ncp5500 ON Semiconductor, ncp5500 Datasheet - Page 9

• Manufacturer Part Number: ncp5500
• Description: 500 Ma Low Dropout Linear Regulator
• Manufacturer: ON Semiconductor

Calculating Resistors for the ADJ Versions
the output to the desired output voltage. With V
to ADJ, the adjustable version will regulate at 1.25 V
4.9% (1250  61.25 mV).
R
and ADJ,
R
and GND,
The term “1.25 V” has a tolerance of 4.9%; the term
“60E-9” can vary in the range 15E-9 to 60E-9.
( [ ] ) will evaluate to less than 1 mV and can be ignored. This
simplifies the output voltage formula to:
V
which is the tolerance of the 1.25 V output when delivering
up to 500 mA of output current.
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 nominal
input voltage. 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 and Ground Current: The quiescent current is
the current which flows through the ground when the LDO
operates without a load on its output: internal IC operation,
bias, etc. When the LDO becomes loaded, this term is called
the Ground current. It is actually the difference between the
input current (measured through the LDO input pin) and the
output current.
V
out
1
2
The adjustable version uses feedback resistors to adjust
Output voltage formula with an external resistor divider:
Where
For values of R
out
= value of the divider resistor connected between ADJ
= value of the divider resistor connected between V
= 1.25 V * ((R1 + R2) / R2)) with a tolerance of 4.9%,
+
1.25 V * 60E-9 @
2
less than 15 KW, the term within brackets
(R
(R
1
1
) R
@ R
NCP5500, NCV5500, NCP5501, NCV5501
2)
2
)
@
(R 1 ) R 2 )
out
R
connected
2
http://onsemi.com
out
9
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
regulator (Figure 21) is:
Where
V
V
I
I
Once the value of P
permissible value of R
Thermal Characteristics table. Those packages with R
less than the calculated value in Equation 2 will keep the die
temperature below 150°C.
dissipate the heat generated by the IC, and an external heat
sink will be required.
Heat Sinks
package to improve the flow of heat away from the IC and
into the surrounding air.
outside environment will have a thermal resistance. Like
series electrical resistances, these resistances are summed to
determine the value of R
where
R
R
R
R
functions of the package type, heat sink and the interface
between them. These values appear in data sheets of heat
sink manufacturers.
further discussed in ON Semiconductor Application Note
AN1040/D.
P
out(max)
GND
out(min)
in(max)
R
R
qJC
qCS
qSA
qJA
The maximum power dissipation for a single output
The value of R
In some cases, none of the packages will be sufficient to
A heat sink effectively increases the surface area of the
Each material in the heat flow path between the IC and the
R
Thermal, mounting, and heat sink considerations are
D(max)
qJA
qJA
qJC
, it too is a function of package type. R
is the junction-to-case thermal resistance,
is the ground current at I
is the case-to-heatsink thermal resistance,
is the heatsink-to-ambient thermal resistance.
+
+ R
appears in the Thermal Characteristics table. Like
is the maximum input voltage,
+ V
is the maximum output current for the application,
is the minimum output voltage,
150 C * T
qJC
°
in(max)
) R
P
D
qJA
qCS
* V
can then be compared with those in the
A
) R
qJA
D(max)
qJA
out(min)
can be calculated:
qSA
:
out(max)
is known, the maximum
I
out(max)
.
) V
qCS
in(max)
and R
I
GND
qSA
(eq. 2)
(eq. 3)
(eq. 1)
qJA
are