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CS8481 Datasheet(PDF) 5 Page - ON Semiconductor

Part No. CS8481
Description  3.3 V/250 mA, 5.0 V/100 mA Micropower Low Dropout Regulator with ENABLE
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Maker  ONSEMI [ON Semiconductor]
Homepage  http://www.onsemi.com
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CS8481 Datasheet(HTML) 5 Page - ON Semiconductor

   
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CS8481
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5
ENABLE
The ENABLE function controls VOUT1. When ENABLE
is high, VOUT1 is on. When ENABLE is low, VOUT1 is off.
Calculating Power Dissipation in a
Dual Output Linear Regulator
The maximum power dissipation for a dual output
regulator (Figure 3) is
PD(max) + VIN(max) * VOUT1(min) IOUT1(max) )
VIN(max) * VOUT2(min) IOUT2(max) ) VIN(max)IQ (1)
where:
VIN(max) is the maximum input voltage,
VOUT1(min) is the minimum output voltage from VOUT1,
VOUT2(min) is the minimum output voltage from VOUT2,
IOUT1(max) is the maximum output current, for the
application,
IOUT2(max) is the maximum output current, for the
application, and
IQ is the quiescent current the regulator consumes at both
IOUT1(max) and IOUT2(max).
Once the value of PD(max) is known, the maximum
permissible value of RqJA can be calculated:
R
QJA +
150
°C * TA
PD
(2)
The value of RqJA can be compared with those in the
package section of the data sheet. Those packages with
RqJA’s 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
heatsink will be required.
Figure 3. Dual Output Regulator With Key
Performance Parameters Labeled.
SMART
REGULATOR
Control
Features
VOUT1
IOUT1
VOUT2
IOUT2
VIN
IIN
IQ
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:
R
QJA + RQJC ) RQCS ) RQSA
(3)
where:
RqJC = the junction−to−case thermal resistance,
RqCS = the case−to−heatsink thermal resistance, and
RqSA = 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, heatsink and the interface
between them. These values appear in heat sink data sheets
of heat sink manufacturers.
Figure 4. Test and Application Circuit
* C1 required if regulator is located far from power supply filter.
** C2 and C3 required for stability. Capacitor must operate at minimum temperature expected during system operations.
ENABLE
VOUT2
VIN
VOUT1
CS8481
GND
Load
VBATT
VCC
I/O
GND
mP
C3**
C1*
C2**
0.1
mF
22
mF
ESR < 8
W
22
mF
ESR < 8
W


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