LTC6995-1/LTC6995-2

16

699512f

For more information www.linear.com/6995

applicaTions inForMaTion

For shorter power on reset times (1ms to 73ms) the timer

startup delay becomes a significant part of the total POR

be modified from the values shown in Table 2. For a POR

10.9. For longer POR times (DIVCODE 2 through 7) the

startup time is insignificant. After power on, the delay fol-

lowingaresetconditionwillbeinthesamerangeasshown

For short POR times, a more precise estimation of the

startup time can be found from the following:

(

50

+80

Supply bounce resets the internal timer so the POR circuit

automatically debounces supply noise. POR timing starts

1.4 volts.

Long Timer One Shots and Delay Generators

The POR circuit of Figure 12 is also useful when the reset

inputsaredriven.Thiscreatesedgetriggeredtimingevents

that are active low and can either be re-triggered or can

stop after one programmed interval. The programmed

time interval can range from only 500µs to over 4 hours

with just resistor value changes.

The circuits in Figure 13 show how a POR or active low

intervalcanbere-startedtoprovideafullsystemresettime.

The Figure 14 circuit requires an indication from the

system being reset that it is ready before timing out. The

LTC6995-2 can accommodate an active high OK signal.

By forcing a reset condition at power on the LTC6995 can

be used to create a long time delayed rising edge triggered

by either a falling edge signal (LTC6995-1) or a rising edge

signal (LTC6995-2) as show in Figure 15.

Figure 13. System Resets On Command with Full POR Time Interval. Reset Pulse Is Debounced Automatically

LTC6995-1

ACTIVE HIGH RESET

RST

GND

SET

OUT

DIV

100k

R2

R1

0.1µF

POR

OUT

POL = 0

RST

TIMER

STOPPED

TIMER

STOPPED

RESET

POR

POR

LTC6995-2

ACTIVE LOW RESET

RST

GND

SET

OUT

DIV

100k

R2

R1

0.1µF

POR

OUT

POL = 0

RST

699512 F13

TIMER

STOPPED

TIMER

STOPPED

RESET

POR

POR