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LM196K
Datasheet
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NSC LM396K, LM196K Datasheet

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 lev­els up to 70 watts. The regulators feature on-chip trimming of reference voltage to
g
0.8% 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 ex­tremely 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 im­mune 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 exceed­ed. Full load current of 10A is available at all output volt­ages, 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 adjust­ment of the reference voltage allows a much tighter specifi­cation 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 require­ments 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
b
55§Ctoa150§C. The
LM396 is specified for a 0
§
Ctoa125§C junction tempera-
ture range.
Features
Y
Output pre-trimmed tog0.8%
Y
10A guaranteed output current
Y
PaProduct Enhancement tested
Y
70W maximum power dissipation
Y
Adjustable outputÐ1.25V to 15V
Y
Internal current and power limiting
Y
Guaranteed thermal resistance
Y
Output voltage guaranteed under worst-case conditions
Y
Output is short circuit protected
Typical Applications
V
OUT
e
(1.25V)
#
R1aR2
R1
J
a
I
ADJ
(R2)
TL/H/9059– 1
*For best TC of V
OUT
, 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.
²
C1 is necessary only if main filter capacitor is more than 6
×
away, assumingÝ18 or larger
leads.
²²
C2 is not absolutely necessary, but is suggest­ed 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 out­put impedance and rejection of transients.
Ê
C3 improves ripple rejection, output imped­ance, 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
C
1995 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
b
55§Ctoa150§C
Power Transistor
b
55§Ctoa200§C
LM396 Control Section 0§Ctoa125§C
Power Transistor 0
§
Ctoa175§C
Storage Temperature
b
65§Ctoa150§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 I
OUT
e
10 mA 1.24 1.25 1.26 1.23 1.25 1.27 V
Reference Voltage V
MIN
s
(V
IN
b
V
OUT
)s20V 1.22 1.25 1.28 1.21 1.25 1.29 V
(Note 2) 10 mA
s
I
OUT
10A, PsP
MAX
Full Temperature Range
Line Regulation V
MIN
s
(V
IN
b
V
OUT
)s20V 0.005 0.01 0.005 0.02 %/V
(Note 3) Full Temperature Range 0.05 0.05 %/V
Load Regulation 10 mAsI
OUT
s
10A 0.1 0.1 %/A
LM196/LM396 V
MIN
s
V
IN
b
V
OUT
s
10V, PsP
MAX
(Note 4) Full Temperature Range 0.15 0.15 %/A
Ripple Rejection C
ADJ
e
25 mF, fe120 Hz 60 74 66 74 dB
(Note 5) Full Temperature Range 54 54 dB
Thermal Regulation V
IN
b
V
OUT
e
5V, I
OUT
e
10A 0.003 0.005 0.003 0.015 %/W
(Note 6)
Average Output Voltage T
jMIN
s
T
j
s
T
jMAX
0.003 0.003 %/§C
Temperature Coefficient (See Curves for Limits)
Adjustment Pin Current 50 100 50 100 mA
Adjustment Pin Current 10 mAsI
OUT
s
10A 3 3 mA
Change (Note 7) 3V
s
V
IN
b
V
OUT
s
20V
PsP
MAX
, Full Temperature Range
Minimum Load Current 2.5Vs(V
IN
b
V
OUT
)s20V 10 10 mA
(Note 9) Full Temperature Range
Current Limit 2.5s(V
IN
b
V
OUT
s
7V 10 14 20 10 14 20 A
(Note 8) V
IN
b
V
OUT
e
20V 1.5 3 8 1.5 3 8 A
Rms Output Noise 10 Hzsfs10 kHz 0.001 0.001 %V
OUT
Long Term Stability T
j
e
125§C, te1000 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)
2
Electrical Characteristics (Note 1) (Continued)
Parameter Conditions
LM196 LM396
Units
Min Typ Max Min Typ Max
Power Dissipation (P
MAX
) 7.0VsV
IN
b
V
OUT
s
12V 70 100 70 100 W
(Note 11) V
IN
b
V
OUT
e
15V 50 50 W
V
IN
b
V
OUT
e
18V 36 36 W
Drop-Out Voltage I
OUT
e
10A, 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 T
j
e
25§C, V
IN
b
V
OUT
e
5V, I
OUT
e
10 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 (P
MAX
) 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
e
20 log
10
[
100/(K
c
V
OUT
)]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 V
IN
b
V
OUT
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 V
IN
b
V
OUT
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 rip­ple. 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 ap­plications 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 re­sistance from junction-to-ambient, including junction-to­case resistance, case-to-heat sink interface resistance (0.1–1.0
§
C/W), and heat sink resistance itself. A good ther­mal joint compound such as Wakefield type 120 or Thermal­loy Thermocote must be used when mounting the LM196, especially if an electrical insulator is used to isolate the reg­ulator 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 mini­mum thermal resistance. Four to six inch pounds is recom­mended. Keep in mind that good electrical, as well as ther­mal, contact must be made to the case.
3
Application Hints (Continued)
§
) 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
(V
IN
b
V
OUT
)c(I
OUT
). To do this, you must know the raw power supply voltage/cur­rent characteristics fairly accurately. For example, consid­er a 10V output with 15V nominal input voltage. At full load of 10A, the regulator will dissipate P
e
(15b10)
c
(10)e50W. If input voltage rises by 10%, power dissipa­tion will increase to (16.5
b
10)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 nor­mally occurs under full load conditions except when the effective DC resistance of the raw supply (DV/DI) is larg­er than (V
IN
*bV
OUT
)/2IfL, where VIN* is the lightly-load-
ed raw supply voltage and I
fL
is full load current. For (VIN*
b
V
OUT
)e5Vb8V, and I
fL
e
5A–10A, this gives a resistance of 0.25X to 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 cur­rent, 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 capac­itor 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 cur­rent (rms) is 2 – 3 times the DC output current of the filter. If the capacitor has just 0.05X DC resistance, this can cause 30W internal power dissipation at 10A output current. Ca­pacitor life is very sensitive to operating temperature, de­creasing 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 regula­tion. 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. Some­times 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.
SA
) 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 i
SA
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 vol­ume of heat sink required is: V
e
50/i
SA
1.5
CU. IN. This holds for natural convection only. If the heat sink is inside a small sealed enclosure, i
SA
will increase substantially be­cause the air is not free to form natural convection currents. Fan-forced convection can reduce i
SA
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 capaci­tor, it is also dependent on output voltage. A 25 mF capaci­tor from the adjustment pin to ground will make ripple rejec­tion independent of output voltage for frequencies above 100 Hz. If lower ripple frequencies are encountered, the ca­pacitor should be increased proportionally.
To keep in mind that the bypass capacitor on the adjust­ment 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 pos­sible 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.
4
Application Hints (Continued)
Although it may not be immediately obvious, best load regu­lation 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
#
R2aR1
R1
J
RweLine Resistance
Connected as shown, Rw is not multiplied by the divider ratio. Rw is about 0.004X per 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, mod­eled as a resistor between the sense pin and the output pin. Load regulation will start to degrade if a resistance higher than 10X is 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 con­sidered with IC regulators. Electrical load regulation occurs in microseconds, thermal regulation due to die thermal gra­dients occurs in the 0.2 ms-20 ms time frame, and regula­tion 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 regu­lation is calculated from
DV
OUT
e
(V
IN
b
V
OUT
)c(DI
OUT
)c(b)
beThermal regulation specified on data sheet.
For V
IN
e
9V, V
OUT
e
5V, DI
OUT
e
10A, and b
e
0.005%/W, this yields a 0.2% change in output voltage. Changes in output voltage due to overall temperature rise are calculated from
V
OUT
e
(V
IN
b
V
OUT
)c(DI
OUT
)c(TC)c(ijA)
TC
e
Temperature coefficient of output voltage.
i
jA
e
Thermal resistance from junction to ambient. ijAis approximately 0.5
§
C/Wai of heat sink.
For the same conditions as before, with TC
e
0.003%/§C,
and i
jA
e
1.5§C/W, the change in output voltage will be
Line Regulation
Electrical line regulation is very good on the LM196Ðtypi­cally 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 ef­fects. 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 follow­ing example:
Assume V
OUT
e
5V, V
IN
e
9V, I
OUT
e
8A
Following a 10% change in input voltage (0.9), the output will change quickly (
s
100 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 ther­mal 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 prop­er analysis. This yields 0.0045
a
0.0144a0.043
e
0.062% using
typical
values for thermal regulation and tem­perature coefficient. For worst-case analysis, the maximum data sheet specifications for thermal regulation and temper­ature 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 recommend­ed because they do not share currents equally. The regula­tor with the highest reference voltage will supply all the cur­rent 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 dis­sipation 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.
5
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