ncv4279a ON Semiconductor, ncv4279a Datasheet - Page 11

• Manufacturer Part Number: ncv4279a
• Description: 5.0 V Micropower 150 Ma Ldo Linear Regulator With Delay, Adjustable Reset, And Sense Output
• Manufacturer: ON Semiconductor

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. When the voltage on the SO goes low and
the RO stays high the current consumption is typically
560 mA at 1 mA load current.
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. The
aluminum electrolytic capacitor is the least expensive
V
V
SO
V
RO
An on−chip comparator is available to provide early
Figure 19 shows the SO Monitor timing waveforms as a
SI,Low
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
11
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.
work for most applications; however, it is not necessarily the
optimized solution. Stability is guaranteed at CQ is min
2.2 mF and max ESR is 10 W. There is no min ESR limit
which was proved with MURATA’s ceramic caps
GRM31MR71A225KA01 (2.2 mF, 10 V, X7R, 1206) and
GRM31CR71A106KA01 (10 mF, 10 V, X7R, 1206) directly
soldered between output and ground pins.
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
less than the calculated value in equation 2 will keep 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 and
voltages are shown in the 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)
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 10 mF 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
, 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,
manufacturers.
R
qJA
R qJA + R qJC ) R qCS ) R qSA
qJA
= (150°C – T
can then be compared with those in the
qJA
qJA
D(max)
can be calculated:
:
A
Thermal,
) / P
are
Q
is known, the maximum
shown in Figure 18 should
D
discussed
mounting,
qCS
and R
in
qSA
(eq. 5)
(eq. 6)
qJA
and
the
are
’s