V6155 datasheet(6/12 Pages) EMMICRO

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V6155

Pin Description

Pin Name

Function

Push-pull active low enable output

Open drain active low reset output.

must be pulled up to V

even if unused

Watchdog timer clear input signal

GND terminal

No connection

Voltage supply

EXT input for RC oscillator tuning

Voltage comparator input

Table 5

Functional Description

VIN Monitoring

The power-on reset and the power-down reset are

generated as a response to the external voltage level on

the V

IN input. The external voltage level is typically

obtained from a voltage divider as shown in Fig. 10. The

user uses an external voltage divider to set the desired

threshold level for power-on reset and power-down reset

in his system. The

internal

comparator reference

voltage is typically 1.275 V.

At power-up the reset output (RES) is held low (see Fig.

6). When V

IN becomes greater than VREF, the RES output

is held low for an additional power-on reset (POR) delay

which is equal to the watchdog time T

WD (typically 100

ms with an external resistor of 110 kW connected at R

pin). The POR delay prevents repeated toggling of RES

even if V

and the INPUT voltage drops out and

recovers. The POR delay allows the microprocessor’s

crystal oscillator time to start and stabilize and ensures

correct recognition of the reset signal to the

microprocessor.

The RES output goes active low generating the power-

down reset whenever V

IN falls below VREF. The sensitivity

or reaction time of the internal comparator to the voltage

level on V

IN is typically 5 ms.

Timer Programming

The on-chip oscillator needs an external resistor R

EXT

connected between the R pin and V

SS (see Fig. 10). It

allows the user to adjust the power-on reset (POR)

delay, watchdog time T

WD and with this also the closed

and open time windows as well as the watchdog reset

pulse width (T

WD/40).

With R

EXT = 110 kW, the typical values are:

- Power-on reset delay: T

POR is 100 ms

- Watchdog time:

WD is 100 ms

- Closed window:

CW is

80 ms

- Open window:

OW is

40 ms

- Watchdog reset:

WDR is 2.5 ms

Note the current consumption increases as the fre-

quency increases.

Watchdog Timeout Period Description

The watchdog timeout period is divided into two parts, a

“closed” window and an “open” window (see Fig. 5) and

is defined by two parameters, T

WD and the Open Window

Percentage (OWP).

The closed window starts just after the watchdog timer

resets and is defined by T

CW = TWD − OWP(TWD).

The open window starts after the closed time window

finishes and lasts till T

WD + OWP(TWD). The open window

time is defined by T

OW = 2 x OWP(TWD).

For example if T

WD = 100 ms (actual value) and OWP =

± 20% this means the closed window lasts during first

the 80 ms (T

CW = 80 ms = 100 ms − 0.2 (100 ms)) and

the open window the next 40 ms (T

OW = 2 x 0.2 (100 ms)

= 40 ms). The watchdog can be serviced between 80

ms and 120 ms after the timer reset. However as the

time base is

± 10% accurate, software must use the

following calculation for servicing signal TCL during the

open window:

Related to curves (Fig. 11 to Fig. 21), especially Fig. 20

and Fig. 21, the relation between T

WD and REXT could

easely be defined. Let us take an example describing

the variations due to production and temperature:

1. Choice, T

WD = 26 ms.

2. Related to Fig. 21, the coefficient (T

WD to REXT) is 1.025

where R

EXT is in kW and TWD in ms.

3. R

EXT (typ.) = 26 x 1.025 = 26.7 kW.

26 ms at +25

°C

a)(26 - 10% = 23.4 ms) (26 + 10% = 28.6 ms)a)

b)(23.4 - 5% = 22.2 ms)

(28.6 + 5% = 30.0 ms)b)

min.: (30.0 - 20% = 24.0 ms) max.: (22.2 + 20% = 26.7 ms)

Typical TCL period of

(24.0 + 26.7) / 2 = 25.4 ms

The ratio between T

WD = 26 ms and the (TCL period)

= 25.4 ms is 0.975.

Then the relation over the production and the full

temperature range is, TCL period = 0.975 x T

or TCL period =

, as typical value.

a) While PRODUCTION value unknown for the custo-

mer when R

EXT ¹ 110 kW.

b) While operating TEMPERATURE range

-40 °C ≤ TA ≤ +85 °C.

5. If you fixed a TCL period = 26 ms

Þ REXT =

= 27.3 kW

If during your production the T

time can be

measured at T

A = +25 °C and the mC can adjust the

TCL period, then the TCL period range will be much

larger for the full operating temperature.

RES

TCL

0.975 x R

EXT

1.025

26 x 1.025

0.975

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