NCV4279_05 ONSEMI [ON Semiconductor], NCV4279_05 Datasheet - Page 11

• Manufacturer Part Number: NCV4279_05
• Description: 5.0 V Micropower 150 mA LDO Linear Regulator with DELAY, Adjustable RESET, and Sense Output
• Manufacturer: ONSEMI [ON Semiconductor]

V
SENSE INPUT (SI) / SENSE OUTPUT (SO) VOLTAGE
MONITOR
warning to the microprocessor of a possible reset signal. The
output is from an open collector driver. The reset signal
typically turns the microprocessor off instantaneously. This
can cause unpredictable results with the microprocessor.
The signal received from the SO pin will allow the
microprocessor time to complete its present task before
shutting down. This function is performed by a comparator
referenced to the band gap voltage. The actual trip point can
be programmed externally using a resistor divider to the
input monitor SI (Figure 18). The values for R
are selected for a typical threshold of 1.20 V on the SI Pin.
SIGNAL OUTPUT
result of the circuit depicted in Figure 18. As the output
voltage (V
crossed. This causes the voltage on the SO output to go low
sending a warning signal to the microprocessor that a reset
signal may occur in a short period of time. T
time the microprocessor has to complete the function it is
currently working on and get ready for the reset
shutdown signal.
STABILITY CONSIDERATIONS
compensating input line reactance. Possible oscillations
caused by input inductance and input capacitance can be
damped by using a resistor of approximately 1.0 W in series
with C
three main characteristics of a linear regulator: startup delay,
load transient response and loop stability.
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
V
SILOW
SO
V
RO
An on−chip comparator is available to provide early
Figure 19 shows the SO Monitor timing waveforms as a
The input capacitor C
The output or compensation capacitor helps determine
The capacitor value and type should be based on cost,
SI
Q
Figure 19. SO Warning Waveform Time Diagram
I.
Q
) falls, the monitor threshold (V
I
in Figure 18 is necessary for
T
WARNING
WARNING
SI1
SILOW
and R
http://onsemi.com
is the
), is
SI2
NCV4279
11
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.
should work for most applications; however, it is not
necessarily the optimized solution. Stability is guaranteed at
values C
temperature range. Actual limits are shown in a graph in the
typical data section.
CALCULATING POWER DISSIPATION IN A SINGLE
OUTPUT LINEAR REGULATOR
regulator (Figure 18) is:
where:
V
V
I
and I
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 heatsink will be required. The current
flow
Measurement Circuit Diagram.
HEATSINKS
package to improve the flow of heat away from the IC and
into the surrounding air.
outside environment will have a thermal resistance. Like
series electrical resistances, these resistances are summed to
determine the value of R
where:
R
R
R
R
functions of the package type, heatsink and the interface
between them. These values appear in data sheets of
heatsink
heatsinking considerations
ON Semiconductor application note AN1040/D, available
on the ON Semiconductor website.
Q(max)
Q(max)
qJA
qJC
qCS
qSA
qJA
P D(max) + [V I(max) * V Q(min) ] I Q(max) ) V I(max) I q (eq. 4)
I(max)
Q(min)
The value for the output capacitor C
The maximum power dissipation for a single output
Once the value of P
The value of R
A heatsink effectively increases the surface area of the
Each material in the heat flow path between the IC and the
R
qJC
’s less than the calculated value in equation 2 will keep
, it too is a function of package type. R
q
= the junction−to−case thermal resistance,
= the case−to−heat sink thermal resistance, and
= the heat sink−to−ambient thermal resistance.
.
is the quiescent current the regulator consumes at
is the maximum output current for the application,
appears in the package section of the data sheet. Like
is the maximum input voltage,
is the minimum output voltage,
Q
and
= 10 mF and an ESR = 10 W within the operating
manufacturers.
R
qJA
R qJA + R qJC ) R qCS ) R qSA
qJA
voltages
= (150°C – T
can then be compared with those in the
qJA
qJA
D(max)
can be calculated:
:
A
Thermal,
) / P
are
are
is known, the maximum
D
discussed
Q
shown
shown in Figure 18
mounting,
qCS
and R
in
in
qSA
(eq. 5)
(eq. 6)
and
the
the
are