NCP565(2004) Просмотр технического описания (PDF) - ON Semiconductor
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NCP565 Datasheet PDF : 12 Pages
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NCP565
Protection Diodes
When large external capacitors are used with a linear
regulator it is sometimes necessary to add protection diodes.
If the input voltage of the regulator gets shorted, the output
capacitor will discharge into the output of the regulator. The
discharge current depends on the value of the capacitor, the
output voltage and the rate at which Vin drops. In the
NCP565 linear regulator, the discharge path is through a
large junction and protection diodes are not usually needed.
If the regulator is used with large values of output
capacitance and the input voltage is instantaneously shorted
to ground, damage can occur. In this case, a diode connected
as shown in Figure 20 is recommended.
1N4002 (Optional)
Vin
Vin
Vout
Vout
NCP565
CAdj
C1 GND Adj
C2
R1
R2
Thermal Considerations
This series contains an internal thermal limiting circuit
that is designed to protect the regulator in the event that the
maximum junction temperature is exceeded. This feature
provides protection from a catastrophic device failure due to
accidental overheating. It is not intended to be used as a
substitute for proper heat sinking. The maximum device
power dissipation can be calculated by:
PD
+
TJ(max) *
RqJA
TA
The devices are available in surface mount D2PAK
package. The package has an exposed metal tab that is
specifically designed to reduce the junction to air thermal
resistance, RqJA, by utilizing the printed circuit board
copper as a heat dissipater. Figure 21 shows typical RqJA
values that can be obtained from a square pattern using
economical single sided 2.0 ounce copper board material.
The final product thermal limits should be tested and
quantified in order to insure acceptable performance and
reliability. The actual RqJA can vary considerably from the
graph shown. This will be due to any changes made in the
copper aspect ratio of the final layout, adjacent heat sources,
and air flow.
Figure 20. Protection Diode for Large
Output Capacitors
80
3.5
PD(max) for TA = +50°C
70
Free Air
Mounted
60
Vertically
50
Minimum
Size Pad
40
RqJA
3.0
2.0 oz. Copper
L
2.5
ÎÎÎÎÎÎÎÎ L
2.0
ÎÎÎÎÎÎÎÎ1.5
30
1.0
0
5.0
10
15
20
25
30
L, LENGTH OF COPPER (mm)
Figure 21. 3−Pin and 5−Pin D2PAK
Thermal Resistance and Maximum Power
Dissipation vs. P.C.B Length
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