UCD3138ARMHT datasheet(68/87 Pages) TI1

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UCD3138A

SLUSC66C – MARCH 2015 – REVISED SEPTEMBER 2016

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Layout

Power Supply Recommendations

9.1

Power Supply Decoupling and Bulk Capacitors

•

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.

10 Layout

10.1 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, and in the end, add a termination circuit;

•

Analog circuit such as ADC sensing lines needs a return current path into the analog circuitry; digital

circuit such as GPIO, PMBus and PWM has a return current path into the digital circuitry; although with

a single plane, still try to avoid to mix analog current and digital current.

•

Don’t 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 4.7 µF decoupling capacitors close to the device power pins,

add visas to connect decoupling caps directly to SGND.

•

Avoid negative current/negative voltage on all pins, so Schottky diodes may need to clamp the voltage;

avoid the voltage spike on all pins more than 3.8 V or less than –0.3 V, 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.

•

RESET pin should have one at least 2.2 µF low ESL capacitor locally decoupled with SGND plane.

This capacitor must be located close to the device RESET pin. It is highly recommended to use a small

resistance (such as 220 Ω) to connect the RESET pin with 3.3 VD.

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