COP8SCR9KMT7 datasheet(23/80 Pages) NSC

23 / 80 page

10.0 Functional Description (Continued)

In Case 1, V

CC rises from 0V and the on-chip RESET is

undefined until the supply is greater than approximately

1.0V. At this time the brownout circuit becomes active and

holds the device in RESET. As the supply passes a level of

about 1.8V, a delay of about 3 ms (t

d) is started and the Idle

Timer is preset to a value between 00F0 and 00FF (hex).

Once V

CC is greater than Vbor and td has expired, the Idle

Timer is allowed to count down (t

id).

Case 2 shows a subsequent dip in the supply voltage which

goes below the approximate 1.8V level. As V

CC drops below

bor, the internal RESET signal is asserted. When VCC rises

back above the 1.8V level, t

d is started. Since the power

supply rise time is longer for this case, t

d has expired before

CC rises above Vbor and tid starts immediately when VCC is

greater than V

bor.

Case 3 shows a dip in the supply where V

CC drops below

bor, but not below 1.8V. On-chip RESET is asserted when

CC goes below Vbor and tid starts as soon as the supply

goes back above V

bor.

If the Brownout Reset feature is enabled, the internal reset

will not be turned off until the Idle Timer underflows. The

internal reset will perform the same functions as external

reset. The device is guaranteed to operate at the specified

frequency down to the specified brownout voltage. After the

underflow, the logic is designed such that no additional

internal resets occur as long as V

CC remains above the

brownout voltage.

The device is relatively immune to short duration negative-

going V

CC transients (glitches). It is essential that good

filtering of V

CC be done to ensure that the brownout feature

works correctly. Power supply decoupling is vital even in

battery powered systems.

There are two optional brownout voltages. The part numbers

for the three versions of this device are:

COP8SBR9, V

bor = low voltage range

COP8SCR9, V

bor = high voltage range

COP8SDR9, BOR is disabled.

Refer to the device specifications for the actual V

bor volt-

ages.

High brownout voltage devices are guaranteed to operate at

10MHz down to the brownout voltage. Low brownout voltage

devices are guaranteed to operate at 3.33MHz down to the

brownout voltage. Devices are not guaranteed to operate

at 10MHz down to the low brownout voltage.

Under no circumstances should the RESET pin be allowed

to float. If the on-chip Brownout Reset feature is being used,

the RESET pin should be connected directly to V

CC. The

RESET input may also be connected to an external pull-up

resistor or to other external circuitry. Any rising edge on the

RESET pin while V

CC is below the specified operating range

may cause unpredictable results. The output of the brownout

reset detector will always preset the Idle Timer to a value

between 00F0 and 00FF (240 to 256 t

C). At this time, the

internal reset will be generated.

If the BOR feature is disabled, then no internal resets are

generated and the Idle Timer will power-up with an unknown

value. In this case, the external RESET must be used. When

BOR is disabled, this on-chip circuitry is disabled and draws

no DC current.

The contents of data registers and RAM are unknown fol-

lowing the on-chip reset.

10138913

FIGURE 10. Brownout Reset Operation

COP8SCR9KMT7 Datasheet(PDF) 23 Page - National Semiconductor (TI)

COP8SCR9KMT7 Datasheet(HTML) 23 Page - National Semiconductor (TI)

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

Datasheet Download

Link URL