LTC1726IS8-2.5(RevB) Ver la hoja de datos (PDF) - Linear Technology

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LTC1726IS8-2.5
(Rev.:RevB)

Triple Supply Monitor and µP Supervisor with Adjustable Reset and Watchdog Timer

Linear Technology 

LTC1726

APPLICATIO S I FOR ATIO

Selecting the Reset and Watchdog

Time-Out Capacitors

The reset time-out period is adjustable in order to accom-

modate a variety of µP applications. The reset time-out

period, tRT, is adjusted by connecting a capacitor, CRT,

between the RT pin and ground. The value of this capacitor

is determined as follows:

CRT = tRT/3.30

with CRT in pF and tRT in µs (i.e., 1500pF ⇒ 4.95ms). The

capacitor should be a low leakage type. A ceramic capacitor

is recommended.

The watchdog period is also adjustable so that the watch-

dog time-out period can be optimized for software execu-

tion. The watchdog time-out period, tWT, is adjusted by

connecting a capacitor, CWT, between the WT pin and

ground. Once the optimum watchdog time-out period (tWT)

is determined, the value of the capacitor is calculated as

follows:

CWT = tWT/21.8

with CWT in pF and tWT in µs (i.e., 1500pF ⇒ 32.7ms). The

capacitor should be a low leakage type. A ceramic capacitor

is recommended.

TYPICAL APPLICATIO S

Disabling the Watchdog Timer

ADJUSTABLE

SUPPLY

LTC1726-5/2.5

1

3.3V

VCC3

5V/2.5V

R1*

2

3

VCC5/

VCC25

VCCA

R2*

4

GND

8

RT

7

WT

6

RST

5

WDI

CRT

SYSTEM

RESET

1726 TA03

*TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL

COMBINATION OF R1 AND R2 ≤ 66.5k

THE WATCHDOG TIMER CAN BE DISABLED BY CONNECTING

THE WDI AND WT PINS TO GROUND. THE PART WILL ACT

STRICTLY AS A TRIPLE SUPPLY MONITOR WITH AN

ADJUSTABLE RESET TIME-OUT PERIOD

Triple Supply Monitor (3.3V, 5V and Adjustable)

ADJUSTABLE SUPPLY

OR DC/DC FEEDBACK

DIVIDER

3.3V

5V

R1*

R2*

LTC1726-5

1

VCC3

2

VCC5

3

VCCA

4

GND

8

RT

7

WT

6

RST

5

WDI

CRT

CWT

SYSTEM RESET

WDI

1726 TA04

*TO PRESERVE THRESHOLD ACCURACY, SET PARALLEL

COMBINATION OF R1 AND R2 ≤ 66.5k

Dual Supply Monitor (3.3V and 5V, Defeat VCCA Input)

LTC1726-5

CRT

1

8

3.3V

VCC3

RT

2

7

5V

VCC5

WT

CWT

3

VCCA

6

RST

SYSTEM RESET

4

GND

5

WDI

WDI

1726 TA05

1726fb

9

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