NCV8612B Datasheet, PDF (11/26 Pages) ON Semiconductor – Ultra-Low Iq Automotive System Power Supply IC Power Saving Triple-Output Linear Regulator

NCV8612B
and overshoot of output voltages. The soft−start function
applies to all 3 regulators.
The soft−start function kicks in for start up, start up via
enable, start up after thermal shutdown, and startup after an
over voltage condition.
LDO3 is not subject to soft−start under all conditions. The
LDO3 output is not affected by overvoltage shutdown, and
therefore is not effected by the soft−start function upon the
device’s return from an over voltage condition. Also, when
VIN_S3 is connected to an independent supply and the
supply is made available after the soft−start function, LDO3
will not have an independent soft−start.
LDO1 Regulator
The LDO1 error amplifier compares the reference voltage
to a sample of the output voltage (VOUT1) and drives the gate
of an internal PFET. The reference is a bandgap design to
give it a temperature−stable output.
LDO2 Regulator
The LDO2 error amplifier compares the reference voltage
to a sample of the output voltage (VOUT2) and drives the gate
of an internal PFET. The reference is a bandgap design to
give it a temperature−stable output.
LDO3 Regulator
The LDO3 error amplifier compares the reference voltage
to a sample of the output voltage (VOUT3) and drives the gate
of an internal PFET. The reference is a bandgap design to
give it a temperature−stable output
LDO3 is an adjustable voltage output. The adjustable
voltage option requires an external resistor divider feedback
network. LDO3 can be adjusted up to 10 V. The internal
reference voltage is 0.996 V. To determine the proper
feedback resistors, the following formula can be used:
V_OUT3 = V_OUT3FB [(R1+R2)/R2]
V_OUT3
R1
V_OUTA FB
R2
Figure 4. Feedback Network
Stability Considerations
The output or compensation capacitors, C_OUTX help
determine three main characteristics of a linear regulator:
startup delay, load transient response and loop stability. The
capacitor values 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 each output capacitor C_OUTX shown in
Figures 22 − 27 should work for most applications;
however, it is not necessarily the optimized solution.
Stability is guaranteed at the following values:
C_OUT1 w 47 mF, ESR v 10 W
C_OUT2 w 47 mF, ESR v 10 W
C_OUT3 w 47 mF, ESR v 10 W
Actual limits are shown in graphs in the Typical
Performance Characteristics section.
Thermal
As power in the NCV8612B increases, it might become
necessary to provide some thermal relief. The maximum
power dissipation supported by the device is dependent
upon board design and layout. Mounting pad configuration
on the PCB, the board material, and the ambient temperature
affect the rate of junction temperature rise for the part. When
the NCV8612B has good thermal conductivity through the
PCB, the junction temperature will be relatively low with
high power applications.
The maximum dissipation the NCV8612B can handle is
given by:
P_D(max) = (T_J(max)−T_A)/R_thJA
See Figure 20 for R_thJA versus PCB Area.
R_thJA could be further decreased by using Multilayer PCB
and/or if Air Flow is taken into account.
IGNOUT Circuitry
The IGNOUT pin is an open drain output Schmitt Trigger,
externally pulled up to 5 V via a 10 kW resistor. The
IGNOUT pin can be used to monitor the ignition signal of
the vehicle, and send a signal to mute an audio amplifier
during engine crank. The IGNIN pin is ESD protected, and
can handle peak transients up to 45 V. An external diode is
recommended to protect against negative voltage spikes.
The IGNOUT circuitry requires the device to be enabled
for proper operation.
V_PP Function
The reset and warning circuits utilize a push−pull output
stage. The high signal is provided by V_PP. V_PP is tied
internally to LDO1. Under this setup, and any setup where
LDO’s 1−3 are tied to V_PP, loss of the V_PP signal can occur
if the pull up voltage is reduced due to over current, thermal
shutdown, or overvoltage conditions.
Reset Outputs
The Reset Output is used as the power on indicator to the
Microcontroller. The NCV8612B Reset circuitry monitors
the output on LDO1.
This signal indicates when the output voltage is suitable
for reliable operation. It pulls low when the output is not
considered to be suitable. The Reset circuitry utilizes a push
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