8.3.1 WAKE

The WAKE pulse is sent out from the TPL5010-Q1 when the programmed time interval starts (except at the beginning of the first cycle or if in the previous interval the DONE has not been received).

This signal is normally low.

8.3.2 DONE

The DONE pin is driven by a µC to signal successful processing of the WAKE signal. The TPL5010-Q1 recognizes a valid DONE signal as a low to high transition; if two or more DONE signals are received within the time interval, only the first DONE signal is processed.

The DONE signal resets the counter of the watchdog only. If the DONE signal is received when the WAKE is still high, the WAKE will go low as soon as the DONE is recognized.

8.3.3 RSTn

To implement the reset interface between the TPL5010-Q1 and the µC a pull-up resistance is required. 100 kΩ is recommended, to minimize current.

During the POR and the reading of the REXT the RSTn signal is LOW.

RSTn is asserted (LOW) for either one of the following conditions:

• 1. If the DELAY/M_RST pin is high for at least two consecutive cycles of the internal oscillator (approximately 20 ms).
• 2. At the beginning of a new time interval if DONE is not received at least 20 ms before the next WAKE rising edge (see Figure 8).

8.4.1 Startup

During startup, after POR, the TPL5010-Q1 executes a one-time measurement of the resistance attached to the DELAY/M_RST pin in order to determine the desired time interval for WAKE. This measurement interval is t_{R_EXT}. During this measurement a constant current is temporarily flowing into R_EXT.

Figure 9. Startup

8.4.2 Normal Operating Mode

During normal operating mode, the TPL5010-Q1 asserts periodic WAKE pulses in response to valid DONE pulses from the µC. If either a manual reset is applied (logic HIGH on DELAY/M_RST pin) or the µC does not issue a DONE pulse within the required time, the TPL5010-Q1 asserts the RSTn signal to the µC and restarts its internal counters. See Figure 8 and Figure 10 .

8.5.1 Configuring the WAKE Interval with the DELAY/M_RST Pin

The time interval between 2 adjacent WAKE pulses (rising edges) is selectable through an external resistance (R_EXT) between the DELAY/M_RST pin and ground. The value of the resistance R_EXT is converted one time after POR. The allowable range of R_EXT is 500 Ω to 170 kΩ. At least a 1% precision resistance is recommended. See Timer Interval Selection Using External Resistance for how to set the WAKE pulse interval using R_EXT.

The time between 2 adjacent RESET signals (falling edges) or between a RESET (falling edge) and a WAKE (rising edge) is given by the sum of the programmed time interval and the t_RSTn (reset pulse width).

8.5.2 Manual Reset

If VDD is connected to the DELAY/M_RST pin, the TPL5010-Q1 recognizes this as a manual reset condition. In this case the time interval is not set. If the manual reset is asserted during the POR or during the reading procedure, the reading procedure is aborted and is re-started as soon as the manual reset switch is released. A pulse on the DELAY/M_RST pin is recognized as a valid manual reset only if it lasts at least 20 ms (observation time is 30 ms).

A valid manual reset resets all the counters inside the TPL5010-Q1. The counters restart only when the high digital voltage at DELAY/M_RST is removed and the next t_RSTn is elapsed.

Figure 10. Manual Reset

8.5.2.2 Circuitry

The manual reset may be implemented using a switch (momentary mechanical action). The TPL5010-Q1 offers 2 possible approaches according to the power consumption constraints of the application.

Figure 11. Manual Reset with SPST Switch

For use cases that do not require the lowest power consumption, using a single pole single throw switch may offer a lower cost solution. The DELAY/M_RST pin may be directly connected to VDD with R_EXT in the circuit. The current drawn from the supply voltage during the reset is given by VDD/R_EXT.

Figure 12. Manual Reset with SPDT Switch

The reset function may also be asserted by switching DELAY/M_RST from R_EXT to VDD using a single pole double throw switch, which will provide a lower power solution for the manual reset, because no current flows.

8.5.3 Timer Interval Selection Using External Resistance

In order to set the time interval, the external resistance R_EXT is selected according the following formula:

Equation 1.

where

• T is the desired time interval in seconds
• R_EXT is the resistance value to use in Ω
• a, b, c are coefficients depending on the range of the time interval

EXAMPLE

Required time interval: 8 s

The coefficient set to be selected is the number 2. The formula becomes:

Equation 2.

The resistance value is 10.18 kΩ.

Table 3 and Table 4 contain example values of t_IP and their corresponding value of R_EXT.

8.5.4 Quantization Error

The TPL5010-Q1 can generate 1650 discrete timer intervals in the range of 100 ms to 7200 s. The first 9 intervals are multiples of 100 ms. The remaining 1641 intervals cover the range between 1 s to 7200 s. Because they are discrete intervals, there is a quantization error associated with each value.

The quantization error can be evaluated according to the following formula:

Equation 3.

Where:

Equation 4.

Equation 5.

where

• R_EXT is the resistance calculated with Equation 1
• a, b, c are the coefficients of the equation listed in Table 2

8.5.5 Error Due to Real External Resistance

R_EXT is a theoretical value and may not be available in standard commercial resistor values. It is possible to closely approach the theoretical R_EXT using two or more standard values in parallel. However, standard values are characterized by a certain tolerance. This tolerance will affect the accuracy of the time interval.

The accuracy can be evaluated using the following procedure:

1. Evaluate the min and max values of R_EXT (R_{EXT_MIN}, R_{EXT_MAX} with Equation 1 using the selected commercial resistance values and their tolerances.
2. Evaluate the time intervals (T_{ADC_MIN}[R_{EXT_MIN}], T_{ADC_MAX}[R_{EXT_MAX}]) with Equation 4.
3. Find the errors using Equation 3 with T_{ADC_MIN}, T_{ADC_MAX}.

The example below illustrates the procedure.

• Desired time interval , T_desired = 600 s
• Required R_EXT, from Equation 1, R_EXT= 57.44 kΩ

From Table 4, R_EXT can be built with a parallel combination of two commercial values with 1% tolerance: R1=107 kΩ, R2=124 kΩ. The uncertainty of the equivalent parallel resistance can be found using Equation 6.

Equation 6.

Where uRn (n=1,2) represent the uncertainty of a resistance,

Equation 7.

The uncertainty of the parallel resistance is 0.82%, meaning the value of R_EXT may range between R_{EXT_MIN} = 56.96 kΩ and R_{EXT_MAX} = 57.90 kΩ.

Using these value of R_EXT, the digitized timer intervals calculated with Equation 4 are respectively T_{ADC_MIN} = 586.85 s and T_{ADC_MAX} = 611.3 s, giving an error range of –1.88% / +2.19%. The asymmetry of the error range is due to the quadratic transfer function of the resistance digitizer.