ncv4275a ON Semiconductor, ncv4275a Datasheet - Page 9

• Manufacturer Part Number: ncv4275a
• Description: 5.0 V, 3.3 V 450 Ma Low-dropout Voltage Regulator With Reset
• Manufacturer: ON Semiconductor

Circuit Description
that provides 5.0 V or 3.3 V, 450 mA protected output and
a signal for power on reset. The regulation is provided by
a PNP pass transistor controlled by an error amplifier with
a bandgap reference, which gives it the lowest possible
drop out voltage and best possible temperature stability.
The output current capability is 450 mA, and the base drive
quiescent current is controlled to prevent over saturation
when the input voltage is low or when the output is
overloaded. The regulator is protected by both current limit
and thermal shutdown. Thermal shutdown occurs above
150°C to protect the IC during overloads and extreme
ambient temperatures. The delay time for the reset output
is adjustable by selection of the timing capacitor. See
Figure 23, Test Circuit, for circuit element nomenclature
illustration.
Regulator
sample of the output voltage (V
PNP series pass transistor by a buffer. The reference is a
bandgap design to give it a temperature−stable output.
Saturation control of the PNP is a function of the load
current and input voltage. Over saturation of the output
power device is prevented, and quiescent current in the
ground pin is minimized.
Regulator Stability Considerations
stabilize the input impedance to avoid voltage line
influences. Using a resistor of approximately 1.0 W in
series with C
stray inductance and capacitance.
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, aluminum or ceramic
capacitors can be used. The range of stability versus
capacitance, load current and capacitive ESR is illustrated
The NCV4275A is an integrated low dropout regulator
The error amplifier compares the reference voltage to a
The input capacitors (C
The output capacitor helps determine three main
V
I
I2
can stop potential oscillations caused by
C
1000 μF
I1
I
I
I1
and C
Q
) and drives the base of a
C
100 nF
C
47 nF
I2
I2
D
) are necessary to
I
D
APPLICATION INFORMATION
D
I
Figure 23. Test Circuit
1
4
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NCV4275A
9
3
GND
I
q
in Figures 2 to 5. Minimum ESR for C
ESR of ceramic capacitors. The aluminum electrolytic
capacitor is the least expensive solution, but, if the circuit
operates at low temperatures (−25°C to −40°C), both the
capacitance and ESR of the capacitor will vary considerably.
The capacitor manufacturer’s data sheet usually provides this
information.
Figure 23, Test Circuit, should work for most applications;
however, it is not necessarily the optimized solution.
Stability is guaranteed for C
(5.0 V Version), 3.5 W (3.3 V Version).
capacitors and additional resistors to emulate ESR. Murata
ceramic capacitors were used, GRM32ER71A226ME20
(22 mF, 10 V, X7R, 1210), GRM31MR71E105KA01 (1 mF,
25 V, X7R, 1206).
Reset Output
microcontroller. This signal indicates when the output
voltage is suitable for reliable operation of the controller.
It pulls low when the output is not considered to be ready.
RO is pulled up to V
5.0 kW in value. The input and output conditions that
control the Reset Output and the relative timing are
illustrated in Figure 24, Reset Timing.
delay time before the reset output signals a valid condition.
The delay for the reset output is defined as the amount of
time it takes the timing capacitor on the delay pin to charge
from a residual voltage of 0.0 V to the upper timing
threshold voltage V
I
on the D pin, the following time delay for 5.0 V regulator
is derived:
t
t
capacitor value.
RD
RD
D,C
The value for the output capacitor C
ESR characteristics were measured with ceramic
The reset output is used as the power on indicator to the
Output voltage regulation must be maintained for the
Other time delays can be obtained by changing the
. By using typical IC parameters with a 47 nF capacitor
= C
= 47 nF (1.8 V) / 5.5 mA = 15.4 ms
5
2
D
V
Q
RO
DU
/ I
D,C
I
RO
DU
C
22 μF
Q
Q
. The charging current for this is
by an external resistor, typically
I
Q
Q
≥ 22 mF and an ESR ≤ 4.5 W
R
5.0 k
ext
Q
= 22 mF is native
Q
V
V
Q
RO
shown in