LM396K - National Semiconductor

TL/H/9059

LM196/LM396 10 Amp Adjustable Voltage Regulator

August 1992

LM196/LM396 10 Amp Adjustable Voltage Regulator

General Description

The LM196 is a 10 amp regulator, adjustable from 1.25V to

15V, which uses a revolutionary new IC fabrication structure

to combine high power discrete transistor technology with

modern monolithic linear IC processing. This combination

yields a high-performance single-chip regulator capable of

supplying in excess of 10 amps and operating at power lev-

els up to 70 watts. The regulators feature on-chip trimming

of reference voltage to g0.8% and simultaneous trimming

of reference temperature drift to 30 ppm/§C typical. Thermal

interaction between control circuitry and the pass transistor

which affects the output voltage has been reduced to ex-

tremely low levels by strict attention to isothermal layout.

This interaction, called thermal regulation, is 100% tested.

These new regulators have all the protection features of

popular lower power adjustable regulators such as LM117

and LM138, including current limiting and thermal limiting.

The combination of these features makes the LM196 im-

mune to blowout from output overloads or shorts, even if

the adjustment pin is accidentally disconnected. All devices

are ‘‘burned-in’’ in thermal shutdown to guarantee proper

operation of these protective features under actual overload

conditions.

Output voltage is continuously adjustable from 1.25V to

15V. Higher output voltages are possible if the maximum

input-output voltage differential specification is not exceed-

ed. Full load current of 10A is available at all output volt-

ages, subject only to the maximum power limit of 70W and

of course, maximum junction temperature.

The LM196 is exceptionally easy to use. Only two external

resistors are used to to set output voltage. On-chip adjust-

ment of the reference voltage allows a much tighter specifi-

cation of output voltage, eliminating any need for trimming in

most cases. The regulator will tolerate an extremely wide

range of reactive loads, and does not depend on external

capacitors for frequency stabilization. Heat sink require-

ments are much less stringent, because overload situations

do not have to be accounted forÐonly worst-case full load

conditions.

The LM196 is in a TO-3 package with oversized (0.060×)

leads to provide best possible load regulation. Operating

junction temperature range is b55§Ctoa

150§C. The

LM396 is specified for a 0§Ctoa

125§C junction tempera-

ture range.

Features

YOutput pre-trimmed to g0.8%

Y10A guaranteed output current

YPaProduct Enhancement tested

Y70W maximum power dissipation

YAdjustable outputÐ1.25V to 15V

YInternal current and power limiting

YGuaranteed thermal resistance

YOutput voltage guaranteed under worst-case conditions

YOutput is short circuit protected

Typical Applications

VOUT e(1.25V) #R1 aR2

R1 JaIADJ (R2)

TL/H/9059– 1

*For best TC of VOUT, R1 should be wirewound

or metal film, 1% or better.

**R2 should be same type as R1, with TC track-

ing of 30 ppm/§C or better.

²C1 is necessary only if main filter capacitor is

more than 6×away, assuming Ý18 or larger

leads.

²²C2 is not absolutely necessary, but is suggest-

ed to lower high frequency output impedance.

Output capacitors in the range of 1 mFto

1000 mF of aluminum or tantalum electrolytic

are commonly used to provide improved out-

put impedance and rejection of transients.

ÊC3 improves ripple rejection, output imped-

ance, and noise. C2 should be 1 mF or larger

close to the regulator if C3 is used.

FIGURE 1. Basic 1.25V to 15V Regulator

C1995 National Semiconductor Corporation RRD-B30M115/Printed in U. S. A.

Absolute Maximum Ratings

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales

Office/Distributors for availability and specifications.

Power Dissipation Internally Limited

Input-Output Voltage Differential 20V

Operating Junction Temperature Range

LM196 Control Section b55§Ctoa

150§C

Power Transistor b55§Ctoa

200§C

LM396 Control Section 0§Ctoa

125§C

Power Transistor 0§Ctoa

175§C

Storage Temperature b65§Ctoa

150§C

Lead Temperature (Soldering, 10 seconds) 300§C

ESD rating to be determined

Electrical Characteristics (Note 1)

Parameter Conditions LM196 LM396 Units

Min Typ Max Min Typ Max

Reference Voltage IOUT e10 mA 1.24 1.25 1.26 1.23 1.25 1.27 V

Reference Voltage VMIN s(VIN bVOUT)s20V 1.22 1.25 1.28 1.21 1.25 1.29 V

(Note 2) 10 mA sIOUT 10A, P sPMAX

Full Temperature Range

Line Regulation VMIN s(VIN bVOUT)s20V 0.005 0.01 0.005 0.02 %/V

(Note 3) Full Temperature Range 0.05 0.05 %/V

Load Regulation 10 mA sIOUT s10A 0.1 0.1 %/A

LM196/LM396 VMIN sVIN bVOUT s10V, P sPMAX

(Note 4) Full Temperature Range 0.15 0.15 %/A

Ripple Rejection CADJ e25 mF, f e120 Hz 60 74 66 74 dB

(Note 5) Full Temperature Range 54 54 dB

Thermal Regulation VIN bVOUT e5V, IOUT e10A 0.003 0.005 0.003 0.015 %/W

(Note 6)

Average Output Voltage TjMIN sTjsTjMAX 0.003 0.003 %/§C

Temperature Coefficient (See Curves for Limits)

Adjustment Pin Current 50 100 50 100 mA

Adjustment Pin Current 10 mA sIOUT s10A 3 3 mA

Change (Note 7) 3V sVIN bVOUT s20V

PsPMAX, Full Temperature Range

Minimum Load Current 2.5V s(VIN bVOUT)s20V 10 10 mA

(Note 9) Full Temperature Range

Current Limit 2.5 s(VIN bVOUT s7V 10 14 20 10 14 20 A

(Note 8) VIN bVOUT e20V 1.5 3 8 1.5 3 8 A

Rms Output Noise 10 Hz sfs10 kHz 0.001 0.001 %VOUT

Long Term Stability Tje125§C, t e1000 Hours 0.3 1.0 0.3 1.0 %

Thermal Resistance Control Circuitry 0.3 0.5 0.3 0.5 §C/W

Junction to Case Power Transistor 1.0 1.2 1.0 1.2 §C/W

(Note 10)

Electrical Characteristics (Note 1) (Continued)

Parameter Conditions LM196 LM396 Units

Min Typ Max Min Typ Max

Power Dissipation (PMAX) 7.0V sVIN bVOUT s12V 70 100 70 100 W

(Note 11) VIN bVOUT e15V 50 50 W

VIN bVOUT e18V 36 36 W

Drop-Out Voltage IOUT e10A, 2.1 2.5 2.1 2.5 V

LM196/LM396 Full Temperature Range 2.75 2.75

Note 1: Unless otherwise stated, these specifications apply for Tje25§C, VIN bVOUT e5V, IOUT e10 mA to 10A.

Note 2: This is a worst-case specification which includes all effects due to input voltage, output current, temperature, and power dissipation. Maximum power

(PMAX) is specified under Electrical Characteristics.

Note 3: Line regulation is measured on a short-pulse, low-duty-cycle basis to maintain constant junction temperature. Changes in output voltage due to thermal

gradients or temperature changes must be taken into account separately. See discussion of Line Regulation under Application Hints.

Note 4: Load regulation on the 2-pin package is determined primarily by the voltage drop along the output pin. Specifications apply for an external Kelvin sense

connnection at a point on the output pin (/4×from the bottom of the package. Testing is done on a short-pulse-width, low-duty-cycle basis to maintain constant

junction temperature. Changes in output voltage due to thermal gradients or temperature changes must be taken into account separately. See discussion of Load

Regulation under Application Hints.

Note 5: Ripple rejection is measured with the adjustment pin bypassed with 25 mF capacitor, and is therefore independent of output voltage. With no load or

bypass capacitor, ripple rejection is determined by line regulation and may be calculated from; RR e20 log10 [100/(K cVOUT)]where K is line regulation

expressed in %/V. At frequencies below 100 Hz, ripple rejection may be limited by thermal effects, if load current is above 1A.

Note 6: Thermal regulation is defined as the change in output voltage during the time period of 0.2 ms to 20 ms after a change in power dissipation in the regulator,

due to either a change in input voltage or output current. See graphs and discussion of thermal effects under Application Hints.

Note 7: Adjustment pin current change is specified for the worst-case combination of input voltage, output current, and power dissipation. Changes due to

temperature must be taken into account separately. See graph of adjustment pin current vs temperature.

Note 8: Current limit is measured 10 ms after a short is applied to the output. DC measurements may differ slightly due to the rapidly changing junction temperature,

tending to drop slightly as temperature increases. A minimum available load current of 10A is guaranteed over the full temperature range as long as power

dissipation does not exceed 70W, and VIN bVOUT is less than 7.0V.

Note 9: Minimum load current of 10 mA is normally satisfied by the resistor divider which sets up output voltage.

Note 10: Total thermal resistance, junction-to-ambient, will include junction-to-case thermal resistance plus interface resistance and heat sink resistance. See

discussion of Heat Sinking under Application Hints.

Note 11: Although power dissipation is internally limited, electrical specifications apply only for power dissipation up to the limits shown. Derating with temperature

is a function of both power transistor temperature and control area temperature, which are specified differently. See discussion of Heat Sinking under Application

Hints. For VIN bVOUT less than 7V, power dissipation is limited by current limit of 10A.

Note 12: Dropout voltage is input-output voltage differential measured at a forced reference voltage of 1.15V, with a 10A load, and is a measurement of the

minimum input/output differential at full load.

Application Hints

Further improvements in efficiency can be obtained by using

Schottky diodes or high efficiency diodes with lower forward

voltage, combined with larger filter capacitors to reduce rip-

ple. However, this reduces the voltage difference between

input and drive pins and may not allow sufficient voltage to

fully saturate the pass transistor. Special transformers are

available from Signal Transformer that have a 1V tap on the

output winding to provide the extra voltage for the drive pin.

The transformers are available as standard items for 5V ap-

plications at 5A, 10A and 20A. Other voltages are available

on special request.

Heat Sinking

Because of its extremely high power dissipation capability,

the

major limitation

in the load driving capability of the

LM196 is

heat sinking

. Previous regulators such as LM109,

LM340, LM117, etc., had internal power limiting circuitry

which limited power dissipation to about 30W. The LM196

is guaranteed to dissipate up to 70W continuously, as long

as the maximum junction temperature limit is not exceeded.

This requires careful attention to all sources of thermal re-

sistance from junction-to-ambient, including junction-to-

case resistance, case-to-heat sink interface resistance

(0.1–1.0§C/W), and heat sink resistance itself. A good ther-

mal joint compound such as Wakefield type 120 or Thermal-

loy Thermocote must be used when mounting the LM196,

especially if an electrical insulator is used to isolate the reg-

ulator from the heat sink. Interface resistance without this

compound will be no better than 0.5§C/W, and probably

much worse. With the compound, and no insulator, interface

resistance will be 0.2§C/W or less, assuming 0.005×or less

combined flatness run-out of TO-3 and heat sink. Proper

torquing of the mounting bolts is important to achieve mini-

mum thermal resistance. Four to six inch pounds is recom-

mended. Keep in mind that good electrical, as well as ther-

mal, contact must be made to the case.

Application Hints (Continued)

The actual heat sink chosen for the LM196 will be deter-

mined by the worst-case continuous full load current, input

voltage and maximum ambient temperature. Overload or

short circuit output conditions do not normally have to be

considered when selecting a heat sink because the thermal

shutdown built into the LM196 will protect it under these

conditions. An exception to this is in situations where the

regulator must recover very quickly from overload. The

LM196 may take some time to recover to within specified

output tolerance following an extended overload, if the regu-

lator is cooling from thermal shutdown temperature (approx-

imately 175§) to specified operating temperature (125§Cor

150§C). The procedure for heat sink selection is as follows:

Calculate worst-case

continuous

average power dissipa-

tion in the regulator from P e(VIN bVOUT)c(IOUT). To

do this, you must know the raw power supply voltage/cur-

rent characteristics fairly accurately. For example, consid-

er a 10V output with 15V nominal input voltage. At full

load of 10A, the regulator will dissipate P e(15 b10) c

(10) e50W. If input voltage rises by 10%, power dissipa-

tion will increase to (16.5 b10) c(10) e65W, a

30%

increase.

It is strongly suggested that a raw supply be

assembled and tested to determine its average DC output

voltage

under full load with maximum line voltage

.Donot

over-design by using unloaded voltage as a worst-case,

since the regulator will not be dissipating any power under

no load conditions. Worst-case regulator dissipation nor-

mally occurs under full load conditions except when the

effective DC resistance of the raw supply (DV/DI) is larg-

er than (VIN*bVOUT)/2IfL, where VIN*is the lightly-load-

ed raw supply voltage and IfL is full load current. For (VIN*

bVOUT)e5V b8V, and IfL e5A–10A, this gives a

resistance of 0.25Xto 0.8X. If raw supply resistance is

higher than this, the regulator power dissipation may be

less

at full load current, then at some intermediate cur-

rent, due to the large drop in input voltage. Fortunately,

most well designed raw supplies have low enough output

resistance that regulator dissipation does maximize at full

load current, or very close to it, so tedious testing is not

usually required to find worst-case power dissipation.

A very important consideration is the size of the filter capac-

itor in the raw supply. At these high current levels, capacitor

size is usually dictated by ripple current ratings rather than

just obtaining a certain ripple voltage. Capacitor ripple cur-

rent (rms) is 2–3 times the DC output current of the filter. If

the capacitor has just 0.05XDC resistance, this can cause

30W internal power dissipation at 10A output current. Ca-

pacitor life is very sensitive to operating temperature, de-

creasing by a factor of two for each 15§C rise in internal

temperature. Since capacitor life is not all that great to start

with, it is obvious that a small capacitor with a large internal

temperature rise is inviting very short mean-time-to-failure.

A second consideration is the loss of usable input voltage to

the regulator. If the capacitor is small, the large dips in the

input voltage may cause the LM196 to drop out of regula-

tion. 2000 mF per ampere of load current is the

minimum

recommended value, yielding about 2 Vp-p ripple of 120 Hz.

Larger values will have longer life and the reduced ripple will

allow lower DC input voltage to the regulator, with subse-

quent cost savings in the transformer and heat sink. Some-

times several capacitors in parallel are better to decrease

series resistance and increase heat dissipating area.

After the raw supply characteristics have been determined,

and worst-case power dissipation in the LM196 is known,

the heat sink thermal resistance can be found from the

graphs titled Maximum Heat Sink Thermal Resistance.

These curves indicate the minimim size heat sink required

as a function of ambient temperature. They are derived from

a case-to-control area thermal resistance of 0.5§C/W and a

case-to-power transistor thermal resistance of 1.2§C/W.

0.2§C/W is assumed for interface resistance. A maximum

control area temperature of 150§C is used for the LM196

and 125§C for the LM396. Maximum power transistor tem-

perature is 200§C for the LM196 and 175§C for the LM396.

For conservative designs, it is suggested that when using

these curves, you assume an ambient temperature 25§C–

50§C higher than is actually anticipated, to avoid running the

regulator right at its design limits of operating temperature.

A quick look at the curves show that heat sink resistance

(iSA) will normally fall into the range of 0.2§C/W–1.5§C/W.

These are

not

small heat sinks. A model 441, for instance,

which is sold by several manufacturers, has a iSA of

0.6§C/W with natural convection and is about five inches on

a side. Smaller sinks are more volumetrically efficient, and

larger sinks, less so. A rough formula for estimating the vol-

ume of heat sink required is: V e50/iSA1.5 CU. IN. This

holds for natural convection only. If the heat sink is inside a

small sealed enclosure, iSA will increase substantially be-

cause the air is not free to form natural convection currents.

Fan-forced convection can reduce iSA by a factor of two at

200 FPM air velocity, and by four at 1000 FPM.

Ripple Rejection

Ripple rejection at the normal ripple frequency of 120 Hz is

a function of both electrical and thermal effects in the

LM196. If the adjustment pin is not bypassed with a capaci-

tor, it is also dependent on output voltage. A 25 mF capaci-

tor from the adjustment pin to ground will make ripple rejec-

tion independent of output voltage for frequencies above

100 Hz. If lower ripple frequencies are encountered, the ca-

pacitor should be increased proportionally.

To keep in mind that the bypass capacitor on the adjust-

ment pin will limit the turn-on time of the regulator. A 25 mF

capacitor, combined with the output divider resistance, will

give an extended output voltage settling time following the

application of input power.

Load Regulation (LM196/LM396)

Because the LM196 is a three-terminal device, it is not pos-

sible to provide true remote load sensing. Load regulation

will be limited by the resistance of the output pin and the

wire connecting the regulator to the load. For the data sheet

specification, regulation is measured 1/4×from the bottom

of the package on the output pin. Negative side sensing is a

true Kelvin connection, with the bottom of the output divider

returned to the negative side of the load.

Application Hints (Continued)

Although it may not be immediately obvious, best load regu-

lation is obtained when the top of the divider is connected

directly

to the output pin,

not to the load

. This is illustrated in

Figure 2

. If R1 were connected to the load, the effective

resistance between the regulator and the load would be

(Rw) c#R2 aR1

R1 J

Rw eLine Resistance

Connected as shown, Rw is not multiplied by the divider

ratio. Rw is about 0.004Xper foot using 16 gauge wire. This

translates to 40 mV/ft at 10A load current, so it is important

to keep the positive lead between regulator and load as

short as possible.

TL/H/9059– 2

FIGURE 2. Proper Divider Connection

The input resistance of the sense pin is typically 6 kX, mod-

eled as a resistor between the sense pin and the output pin.

Load regulation will start to degrade if a resistance higher

than 10Xis inserted in series with the sense. This assumes

a worst-case condition of 0.5V between output and sense

pins. Lower differential voltage will allow higher sense series

resistance.

Thermal Load Regulation

Thermal, as well as electrical, load regulation must be con-

sidered with IC regulators. Electrical load regulation occurs

in microseconds, thermal regulation due to die thermal gra-

dients occurs in the 0.2 ms-20 ms time frame, and regula-

tion due to overall temperature changes in the die occurs

over a 20 ms to 20 minute period, depending on the time

constant of the heat sink used. Gradient induced load regu-

lation is calculated from

DVOUT e(VIN bVOUT)c(DIOUT)c(b)

beThermal regulation specified on data sheet.

For VIN e9V, VOUT e5V, DIOUT e10A, and be

0.005%/W, this yields a 0.2% change in output voltage.

Changes in output voltage due to overall temperature rise

are calculated from

VOUT e(VINbVOUT)c(DIOUT)c(TC) c(ijA)

TC eTemperature coefficient of output voltage.

ijA eThermal resistance from junction to ambient. ijA is

approximately 0.5§C/W aiof heat sink.

For the same conditions as before, with TC e0.003%/§C,

and ijA e1.5§C/W, the change in output voltage will be

0.18%. Because these two thermal terms can have either

polarity, they may subtract from, or add to, electrical load

regulation. For worst-case analysis, they must be assumed

to add. If the output of the regulator is trimmed under load,

only that portion of the load that changes need be used in

the previous calculations, significantly improving output ac-

curacy.

Line Regulation

Electrical line regulation is very good on the LM196Ðtypi-

cally less than 0.005% change in output voltage for a 1V

change in input. This level of regulation is achieved only for

very low load currents, however, because of thermal ef-

fects. Even with a thermal regulation of 0.002%.W, and a

temperature coefficient of 0.003%/§C, DC line regulation

will be dominated by thermal effects as shown by the follow-

ing example:

Assume VOUT e5V, VIN e9V, IOUT e8A

Following a 10% change in input voltage (0.9), the output

will change quickly (s100 ms), due to electrical effects, by

(0.005%V) c(0.9V) e0.0045%. In the next 20 ms, the

output will change an additional (0.002%/W) c(8A) c

(0.9V) e0.0144% due to thermal gradients across the die.

After a much longer time, determined by the time constant

of the heat sink, the output will change an additional

(0.003%/§C) c(8A) c(0.9V) c(2§C/W) e0.043% due to

the temperature coefficient of output voltage and the ther-

mal resistance from die to ambient. (2§C/W was chosen for

this calculation). The sign of these last two terms varies

from part to part, so no assumptions can be made about any

cancelling effects. All three terms must be added for a prop-

er analysis. This yields 0.0045 a0.0144 a0.043 e

0.062% using

typical

values for thermal regulation and tem-

perature coefficient. For worst-case analysis, the maximum

data sheet specifications for thermal regulation and temper-

ature coefficient should be used, along with the

actual

ther-

mal resistance of the heat sink being used.

Paralleling Regulators

Direct paralleling of regulators is not normally recommend-

ed because they do not share currents equally. The regula-

tor with the highest reference voltage will supply all the cur-

rent to the load until it current limits. With an 18A load, for

instance, one regulator might be operating in current limit at

16A while the second device is only carrying 2A. Power dis-

sipation in the high current regulator is extremely high with

attendant high junction temperatures. Long term reliability

cannot be guaranteed under these conditions.

Quasi-paralleling may be accomplished if load regulation is

not critical. The connection shown in

Figure 5a

will typically

share to within 1A, with a worst-case of about 3A. Load

regulation is degraded by 150 mV at 20A loads. An external

op amp may be used as in

Figure 5b

to improve load regula-

tion and provide remote sensing.

Application Hints (Continued)

Input and Output Capacitors

The LM196 will tolerate a wide range of input and output

capacitance, but long wire runs or small values of output

capacitance can sometimes cause problems. If an output

capacitor is used, it should be 1 mF or larger. We suggest 10

mF solid tantalum if significant improvements in high fre-

quency output impedance are needed (see output imped-

ance graph). This capacitor should be as close to the regu-

lator as possible, with short leads, to reduce the effects of

lead inductance. No input capacitor is needed if the regula-

tor is within 6 inches of the power supply filter capacitor,

using 18 gauge stranded wire. For longer wire runs, the

LM196 input should be bypassed locally with a 4.7 mF (or

larger) solid tantalum capacitor, or a 100 mF (or larger) alu-

minum electrolytic capacitor.

Correcting for Output Wire Losses (LM196/LM396)

Three-terminal regulators can only provide partial Kelvin

load sensing (see Load Regulation). Full remote sensing

can be added by using an external op amp to cancel the

effect of voltage drops in the unsensed positive output lead.

Figure 7

, the LM301A op amp forces the voltage loss

across the unsensed output lead to appear across R3. The

current through R3 then flows out the Vbpin of the op amp

through R4. The voltage drop across R4 will raise the output

voltage by an amount equal to the line loss, just cancelling

the line loss itself. A small (j40 mV) initial output voltage

error is created by the quiescent current of the op amp.

Cancellation range is limited by the maximum output current

of the op amp, about 300 mV as shown. This can be raised

by increasing R3 or R4 at the expense of more initial output

error.

Transformers and Diodes

Proper transformer ratings are very important in a high cur-

rent supply because of the conflicting requirements of effi-

ciency and tolerance to low-line conditions. A transformer

with a high secondary voltage will waste power and cause

unnecessary heating in the regulator. Too low a secondary

voltage will cause loss of regulation under low-line condi-

tions. The following formulas may be used to calculate the

required secondary voltage and current ratings using a full-

wave center tap:

Vrms e#VOUT aVREG aVRECT aVRIPPLE

02J

#VNOM

VLOW J#(1.1)*J

Irms e(IOUT) (1.2) (Full-wave center tap)

where:

VOUT eDC regulated output voltage

VREG eMinimum input-output voltage of regulator

VRECT eRectifier forward voltage drop at three times DC

output current

VRIPPLE e1/2 peak-to-peak capacitor ripple voltage

e(5.3 c10b3)(I

OUT)

*The factor of 1.1 is only an approximate factor accounting for load regula-

tion of the transformer.

VNOM eNominal line voltage AC rms

VLOW eLow line voltage AC rms

IOUT eDC output current

Example: IOUT e10A, VOUT e5V

Assume: VREG e2.2V, VRECT e1.2V

VRIPPLE e2 Vp-p, VNOM e115V,

VLOW e105V

Vrms e#5a2.2 a1.2 a1

02J#115

105 J1.1

e8.01 Vrms

Capacitor C e(5.3 c10b3)(I

OUT)

2cVRIPPLE

e(5.3 c10b3)(10)

2e26,500 mF

The diodes used in a full-wave rectified capacitor input sup-

ply must have a DC current rating considerably higher than

the average current flowing through them. In a 10A supply,

for instance, the average current through each diode is only

5A, but the diodes should have a rating of 10A–15A. There

are many reasons for this, both thermal and electrical. The

diodes conduct current in pulses about 3.5 ms wide with a

peak value of 5–8 times the average value, and an rms

value 1.5–2.0 times the average value. This results in long

term diode heating roughly equivalent to 10A DC current.

The most demanding condition however, may be the one

cycle surge through the diode during power turn on. The

peak value of the surge is about 10–20 times the DC output

current of the supply, or 100A–200A for a 10A supply. The

diodes must have a one cycle non-repetitive surge rating of

200A or more, and this is usually not found in a diode with

less than 10A average current rating. Keep in mind that

even though the LM196 may be used at current levels be-

low 10A, the diodes may still have to survive shorted output

conditions where average current could rise to 12A–15A.

Smaller transformers and filter capacitors used in lower cur-

rent supplies will reduce surge currents, but unless specific

information is available on worst-case surges, it is best not

to economize on diodes. Stud-mounted devices in a DO-4

package are recommended. Cathode-to-case types may be

bolted directly to the same heat sink as the LM196 because

the case of the regulator is its power input. Part numbers to

consider are the 1N1200 series rated at 12A average cur-

rent in a DO-4 stud package. Additional types include com-

mon cathode duals in a TO-3 package, both standard and

Schottky, and various duals in plastic filled assemblies.

Schottky diodes will improve efficiency, especially in low

voltage applications. In a 5V supply for instance, Schottky

diodes will decrease wasted power by up to 6W, or alterna-

tively provide an additional 5% ‘‘drop out’’ margin for low-

line conditions. Several manufacturers are producing ‘‘high

efficiency’’ diodes with a forward voltage drop nearly as

good as Schottkys at high current levels. These devices do

not have the low breakdown voltages of Schottkys, so are

much less prone to reverse breakdown induced failures.

Typical Performance Characteristics

Reference Drift Differential*

Minimum Input-Output

Differential*

Minimum Input-Output

TL/H/9059– 3

*VIN is reduced until output drops 2% *VIN is reduced until output drops 2%

Current Limit Dissipation*

Maximum Power

Thermal Resistance*

Maximum Heat Sink

TL/H/9059– 4

*As limited by maximum junction temperature. *See ‘‘Heat Sinking’’ under Applications Hints.

Thermal Resistance*

Maximum Heat Sink

Joint Compound

Resistance Using Thermal

TO-3 Interface Thermal

Thermal Regulation

TL/H/9059– 5

*See ‘‘Heat Sinking’’ under Application Hints.

Typical Performance Characteristics (Continued)

Reference Voltage Noise*Ripple Rejection Ripple Rejection

TL/H/9059– 6

*To obtain output noise, multiply by

VOUT/1.25 if adjustment pinis not bypassed.

Adjustment Current (C e25 mF)

Adjustment Pin Bypassed

Output Impedance

Output Impedance*

TL/H/9059– 7

*For output voltages other than 5V, multiply ver-

tical scale readings by VOUT/5.

Adjustment Pin Bypassed

Line Transient Response

Adjustment Pin Bypassed

Load Transient Response

Line Transient Response*

TL/H/9059– 8

*With no adjustment pin bypass. For output volt-

ages other than 5V, multiply vertical scale by

VOUT/5.

Typical Performance Characteristics (Continued)

Load Transient Response*

TL/H/9059– 9

*With no adjustment pin bypass. For output volt-

ages other than 5V, multiply vertical scale by

VOUT/5.

Typical Applications (Continued)

TL/H/9059– 10

*Regulation can be improved by adding an LM336 reference diode to increase the effective reference

voltage to 3.75V. Load and line regulation are improved by 3:1, including thermal effects.

FIGURE 3. Improving Regulation*

TL/H/9059– 11

*R3 is selected to supply partial load current. Therefore, a minimum load

must always be maintained to prevent the regulated output from rising un-

controlled. R3 must be greater than (VMAX bVOUT)/IMIN, where VMAX is

worst-case high input voltage, and IMIN is the minimum load current. R3

must be rated for at least (VIN bVOUT)2/R3 watts. Regulator power dissipa-

tion will be reduced by a factor of 2–3 in a typical situation where minimum

load current is 1/2 full load current. Regulator dissipation will peak at:

VIN e(R3)(IOUT)

2aVOUT

and will be equal to:

PMAX e(R3)(IOUT)2

4Assuming: (R3)(IOUT)sVMAX bVOUT

A few words of caution; (1) R3 power rating must be increased to (VMAX)2/

R3 if continuous output shorts are possible. (2) Under normal load condi-

tions, system power dissipation is not changed, but under short circuit condi-

tions

system

power dissipation increases by (VIN)2/R3 watts over the al-

ready high power of a shorted regulator. The LM196 will not be harmed and

neither will R3 if it is rated properly, but the raw supply components must be

able to withstand the overload also. Thermal shutdown of the LM196 will

probably occur for sustained shorts, somewhat alleviating the problem.

FIGURE 4. Reducing Regulator Power Dissipation

Typical Applications (Continued)

TL/H/9059– 12

FIGURE 5a. Paralleling Regulators TL/H/9059– 13

*2 feet of Ý18 CU wire

**Total voltage drop across output wire and connector should not exceed 0.3V

FIGURE 5b

TL/H/9059– 14

Output will be within g20 mV at 25§C, no load. Regulation of tracking units is improved by VOUT/1.25 compared to a normal connection.

Regulation of master unit is unchanged. Load or input voltage changes on slave units do not affect other units, but all units will be affected

by changes on master. A short on any output will cause all other outputs to drop to approximately 2V.

FIGURE 6. Tracking Regulators

Typical Applications (Continued)

TL/H/9059– 15

*Parasatic line resistance created by wiring

connectors, or parallel ballasting.

FIGURE 7. Correcting for Line Losses

TL/H/9059– 16

Power NPNs have low collecter resistance, and do not require collector bond wires. Collectors are all common to substrate.

Standard NPNs are still isolated.

FIGURE 8. Process Technology

Connection Diagram

Metal Can Package

TL/H/9059– 18

Bottom View

Order Number LM196K STEEL or LM396K STEEL

See NS Package Number K02B

Schematic Diagram*

TL/H/9059– 17

*Drive is tied to VIN and sense is tied to VOUT on LM196 and LM396.

LM196/LM396 10 Amp Adjustable Voltage Regulator

Physical Dimensions inches (millimeters)

TO-3 Metal Can Package (K)

Order Number LM196K STEEL

or LM396K STEEL

NS Package Number K02B

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systems which, (a) are intended for surgical implant support device or system whose failure to perform can

into the body, or (b) support or sustain life, and whose be reasonably expected to cause the failure of the life

failure to perform, when properly used in accordance support device or system, or to affect its safety or

with instructions for use provided in the labeling, can effectiveness.

be reasonably expected to result in a significant injury

to the user.

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