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LT1303/LT1303-5 Micropower High Efficiency DC/DC Converters with Low-Battery Detector Adjustable and Fixed 5V
FEATURES
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DESCRIPTION
The LT(R)1303/LT1303-5 are micropower step-up high efficiency DC/DC converters using Burst ModeTM operation. They are ideal for use in small, low-voltage batteryoperated systems. The LT1303-5 accepts an input voltage between 1.8V and 5V and converts it to a regulated 5V. The LT1303 is an adjustable version that can supply an output voltage up to 25V. Quiescent current is only 120A from the battery and the shutdown pin further reduces current to 10A. The low-battery detector provides an opencollector output that goes low when the input voltage drops below a preset level. The on-chip NPN power switch has a low 170mV saturation voltage at a switch current of 1A. The LT1303/LT1303-5 are available in 8-lead PDIP or SO packages, easing board space requirements. For higher output current, please see the LT1305 or LT1302.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation.
5V at 200mA from a 2V Input Supply Voltage As Low As 1.8V Up to 88% Efficiency 120A Quiescent Current Low-Battery Detector Low VCESAT Switch: 170mV at 1A Typ Uses Inexpensive Surface Mount Inductors 8-Lead PDIP or SO Package
APPLICATIONS
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EL Panel Drivers 2-Cell and 3-Cell to 5V Conversion Palmtop Computers Portable Instruments Bar-Code Scanners PDAs Wireless Systems
TYPICAL APPLICATION
L1 22H 316k 1% 1N5817
90 80
VIN LBI
SW SENSE LT1303-5 100k LBO PGND 100F
EFFICIENCY (%)
+
2 CELLS 100F
VOUT, 5V 200mA LOW BATTERY GOES LOW AT VBAT = 2.2V
412k 1% SHUTDOWN SHDN GND
70 60 50 40
+
L1 = SUMDIA CD54-220
LT1303 TA02
30
Figure 1. 2-Cell to 5V DC/DC Converter with Low-Battery Detect
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5V Output Efficiency
VIN = 4V VIN = 2V
VIN = 2.5V VIN = 3V
0.1
1
10
100
1000
LT1303 TA01
LOAD CURRENT (mA)
1
LT1303/LT1303-5
ABSOLUTE MAXIMUM RATINGS
VIN Voltage .............................................................. 10V SW1 Voltage ............................................................ 25V Sense Voltage (LT1303-5) ....................................... 20V FB Voltage (LT1303) ................................................ 10V Shutdown Voltage ................................................... 10V LBO Voltage ............................................................. 10V LBI Voltage .............................................................. 10V Maximum Power Dissipation ............................. 500mW Operating Temperature Range ..................... 0C to 70C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
PACKAGE/ORDER INFORMATION
TOP VIEW GND 1 LBO 2 SHDN 3 FB (SENSE)* 4 N8 PACKAGE 8-LEAD PDIP S8 PACKAGE 8-LEAD PLASTIC SO *FIXED VERSION TJMAX = 100C, JA = 130C/W (N8) TJMAX = 100C, JA = 150C/W (S8) 8 7 6 5 PGND SW VIN LBI
ORDER PART NUMBER LT1303CN8 LT1303CS8 LT1303CN8-5 LT1303CS8-5 S8 PART MARKING 1303 13035
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL IQ VIN PARAMETER Quiescent Current Input Voltage Range
TA = 25C, VIN = 2.0V, unless otherwise noted.
MIN
q q q
CONDITIONS VSHDN = 0.5V, VSEL = 5V, VSENSE = 5.5V VSHDN = 1.8V
DC tON VCESAT
Feedback Voltage Output Sense Voltage Comparator Hysteresis Output Hysteresis Feedback Pin Bias Current Oscillator Frequency Oscillator TC Maximum Duty Cycle Switch On Time Output Line Regulation Switch Saturation Voltage Switch Leakage Current Peak Switch Current LBI Trip Voltage LBI Input Bias Current LBO Output Low LBO Leakage Current Shutdown Pin High Shutdown Pin Low Shutdown Pin Bias Current
LT1303 LT1303-5 LT1303 (Note 1) LT1303-5 (Note 1) LT1303, VFB = 1V Current Limit Not Asserted
q q q q q
1.8 2.0 1.22 4.8
TYP 120 7 1.55 1.24 5.0 6 22 7 155 0.2 86 5.6 0.06 130 0.1 1.0 0.9 1.24 7 0.11 0.1
MAX 200 15
120
q
1.26 5.2 12.5 50 20 185 95 0.15 200 10 1.25 1.15 1.27 20 0.4 5 0.5 20 1
75
Current Limit Not Asserted 1.8V < VIN < 6V ISW = 700mA VSW = 5V, Switch Off VIN = 2V VIN = 5V VLBI = 1V ILOAD = 100A VLBI = 1.3V, VLBO = 5V
q q q q q q q q q
0.75 0.65 1.21
VSHDNH VSHDNL ISHDN
1.8 8.0 3.0 0.1
VSHDN = 5V VSHDN = 2V VSHDN = 0V
q q q
UNITS A A V V V V mV mV nA kHz %/C % s %/V mV A A A V nA V A V V A A A
The q denotes specifications which apply over the 0C to 70C operating temperature range.
Note 1: Hysteresis specified is DC. Output ripple may be higher if output capacitance is insufficient or capacitor ESR is excessive.
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WW
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LT1303/LT1303-5
TYPICAL PERFORMANCE CHARACTERISTICS
VCESAT vs Switch Current
250 225 200 175
150 125 100 75 50 25 0 0.1 1.0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 SWITCH CURRENT (A)
LT1303 G01
160 150 140 130 120 110 100 -50 -25 25 50 0 TEMPERATURE (C) 75 100
RESISTANCE (k)
VCESAT (mV)
VCESAT (mV)
LT1303 FB Voltage
1.250 1.245 1.240
FEEDBACK VOLTAGE (V)
SENSE VOLTAGE (V)
1.230 1.225 1.220 1.215 1.210 1.205 1.200 -50 -25 25 50 0 TEMPERATURE (C) 75 100
5.02 5.00 4.98 4.96 4.94 4.92 4.90 -50 -25 25 50 0 TEMPERATURE (C) 75 100
LBI VOLTAGE (V)
1.235
LBI Pin Bias Current
20 18 16
BIAS CURRENT (nA)
14 12 10 8 6 4 2 0 -50 -25 25 50 0 TEMPERATURE (C) 75 100
14 12 10 8 6 4 2 0 -50 -25 25 50 0 TEMPERATURE (C) 75 100
SWITCH CURRENT (A)
BIAS CURRENT (nA)
UW
LT1303 G07
VCESAT vs Temperature
200 190 180 170
800 700 600 500 400
LT1303-5 Sense Pin Resistance to Ground
1000 900
ISW = 700mA
300 -50
-25
50 25 0 TEMPERATURE (C)
75
100
LT1303 G02
LT1303 GO3
LT1303-5 Sense Voltage
5.10 5.08 5.06 5.04
1.250 1.245 1.240 1.235 1.230 1.225 1.220 1.215 1.210 1.205
Low Battery Detect Trip Point
1.200 -50
-25
25 50 0 TEMPERATURE (C)
75
100
LT1330 G04
LT1303 G05
LT1303 G06
FB Pin Bias Current
20 18 16
1.50 1.40 1.30 1.20 1.10 1.00 0.90 0.80 0.70
Switch Current Limit
VIN = 2V
0.60 -50
-25
0 25 50 TEMPERATURE (C)
75
100
LT1303 G08
LT1303 G09
3
LT1303/LT1303-5
TYPICAL PERFORMANCE CHARACTERISTICS
Switch On-Time
8 7 6 5 4 3 2 -50 FREQUENCY (kHz)
200 190 180
160 150 140 130 120 110
DUTY CYCLE (%)
-25 25 50 0 TEMPERATURE (C) 75 100
ON-TIME (s)
-25
0 25 50 TEMPERATURE (C)
Quiescent Current
200 190
QUIESCENT CURRENT (A)
SWITCH OFF VIN = 2V
QUIESCENT CURRENT (A)
170 160 150 140 130 120 110 100 -50
300
SWITCH CURRENT (mA)
180
-25
25 50 0 TEMPERATURE (C)
Transient Response Figure 1 Circuit
VOUT 100mV/DIV AC COUPLED 5V VOUT 1V/DIV
ILOAD
200mA 0mA
200s/DIV VIN = 2V VOUT = 5V
4
UW
75
Oscillator Frequency
100 95 90 85 80 75 70 65 60 55
Maximum Duty Cycle
170
100
100 -50
50 -50
-25
25 50 0 TEMPERATURE (C)
75
100
LT1303 G10
LT1303 G11
LT1303 G12
Quiescent Current
500 TA = 25C SWITCH OFF 400 1100 1200
Switch Current Limit
L = 33H VL = 3V
1000
200
900
100
800
0
75
100
0
2
6 4 INPUT VOLTAGE (V)
8
10
LT1303 G14
700
0
2
6 4 INPUT VOLTAGE (V)
8
10
LT1303 G15
LT1303 G13
Shutdown Pin Response
VLBO 2V/DIV
Low Battery Detector Transient Response
VSHDN 5V/DIV
LT1303 G16
VLBI 500s/DIV RLOAD = 100 VIN = 2V VOUT = 5V COUT = 100F
VTRIP +10mV VTRIP -10mV 5s/DIV RPULL-UP = 47k
LT1303 G18
LT1303 G17
LT1303/LT1303-5 PIN FUNCTIONS
GND (Pin 1): Signal Ground. Tie to PGND under the package. LBO (Pin 2): Open-Collector Output of Low-Battery Comparator. Can sink 100A. Disabled when device is in shutdown. SHDN (Pin 3): Shutdown. Pull high to shut down the device. Ground for normal operation. FB/Sense (Pin 4): On 1303 (adjustable) this pin connects to the main comparator C1 input. On LT1303-5 this pin connects to the resistor string that sets output voltage at 5V. LBI (Pin 5): Low-Battery Comparator Input. When voltage on this pin below 1.24V, LBO is low. VIN (Pin 6): Supply Pin. Must be bypassed with a large value electrolytic to ground. Keep bypass within 0.2" of the device. SW (Pin 7): Switch Pin. Connect inductor and diode here. Keep layout short and direct to minimize radio frequency interference. PGND (Pin 8): Power ground. Tie to signal ground (pin1) under the package. Bypass capacitor from VIN should be tied directly to PGND within 0.2" of the device.
BLOCK DIAGRA S
VIN
+
C1 6
C2
4
FB
-
C1
OFF OSCILLATOR A3 DRIVER Q2 1x Q1 160x
R2
REFERENCE 1.24V
+ -
C3
+
GND 1 5 LBI 2 LBO SHUTDOWN 3 8 PGND
Figure 2. LT1303 Block Digram
-
R1
HYSTERETIC COMPARATOR
+
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L1 VIN SW
D1
+
C2
7 CURRENT COMPARATOR 18mV R1 3
LT1303 BD01
5
LT1303/LT1303-5
BLOCK DIAGRA S
4 FB 6 VIN 7 CURRENT COMPARATOR C2 18mV SW
R1 474k HYSTERETIC COMPARATOR
-
C1 R2 156k REFERENCE 1.24V
OFF OSCILLATOR A3 DRIVER Q2 1x Q1 160x
+ -
C3
+
GND 1 5 LBI 2 LBO SHUTDOWN 3 8 PGND
Figure 3. LT1303-5 Block Diagram
OPERATION
Operation of the LT1303 is best understood by referring to the Block Diagram in Figure 2. When C1's negative input, related to the output voltage by the appropriate resistordivider ratio, is higher than the 1.24V reference voltage, C1's output is low. C2, A3 and the oscillator are turned off, drawing no current. Only the reference and C1 consume current, typically 140A. When C1's negative input drops below 1.24V and overcomes C1's 6mV hysteresis, C1's output goes high, enabling the oscillator, current comparator C2 and driver A3. Quiescent current increases to 2mA as the device goes into active switching mode. Q1 then turns on in controlled saturation for nominally 6s or until current comparator C2 trips, whichever comes first. The switch then turns off for approximately 1.5s, then turns on again. The LT1303's switching causes current to alternately build up in L1 and dump into output capacitor C4 via D1, increasing the output voltage. When the output is high enough to cause C1's output to go high, switching action ceases. Capacitor C4 is left to supply current to the load until VOUT decreases enough to force C1's output high, and the entire cycle repeats. Figure 4 details relevant waveforms. C1's cycling causes low-to-mid-frequency ripple voltage on the output. Ripple can be reduced by making the output capacitor large. The 100F unit specified results in ripple of 50mV to 100mV on the 5V output. A 220F capacitor will decrease ripple by approximately 50%.
VOUT 100mV/DIV AC COUPLED VSW 5V/DIV IL 1A/DIV 20s/DIV
LT1303 F04
Figure 4. Burst Mode Operation in Action
If switch current reaches 1A, causing C2 to trip, switch ontime is reduced and off-time increases slightly. This allows continuous operation during bursts. C2 monitors the voltage across 3 resistor R1 which is directly related to the switch current. Q2's collector current is set by the emitter-area ratio to 0.6% of Q1's collector current. When R1's voltage drop exceeds 18mV, corresponding to 1A switch current, C2's output goes high, truncating the ontime portion of the oscillator cycle and increasing off-time
6
+
-
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R1 3
LT1303 BD02
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LT1303/LT1303-5 OPERATION
to about 2s. Response time of C2, which determines minimum on-time, is approximately 300ns. Low Battery Detector The low battery detector is enabled when SHDN is low and disabled when SHDN is high. The comparator has no
VBAT LT1303 5V
R1
R2 49.9k 1% R1 = (VTRIP -1.24V) (43.5k) HYSTERESIS 30mV
Figure 5. R3 Adds Hysteresis to Low-Battery Detector
APPLICATIONS INFORMATION
Inductor Section Inductors suitable for use with the LT1303 usually fall in the 5H to 50H range. The inductor must: (1) handle current of 1.25A without saturating, (2) have enough inductance to provide a di/dt lower than 400mA/s, and (3) have low enough DC resistance to avoid excessive heating or efficiency losses. Higher value inductors will deliver more power but tend to be physically larger. Most ferrite core drum or rod inductors such as those specified in Table 1 are suitable for use. It is acceptable to bias openflux inductors (e.g. Sumida CD54) into saturation by 10 to 20% without adverse effects.
Table 1. Recommended Inductors
VENDOR Coilcraft Coiltronics SERIES D03316 D01608 OCTAPAK CTX20-1 CTX20-2 CTX33-4 CD54 GA10 PHONE APPROPRIATE VALUES NUMBERS 10H to 47H (708) 639-6400 10H (407) 241-7876 20H 20H 33H 10H to 33H (708) 956-0666 10H to 33H (716) 532-2234
Sumida Gowanda
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hysteresis built in, but hysteresis can be added by connecting a high-value resistor from LBI to LBO as shown in Figure 5. The internal reference can be accessed via the comparator as shown in Figure 6.
VIN 100k 2N3906 VIN LBO LT1303 VREF OUTPUT R2
1.24V
- +
R3 2M
R4 47k
+
2.2F
LBI R1 GND
LT1303 F05
VREF = 1.24V 1 + R2 R1 VIN VREF + 200mV R1 + R2 33k
()
LT1303 F06
Figure 6. Accessing Internal Reference
Figure 7 shows inductor current of a suitable inductor, di/dt is controlled at all times. The rapid rise in current shown in Figure 8 results from this inductor saturating at approximately 1A. Saturation occurs when the inductor cannot hold any more magnetic energy in the core. Current then increases rapidly, limited only by the resistance of the winding. Figure 9's inductor has high DC resistance which results in the exponential time constant shape of the inductor current.
IL 500mA/DIV
5s/DIV
LT1303 F07
Figure 7. Properly Chosen Inductor Does Not Saturate
7
LT1303/LT1303-5
APPLICATIONS INFORMATION
Capacitor Selection Input and output capacitors should have low ESR for best efficiency. Recommended capacitors include AVX TPS series, Sprague 595D series, and Sanyo OS-CON. The output capacitor's ESR determines the high frequency ripple amplitude. A 100F capacitor is the minimum recommended for a 5V output. Higher output voltages can use lower capacitance values. For example, a 12V output can use a 33F or 47F capacitor. The VIN pin of the LT1303 should be decoupled with a 47F or 100F capacitor at the pin. When driving a transformer, an additional decoupling network of 10 and 0.1F ceramic is recommended as shown in Figure 10.
VIN 10
LT1303 F08
Figure 8. This Inductor Saturates at IL1A. A Poor Choice
LT1303 F09
Figure 9. Slight Exponential Shape to Inductor Current Waveform Indicates Excessive DC Resistance
Diode Selection The LT1303's high switching speed demands a high speed rectifier. Schottky diodes are preferred for their low forward drop and fast recovery. Suitable choices include the 1N5817, MBRS120LT3, and MBR0520LT1. Do not use signal diodes such as 1N4148. They cannot carry 1A current. Also avoid "general-purpose" diodes such as 1N4001. These are far too slow and are unsuitable for any switching regulator application. For high temperature applications a silicon diode such as the MUR105 will have less leakage.
8
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47F 0.1F CERAMIC
VIN
SW
LT1303
***
PGND
GND
LT1303 F10
Figure 10. 10-1F Network to LT1303 VIN Pin Provides Additional Decoupling. Recommended When Driving Transformers. Table 2. Recommended Capacitors
VENDOR AVX Sanyo Panasonic Sprague SERIES TPS OS-CON HFQ 595D TYPE Surface Mount Through-Hole Through-Hole Surface Mount PHONE NUMBERS (803) 448-9411 (619) 661-6835 (201) 348-5200 (603) 224-1961
LT1303/LT1303-5
TYPICAL APPLICATIONS
Setting Output Voltage on LT1303
L1 VIN VIN SW VOUT R2 FB GND PGND R1 1N5817
INPUT 1.8V TO 4.5V 100k 2N3906 VIN LBO 100F VREF OUTPUT 1.24V
* SUMIDA CD54-220MC
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+
100F
LT1303
+
100F
VOUT = 1.24V 1 + R2 R1
()
1303 TA03
5V Step-Up Converter with Reference Output
22H* 1N5817
SW SENSE LT1303-5 OUTPUT 5V
+
+
SHDN 100F
LBI 2.2F 33k GND
PGND
1303 TA04
9
LT1303/LT1303-5
TYPICAL APPLICATIONS
4-, 5-Cell to 5V Converter with Output Disconnect
VIN 2V TO 8V VIN
3-Cell to 3.3V Boost/Linear Converter with Output Disconnect
VIN 2V TO 6V VIN SHUTDOWN SHDN
+
33F LBI GND
*SUMIDA CD54-100MC **AVX TPS 330F/6.3V 1% METAL FILM
10
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510 10H* MBRS130T3 ZTX788B SW SENSE VOUT 5V 100mA
+
33F GND
LT1303-5 SHDN PGND SHUTDOWN
+
33F
+
220F**
*SUMIDA CD54-100MC **AVX TPS 220F/10V
LT1303TA05
10H*
MBRS130T3
Si9433
100k SW LB0 LT1303 FB PGND 1.96k 100
+
33F
200k VOUT 3.3V/200mA
+
121k
330F** x2
LT1303 TA07
LT1303/LT1303-5
TYPICAL APPLICATIONS
EL Panel Driver
T1** 1:15 4,5 10 MUR160 C1* 50pF 1N5818 3.3M
VIN 1.5V TO 8V
+
47F 0.1F CERAMIC
100Hz TO 1000Hz SQUARE WAVE DRIVE *ADD C1 FOR OPEN-PANEL PROTECTION **DALE LPE5047-A132 1:15 TURNS RATIO (605) 666-9301 R1 ADJUSTS VOUT 83VRMS TO 115VRMS
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of circuits as described herein will not infringe on existing patent rights.
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*6
10 4.7F 160V
1,2
*
+
1k 1/2W 10k
VIN
SW
3.3M EL PANEL 3.3M 1N4148
LT1303 SHDN GND FB PGND
MPSA42 51k
SHUTDOWN R1 25k
LT1303 TA06
11
LT1303/LT1303-5
PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted.
N8 Package 8-Lead Plastic DIP
0.300 - 0.325 (7.620 - 8.255) 0.045 - 0.065 (1.143 - 1.651) 0.130 0.005 (3.302 0.127) 0.400* (10.160) MAX 8 7 6 5
0.009 - 0.015 (0.229 - 0.381)
0.065 (1.651) TYP 0.005 (0.127) MIN 0.100 0.010 (2.540 0.254) 0.125 (3.175) MIN 0.018 0.003 (0.457 0.076) 0.015 (0.380) MIN
(
+0.025 0.325 -0.015 8.255 +0.635 -0.381
)
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
0.053 - 0.069 (1.346 - 1.752)
0.016 - 0.050 0.406 - 1.270
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
RELATED PARTS
PART NUMBER LT1129 LT1182/83/84 LT1301 LT1302 LT1305 LT1372 LTC (R)1472 DESCRIPTION Micropower Low Dropout Regulator LCD and CCFL Backlight Controller 5V to 12V/200mA Step-Up DC/DC Converter 2-Cell to 5V/600mA Step-Up DC/DC Converter Micropower 2A Switch DC/DC Converter with Low-Battery Detect 500kHz Step-Up PWM, 1.5A Switch PCMCIA Host Switch with Protection COMMENTS 700mA Output Current in SO-8 Package High Efficiency and Excellent Backlight Control Range 120A Quiescent Current 200A Quiescent Current 2V to 5V at 400mA Low Noise, Fixed Frequency Operation Includes Current Limit and Thermal Shutdown
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
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0.255 0.015* (6.477 0.381)
1
2
3
4
N8 0695
S8 Package 8-Lead Plastic SOIC
0.189 - 0.197* (4.801 - 5.004) 0.004 - 0.010 (0.101 - 0.254) 8 7 6 5
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) BSC
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
1
2
3
4
SO8 0695
LT/GP 0195 10K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1995

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