CS5208-1GT3 - Cherry Semiconductor

Features

VOUT

VIN

CS5208-1 3.3V @ 8A

300mF

Load

200

124

0.1mF

100mF

5.0V

Adj

■1.25V to 4.5V VOUT at 8A

■Dropout Voltage < 1.0V @ 8A

■1.5% Trimmed Reference

■Fast Transient Response

■Thermal Shutdown

■Current Limit

■Short Circuit Protection

Package Options

CS5208-1

8A LDO 3-Pin Adjustable Linear Regulator

CS5208-1

Description

The CS5208-1 linear regulator pro-

vides 8A at adjustable voltages

from 1.25V to 4.5V. This adjustable

device requires two external resis-

tors 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 micropro-

cessor supply. The fast loop

response and low dropout voltage

make this regulator ideal for appli-

cations where low voltage opera-

tion and good transient response

are important.

The circuit is designed to operate

with dropout voltages as low as

1.0V at 8A.

The regulator is protected against

overload conditions with overcur-

rent and thermal shutdown

protection circuitry.

The regulator is available in a

TO-220 package.

Applications Diagram

3 Lead TO-220

1. Adjust

2. VOUT

3. VIN

Tab = VOUT

Cherry Semiconductor Corporation

2000 South County Trail, East Greenwich, RI 02818

Tel: (401)885-3600 Fax: (401)885-5786

Email: info@cherry-semi.com

Web Site: www.cherry-semi.com

A Company

Rev. 6/11/97

Package Pin Description

PACKAGE PIN # PIN SYMBOL FUNCTION

Electrical Characteristics: 0¡C²TA² 70¡C, 0¡C²TJ² 150¡C, VAdj = 0V unless otherwise specified.

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

CS5208-1

Absolute Maximum Ratings

Input Voltage ...............................................................................................................................................................................6V

Operating Junction Temperature Range..........................................................................................................0¡C ² TJ² 150¡C

Storage Temperature Range ...............................................................................................................................-65¡C to +150¡C

Lead Temperature Soldering: Wave Solder (through hole styles only).........................................10 sec. max, 260¡C peak

ESD Damage Threshold ...........................................................................................................................................................2kV

3L TO-220

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 70µA.

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.

OUT This pin is connected to the emitter of the power pass transistor and

provides a regulated voltage capable of sourcing 8A of current.

IN This is the supply voltage for the regulator . For the device to regu-

late, this voltage should be between 1.1V and 1.30V (depending on

the output current) greater than the output voltage.

Reference Voltage VIN=2.75V to 5.5V, IOUT=10mA to 8A 1.234 1.253 1.271 V

(-1.5%) (+1.5%)

Line Regulation VIN=2.75V to 5.5V, IOUT=10mA .02 .20 %

Load Regulation VIN=2.75V,IOUT=10mA to 8A .04 .50 %

Minimum Load Current VIN=5V, ÆVOUT= +1.5% 5 10 mA

(Note 1)

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

Current Limit VIN=2.75V,ÆVOUT= -1.5% 8.1 9.0 A

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

Ripple Rejection VIN=3.25V Avg, 60 80 dB

(Note 2) VRipple=1VP-P@120Hz,

IOUT=4A,CAdj=0.1µF; COUT = 22µF

Thermal Regulation (Note 2) 30ms Pulse, TA=25¡C 0.002 %/W

Dropout Voltage IOUT=100mA 0.92 1.15 V

(Minimum VIN -VOUT)I

OUT=1A 0.93 1.15 V

(Note 3) IOUT=2.75A 0.94 1.15 V

IOUT=4A 0.95 1.15 V

IOUT=8A 0.96 1.30 V

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

Temperature Stability 0.5 %

Thermal Shutdown (Note 4) 150 180 210 ¡C

Thermal Shutdown Hysteresis 25 ¡C

(Note 4)

Note 1: 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.

Note 2: This parameter is guaranteed by design and is not 100% production tested.

Note 3: Dropout voltage is defined as the minimum input/output voltage differential required to maintain 1.5% regulation.

Note 4: This parameter is guaranteed by design, but not parametrically tested in production. However, a 100% thermal shutdown

functional test is performed on each part.

Block Diagram

VIN

BIAS

and

TSD EA IA

VOUT

Adj

VREF

CS5208-1

Typical Performance Characteristics

0 10 20 30 40 50 60 70 80 90 100 110 120 130

-0.150

-0.125

-0.100

-0.075

-0.050

-0.025

-0.000

0.025

0.050

0.075

0.100

TJ (°C)

Output Voltage Deviation (%)

IO=10mA

VIN=2.75V

Output V oltage Deviation (%)

Output Current (A)

TCase=0°C

TCase =25°C

TCase=125°C

0.00 8.00

0.000

0.200

0.225

0.250

0.175

0.150

0.125

0.100

0.075

0.050

0.025

1.00 2.00 3.00 4.00 5.00 6.00 7.00

0 10 20 30 40 50 60 70 80 90 100 110 120 130

60.00

65.00

70.00

75.00

80.00

85.00

90.00

Case

(°C)

Adjust Pin Current (mA)

=10mA

Reference Voltage vs. Temperature Load Regulation vs. Output Current

Adjust Pin Current vs Temperature

72.4

72.2

72.0

71.8

71.6

71.4

71.2

71.0

70.8

70.6

70.4

0.0 0.8 1.6 3.2 4.0 5.6 6.4 7.2

IOUT (A)

Adjust Pin Current (mA)

70.2

70.0

72.6

2.4 4.8 8.0

Adjust Pin Current vs. IOUT

Application Notes

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 includ-

ed in the Stability Considerations section.

Design Guidelines

This LDO adjustable regulator has an output voltage range

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

put voltage as shown in Figure 1. The regulatorÕs voltage

sensing error amplifier maintains a fixed 1.25V reference

between the output pin and the adjust pin.

A resistor divider network R1and R2causes a fixed current

to flow to ground. This current creates a voltage across R2

that adds to the 1.25V across R1and sets the overall output

voltage. The adjust pin current (typically 50µA) also flows

through R2and 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 ´+ R2´IAdj

The term IAdj ´R2represents the error added by the adjust

pin current.

R1is chosen so that the minimum load current is a least

10mA. R1and R2should be of the same composition for

best tracking over temperature. The divider resistors

should be placed as close to the IC as possible and connect-

ed to the output with a separate metal trace.

R1+ R2

Adjustable Operation

Theory of Operation

CS5208-1

20.0

18.0

16.0

14.0

12.0

10.0

8.0

6.0

4.0

2.0

0.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Output Current (A)

VIN-VOUT (V)

4.0 4.5 5.0 5.5

Dropout Voltage (V)

Output Current (A)

0.00

0.25

0.50

0.75

1.00

1.25

0.0 7.06.0

5.04.03.02.01.0 8.0

1.00 2.00 3.00 4.00 5.00

Minimum Load Current (mA)

VIN – VOUT (V)

0.80

0.82

0.88

0.90

0.98

1.00

TCASE = 23°C

0.84

0.86

0.92

0.94

0.96

TCASE = 125°C

TCASE = 0°C

Typical Performance Characteristics: continued

Dropout Voltage vs. Output Current Short Circuit Current vs. VIN - VOUT

Minimum Load Current vs. VIN - VOUT

20.0

30.0

50.0

70.0

90.0

Frequency (Hz)

Ripple Rejection (dB)

80.0

60.0

40.0

10.0

- V

OUT

= 2V

Ripple

= 1V

OUT

= 4A

Adj

= 0.1mF

OUT

= 22mF

Ripple Rejection vs. Frequency

CS5208-1

Application Notes: continued

Figure 1.

While not required, a bypass capacitor connected between

the adjust pin and ground will improve transient response

and ripple rejection. A 0.1µF tantalum capacitor is recom-

mended for Òfirst cutÓ design. Value and type may be var-

ied to optimize performance vs price.

The CS5208-1 linear regulator has an absolute maximum

specification of 6V for the voltage difference between VIN

and VOUT. However, the IC may be used to regulate volt-

ages in excess of 6V. 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 mil-

liseconds, while the regulator responds in less than one

microsecond. In this case, the linear regulator begins charg-

ing the output capacitor as soon as the VIN to VOUT differ-

ential is large enough that the pass transistor conducts cur-

rent. 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 tran-

sistor 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 6V is not exceeded.

However, the maximum ratings of the IC will be exceeded

in a short circuit condition. Short circuit conditions will

result in the immediate operation of the pass transistor

outside of its safe operating area. Over-voltage stresses will

then cause destruction of the pass transistor before over-

current or thermal shutdown circuitry can become active.

Additional circuitry may be required to clamp VIN to VOUT

differential to less than 6V if failsafe operation is required.

One possible clamp circuit is illustrated below; however,

the design of clamp circuitry must be done on an applica-

tion 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 cir-

cuit conditions indefinitely while protecting the IC.

Figure 2.

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 capaci-

tor with almost zero ESR can cause instability. The alu-

minum electrolytic capacitor is the least expensive solu-

tion. However, when the circuit operates at low tempera-

tures, both the value and ESR of the capacitor will vary

considerably. The capacitor manufacturerÕs data sheet pro-

vides this information.

A 300µF tantalum capacitor will work for most applica-

tions, 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 large changes in load

current so the output capacitor must supply the instanta-

neous load current. The ESR of the output capacitor causes

an immediate drop in output voltage given by:

ÆV = ÆI ´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 net-

work should be as close to the load as possible for the best

results.

Protection Diodes

When large external capacitors are used with a linear regu-

lator 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 capaci-

tor, 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 need-

ed. If the regulator is used with large values of output

capacitance and the input voltage is instantaneously short-

Stability Considerations

VIN VOUT

VAdj

EXTERNAL SUPPLY

Other Adjustable Operation Considerations

VOUT

VIN

CS5208-1

Adj

CS5208-1

ed to ground, damage can occur. In this case, a diode con-

nected as shown in Figure 3 is recommended.

A rule of thumb useful in determining if a protection diode

is required is to solve for current

I = , 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 duration required for VIN to transition

from high to being shorted.

If the calculated current is greater than or equal to the typi-

cal short circuit current value provided in the specifica-

tions, serious thought should be given to including a pro-

tection diode.

Figure 3.

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 to

become activated above a die junction temperature of

150¡C and to shut down the regulator output. This circuit-

ry 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 oper-

ate at high junction temperatures. Therefore, it is important

to calculate the power dissipation and junction tempera-

tures 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, ther-

mal compound in necessary to ensure proper heat flow.

For added safety, this high current LDO includes an inter-

nal thermal shutdown circuit

The thermal characteristics of an IC depend on the follow-

ing four factors. Junction temperature, ambient tempera-

ture, die power dissipation, and the thermal resistance

from the die junction to ambient air. The maximum junc-

tion temperature can be determined by:

TJ(max) = TA(max) + PD(max) ´RQJA

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:

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 which is measured in degrees per watt.

Like series electrical resistances, these thermal resistances

are summed to determine the total thermal resistance

between the die junction and the surrounding air, RQJA.

This total thermal resistance is comprised of three compo-

nents. These resistive terms are measured from junction to

case (RQJC), case to heat sink (RQCS), and heat sink to ambi-

ent air (RQSA ). The equation is:

RQJA = RQJC + RQCS + RQSA

RQJC is rated @ 1.4¡C/W for the CS5208-1. For a high cur-

rent regulator such as the CS5208-1 the majority of heat is

generated in the power transistor section. The value for

RQSA depends on the heat sink type, while the RQCS

depends on factors such as package type, heat sink inter-

face (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 RQJA can be calculated and the proper heat sink

selected. For further discussion on heat sink selection, see

our Cherry application note ÒThermal Management for

Linear Regulators.Ó

VOUT

VIN

CS5208-1

Adj

C ´V

Application Notes: continued

CS5208-1

Thermal Data 3L

TO-220

RQJC typ 1.4 ûC/W

RQJA typ 50 ûC/W

Package Specification

PACKAGE DIMENSIONS IN mm (INCHES)

Cherry Semiconductor Corporation reserves the

right to make changes to the specifications without

notice. Please contact Cherry Semiconductor

Corporation for the latest available information.

PACKAGE THERMAL DATA

Ordering Information

Part Number Description

CS5208-1GT3 3L TO-220 Straight

3 Lead TO-220 (T) Straight

5.33 (.210)

4.83 (.190)

2.79 (.110)

2.29 (.090)

1.02 (.040)

0.63 (.025)

0.56 (.022)

0.38 (.014)

1.40 (.055)

1.14 (.045)

4.83 (.190)

4.06 (.160)

6.17 (.243) REF

1.14 (.045)

1.52 (.060)

1.14 (.045)

1.40 (.055)

2.87 (.113)

2.62 (.103)

6.55 (.258)

5.94 (.234)

14.22 (.560)

13.72 (.540)

2.92 (.115)

2.29 (.090)

9.78 (.385)

10.54 (.415)

3.71 (.146)

3.96 (.156)

14.99 (.590)

14.22 (.560)