RSTn

TCAL

WAKE

DONE

TIMER

PGOOD

tC

t

TPL5000

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SNAS628B – JULY 2013 – REVISED DECEMBER 2014

Feature Description (continued)

Figure 6. Watchdog and Supervisor Feature

8.3.1.1 Calibration Pulse

The TPL5000 is based on a ultra-low power oscillator which has a relatively low frequency and low accuracy;

however, it shows very good cycle-to-cycle repeatability and very low temperature drift. In most of the

applications, the accuracy of the oscillator is enough, but if a more accurate measure of the delay period is

required, it is possible to measure the base period of the internal oscillator. A single pulse, which has the same

duration as the base period of the internal oscillator, is present at the TCAL pin of the TPL5000. This pulse starts

after a half period of the internal oscillator from either the falling edge of the RESET pulse, or the rising edge of

the WAKE pulse.

A microcontroller connected to the TPL5000 can routinely measure the width of the TCAL pulse using a counter

and an external crystal. Once the base period of the TPL5000 is measured, the actual time delay is calculated by

multiplying the measured period by a factor, N (see Table 1), dependent on the nominal selected time delay.

The resolution and the accuracy of the measurement depend on the external crystal. Since the frequency of the

internal oscillator of the TPL5000 is very stable, the measurement of the calibration pulse is suggested only when

a high gradient of ambient temperature is observed. The measurement of the TCAL pulse is useful in battery-

powered applications that implement a precise battery life counter in the microcontroller.

8.3.1.2 Overview of the Timing Signals: WAKE, RSTN, TCAL and DONE

Figure 7 shows the timing of WAKE, RSTn, and TCAL with respect to DONE. The frame, A, shows a typical

sequence after the PGOOD, low to high, transition. As soon as PGOOD is high, the internal oscillator is powered

ON. At the end of the delay period (tDP), a reset signal (RSTn), followed by a calibration pulse, TCAL, is sent out.

The calibration pulse starts after a half period of the internal oscillator from the falling edge of the reset, and lasts

one internal oscillator period.

The frame, B, shows a standard sequence. A "DONE" signal has been received in the previous delay period, so

at the end of the next delay period, a "WAKE", followed by a calibration pulse, is sent out. The WAKE signal

stays high for 2 internal oscillator periods. The calibration pulse starts after a half period of the internal oscillator

from the rising edge of the WAKE signal, and lasts one internal oscillator period. In this frame, the TPL5000

receives a "DONE" signal before the end of the delay period.

The frame, C, still shows a standard sequence, but in this case, the TPL5000 receives the DONE signal when

both WAKE and TCAL pulses are still high. As soon as the TPL5000 recognizes the DONE resets the counter

and puts WAKE and TCAL in the default condition (both signal low).

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