ncv8508b ON Semiconductor, ncv8508b Datasheet - Page 9

• Manufacturer Part Number: ncv8508b
• Description: Ncv8508b 5.0 V, 250 Ma Ldo With Watchdog And Reset
• Manufacturer: ON Semiconductor

Functional Description
low current consumption mode whenever it is not
performing a main routine. The Wakeup signal is generated
continuously and is used to interrupt a microcontroller that
is in sleep mode. The nominal output is a 5.0 V square wave
(voltage generated from V
a frequency that is determined by a timing resistor, R
Wakeup output, it must issue a Watchdog pulse and check its
inputs to decide if it should resume normal operations or
remain in the sleep mode.
Wakeup to go low within 2.0 ms (typ) and remain low until
the next Wakeup cycle (see Figure 17). Other Watchdog
pulses received within the same cycle are ignored (Figure 3).
voltage is in regulation. During operation, if the output
voltage shifts below the regulation limits, the RESET
toggles low and remains low until proper output voltage
regulation is restored. After the RESET delay, RESET
returns high.
Watchdog signal (WDI) from the microprocessor. The
absence of a falling edge on the Watchdog input during one
Wakeup cycle will cause a RESET pulse to occur at the end
of the Wakeup cycle. (see Figure 4).
regardless of the cause of the RESET. After the RESET
returns high, the Wakeup cycle begins again (see Figure 4).
RESET high to Wakeup delay time are all set by one external
resistor R
the tolerance of the NCV8508B must be taken into account
To reduce the drain on the battery, a system can go into a
When the microprocessor receives a rising edge from the
The first falling edge of the Watchdog signal causes the
During power up, RESET is held low until the output
The Watchdog circuitry continuously monitors the input
The Wakeup output is pulled low during a RESET
The RESET Delay Time, Wakeup signal frequency and
Wakeup Period = (4.17 × 10
RESET Delay Time = (5.21 × 10
RESET HIGH to Wakeup Delay Time = (2.08 × 10
Resistor temperature coefficient and tolerance as well as
Delay
.
OUT
) with a duty cycle of 50% at
−7
)R
Delay
−8
)R
Delay
CIRCUIT DESCRIPTION
−7
)R
http://onsemi.com
Delay
Delay
.
9
in order to get the correct system tolerance for each
parameter.
RESET
Wakeup
WDI
Wakeup
Figure 18. Wakeup Response to RESET (Low
Figure 17. Wakeup Response to WDI
Response
to RESET
Wakeup
Response
Wakeup
to WDI
Voltage)