NCV4299
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14
APPLICATION DESCRIPTION
NCV4299
The NCV4299 is a family of precision micropower
voltage regulators with an output current capability of
150 mA at 5.0 V and 3.3 V.
The output voltage is accurate within "2% with a
maximum dropout voltage of 0.5 V at 100 mA. Low
quiescent current is a feature drawing only 90 mA with a
100 mA load. This part is ideal for any and all battery
operated microprocessor equipment.
Microprocessor control logic includes an active reset
output RO (with delay), and a SI/SO monitor which can be
used to provide an early warning signal to the
microprocessor of a potential impending reset signal. The
use of the SI/SO monitor allows the microprocessor to finish
any signal processing before the reset shuts the
microprocessor down. Internal output resistors on the RO
and SO pins pulling up to the output pin Q reduce external
component count. An inhibit function is available on the
14-lead part. With inhibit active, the regulator turns off and
the device consumes less that 1.0 mA of quiescent current.
The active reset circuit operates correctly at an output
voltage as low as 1.0 V. The reset function is activated
during the powerup sequence or during normal operation if
the output voltage drops outside the regulation limits.
The reset threshold voltage can be decreased by the
connection of an external resistor divider to the RADJ lead.
The regulator is protected against reverse battery, short
circuit, and thermal overload conditions. The device can
withstand load dump transients making it suitable for use in
automotive environments.
NCV4299 Circuit Description
The low dropout regulator in the NCV4299 uses a PNP
pass transistor to give the lowest possible dropout voltage
capability. The current is internally monitored to prevent
oversaturation of the device and to limit current during over
current conditions. Additional circuitry is provided to
protect the device during overtemperature operation.
The regulator provides an output regulated to 2%.
Other features of the regulator include an undervoltage
reset function and a sense circuit. The reset function has an
adjustable time delay and an adjustable threshold level. The
sense circuit trip level is adjustable and can be used as an
early warning signal to the controller. An inhibit function
that turns off the regulator and reduces the current
consumption to less than 1.0 mA is a feature available in the
14 pin package.
Output Regulator
The output is controlled by a precision trimmed reference.
The PNP output has saturation control for regulation while
the input voltage is low, preventing oversaturation. Current
limit and voltage monitors complement the regulator design
to give safe operating signals to the processor and control
circuits.
Stability Considerations
The input capacitor C
I
is necessary for compensating
input line reactance. Possible oscillations caused by input
inductance and input capacitance can be damped by using a
resistor of approximately 1.0 W in series with C
I
.
The output or compensation capacitor helps determine
three main characteristics of a linear regulator: startup delay,
load transient response and loop stability.
The capacitor value and type should be based on cost,
availability, size and temperature constraints. A tantalum or
aluminum electrolytic capacitor is best, since a film or
ceramic capacitor with almost zero ESR can cause
instability. The aluminum electrolytic capacitor is the least
expensive solution, but, if the circuit operates at low
temperatures (-25°C to -40°C), both the value and ESR of
the capacitor will vary considerably. The capacitor
manufacturer's data sheet usually provides this information.
The value for the output capacitor C
Q
shown in Figures 39
and 40 should work for most applications, however, it is not
necessarily the optimized solution. Stability is guaranteed at
values C
Q
w 22 mF and an ESR v 5.0 W within the
operating temperature range. Actual limits are shown in a
graph in the typical performance characteristics section.
