PIC17C44-08SLASHP datasheet(18/240 Pages) MICROCHIP

18 / 240 page

PIC17C4X

DS30412C-page 18

FIGURE 4-5:

OSCILLATOR START-UPTIME

FIGURE 4-6:

USING ON-CHIP POR

FIGURE 4-7:

BROWN-OUT PROTECTION

CIRCUIT 1

VDD

MCLR

OSC2

OST TIME_OUT

PWRT TIME_OUT

INTERNAL RESET

TOSC1

TOST

TPWRT

This ﬁgure shows in greater detail the timings involved

with the oscillator start-up timer. In this example the

low frequency crystal start-up time is larger than

power-up time (TPWRT).

Tosc1 = time for the crystal oscillator to react to an

oscillation level detectable by the Oscillator Start-up

Timer (ost).

TOST = 1024TOSC.

VDD

MCLR

PIC17CXX

VDD

This circuit will activate reset when VDD goes below

(Vz + 0.7V) where Vz = Zener voltage.

VDD

33k

10k

40 k

Ω

VDD

MCLR

PIC17CXX

FIGURE 4-8:

PIC17C42 EXTERNAL

POWER-ON RESET CIRCUIT

(FOR SLOW VDD

POWER-UP)

FIGURE 4-9:

BROWN-OUT PROTECTION

CIRCUIT 2

Note 1: An external Power-on Reset circuit is

required only if VDD power-up time is too

slow. The diode D helps discharge the

capacitor quickly when VDD powers

down.

2: R < 40 k

Ω is recommended to ensure

that the voltage drop across R does not

exceed 0.2V (max. leakage current spec.

on the MCLR/VPP pin is 5

µA). A larger

voltage drop will degrade VIH level on the

MCLR/VPP pin.

3: R1 = 100

Ω to 1 kΩ will limit any current

ﬂowing into MCLR from external capaci-

tor C in the event of MCLR/VPP pin

breakdown due to Electrostatic Dis-

charge (ESD) or (Electrical Overstress)

EOS.

VDD

MCLR

PIC17C42

VDD

This brown-out circuit is less expensive, albeit less

accurate. Transistor Q1 turns off when VDD is below a

certain level such that:

VDD •

R1 + R2

= 0.7V

40 k

Ω

VDD

MCLR

PIC17CXX

VDD

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