Application Brief

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Application Brief

Voltage Monitoring with Programmable ResetAssertion Timing Using the TPS3899

Logan Cable
This technical note expands on the ProgrammablePush-Button, Pulse Detector, and Pulse GeneratorSolutions (SBVA061) applications note and discusses
the sense delay programmable timing feature addedwith the TPS3899 voltage supervisor.
The sense delay is the delay time for which the sense
voltage needs to be under the voltage threshold inorder to assert a reset. On previous TI voltagesupervisors this delay was small and fixed, however,on the TPS3899, sense delay time can be
programmed from several hundred microseconds up
to several seconds.
There are many applications for which a sense delay
would be useful. One application of sense delay is
minimum pulse width detection which is useful forpush-button holding functionality, control systems,communications, timing measurement devices, andtiming fault detections. Another application ispreventing false resets on noisy voltages.
Push-Button with Holding Requirements
One application of minimum pulse width detection
using the TPS3899 is a push-button that needs to beheld for a duration of time in order to activate.
Voltage supervisors when used for push-button
programming typically have programmability on thedeassertion of a reset but not on the assertion of areset. The TPS3899 voltage supervisor has the CTR
pin for programming deassertion delay (reset delay)
and the additional CTS pin for programming assertion
delay (sense delay).
Using the TPS3899, a push-button can now be
programmed to have a user-customized holdrequirement before the signal can be asserted. The
typical topology of this circuit using the open-drain
active low variant of TPS3899 is shown in Figure 1-1(Note: If using the push-pull variants pull-up resistor
on the reset output will need to be removed).

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VDD

VDD
SENSE

RESET

TPS3899DL

Push-Button
Input

CTS

CTR
GND

Figure 1. Programmable Push-button Circuit
Using TPS3899
The RESET output will be inputted to the desired
device as a “button pressed” signal and will only beasserted if the push-button is held down for theminimum length of programmed time. The pushbutton is connected to the sense pin and ground.
When pressed, the push-button will tie the sense pin
to ground causing VSENSE to be lower than the input
threshold voltage. If the button is pressed for theduration of tSENSE, then the RESET output will assert.
After the button is released, the RESET output will
deassert after the duration of tRESET. See Figure 1-2
for the timing diagram of a button press.

PB

SENSE
VIT- + VHYS
VIT-tSENSEtRESETRESETFigure 2. Programmable Push-button Circuit
Timing Diagram

Voltage Monitoring with Programmable Reset Assertion Timing Using theTPS3899
Copyright © 2020 Texas Instruments Incorporated

1Application BrieftSENSE and tRESET are programmed through thecapacitor values placed on the CTS and CTR pins
respectively. Placing a larger capacitor on the pin
increases the delays and placing a smaller capacitor
decreases the delay.
See Table 1 for example options on the push-button
timing. By adjusting the capacitor on CTS, the holdrequirement for the push-button changes. For
example, placing a 10µF capacitor on CTS makes thehold requirement for the push-button 6.19s.

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Table 1-1. Programmable Delay on CTS and CTR

CTS = 0.1 µF,tSENSEtRESET(Sense Delay)(Reset Delay)

61.9ms61.9ms

619ms

619ms

6.19s

6.19s

CTR = 0.1µF
CTS = 1µF,
CTR = 1uF
CTS = 10 µF,
CTR = 10 µF (max.)

2

Voltage Monitoring with Programmable Reset Assertion Timing Using theTPS3899
Copyright © 2020 Texas Instruments Incorporated

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