ncv8613b ON Semiconductor, ncv8613b Datasheet - Page 10

• Manufacturer Part Number: ncv8613b
• Description: Ncv8613b Ultra-low Iq Automotive System Power Supply Ic Power Saving Triple-output Linear Regulator
• Manufacturer: ON Semiconductor

Auto Switchover Circuitry
continuous operation of the device, automatically switching
the input voltage from the ASO_RAIL input, to the VIN−B
input, to the VIN−H input depending on conditions. The
primary input voltage pin is ASO_RAIL, which is driven
from the 8 V supply. When this voltage is present it will drive
the output voltages. Regardless of whether the 8 V supply is
available, the reference and core functions of the device will
be driven by the higher of VIN−B and VIN−H. The
switchover control circuitry will be powered solely by the
8 V supply, via VIN−A.
P−FET switches will be pulled to ground, turning the
switches on. In this condition, the VIN−B and VIN−H
voltages will be diode or’ed, with the higher voltage
powering the chip. The VIN−H voltage will be one diode
lower than the VIN−B voltage, thereby forcing the VIN−B
voltage to be dominant supply.
are not present, the VIN−H supply will be powering the
device. The VIN−H supply is then fed from a recommended
1000 mF cap. The duration of VIN−H supply is dependent on
output current. It is intended as protection against temporary
loss of battery conditions.
condition on the battery line, a bleed transistor has been
included on the VIN−H line. With the large hold−up cap on
VIN−H, the voltage on that pin has the potential to remain
in an elevated position for an extended period of time. The
main
Overvoltage Shutdown of the device. In order to avoid this
condition, a transistor that is connected to the
Overvoltage Shutdown signal is tied to the VIN−H line. This
transistor will become active in a high voltage event,
allowing the hold−up cap to discharge the excess voltage in
a timely manner.
1 mF capacitor. It is required for proper operation of the
device that C
prepares the regulator in anticipation of change in input
voltage. The event results in a hitch in the output waveforms,
as can be seen in Figure 3.
The auto switchover circuit is designed to insure
When the 8 V supply is not present, the gates of the 2
In the event that both the 8 V supply and the VIN−B supply
In the event of a double battery, or prolonged high voltage
In the Block Diagram, Figure 1, C
During a switchover event, a timer in the output stages
result
ASO_RAIL
of
this
is no larger than 1 mF.
condition
ASO_RAIL
would
is listed as a
CIRCUIT DESCRIPTION
be
http://onsemi.com
an
10
VIN−B/VIN−H Minimum Operating Voltage
either the VIN−B or VIN−H supply. The higher of the two
voltages will dominate and power the reference. This
provides quick circuit response on start−up, as well as a
stable reference voltage. Since the VIN−B voltage will come
up much more quickly than the VIN−H voltage, initially, the
VIN−B voltage will be running the reference. In the case of
any transient drops on VIN−B, the VIN−H supply, with its
large hold−up capacitor, will then be the dominant voltage,
and will be powering the reference.
must be at least 4.5 V. Below that voltage the reference will
not operate properly, leading to incorrect functioning by the
device. VIN−B or VIN−H must be greater than 4.5 V
regardless of the voltage on the VIN−A pin.
Internal Soft−Start
function. This function is included to limit inrush currents
and overshoot of output voltages. The soft−start function
applies to all 3 regulators.
enable, start up after thermal shutdown, and startup after an
over voltage condition.
LDO3 output is not affected by overvoltage shutdown, and
Figure 3. V
The internal reference and core functions are powered by
For proper operation of the device, VIN−B or VIN−H
The NCV8613B is equipped with an internal soft−start
The soft−start function kicks in for start up, start up via
LDO3 is not subject to soft−start under all conditions. The
I
C
OUT
OUT
= 100 mA
= 47 mF
OUTX
Response to ASO Switchover Event