ 3%).
– 2^nd area is from Fpmic up to Fpcb (typ 20-100MHz) where a PCB’s inherent characteristics (i.e.
parasitic capacitance, planar spreading inductances) dominate. A PDN’s Z will naturally increase
with frequency. At frequencies between Fpmic up to Fpcb, the goal is to maintain a smoothly
increasing Z to be less than Zt2. This will ensue that the high frequency content of a max transient
current event will not cause a voltage drop to be more than 5% of the min supply voltage.
374 Applications, Implementation, and Layout
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