CS5205A-1GT3 データシートの表示（PDF） - ON Semiconductor
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CS5205A-1GT3 Datasheet PDF : 8 Pages
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CS5205A−1
VIN
C1
IN4002 (optional)
VIN
VOUT
CS5205A−1
Adj
CAdj
VOUT
R1
C2
R2
Figure 8. Protection Diode Scheme for Adjustable
Output Regulator
Output Voltage Sensing
Since the CS5205A−1 is a three terminal regulator, it is not
possible to provide true remote load sensing. Load
regulation is limited by the resistance of the conductors
connecting the regulator to the load.
Best load regulation occurs when R1 is connected directly
to the output pin of the regulator as shown in Figure 9. If R1
is connected to the load, RC is multiplied by the divider ratio
and the effective resistance between the regulator and the
load becomes
ǒ Ǔ RC
R1 ) R2
R1
where RC = conductor parasitic resistance.
VIN
VIN
VOUT
Conductor Parasitic
RC
Resistance
CS5205A−1
R1
Adj
RLOAD
R2
Figure 9. Grounding Scheme for Adjustable Output
Regulator to Minimize Parasitics
Calculating Power Dissipation and Heat Sink
Requirements
The CS5205A−1 linear regulator includes thermal shutdown
and safe operating area circuitry to protect the device. High
power regulators such as these usually operate at high junction
temperatures so it is important to calculate the power
dissipation and junction temperatures accurately to ensure that
an adequate heat sink is used.
The case is connected to VOUT on the CS5205A−1,
electrical isolation may be required for some applications.
Thermal compound should always be used with high current
regulators such as these.
The thermal characteristics of an IC depend on the
following four factors:
1. Maximum Ambient Temperature TA (°C)
2. Power dissipation PD (Watts)
3. Maximum junction temperature TJ (°C)
4. Thermal resistance junction to ambient RΘJA (°C/W)
These four are related by the equation
TJ + TA ) PD RQJA
(1)
The maximum ambient temperature and the power
dissipation are determined by the design while the
maximum junction temperature and the thermal resistance
depend on the manufacturer and the package type.
The maximum power dissipation for a regulator is:
PD(max) + {VIN(max) * VOUT(min)}IOUT(max) ) VIN(max)IQ
(2)
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
IQ is the maximum quiescent current at IOUT(max).
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 has a thermal resistance. Like series
electrical resistances, these resistances are summed to
determine RΘJA, the total thermal resistance between the
junction and the surrounding air.
1. Thermal Resistance of the junction to case, RΘJC
(°C/W)
2. Thermal Resistance of the case to Heat Sink, RΘCS
(°C/W)
3. Thermal Resistance of the Heat Sink to the ambient
air, RΘSA (°C/W)
These are connected by the equation:
RQJA + RQJC ) RQCS ) RQSA
(3)
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