UCD3138 datasheet(75/99 Pages) TI2

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Figure 12-4. Clamping Diodes for DPWM

12.1.4.5 EAP and EAN Pins

There are three front-end ADCs to sense the feedback signals in the UCD family. These ADCs are dual-ended

sensing input circuitry with good common mode noise rejection. Keep the distance between the two traces as

short as possible when the differential sensing method is used. A local filter close to the EAP and EAN pins is

required as shown in Figure 12-5. Because EAP and EAN are used for feedback loop, C must be selected from

the range of 100 pF to 1000 pF. R is preferred to use low resistance.

Figure 12-5. Local Filter on EAPx and EANx Pins

12.1.4.6 ADC Pins

Use low ESL and ESR ceramic capacitors on ADC pins to decouple with SGND. The capacitor value is selected

such that the cut-off frequency is at least one tenth the sampling frequency if there is no dynamic requirement.

This can help reduce noise coupled during signal transmission.

ADC input is a single-ended signal. If the sensing trace is long, move it away from radiation sources and add

ground shielding between the signal and radiation sources. If there exists a resistor between signal output and

ADC input, the resistor should be located close to the ADC pin. The resistance needs to be less than 1 kΩ.

For example, the sampling frequency is 10 kHz. The cut off frequency of LPF is 1 kHz. With a 1-kΩ equivalent

resistor, select a 0.15-μF capacitor.

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UCD3138

SLUSAP2J – MARCH 2012 – REVISED NOVEMBER 2021

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