PS37044AJOFDDFR datasheet(18/34 Pages) TI

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8.3.2 SENSEx Input

The SENSEx input can monitor supply rails from 0 V to 5.55 V, regardless of the device supply voltage used.

The SENSEx pins are used to monitor critical voltage rails or push-button inputs. If the voltage on this pin drops

below VIT-(UV) or goes above VIT+(OV), then RESETx/RESETx is asserted. When the voltage on the SENSEx pin

rises above the positive threshold voltage VIT-(UV) + VHYS or goes below the negative threshold voltage VIT+(OV) -

VHYS,

RESETx/RESETx deasserts after the set RESETx/RESETx delay time. The internal comparators have built-in

hysteresis to ensure well-defined RESETx/RESETx assertions and deassertions even when there are small

changes on the voltage rail being monitored.

The TPS3704x combines comparators with a precision reference voltage and a trimmed resistor divider. This

configuration optimizes device accuracy because all resistor tolerances are accounted for in the accuracy and

performance specifications. The TPS3704x device is relatively immune to short transients on the SENSEx pin.

Although not required in most cases, for noisy applications, good analog design practice is to place a 10-nF

to 100-nF bypass capacitor at the SENSEx inputs to reduce sensitivity to transient voltages on the monitored

signals.

8.3.2.1 Immunity to SENSEx Pins Voltage Transients

The TPS3704x is immune to short voltage transient spikes on the input SENSEx pins. Sensitivity to transients

depends on both transient duration and overdrive (amplitude) of the transient.

Overdrive is defined by how much the VSENSEx exceeds the specified threshold, and is important to know

because the smaller the overdrive, the slower the response of the (RESETx/RESETx) outputs. Threshold

overdrive is calculated as a percent of the threshold in question, as shown in Equation 1:

Overdrive % = | (VSENSEx - (VIT-(UV) or VIT+(OV))) / VIT (Nominal) × 100% |

(1)

where:

• VSENSEx is the voltage at the SENSEx pin

• VIT (Nominal) is the nominal threshold voltage

• VIT-(UV) and VIT+(OV) represent the actual undervoltage or overvoltage tripping voltage

8.3.2.1.1 SENSEx Hysteresis

Overvoltage and undervoltage comparators include built-in hysteresis that provides noise immunity and ensures

stable operation. For example, if the voltage on the SENSEx pin falls below VIT-(UV) or above VIT+(OV), then

RESETx/RESETx is asserted. When the voltage on the SENSEx pin is between the positive and negative

threshold voltages, RESETx/RESETx deasserts after the set RESETx/RESETx delay time. Figure 8-5 shows the

relation between VIT-(UV),VIT+(OV) and the hysteresis voltage (VHYS).

VSENSEx

VIT-(UV) + VHYS

VIT-(UV)

VRESETx

VOL

VIT+(OV) - VHYS

VIT+(OV)

Window

(VIT)

Figure 8-5. SENSEx Pin Hysteresis

TPS3704

SNVSBZ2B – MARCH 2021 – REVISED DECEMBER 2021

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