NCP100 View Datasheet(PDF) - ON Semiconductor
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NCP100 Datasheet PDF : 12 Pages
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NCP100
APPLICATIONS INFORMATION
The NCP100 is an adjustable shunt regulator similar to the
industry standard 431−type regulators. Each device is laser
trimmed at wafer probe to allow for tight reference accuracy
and low reference voltage shift over the full operating
temperature range of −40°C to +85°C (Figure 7).
The nominal value for the reference is 0.698 V. This lower
voltage allows the device to be used in low voltage
applications where the traditional 1.25 V and 2.5 V
references are not suitable.
Rin
Vin
R1
VKA
IK
CL
LOAD
R2 VREF
Figure 21. Typical Application Circuit
The typical application circuit for this device is shown in
Figure 21. The cathode voltage can be programmed between
0.9 V to 6.0 V to allow for proper operation by setting the
R1/R2 resistor divider network values. The following
equation can be used in calculating the cathode voltage
(VKA). Note, if VKA is known then the ratio of R1 and R2
can be determined from this equation as well.
ǒ Ǔ VKA + VREF
1
)
R1
R2
) IREF R1
The table below shows the required R1/R2 values using
1.0% resistors for commonly used voltages.
In Figure 21, the input resistor (Rin) is nominally set to
1.0 kW. For proper operation, once Vin, R1 and R2 are set,
the resistance and power value of Rin can be determined by
the following equation.
Rin
+
IK
Vin * VKA
ǒ Ǔ ) IL )
VKA
R1)R2
The maximum current that will flow through Rin must be
determined. This is the sum of the maximum values of cathode
current, resistor divider network current, and load current. With
Vin, set, the difference (Vin−VKA) is now constant. This value
is divided by the maximum current calculated above to arrive
at the value of Rin. Once the value of Rin is calculated, it’s
minimum power rating is easily derived by:
Pin + (Iin)2 Rin
Once these values are determined, it should be verified
that the minimum and maximum values of IK are within the
recommended range of 0.1 mA to 20 mA under the worst
case conditions.
For stability, the NCP100 requires an output capacitor
between the cathode and anode. Figure 19 shows the
capacitance boundary values required for stable operation
across the −40°C to 85°C temperature range. The goal is to
remain to the right of the curve for any programmed cathode
voltages. For example, if the VKA is programmed to 1.0 V,
then a load capacitor value of 3.0 mF or greater would be
selected. The load capacitor’s Equivalent Series Resistance,
ESR, should be less than 4.0 W. Both the capacitance and
ESR values should be checked across the anticipated
application temperature range to insure that the values meet
the requirements stated above.
Vin
VKA
R1
R2
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Because the error amplifier is a CMOS design the value
of IREF is extremely low allowing it to be neglected for most
applications. The low IREF also allows for higher R1 and R2
values keeping current consumption very low.
The NCP100 is especially well suited for lower voltage
applications, particularly at VKA = 1.0 V. As is seen in
Figures 7 and 8, this device exhibits excellent cathode and
reference voltage flatness across the −40°C to +85°C
temperature range.
1.0 k
Iin
R1
100 k
Vcomp
VREF
Rcomp
IK
+
CL
VKA
Figure 22. Negative Dynamic Impedance Circuit
One unique use for the NCP100 is that it can be configured
for negative dynamic impedance as shown in Figure 22.
This circuit is equivalent to Figure 21 with the addition of a
small value resistor Rcomp in the cathode circuit. The
regulated voltage output remains across the NCP100
cathode and anode leads. The voltage programming and
stability requirements remain the same as in the typical
application shown in Figure 21.
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