PS37044AJOFDDFR datasheet(21/34 Pages) TI

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9.1.2 Adjustable Voltage Thresholds

The TPS3704x maximum accuracy (1%) allows for adjustable voltage thresholds using external resistors without

adding major inaccuracies to the device. In case that the desired monitored voltage is not available, external

resistor dividers can be used to set the desired voltage thresholds. Figure 9-2 illustrates an example of how to

adjust the voltage threshold with external resistor dividers. The resistors can be calculated depending on the

desired voltage threshold and device part number. TI recommends using an adjustable voltage threshold device

variant because of the bypass mode of internal resistor ladder.

For example, consider a 2.0 V rail being monitored (VMON) using the TPS3704 0.8 V adjustable variant. Using

Equation 2, R1 = 15 kΩ given that R2 = 10 kΩ, VMON = 2 V, and VSENSE1 = 0.8 V. This device is typically meant

to monitor a 0.8 V rail with ±4% voltage thresholds. This means that the device undervoltage threshold (VIT-(UV))

and overvoltage threshold (VIT+(OV)) is 0.768 V and 0.832 V respectively. Using Equation 2, VMON = 1.92 V

when VSENSE1 = VIT-(UV). This can be denoted as VMON-, the monitored undervoltage threshold where the device

will assert a reset signal. Using Equation 2 again, the monitored overvoltage threshold (VMON+) = 2.08 V when

VSENSE1 = VIT+(OV). If a wider tolerance or UV only threshold is desired, use a device variant shown on

Table 12-2 to determine what device part number matches your application.

VSENSE1 = VMON × (R2 / (R1 + R2))

(2)

There are inaccuracies that must be taken into consideration while adjusting voltage thresholds. Aside from the

tolerance of the resistor divider, there is an internal resistance of the SENSE1 pin that may affect the accuracy

of the resistor divider. Although expected to be very high impedance, users are recommended to calculate the

values for design specifications. The internal sense resistance RSENSE1 can be calculated by the sense voltage

VSENSE1 divided by the sense current ISENSE1 as shown in Equation 4. VSENSE1 can be calculated using

Equation 2 depending on the resistor divider and monitored voltage. ISENSE1 can be calculated using Equation 3.

ISENSE1 = [(VMON – VSENSE1) / R1] – (VSENSE1 / R2)

(3)

RSENSE1 = VSENSE1 / ISENSE1

(4)

TPS37041

SENSE1

RESET1

VDD

10 k

MON

SENSE1

GND

Figure 9-2. Adjustable Voltage Threshold with External Resistor Dividers

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TPS3704

SNVSBZ2B – MARCH 2021 – REVISED DECEMBER 2021

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