UCD3138A64 datasheet(71/84 Pages) TI2

71 / 84 page

UCD3138128, UCD3138A64

www.ti.com

SLUSBZ8B – JUNE 2014 – REVISED FEBRUARY 2017

Product Folder Links: UCD3138128 UCD3138A64

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11 Power Supply Recommendations

•

Both 3.3 VD and 3.3 VA should have a local 4.7 µF capacitor placed as close as possible to the device pins

•

BP18 should have a 1 µF capacitor.

12 Layout

12.1 Device Grounding and Layout Guidelines

•

Single ground is recommended: SGND. A multilayer such as 4 layers board is recommended so that one

solid SGND is dedicated for return current path, referred to the layout example.

•

Apply multiple different capacitors for different frequency range on decoupling circuits. Each capacitor has

different ESL, Capacitance and ESR, and they have different frequency response.

•

Avoid long traces close to radiation components, and place them into an internal layer, and it is preferred to

have grounding shield.

•

Analog circuits and digital circuits should have separate return to ground; although with a single plane, still try

to avoid mixing analog current and digital current.

•

Do not use a ferrite bead or larger than 3-Ω resistor to connect between V33A and V33D.

•

Both 3.3VD and 3.3VA should have local decoupling capacitors close to the device power pins, add vias to

connect decoupling caps directly to SGND.

•

Avoid negative current/negative voltage on all pins, so Schottky clamping diodes may be needed to limit the

voltage; avoid more than 3.8 V or less than –0.3 V voltage spikes on all pins; add Schottky diodes on the pins

which could have voltage spikes during surge test; be aware that a Schottky has relatively higher leakage

current, which can affect the voltage sensing at high temperature.

•

If V33 slew rate is less than 2.5 V/ms the RESET pin should have a 2.21-k

Ω resistor between the reset pin

and V33D and a 2.2-µF capacitor from RESET to ground. For more details please refer to the UCD3138

Family - Practical Design Guideline. This capacitor must be located close to the device RESET pin.

•

RSVD (Pin 61) should be connected to BP18 through 1-kΩ resistor.

•

Configure unused GPIO pins to be inputs or connect them to the ground (DGND or SGND); when an external

pull-up resistor is used for GPIO, the pull-up resistor needs to be 1 kΩ or higher.

•

For more details please refer to the UCD3138 Family - Practical Design Guideline.

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