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CS5205A-1GT3

P1-P3P4-P6P7-P8
CS5205A−1
http://onsemi.com
4
APPLICATIONS INFORMATION
The CS5205A−1 linear regulator provides an adjustable
voltage at currents up to 5.0 A. The regulator is protected
against short circuit, and include thermal shutdown and safe
area protection (SOA) circuitry. The SOA protection
circuitry decreases the maximum available output current as
the input−output differential voltage increases.
The CS5205A−1 has a composite PNP−NPN output
transistor and requires an output capacitor for stability. A
detailed procedure for selecting this capacitor is included in
the Stability Considerations section.
Adjustable Operation
The adjustable regulator (CS5205A−1) has an output
voltage range of 1.25 V to 13 V. An external resistor divider
sets the output voltage as shown in Figure 7. The regulator
maintains a fixed 1.25 V (typical) reference between the
output pin and the adjust pin.
A resistor divider network R1 and R2 causes a fixed
current to flow to ground. This current creates a voltage
across R2 that adds to the 1.25 V across R1 and sets the
overall output voltage. The adjust pin current (typically
50 μA) also flows through R2 and adds a small error that
should be taken into account if precise adjustment of V
OUT
is necessary.
The output voltage is set according to the formula:
V
OUT
+ V
REF
ǒ
R1 ) R2
R1
Ǔ
) I
Adj
R2
The term I
Adj
× R2 represents the error added by the adjust
pin current.
R1 is chosen so that the minimum load current is at least
10 mA. R1 and R2 should be the same type, e.g. metal film
for best tracking over temperature. The adjust pin is
bypassed to improve the transient response and ripple
rejection of the regulator.
C
Adj
I
Adj
Figure 7. Resistor Divider Scheme for the Adjustable
Version
V
REF
R
2
R
1
C
2
V
OUT
V
IN
C
1
V
IN
V
OUT
Adj
CS5205A−1
Stability Considerations
The output or compensation capacitor helps determine
three main characteristics of a linear regulator: start−up
delay, load transient response and loop stability.
The capacitor value and type is based on cost, availability,
size and temperature constraints. A tantalum or aluminum
electrolytic capacitor is best, since a film or ceramic
capacitor with almost zero ESR, can cause instability. The
aluminum electrolytic capacitor is the least expensive
solution. However, when the circuit operates at low
temperatures, both the value and ESR of the capacitor will
vary considerably. The capacitor manufacturers data sheet
provides this information.
A 22 μF tantalum capacitor will work for most
applications, but with high current regulators such as the
CS5205A−1 the transient response and stability improve
with higher values of capacitor. The majority of applications
for this regulator involve large changes in load current so the
output capacitor must supply the instantaneous load current.
The ESR of the output capacitor causes an immediate drop
in output voltage given by:
DV + DI ESR
For microprocessor applications it is customary to use an
output capacitor network consisting of several tantalum and
ceramic capacitors in parallel. This reduces the overall ESR
and reduces the instantaneous output voltage drop under
load transient conditions. The output capacitor network
should be as close as possible to the load for the best results.
Protection Diodes
When large external capacitors are used with a linear
regulator it is sometimes necessary to add protection diodes.
If the input voltage of the regulator gets shorted, the output
capacitor will discharge into the output of the regulator. The
discharge current depends on the value of the capacitor, the
output voltage and the rate at which V
IN
drops. In the
CS5205A−1 linear regulator, the discharge path is through
a large junction and protection diodes are not usually
needed. If the regulator is used with large values of output
capacitance and the input voltage is instantaneously shorted
to ground, damage can occur. In this case, a diode connected
as shown in Figure 8 is recommended.
CS5205A−1
http://onsemi.com
5
Figure 8. Protection Diode Scheme for Adjustable
Output Regulator
C
2
V
OUT
V
IN
C
1
V
IN
V
OUT
Adj
CS5205A−1
IN4002 (optional)
C
Adj
R
1
R
2
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, R
C
is multiplied by the divider ratio
and the effective resistance between the regulator and the
load becomes
R
C
ǒ
R1 ) R2
R1
Ǔ
where R
C
= conductor parasitic resistance.
Figure 9. Grounding Scheme for Adjustable Output
Regulator to Minimize Parasitics
V
IN
V
IN
V
OUT
Adj
CS5205A−1
Conductor Parasitic
Resistance
R
1
R
LOAD
R
2
R
C
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 V
OUT
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 T
A
(°C)
2. Power dissipation P
D
(Watts)
3. Maximum junction temperature T
J
(°C)
4. Thermal resistance junction to ambient R
Θ
JA
(°C/W)
These four are related by the equation
T
J
+ T
A
) P
D
R
QJA
(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:
P
D(max)
+
{
V
IN(max)
* V
OUT(min)
}
I
OUT(max)
) V
IN(max)
I
Q
(2)
where:
V
IN(max)
is the maximum input voltage,
V
OUT(min)
is the minimum output voltage,
I
OUT(max)
is the maximum output current, for the application
I
Q
is the maximum quiescent current at I
OUT(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 R
Θ
JA
, the total thermal resistance between the
junction and the surrounding air.
1. Thermal Resistance of the junction to case, R
Θ
JC
(°C/W)
2. Thermal Resistance of the case to Heat Sink, R
Θ
CS
(°C/W)
3. Thermal Resistance of the Heat Sink to the ambient
air, R
Θ
SA
(°C/W)
These are connected by the equation:
R
QJA
+ R
QJC
) R
QCS
) R
QSA
(3)
CS5205A−1
http://onsemi.com
6
The value for R
Θ
JA
is calculated using equation (3) and
the result can be substituted in equation (1).
The value for R
Θ
JC
is normally quoted as a single figure
for a given package type based on an average die size. For
a high current regulator such as the CS5205A−1 the majority
of the heat is generated in the power transistor section. The
value for R
Θ
SA
depends on the heat sink type, while R
Θ
CS
depends on factors such as package type, heat sink interface
(is an insulator and thermal grease used?), and the contact
area between the heat sink and the package. Once these
calculations are complete, the maximum permissible value
of R
Θ
JA
can be calculated and the proper heat sink selected.
For further discussion on heat sink selection, see application
note “Thermal Management,” document number
AND8036/D, available through the Literature Distribution
Center or via our website at http://onsemi.com.
ORDERING INFORMATION
Orderable Part Number Type Package Shipping†
CS5205A−1GT3 5.0 A, Adj. Output TO−220−3, Straight 50 Units/Rail
CS5205A−1GDP3 5.0 A, Adj. Output D
2
PAK−3 50 Units/Rail
CS5205A−1GDPR3 5.0 A, Adj. Output D
2
PAK−3 750 Tape & Reel
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
P1-P3P4-P6P7-P8

CS5205A-1GT3

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Buy CS5205A-1GT3
Manufacturer:
ON Semiconductor
Description:
IC REG LINEAR POS ADJ 5A TO220AB
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