NCV8508B
http://onsemi.com
9
DEFINITION OF TERMS
Dropout Voltage: The input−output voltage differential at
which the circuit ceases to regulate against further reduction
in input voltage. Measured when the output voltage has
dropped 100 mV from the nominal value obtained at 14 V
input, dropout voltage is dependent upon load current and
junction temperature.
Input Voltage: The DC voltage applied to the input
terminals with respect to ground.
Line Regulation: The change in output voltage for a
change in the input voltage. The measurement is made under
conditions of low dissipation or by using pulse techniques
such that the average chip temperature is not significantly
affected.
Load Regulation: The change in output voltage for a
change in load current at constant chip temperature.
Quiescent Current: The part of the positive input current
that does not contribute to the positive load current. The
regulator ground lead current.
Ripple Rejection: The ratio of the peak−to−peak input
ripple voltage to the peak−to−peak output ripple voltage.
Current Limit: Peak current that can be delivered to the
output.
DETAILED OPERATING DESCRIPTION
The NCV8508B is a precision micropower voltage
regulator with very low quiescent current (100 mA typical at
250 mA load). A typical dropout voltage is 450 mV at
150 mA for 5 V option. Microprocessor control logic
includes Watchdog, Wakeup and RESET
. This unique
combination of extremely low quiescent current and full
microprocessor control makes the NCV8508B ideal for use
in battery operated, microprocessor controlled equipment in
addition to being a good fit in the automotive environment.
The NCV8508B Wakeup function brings the
microprocessor out of Sleep mode. The microprocessor in
turn signals its Wakeup status back to the NCV8508B by
issuing a Watchdog signal.
The Watchdog logic function monitors an input signal
(WDI) from the microprocessor. The NCV8508B responds
to the falling edge of the Watchdog signal which it expects
at least once during each Wakeup period. When the correct
Watchdog signal is received, a falling edge is issued on the
Wakeup signal line.
RESET
is independent of V
IN
and operates correctly to an
output voltage as low as 1.0 V. A signal is issued in any of
three situations. During power up, the RESET
is held low
until the output voltage is in regulation. During operation, if
the output voltage shifts below the regulation limits, the
RESET
toggles low and remains low until proper output
voltage regulation is restored. Finally, a RESET
signal is
issued if the regulator does not receive a Watchdog signal
within the Wakeup period.
The RESET
pulse width, Wakeup signal frequency, and
Wakeup delay time are all set by one external resistor,
R
Delay
.
The Delay pin is a buffered bandgap voltage (1.25 V). It
can be used as a reference for an external tracking regulator
as shown in Figure 17.
The regulator is protected against short circuit and thermal
runaway conditions. The device runs through 45 volt
transients, making it suitable for use in automotive
environments.
V
OUT
GND
V
IN
NCV8508B
1.0 mF
0.1 mF
Delay
V
BAT
V
IN
Figure 17. Application Circuit
CS8182
10 mF
0.1 mF
60 k
GND
Adj
MRA4004T3
V
REF
/ENABLE
3.9 k
12 k
200 mA
5 V
