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8.1.2.2 Adjustable Capacitor Timing

Adjustable tWD timing is achievable by connecting a capacitor to the CWD pin. If this method is used, please

consult Equation 1 for calculating typical tWD values using ideal capacitors. Capacitor tolerances cause the

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 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

1.8V

Microcontroller

SET1

VDD

GND

WD-EN

SET0

WDI

GPIO

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 1.65 V

Watchdog Timeout Period

Typical timeout period of 1.6 s

RESET Delay

Typical reset delay of 200 ms

Startup Delay

Minimum startup delay of 700 ms

Minimum startup delay of 900 ms

Output Logic

Open-drain

Maximum Device Current Consumption

20 μA

250 nA typical, 3 μA 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 1.8 V. The minimum supply voltage is

10% lower than the nominal supply voltage, or 1.62 V. Setting a 1.65 V threshold makes sure that the device

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

TPS35

SNVSCF5A – JUNE 2023 – REVISED DECEMBER 2023

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