CS52015-1 datasheet(6/9 Pages) ONSEMI | 1.5 A Adjustable Linear Regulator

6 page

CS52015−1

http://onsemi.com

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 VIN drops. In the

CS52015−1 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 13 is recommended.

Figure 13. Protection Diode for Large Output

Capacitors

VIN

CS52015−1

VOUT

Adj

VOUT

VIN

CAdj

IN4002 (Optional)

Output Voltage Sensing

Since the CS52015−1 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.

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 14. 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.

R1 ) R2

where RC = conductor parasitic resistance.

Figure 14. Grounding Scheme for Adjustable Output

Regulator to Minimize Parasitic Resistance Effects

VIN

VOUT

Adj

CS52015−1

Conductor Parasitic

Resistance

RLOAD

Calculating Power Dissipation and Heat Sink

Requirements

The CS52015−1 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 VOUT on the CS52015−1,

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 RqJA (°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 RqJA, the total thermal resistance between the

junction and the surrounding air.

1. Thermal Resistance of the junction to case, RqJC

(°C/W)

2. Thermal Resistance of the case to Heat Sink, RqCS

(°C/W)

3. Thermal Resistance of the Heat Sink to the ambient

air, RqSA (°C/W)

These are connected by the equation:

RQJA + RQJC ) RQCS ) RQSA

(3)

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