TPS3610U18, TPS3610T50

BATTERY BACKUP SUPERVISORS FOR RAM RETENTION

SLVS327B – DECEMBER 2000 – REVISED DECEMBER 2002

10

POST OFFICE BOX 655303

detailed description (continued)

manual switchover (MSWITCH)

Table 1. Switchover Modes

MSWITCH

STATUS

V

mode

GND

VDD mode

VDD mode

VDD

Switch to battery-backup mode

Batter back p mode

GND

Battery-backup mode

Battery-backup mode

VDD

Battery-backup mode

If the manual switchover feature is not used, MSWITCH must be connected to ground.

watchdog

In a microprocessor- or DSP-based system, it is important not only to supervise the supply voltage, but also to

ensure correct program execution. The task of a watchdog is to ensure that the program is not stalled in an

indefinite loop. The microprocessor, microcontroller or DSP has to toggle the watchdog input within typically

0.8 s to avoid the occurence of a time-out. Either a low-to-high or a high-to-low transition resets the internal

watchdog timer. If the input is unconnected, the watchdog is disabled and is retriggered internally.

saving current while using the watchdog

The watchdog input is internally driven low during the first 7/8 of the watchdog time-out period, then the input

momentarily pulses high, resetting the watchdog counter. For minimum watchdog input current (minimum

overall power consumption), WDI should be left low for the majority of the watchdog time-out period, and pulsed

low-high-low once within 7/8 of the watchdog time-out period to reset the watchdog timer. If instead WDI is

externally driven high for the majority of the timeout period, a current of, e.g., 5 V/40 k

Ω ≈ 125 µA, can flow into

WDI.

VIT

WDI

RESET

td

td

t(tout)

VOUT

td

Undefined

Figure 5. Watchdog Timing