ncv4279c ON Semiconductor, ncv4279c Datasheet - Page 7

• Manufacturer Part Number: ncv4279c
• Description: 5.0 V Micropower 150 Ma Ldo Linear Regulator With Delay, Adjustable Reset, And Monitor Flag
• Manufacturer: ON Semiconductor

control function RESET (Figure 11).
RESET Function
powers up. After V
threshold, the DELAY timer is started. When the DELAY
timer passes 1.8 V, the RESET signal goes high. A discharge
of the DELAY timer is started when V
below the RESET threshold. When the DELAY timer level
drops below 0.45 V, the RESET signal is brought low.
controlled by a low voltage detection circuit. The circuit is
functionally independent of the rest of the IC thereby
guaranteeing that the RESET signal is valid for V
as 1.0 V.
Adjustable Reset Function
external resistor divider to the R
lead, as displayed in Figure 12. This lead is grounded to
select the default value of 4.6 V.
The NCV4279C contains a microprocessor- -compatible
A RESET signal (low voltage) is generated as the IC
The RESET output is an open collector NPN transistor,
The reset threshold can be made lower by connecting an
REGULATOR CONTROL FUNCTIONS
R
ADJ
Delay
NCV4279C
Figure 12. Adjustable RESET
C
RESET
DELAY
DELAY
V
OUT
V
RESET
IN
V
OUT
OUT
increases above the RESET
Power on
Reset
Td
ADJ
R
RST
Figure 11. Reset and Delay Circuit Wave Forms
lead from the V
OUT
V Dip
Input
drops and stays
Under--voltage
C
OUT
CIRCUIT DESCRIPTION
OUT
to mP and
System
Power
to mP and
RESET
Port
http://onsemi.com
as low
OUT
7
Td
DELAY Function
external capacitor) on the RESET output lead.
2.5 mA) to the external DELAY capacitor at the following
times:
FLAG/Monitor Function
warning to the microprocessor of a possible reset signal. The
reset signal typically turns the microprocessor off
instantaneously. This can cause unpredictable results with
the microprocessor. The signal received from the FLAG pin
will allow the microprocessor time to complete its present
task before shutting down. This function is performed by a
comparator referenced to the bandgap voltage. The actual
trip point can be programmed externally using a resistor
divider to the input monitor (MON) (Figure 13). The typical
threshold is 1.20 V on the MON Pin.
V
Secondary
BAT
The reset delay circuit provides a delay (programmable by
The DELAY lead provides source current (typically
An on- -chip comparator is available to provide an early
Spike
1. During Power Up (once the regulation threshold
2. After a reset event has occurred and the device is
has been exceeded).
back in regulation. The DELAY capacitor is
discharged when the regulation (RESET threshold)
has been violated. When the DELAY capacitor
discharges to 0.45 V, the RESET signal pulls low.
Figure 13. FLAG/Monitor Function
Overload
Output
V
MON
R
Delay
IN
ADJ
NCV4279C
RESET
GND
FLAG
V
OUT
1.8V V
RESET Threshold
0.45V V
DT
LD
C
OUT
V
I/O
RESET
CC
mP