NCP5501(2006) データシートの表示（PDF） - ON Semiconductor
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NCP5501 Datasheet PDF : 9 Pages
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NCP5500, NCV5500, NCP5501, NCV5501
DEFINITION OF TERMS
Dropout Voltage: The input−to−output voltage differential
at which the circuit ceases to regulate against further
reduction input voltage. Measured when the output voltage
has dropped 2% relative to the value measured at 6.0 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. Pulse loading
techniques are employed such that the average chip
temperature is not significantly affected.
Quiescent Current: The part of the positive input current
that does not contribute to the positive load current. The
regulator ground pin current with no load.
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.
Calculating Power Dissipation
The maximum power dissipation for a single output
regulator (Figure 3) is:
ƪ ƫ PD(max) + VIN(max) * VOUT(min) IOUT(max) ) VIN(max)Iq (eq. 1)
Where
VIN(max) is the maximum input voltage,
VOUT(min) is the minimum output voltage,
IOUT(max) is the maximum output current for the application,
IGND is the ground current at IOUT(max).
Once the value of PD(max) is known, the maximum
permissible value of RqJA can be calculated:
RqJA
+
ǒ150°C *
PD
TAǓ
(eq. 2)
The value of RqJA can then be compared with those in the
package section of the data sheet. Those packages with RqJA
less than the calculated value in Equation 2 will keep the die
temperature below 150°C.
In some cases, none of the packages will be sufficient to
dissipate the heat generated by the IC, and an external heat
sink will be required.
Heat sinks
A heat sink effectively increases the surface area of the
package to improve the flow of heat away from the IC and
into the surrounding air.
Each material in the heat flow path between the IC and the
outside environment will have a thermal resistance. Like
series electrical resistances, these resistances are summed to
determine the value of RqJA:
RqJA + RqJC ) RqCS ) RqSA
(eq. 3)
where
RqJC is the junction−to−case thermal resistance,
RqCS is the case−to−heatsink thermal resistance,
RqSA is the heatsink−to−ambient thermal resistance.
RqJC appears in the package section of the data sheet. Like
RqJA, it too is a function of package type. RqCS and RqSA are
functions of the package type, heat sink and the interface
between them. These values appear in data sheets of heat
sink manufacturers.
Thermal, mounting, and heat sink considerations are
further discussed in ON Semiconductor Application Note
AN1040/D.
http://onsemi.com
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