TPS3600D20, TPS3600D25, TPS3600D33, TPS3600D50

BATTERY BACKUP SUPERVISORS FOR LOW POWER PROCESSORS

SLVS336B − DECEMBER 2000 − REVISED JANUARY 2007

9

detailed description (continued)

manual switchover (MSWITCH)

MSWITCH

STATUS

VDD mode

GND

VDD mode

VDD mode

VDD

Switch to battery-backup mode

Battery-backup 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 not only important to supervise the supply voltage, it is also

important to ensure the 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 the DSP have to toggle the watchdog input

within typically 0.8 s to avoid a time-out from occurring. 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 will be 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 momentarily

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

consumption), leave WDI low for the majority of the watchdog time-out period, pulsing it 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 time-out 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 4. Watchdog Timing

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