8 Application and Implementation

Note

Information in the following applications sections is not part of the TI component specification,

and TI does not warrant its accuracy or completeness. TI’s customers are responsible for

determining suitability of components for their purposes, as well as validating and testing their design

implementation to confirm system functionality.

8.1 Application Information

The following sections describe in detail proper device implementation, depending on the final application

requirements.

8.1.1 CRST Delay

The TPS3430 features three options for setting the reset delay (tRST): connecting a capacitor to the CRST pin,

connecting a pull-up resistor to VDD, and leaving the CRST pin unconnected. Figure 8-1 shows a schematic

drawing of all three options. To determine which option is connected to the CRST pin, an internal state machine

controls the internal pulldown device and measures the pin voltage. This sequence of events takes 381 μs (tINIT)

to determine which timing option is used. Every time WDO is asserted, the state machine determines what is

connected to the pin.

VDD

CCRST

Cap

Control

375 nA

CRST

VDD

CRST

CRST

User Programmable

Capacitor to GND

10 NŸ 5HVLVWRU

to VDD

CRST

Unconnected

TPS3430

TPS3430

TPS3430

VDD

VDD

Cap

Control

375 nA

VDD

Cap

Control

375 nA

VDD

Figure 8-1. CRST Charging Circuit

8.1.1.1 Factory-Programmed Watchdog Reset Delay Timing

To use the factory-programmed timing options, the CRST pin must either be left unconnected or pulled up to

VDD through a 10-kΩ pull-up resistor. Using these options enables a high-precision, 15% accurate reset delay

timing, as shown in Table 8-1.

Table 8-1. Watchdog Reset Delay Time for Factory-Programmed Timing

CRST

WDO DELAY TIME (tRST)

UNIT

MIN

TYP

MAX

NC

170

200

230

ms

10 kΩ to VDD

8.5

10

11.5

ms

8.1.1.2 CRST Programmable Watchdog Reset Delay

The TPS3430 uses a CRST pin charging current (ICRST) of 375 nA. When using an external capacitor, the rising

WDO delay time can be set to any value between 700 µs (CCRST = 100 pF) and 3.2 seconds (CCRST = 1 µF).

TPS3430

SBVS366A – JULY 2018 – REVISED OCTOBER 2021

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