actual device timing to vary such that the minimum of tWD can decrease and the maximum of tWD can increase

by the capacitor tolerance. For the most accurate timing, use ceramic capacitors with COG dielectric material.

8.2 Typical Applications

8.2.1 Design 1: Monitoring a Microcontroller Supply Voltage and Watchdog Timer

The TPS35-Q1 features high-accuracy (1.2% maximum) voltage supervising along with on-the-fly adjustable

watchdog timing to monitor critical processing elements in systems.

VDD

GND

TPS35-Q1

1.8V

Microcontroller

SET1

VDD

MR

GND

WD-EN

SET0

WDI

GPIO

GPIO

GPIO

Copyright © 2023, Texas Instruments Incorporated

RESET

RESET

Figure 8-1. Microcontroller Supply and Watchdog Monitoring Circuit

8.2.1.1 Design Requirements

Table 8-2. Design Parameters

PARAMETER

DESIRED REQUIREMENT

DESIGN RESULT

Threshold Voltage

Typical threshold voltage of 1.65V

Typical threshold voltage of 1.65V

Watchdog Timeout Period

Typical timeout period of 1.6s

Typical timeout period of 1.6s

RESET Delay

Typical reset delay of 200ms

Typical reset delay of 200ms

Startup Delay

Minimum startup delay of 700ms

Minimum startup delay of 900ms

Output Logic

Open-drain

Open-drain

Maximum Device Current Consumption

20μA

250nA typical, 3μA maximum

8.2.1.2 Detailed Design Procedure

8.2.1.2.1 Setting the Voltage Threshold

The negative-going threshold voltage, VIT-, is set by the device variant. Equation 4 shows how to calculate the

"Threshold Voltage" section of the orderable part number.

OPN "Threshold Voltage" number = (VIT- - 1) / 0.05

(4)

In this example, the nominal supply voltage for the microcontroller is 1.8V. The minimum supply voltage is 10%

lower than the nominal supply voltage, or 1.62V. Setting a 1.65V threshold makes sure that the device resets just

before the supply voltage reaches the minimum allowed. Thus a 1.65V threshold is chosen and, using Equation

4, the part number is reduced to TPS35xx13xxxxxxxQ1. Since the hysteresis is 5% typical, the positive-going

threshold voltage, VIT+, is 1.73V.

TPS35-Q1

SLVSGE8B – NOVEMBER 2022 – REVISED AUGUST 2024

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