CS8221 Cherry Semiconductor Corporation, CS8221 Datasheet - Page 4

• Manufacturer Part Number: CS8221
• Description: Micropower 5V/ 100mA Low Dropout Linear Regulator
• Manufacturer: Cherry Semiconductor Corporation

tor will usually cost less and occupy less board space. If
the output oscillates within the range of expected operat-
ing conditions, repeat steps 3 and 4 with the next larger
standard capacitor value.
Step 6: Test the load transient response by switching in
various loads at several frequencies to simulate its real
working environment. Vary the ESR to reduce ringing.
Step 7: Remove the unit from the environmental chamber
and heat the IC with a heat gun. Vary the load current as
instructed in step 5 to test for any oscillations.
Once the minimum capacitor value with the maximum
ESR is found, a safety factor should be added to allow for
the tolerance of the capacitor and any variations in regula-
tor performance. Most good quality aluminum electrolytic
capacitors have a tolerance of ±20% so the minimum value
found should be increased by at least 50% to allow for this
tolerance plus the variation which will occur at low tem-
peratures. The ESR of the capacitor should be less than
50% of the maximum allowable ESR found in step 3
above.
The maximum power dissipation for a single output regu-
lator (Figure 2) is:
where:
Once the value of P
sible value of R
Figure 2. Single output regulator with key performance parameters
labeled.
V
V
V
I
tion, and
I
I
IN
OUT(max)
Q
OUT(max)
IN(max)
OUT(min)
P
is the quiescent current the regulator consumes at
D(max)
I
IN
is the maximum input voltage,
.
in a Single Output Linear Regulator
is the maximum output current for the applica-
is the minimum output voltage,
= {V
Calculating Power Dissipation
QJA
IN(max)
R
QJA
can be calculated:
D(max)
=
ÐV
CS8221
150¡C - T
OUT(min)
is known, the maximum permis-
P
D
I
Q
}I
A
OUT(max)
+V
I
OUT
IN(max)
Application Notes: continued
I
Q
V
OUT
(1)
(2)
4
The value of R
the package section of the data sheet. Those packages
with R
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
heatsink will be required.
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 R
where:
R
R
are functions of the package type, heatsink and the inter-
face between them. These values appear in heat sink data
sheets of heat sink manufacturers.
QJC
QJA
R
R
R
QJC
QCS
QSA
, it too is a function of package type. R
appears in the package section of the data sheet. Like
QJA
= the junctionÐtoÐcase thermal resistance,
= the caseÐtoÐheatsink thermal resistance, and
= the heatsinkÐtoÐambient thermal resistance.
's less than the calculated value in equation 2
QJA
R
QJA
can then be compared with those in
= R
QJC
Heat Sinks
+ R
QJA
:
QCS
+ R
QSA
QCS
and R
QSA
(3)