NCV8664 ON Semiconductor, NCV8664 Datasheet - Page 9

• Manufacturer Part Number: NCV8664
• Description: 5.0v, 3.3v/150ma Very Low Quiescent Current Ldo
• Manufacturer: ON Semiconductor

Circuit Description
fixed output regulator. Careful management of light load
consumption combined with a low leakage process results
in a typical quiescent current of 22 mA. The device has
current capability of 150 mA, with 600 mV of dropout
voltage at full rated load current. The regulation is provided
by a PNP pass transistor controlled by an error amplifier
with a bandgap reference. The regulator is protected by
both current limit and short circuit protection. Thermal
shutdown occurs above 150°C to protect the IC during
overloads and extreme ambient temperatures.
Regulator
sample of the output voltage (V
a 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. The NCV8664 is equipped with
foldback current protection. This protection is designed to
reduce the current limit during an overcurrent situation.
Regulator Stability Considerations
compensating input line reactance. Possible oscillations
caused by input inductance and input capacitance can be
damped by using a resistor of approximately 1 W in series
with C
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.
Tantalum, aluminum electrolytic, film, or ceramic
capacitors are all acceptable solutions, however, attention
must be paid to ESR constraints. 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
applications; however, it is not necessarily the optimized
solution. Stability is guaranteed at values C
ESR ≤ 9 W for 5.0 V version, and C
≤ 18 W for 3.3 V version, within the operating temperature
range. Actual limits are shown in a graph in the Typical
Performance Characteristics section.
The NCV8664 is a precision trimmed 3.3 V and 5.0 V
The error amplifier compares the reference voltage to a
The input capacitor C
IN
. The output or compensation capacitor, C
OUT
shown in Figure 2 should work for most
IN
in Figure 2 is necessary for
out
) and drives the base of
OUT
≥ 22 mF and ESR
OUT
≥ 10 mF and
http://onsemi.com
OUT
NCV8664
9
Calculating Power Dissipation in a Single Output
Linear Regulator
regulator (Figure 3) is:
Where:
application, and I
consumes at I
permissible value of R
package section of the data sheet. Those packages with
R
the die temperature below 150°C. In some cases, none of
the packages will be sufficient to dissipate the heat
generated by the IC, and an external heat sink will be
required. The current flow and voltages are shown in the
Measurement Circuit Diagram.
Heat Sinks
package to improve the flow of heat away from the IC and
into the surrounding air. Each material in the heat flow path
between the IC and the outside environment will have a
thermal resistance. Like series electrical resistances, these
resistances are summed to determine the value of R
Where:
R
interface between them. These values appear in data sheets
of heat sink manufacturers. Thermal, mounting, and heat
sinking are discussed in the ON Semiconductor application
note AN1040/D, available on the ON Semiconductor
Website.
qJA
qSA
The maximum power dissipation for a single output
V
V
I
Once the value of P
The value of R
A heat sink effectively increases the surface area of the
R
R
R
R
Like R
Q(max)
qJC
qCS
qSA
qJA
IN(max)
OUT(min)
's less than the calculated value in Equation 2 will keep
are functions of the package type, heat sink and the
= the junction-to-case thermal resistance,
appears in the package section of the data sheet.
= the case-to-heat sink thermal resistance, and
= the heat sink-to-ambient thermal resistance.
qJA
P D(max) + [V IN(max) * V OUT(min) ] @
is the maximum output current for the
is the maximum input voltage,
, it too is a function of package type. R
R qJA + R qJC ) R qCS ) R qSA
is the minimum output voltage,
Q(max)
qJA
q
P qJA +
is the quiescent current the regulator
.
can then be compared with those in the
I Q(max) ) V I(max) @ I q
qJA
D(Max)
can be calculated:
150
o
P D
is known, the maximum
C * T A
qCS
(eq. 1)
(eq. 2)
(eq. 3)
qJA
and
: