PIC17C752-08SLASHCL datasheet(29/328 Pages) MICROCHIP

29 / 328 page

DS30289A-page 29

PIC17C7XX

5.1.5

BROWN-OUT RESET (BOR)

PIC17C7XX devices have on-chip Brown-out Reset cir-

cuitry. This circuitry places the device into a reset when

the device voltage falls below a trip point (BVDD). This

ensures that the device does not continue program

execution outside the valid operation range of the

device. Brown-out resets are typically used in AC line

applications or large battery applications where large

loads may be switched in (such as automotive).

The BODEN conﬁguration bit can disable (if clear/pro-

grammed) or enable (if set) the Brown-out Reset cir-

cuitry. If VDD falls below BVDD (Typically 4.0V,

parameter #D005 in electrical speciﬁcation section), for

greater than parameter #35, the brown-out situation will

reset the chip. A reset is not guaranteed to occur if VDD

falls below BVDD for less than parameter #35. The chip

will remain in Brown-out Reset until VDD rises above

BVDD. The Power-up Timer and Oscillator Start-up

Timer will then be invoked. This will keep the chip in

reset the greater of 96 ms and 1024 TOSC. If VDD drops

below BVDD while the Power-up Timer/Oscillator

Start-up Timer is running, the chip will go back into a

Brown-out

Reset. The

Power-up Timer/Oscillator

Start-up Timer will be initialized. Once VDD rises above

BVDD, the Power-up Timer/Oscillator Start-up Timer

will start their time delays. Figure 5-10 shows typical

Brown-out situations.

In some applications, the Brown-out reset trip point of

the device may not be at the desired level. Figure 5-8

and Figure 5-9 are two examples of external circuitry

that may be implemented. Each needs to be evaluated

to determine if they match the requirements of the

application.

Note:

Before using the on-chip brown-out for a

voltage

supervisory

function,

please

review the electrical speciﬁcations to

ensure that they meet your requirements.

FIGURE 5-8:

EXTERNAL BROWN-OUT

PROTECTION CIRCUIT 1

FIGURE 5-9:

EXTERNAL BROWN-OUT

PROTECTION CIRCUIT 2

VDD

33k

10k

Ω

40 k

Ω

VDD

MCLR

PIC17CXXX

This circuit will activate reset when VDD goes below

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

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

PIC17CXXX

VDD

FIGURE 5-10: BROWN-OUT SITUATIONS

Greater of 96 ms

BVDD Max.

BVDD Min.

VDD

Internal

Reset

BVDD Max.

BVDD Min.

VDD

Internal

Reset

< 96 ms

BVDD Max.

BVDD Min.

VDD

Internal

Reset

and 1024 Tosc

Greater of 96 ms

and 1024 Tosc

Greater of 96 ms

and 1024 Tosc

PIC17C752-08/CL датащи(PDF) 29 Page - Microchip Technology

PIC17C752-08/CL датащи(HTML) 29 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL