CS5208-1-D - ON Semiconductor

 Semiconductor Components Industries, LLC, 2002

May, 2002 – Rev. 5 1Publication Order Number:

CS5208–1/D

CS5208-1

8.0 A LDO 3-Pin Adjustable

Linear Regulator

The CS5208–1 linear regulator provides 8.0 A at adjustable

voltages from 1.25 V to 4.5 V. This adjustable device requires two

external resistors to set the output voltage and provide the minimum

load current for proper regulation.

This regulator is intended for use as a post regulator and

microprocessor supply. The fast loop response and low dropout

voltage make this regulator ideal for applications where low voltage

operation and good transient response are important.

The circuit is designed to operate with dropout voltages as low as

1.0 V at 8.0 A.

The regulator is protected against overload conditions with

overcurrent and thermal shutdown protection circuitry.

The regulator is available in a TO–220 package.

Features

•1.25 V to 4.5 V VOUT at 8.0 A

•Dropout Voltage < 1.0 V @ 8.0 A

•1.5% Trimmed Reference

•Fast Transient Response

•Thermal Shutdown

•Current Limit

•Short Circuit Protection

Figure 1. Applications Diagram

CS5208–1

VIN VOUT

Adj

100 µF

5.0 V

0.1 µFLoad

124

200 300 µF

3.3 V @ 8.0 A

Device Package Shipping

ORDERING INFORMATION

CS5208–1GT3 TO–220* 50 Units/Rail

*TO–220 is 3–pin, straight leaded.

TO–220

THREE LEAD

T SUFFIX

CASE 221A

PIN CONNECTIONS AND

MARKING DIAGRAMS

CS5208–1

AWLYWW

A = Assembly Location

WL, L = Wafer Lot

YY, Y = Year

WW, W = Work Week

Tab = VOUT

Pin 1. Adjust

2. VOUT

3. VIN

123

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MAXIMUM RATINGS*

Parameter Value Unit

Input Voltage 6.0 V

Operating Junction Temperature Range 0 ≤ TJ ≤ 150 °C

Storage Temperature Range –60 to +150 °C

Lead Temperature Soldering: Wave Solder (through hole styles only) Note 1 260 Peak °C

ESD Damage Threshold 2.0 kV

1. 10 second maximum.

*The maximum package power dissipation must be observed.

ELECTRICAL CHARACTERISTICS ( 0°C ≤ TA ≤ 70°C, 0°C ≤ TJ ≤ 150°C, VAdj = 0 V, unless otherwise specified.)

Characteristic Test Conditions Min Typ Max Unit

Adjustable Output Voltage

Reference Voltage VIN = 2.75 V to 5.5 V,

IOUT = 10 mA to 8.0 A 1.234

(–1.5%) 1.253 1.271

(+1.5%) V

Line Regulation VIN = 2.75 V to 5.5 V, IOUT = 10 mA – 0.02 0.20 %

Load Regulation VIN = 2.75 V, IOUT = 10 mA to 8.0 A – 0.04 0.50 %

Minimum Load Current (Note 2) VIN = 5.0 V, ∆VOUT = +1.5% – 5.0 10 mA

Adjust Pin Current VIN = 2.75 V, IOUT = 10 mA – 70 120 µA

Current Limit VIN = 2.75 V, ∆VOUT = –1.5% 8.1 9.0 – A

Short Circuit Current VIN = 2.75 V, VOUT = 0 V 6.0 8.5 – A

Ripple Rejection (Note 3) VIN = 3.25 V Avg, VRIPPLE = 1.0 VP–P @ 120 Hz,

IOUT = 4.0 A, CAdj = 0. 1 µF; COUT = 22 µF60 80 – dB

Thermal Regulation (Note 3) 30 ms Pulse, TA = 25°C – 0.002 – %/W

Dropout Voltage (Minimum VIN–VOUT)

(Note 4) IOUT = 100 mA

IOUT = 1.0 A

IOUT = 2.75 A

IOUT = 4.0 A

IOUT = 8.0 A

–

0.92

0.93

0.94

0.95

0.96

1.15

1.30

RMS Output Noise Freq = 10 Hz to 10 kHz, TA = 25°C – 0.003 – %VOUT

Temperature Stability – – 0.5 – %

Thermal Shutdown (Note 5) – 150 180 210 °C

Thermal Shutdown Hysteresis (Note 5) – – 25 – °C

2. The minimum load current is the minimum current required to maintain regulation. Normally the current in the resistor divider used to set the

output voltage is selected to meet the minimum load current requirement.

3. This parameter is guaranteed by design and is not 100% production tested.

4. Dropout voltage is defined as the minimum input/output voltage differential required to maintain 1.5% regulation.

5. This parameter is guaranteed by design, but not parametrically tested in production. However, a 100% thermal shutdown functional test is

performed on each part.

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PACKAGE PIN DESCRIPTION

Package Pin Number

TO–220 Pin Symbol Function

1 Adjust This pin is connected to the low side of the internally trimmed 1.5% bandgap reference

voltage and carries a bias current of about 70 µA. A resistor divider from Adj to VOUT and from

Adj to ground sets the output voltage. Also, transient response can be improved by adding a

small bypass capacitor from this pin to ground.

2 VOUT This pin is connected to the emitter of the power pass transistor and provides a regulated

voltage capable of sourcing 8.0 A of current.

3 VIN This is the supply voltage for the regulator. For the device to regulate, this voltage should be

between 1.1 V and 1.30 V (depending on the output current) greater than the output voltage.

Figure 2. Block Diagram

BIAS

and

TSD VREF –

–

EA IA

VIN

VOUT

Adj

TYPICAL PERFORMANCE CHARACTERISTICS

TJ (°C) Output Current (A)

Figure 3. Reference Voltage vs.

Temperature Figure 4. Load Regulation vs. Output

Current

Output Voltage Deviation (%)

0.100

0.075

0.050

0.025

–0.025

–0.050

–0.075

–0.100

–0.125

–0.150

0.250

0.225

0.200

0.175

0.150

0.125

0.100

0.075

0.050

0.025

10 20 30 40 50 60 70 80 90 100 110 120130 1 2 3 4 5 6 7 8

TCASE = 0°C

TCASE = 125°C

TCASE = 25°C

IO = 10 mA

VIN = 2.75 V

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TCase (°C) IOUT (A)

Figure 5. Adjust Pin Current vs.

Temperature Figure 6. Adjust Pin vs. IOUT

Output Current (A) VIN – VOUT (V)

Figure 7. Dropout Voltage vs. Output

Current Figure 8. Short Circuit vs. VIN – VOUT

72.6

0.8

Adjust Pin Current (µA)

Dropout Voltage (V)

Output Current (A)

1.25

0.5

VIN – VOUT (V) Frequency (Hz)

Figure 9. Minimum Load Current vs. VIN – VOUT Figure 10. Ripple Rejection vs. Frequency

Minimum Load Current (mA)

Ripple Rejection (dB)

1 101

901.00

60 0 20 30 40 50 60 70 80 90 100 110 120 130

72.4

72.2

72.0

71.8

71.6

71.4

71.2

71.0

70.8

70.6

70.4

70.2

700.0 1.6 2.4 3.2 4.0 4.8 5.6 6.4 7.2 8.0

1.00

0.75

0.50

0.25

00 2345678 0.0 1.01.52.02.53.03.54.04.55.05.5

0.98

0.96

0.94

0.92

0.90

0.88

0.86

0.84

0.82

0.80 2345 10

2103104105106

TCASE = 0°C

TCASE = 125°C

TCASE = 25°C

IO = 10 mA

VIN – VOUT = 2.0 V

VRIPPLE = 1.0 VPP

IOUT = 4.0 A

CAdj = 0.1 µF

COUT = 22 µF

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APPLICATION NOTES

THEORY OF OPERATION

The CS5208–1 linear regulator has a composite

PNP–NPN output stage that requires an output capacitor for

stability. A detailed procedure for selecting this capacitor is

included in the Stability Considerations section.

ADJUSTABLE OPERATION

Design Guidelines

This LDO adjustable regulator has an output voltage

range of 1.25 V to 4.5 V. An external resistor divider sets the

output voltage as shown in Figure 11. The regulator’s

voltage sensing error amplifier maintains a fixed 1.25 V

reference between the output pin and the adjust pin.

A r esistor divider network R 1 and R2 causes a f ixed c urrent

to f low t o g round. T his c urrent c reates a v oltage a cross R 2 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 VOUT is necessary. The

output voltage is set according to the formula:

VOUT VREF R1R2

R1R2IAdj

The term IAdj × 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 of the same composition for best

tracking over temperature. The divider resistors should be

placed as close to the IC as possible and connected to the

output with a seperate metal trace.

Figure 11.

VIN

CS5208–1

VOUT

Adj R1

While not required, a bypass capacitor connected between

the adjust pin and ground will improve transient response

and ripple rejection. A 0.1 µF tantalum capacitor is

recommended for “first cut” design. Value and type may be

varied to optimize performance vs price.

OTHER ADJUSTABLE OPERATION CONSIDERATIONS

The CS5208–1 linear regulator has an absolute maximum

specification o f 6.0 V for the voltage difference between VIN

and V OUT. However , the IC may be used to regulate voltages

in excess of 6.0 V. The main considerations in such a design

are power–up and short circuit capability.

In most applications, ramp–up of the power supply to VIN

is fairly slow, typically on the order of several tens of

milliseconds, while the regulator responds in less than one

microsecond. In this case, the linear regulator begins

charging the output capacitor as soon as the VIN to VOUT

differential is l a rge enough that the pass transistor conducts

current. VOUT is essentially at ground, and VIN is on the

order of several hundred millivolts, so the pass transistor is

in dropout. As VIN increases, the pass transistor will remain

in dropout, and current is passed to the load until VOUT is in

regulation. Further increase in VIN brings the pass transistor

out of dropout. The result is that the output voltage follows

the power supply ramp–up, staying in dropout until the

regulation point is reached. In this manner, any output

voltage may be regulated. There is no theoretical limit to the

regulated voltage as long as the VIN to VOUT differential of

6.0 V is not exceeded.

However , t he m aximum r atings o f t he I C w ill b e e xceeded

in a short c ircuit c ondition. S hort c ircuit c onditions w ill r esult

in t he i mmediate o peration o f t he p ass t ransistor o utside o f i ts

safe operating area. Over–voltage stresses will then cause

destruction of the pass transistor before overcurrent or

thermal shutdown circuitry can become active. Additional

circuitry may be required to clamp VIN to VOUT differential

to less than 6.0 V if failsafe operation is required. One

possible c lamp c ircuit i s i llustrated i n F igure 12; however, t he

design of clamp circuitry must be done on an application by

application basis. Care must be taken to ensure the clamp

actually protects the design. Components used in the clamp

design must be able to withstand the short circuit conditions

indefinitely while protecting the IC.

Figure 12.

VIN VOUT

VAdj

EXTERNAL SUPPLY

CS5208–1

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STABILITY CONSIDERATIONS

The output 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 manufacturer’s data sheet

provides this information.

A 300 µF tantalum capacitor will work for most

applications, but with high current regulators such as the

CS5208–1 the transient response and stability improve with

higher values of capacitance. The majority of applications

for this regulator involve lar ge 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:

VI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

transient load conditions. The output capacitor network

should be a s close to the load as possible for the best results.

Protection Diodes

When large external capacitors are used with a linear

regulator it i s 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

CS5208–1 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 a n d

the input voltage is instantaneously shorted to ground,

damage can occur. In this case, a diode connected as shown

in Figure 13 is recommended.

A rule of thumb useful in determining if a protection diode

is required is to solve for current

ICV

where:

I is the current flow out of the load capacitance when VIN

is shorted,

C is the value of the load capacitance,

V is the output voltage, and

T is the time duaration required for VIN to transition from

high to being shorted.

If the calculated current is greater than or equal to the

typical short circuit current value provided in the

specifications, serious thought should be given to including

a protection diode.

Figure 13.

VIN

CS5208–1

VOUT

Adj

Current Limit

The internal current limit circuit limits the output current

under excessive load conditions and protects the regulator.

Short Circuit Protection

The device includes foldback short circuit current limit

that clamps the output current at approximately two amperes

less than its current limit value.

Thermal Shutdown

The thermal shutdown circuitry is guaranteed by design t o

become activated above a die junction temperature of 150°C

and to shut down the regulator output. This circuitry

includes a thermal hysteresis circuit with 25°C of typical

hysteresis, thereby allowing the regulator to recover from a

thermal fault automatically.

Calculating Power Dissipation and Heat Sink

Requirements

High power regulators such as the CS5208–1 usually

operate at high junction temperatures. Therefore, it is

important to calculate the power dissipation and junction

temperatures accurately to ensure that an adequate heat sink

is used. Since the package tab is connected to VOUT on the

CS5208–1, electrical isolation may be required for some

applications. Also, as with all high power packages, thermal

compound is necessary to ensure proper heat flow. For

added safety, this high current LDO includes an internal

thermal shutdown circuit

The thermal characteristics of an IC depend on the

following four factors. Junction temperature, ambient

temperature, die power dissipation, and the thermal

resistance from the die junction to ambient air. The

maximum junction temperature can be determined by:

TJ(max) TA(max) PD(max) RJA

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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) IIN(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 the total thermal

resistance between the die junction and the surrounding air,

RΘJC. This total thermal resistance is comprised of three

components. These resistive terms are measured from

junction to case (RΘJC), case to heat sink (RΘCS), and heat

sink to ambient air (RΘSA). The equation is:

RJA RJC RCS RSA

RΘJC is rated @ 1.4°C/W for the CS5208–1. For a high

current regulator such as the CS5208–1 the majority of heat

is generated in the power transistor section. The value for

RΘSA depends on the heat sink type, while the RΘCS 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 RΘJA 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.

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PACKAGE DIMENSIONS

TO–220

THREE LEAD

T SUFFIX

CASE 221A–08

ISSUE AA

NOTES:

1. DIMENSIONING AND TOLERANCING PER ANSI

Y14.5M, 1982.

2. CONTROLLING DIMENSION: INCH.

123

–T– SEATING

PLANE

3 PL

–B–

–Y–

0.25 (0.010) Y

DIM MIN MAX MIN MAX

MILLIMETERSINCHES

A0.560 0.625 14.23 15.87

B0.380 0.420 9.66 10.66

C0.140 0.190 3.56 4.82

D0.025 0.035 0.64 0.89

F0.139 0.155 3.53 3.93

G0.100 BSC 2.54 BSC

H--- 0.280 --- 7.11

J0.012 0.045 0.31 1.14

K0.500 0.580 12.70 14.73

L0.045 0.060 1.15 1.52

N0.200 BSC 5.08 BSC

Q0.100 0.135 2.54 3.42

R0.080 0.115 2.04 2.92

S0.020 0.055 0.51 1.39

T0.235 0.255 5.97 6.47

U0.000 0.050 0.00 1.27

V0.045 --- 1.15 ---

PACKAGE THERMAL DATA

Parameter TO–220

THREE LEAD Unit

RΘJC Typical 1.4 °C/W

RΘJA Typical 50 °C/W

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changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any

particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all

liability, including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or

specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be

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