NCV8881
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IGNITION BUFFER
The Ignition Buffer output IGNBUF reports the EN pin
voltage level (high or low) detected by the EN input circuitry
when the EN signal is latched. The NCV8881 will pull the
IGNBUF output low if the Enable signal is low, and release
the IGNBUF output if the Enable signal is high. The
IGNBUF output is an open drain device which requires an
external pullup resistor to a logic supply. IGNBUF is no
longer controlled by EN when EN transitions low if the EN
signal is not latched.
THERMAL SHUTDOWN
A thermal shutdown circuit will inhibit switching, reset
the Softstart circuit, and power down the 5P0 and 8P5
outputs if internal die temperature exceeds a safe level.
Operation is automatically restored when die temperature
has dropped below the thermal restart threshold regardless
of the state of the EN signal.
5P0 OUTPUT
CURRENT LIMIT
5P0 output current is limited above the specified output
current capability in order to limit inrush current at turnon
and also minimize power dissipation in the event of an
output short circuit.
OUTPUT UNDERVOLTAGE MONITOR
Either the 5P0 output voltage must exceed V
5UVSTT
or the
8P5 output voltage must exceed V
8UVSTT
before the SMPS
will begin softstart. If the output is below V
5UVSTP
, the
LDOMON output will be pulled low.
STABILITY CONSIDERATIONS
The output capacitor helps determine three main
performance characteristics of a linear regulator: starting
delay, load transient response, and loop stability. The
optimum capacitor type and value will depend on these three
characteristics, as well as cost, availability, size and
temperature constraints. Tantalum, aluminum electrolytic,
film, and ceramic are all acceptable capacitor types for most
applications. Values of 1 mF or more work in many cases,
however attention must be paid to the Equivalent Series
Resistance (ESR). Aluminum electrolytic capacitors are the
least expensive solution but both the value and ESR of this
type of capacitor change considerably at low temperatures
(25癈 or 40癈). The capacitor manufacturers data sheet
must be consulted for this information. Stability under all
load and temperature conditions is guaranteed by a capacitor
value greater than or equal to 4.7 mF and ESR between 0.2
and 5 W.
Besides powering external loads, the 5P0 output can be
used to provide a regulated voltage to an ROSC pullup
resistor as a convenient way to decrease the factoryset
switching frequency.
8P5 OUTPUT
The regulated voltage provided by the 8P5 output is used
to power the internal gate drive circuitry, but can also
provide current to modest external circuit loads that can
tolerate significant spike noise at the SMPS switching
frequency.
CURRENT LIMIT
8P5 output current is limited above the specified output
current capability in order to limit inrush current at turnon
and also minimize power dissipation in the event of an
output short circuit.
OUTPUT UNDERVOLTAGE MONITOR
Either the 8P5 output voltage must exceed V
8UVSTT
or the
5P0 output voltage must exceed V
5UVSTT
before the SMPS
will begin softstart. The LDOMON output will be pulled
low if the 8P5 output voltage is below V
8UVSTP
.
OUTPUT OVERVOLTAGE CLAMP
If current is forced into the 8P5 output, a clamp will limit
the voltage in order to protect the gate driver circuit from
excessive voltage.
STABILITY CONSIDERATIONS
The output capacitor helps determine three main
performance characteristics of a linear regulator: starting
delay, load transient response, and loop stability. The
optimum capacitor type and value will depend on these three
characteristics, as well as cost, availability, size and
temperature constraints. Tantalum, aluminum electrolytic,
film, and ceramic are all acceptable capacitor types for most
applications. Values of 1 mF or more work in many cases,
however attention must be paid to the Equivalent Series
Resistance (ESR). Aluminum electrolytic capacitors are the
least expensive solution but both the value and ESR of this
type of capacitor change considerably at low temperatures
(25癈 or 40癈). The capacitor manufacturers data sheet
must be consulted for this information. Stability under all
load and temperature conditions is guaranteed by a capacitor
value greater than or equal to 4.7 mF and ESR between 0.2 W
and 5 W.
SMPS OPERATION
LDO OUTPUT UNDERVOLTAGE MONITOR
Besides requiring the input voltage to be above V
STRT
and the EN input to be above V
ENSTHH
, either the 5P0
output voltage must exceed V
5UVSTT
or the 8P5 output
voltage must exceed V
8UVSTT
before the SMPS will begin
softstart.
SOFTSTART
Upon being enabled and released from all fault
conditions, and after one of the LDO outputs reaches