CS5201-1GDP3 Cherry Semiconductor Corporation, CS5201-1GDP3 Datasheet - Page 6

• Manufacturer Part Number: CS5201-1GDP3
• Description: 1A Adjustable Linear Regulator
• Manufacturer: Cherry Semiconductor Corporation

Figure 3. Protection diode for large output capacitors.
Since the CS5201-1 is a three terminal regulator, it is not
possible to provide true remote load sensing. Load regula-
tion is limited by the resistance of the conductors connect-
ing the regulator to the load.
For the adjustable regulator, the best load regulation
occurs when R1 is connected directly to the output pin of
the regulator as shown in Figure 4. If R1 is connected to the
load, R
resistance between the regulator and the load becomes
Figure 4. Grounding scheme for the adjustable output regulator to min-
imize parasitic resistance effects.
The CS5201-1 linear regulator includes thermal shutdown
and current limit 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 V
cal isolation may be required for some applications.
Thermal compound should always be used with high cur-
rent regulators such as these.
V
Calculating Power Dissipation and Heat Sink Requirements
IN
V
IN
C
C
1
is multiplied by the divider ratio and the effective
R
V
C
IN
= conductor parasitic resistance
V
IN
CS5201-1
Output Voltage Sensing
CS5201-1
Adj
R
Adj
C
IN4002
´
C
V
OUT
(
Adj
OUT
R1 + R2
V
on the CS5201-1, and electri-
OUT
R1
(optional)
R
R
1
2
R
)
C
conductor parasitic
resistance
R
R
1
Applications Information: continued
2
C
2
V
OUT
R
LOAD
6
The thermal characteristics of an IC depend on the follow-
ing four factors:
1. Maximum Ambient Temperature T
2. Power dissipation P
3. Maximum junction temperature T
4. Thermal resistance junction to ambient R
These four are related by the equation
The maximum ambient temperature and the power dissi-
pation 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:
where
V
V
I
I
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 R
junction and the surrounding air.
1. Thermal Resistance of the junction to case, R
2. Thermal Resistance of the case to Heat Sink, R
3. Thermal Resistance of the Heat Sink to the ambient air,
These are connected by the equation:
The value for R
The value for R
based on an average die size. For a high current regulator
such as the CS5201-1 the majority of the heat is generated
in the power transistor section. The value for R
depends on the heat sink type, while R
tors such as package type, heat sink interface (is an insula-
tor and thermal grease used?), and the contact area
between the heat sink and the package. Once these calcula-
tions are complete, the maximum permissible value of
R
For further discussion on heat sink selection, see applica-
tion note ÒThermal Management for Linear Regulators.Ó
result can be substituted in equation (1).
P
OUT(max)
Q
QJA
IN(max)
OUT(min)
D(max)
is the maximum quiescent current at I
R
QSA
can be calculated and the proper heat sink selected.
={V
(¡C/W)
is the maximum input voltage,
is the maximum output current, for the application
is the minimum output voltage,
IN(max)
QJA
QJC
, the total thermal resistance between the
QJA
R
T
ÐV
is 3.5ûC/W for a given package type
J
QJA
is calculated using equation (3) and the
= T
OUT(min)
D
= R
A
(Watts)
+ P
QJC
D
}I
+ R
´ R
OUT(max)
QCS
QJA
J
+ R
(¡C)
A
QCS
+V
(¡C)
OUT
QSA
IN(max)
depends on fac-
QJA
(max).
QJC
(C/W)
QCS
QSA
I
Q
(¡C/W)
(¡C/W)
(1)
(2)
(3)