TLV841 datasheet(21/34 Pages) TI

21 / 34 page

9.2.2 Detailed Design Procedure

The TLV841SADL01 can monitor any voltage above 0.505 V using an external voltage divider. This device has

a negative going input threshold voltage of 0.505 V; however, the design needs to assert a reset when VDD

drops below 2.90 V. By using a resistor divider (R1 = 47.5 kΩ, R2 = 10 kΩ) the negative going threshold voltage

becomes 2.90 V. The device's positive going voltage threshold is VIT- + VHYS. The typical VHYS is 25 mV. This

in combination with the resistor divider makes the design's positive going threshold voltage equal to 3.05 V. If

VDD falls below 2.90 V, RESET will assert. If VDD rises above 3.05 V, RESET will deassert. See Figure 9-2 for a

timing diagram detailing the voltage levels and reset assertion/deassertion conditions.

RESET

tD-HL

SENSE

VIT- = 2.90V

3.3 V

VIT- + VHYS = 3.05V

Push-bu on

input

tD-HL

Figure 9-2. Design 1 Timing Diagram

This design will also enter a reset condition when the "push-button input" is asserted. The push-button is tied

to ground and when pressed will drop the SENSE voltage to 0 V, making the device assert a reset. As a good

analog practice, a 0.1 µF capacitor was also placed on VDD.

The desired reset timing conditions are sense propagation delay time (tP_HL of 25 μs (how long it takes to assert

RESET) and a reset delay time of 40 μs (how long it takes to deassert RESET). TLV841EVM Propagation Delay

Time Delay (tD_HL) and TLV841EVM RESET Time Delay (tD) are the results of the described application where

the measured propagation delay and reset delay time are shown respectively.

For the requirement of a maximum output current, an external pull-up resistor needs to be selected so that the

current through the external pull-up resistor exceeds no more than 150 µA. When the reset output is low, the

voltage drop across the external pull-up resistor is equal to VDD. Ohm’s law is used to calculate the minimum

resistor value. The resistor needs to be greater than 22 kΩ in order to pull less than 150 µA in the reset asserted

low condition. A resistor value of 30.1 kΩ was selected to accomplish this.

Note that this design does not account for tolerances.

www.ti.com

TLV841

SLVSFO5C – APRIL 2020 – REVISED JULY 2021

Submit Document Feedback

Product Folder Links: TLV841

TLV841 Datasheet(PDF) 21 Page - Texas Instruments