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LTC1480 3.3V Ultra-Low Power RS485 Transceiver
FEATURES
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DESCRIPTIO
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True RS485 from a Single 3.3V Supply Low Power: ICC = 500A Max with Driver Disabled ICC = 600A Max with Driver Enabled, No Load 1A Quiescent in Shutdown Mode ESD Protection to 10kV on Receiver Inputs and Driver Outputs -7V to 12V Common-Mode Range Permits 7V Ground Difference Between Devices on the Data Line Thermal Shutdown Protection Power Up/Down Glitch-Free Driver Outputs Permit Live Insertion or Removal of Transceiver Driver Maintains High Impedance in Three-State or with the Power Off Up to 32 Transceivers on the Bus 50ns Typical Driver Propagation Delays with 10ns Skew Pin Compatible with the LTC485
The LTC(R)1480 is an ultra-low power differential line transceiver which provides full RS485 compatibility while operating from a single 3.3V supply. It is designed for data transmission standard RS485 applications with extended common-mode range (12V to -7V). It also meets the requirements of RS422 and features high speed operation up to 2.5Mb/s. The CMOS design offers significant power savings without sacrificing ruggedness against overload or ESD damage. Typical quiescent current is only 300A while operating and 1A in shutdown. The driver and receiver feature three-state outputs, with the driver outputs maintaining high impedance over the entire common-mode range. Excessive power dissipation caused by bus contention or faults is prevented by a thermal shutdown circuit which forces the driver outputs into a high impedance state. The receiver has a fail-safe feature which guarantees a high output state when the inputs are left open. I/O pins are protected against multiple ESD strikes of up to 10kV. The LTC1480 is fully specified over the commercial and extended industrial temperature range. The LTC1480 is available in 8-pin SO and DIP packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATI
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Battery-Powered RS485/RS422 Applications Low Power RS485/RS422 Transceiver Level Translator
TYPICAL APPLICATI
3.3V LTC1480 RO 1 RE DE D1 2 3 4 D R 8 7 6 5 B 120 A
3.3V RS485 Network
3.3V LTC1480 SHIELD SHIELD B 120 A 3.3V 8 B 7 A 6 5 6 5 D 3 4 8 7 R 1 RO
OUTPUT VOLTAGE (V)
2
RE DE D1
R 1 RO 2 RE 3
LTC1480 D
4 DE D1
LTC1480 * TA01
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Driver Differential Output Voltage vs Output Current
3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 0 10 20 30 40 50 60 70 OUTPUT CURRENT (mA) 80 90 VCC = 3.3V TA = 25C
LTC1480 * TA02
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1
LTC1480 ABSOLUTE
(Note 1)
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RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW RO 1 RE 2 DE 3 DI 4 N8 PACKAGE 8-LEAD PDIP D R 8 7 6 5 VCC B A GND
Supply Voltage (VCC) ................................................ 7V Control Input Voltage ..................... - 0.3V to VCC + 0.3V Driver Input Voltage ....................... - 0.3V to VCC + 0.3V Driver Output Voltage ........................................... 14V Receiver Input Voltage .......................................... 14V Receiver Output Voltage ................ - 0.3V to VCC + 0.3V Operating Temperature Range LTC1480C........................................ 0C TA 70C LTC1480I .................................... - 40C TA 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
S8 PACKAGE 8-LEAD PLASTIC SO
ORDER PART NUMBER LTC1480CN8 LTC1480IN8 LTC1480CS8 LTC1480IS8 S8 PART MARKING 1480 1480I
TJMAX = 125C, JA = 130C/ W (N8) TJMAX = 125C, JA = 150C/ W (S8)
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL VOD1 VOD2 VOD VOC VOC VIH VIL IIN1 IIN2 VTH VTH VOH VOL IOZR RIN ICC ISHDN IOSD1 IOSD2 IOSR PARAMETER Differential Driver Output Voltage (Unloaded) Differential Driver Output Voltage (with Load) Change in Magnitude of Driver Differential Output Voltage for Complementary Output States Driver Common-Mode Output Voltage Change in Magnitude of Driver Common-Mode Output Voltage for Complementary Output States Input HIGH Voltage Input LOW Voltage Input Current Input Current (A, B) Differential Input Threshold Voltage for Receiver Receiver Input Hysteresis Receiver Output HIGH Voltage Receiver Output LOW Voltage Three-State (High Impedance) Output Current at Receiver Receiver Input Resistance Supply Current Supply Current in Shutdown Mode Driver Short-Circuit Current, VOUT = HIGH Driver Short-Circuit Current, VOUT = LOW Receiver Short-Circuit Current
VCC = 3.3V (Notes 2, 3)
CONDITIONS IO = 0V R = 27 (RS485), Figure 1 R = 50 (RS422) R = 27 or R = 50, Figure 1 R = 27 or R = 50, Figure 1 R = 27 or R = 50, Figure 1 DE, DI, RE DE, DI, RE DE, DI, RE DE = 0, VCC = 0V or 3.6V, VIN = 12V DE = 0, VCC = 0V or 3.6V, VIN = - 7V - 7V VCM 12V VCM = 0V IO = - 4mA, VID = 200mV IO = 4mA, VID = - 200mV VCC = Max, 0.4V VO 2.4V - 7V VCM 12V No Load, Output Enabled No Load, Output Disabled DE = 0, RE = VCC - 7V VO 12V - 7V VO 12V 0V VO VCC
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MIN 1.5 2.0
TYP
MAX 3.3 3.3 0.2 2 0.2
UNITS V V V V V V V
2 0.8 2 1.0 - 0.8 - 0.2 70 2 0.4 1 12 400 300 1 35 35 7 600 500 10 250 250 85 0.2
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V A mA mA V mV V V A k A A A mA mA mA
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LTC1480
SWITCHI G CHARACTERISTICS
SYMBOL tPLH tPHL tSKEW tR, tF tZH tZL tLZ tHZ tPLH tPHL tSKD tZL tZH tLZ tHZ fMAX tSHDN tZH(SHDN) tZL(SHDN) tZH(SHDN) tZL(SHDN) PARAMETER Driver Input to Output Driver Input to Output Driver Output to Output Driver Rise or Fall Time Driver Enable to Output HIGH Driver Enable to Output LOW Driver Disable Time from LOW Driver Disable Time from HIGH Receiver Input to Output Receiver Input to Output
tPLH - tPHL Differential Receiver Skew
Receiver Enable to Output LOW Receiver Enable to Output HIGH Receiver Disable from LOW Receiver Disable from HIGH Maximum Data Rate Time to Shutdown Driver Enable from Shutdown to Output HIGH Driver Enable from Shutdown to Output LOW Receiver Enable from Shutdown to Output HIGH Receiver Enable from Shutdown to Output LOW
The q denotes specifications which apply over the full operating temperature range. Note 1: Absolute maximum ratings are those beyond which the safety of the device cannot be guaranteed.
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Temperature
425 400
SUPPLY CURRENT (A)
OUTPUT CURRENT (mA)
375 350 325 300 275 250 225 VCC = 3.3V
DIFFERENTIAL VOLTAGE (V)
THERMAL SHUTDOWN WITH DRIVER ENABLED
DRIVER DISABLED
200 -50 -25
0
25 50 75 100 125 150 175 TEMPERATURE (C)
LT1480 * TPC01
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VCC = 3.3V (Notes 2, 3)
MIN
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CONDITIONS RDIFF = 54, CL1 = CL2 = 100pF, (Figures 3 and 5)
TYP 50 50 10 15 70 70 70 70
MAX 80 80 20 40 120 120 120 120 200 200 80 80 80 80 600 120 120 4500 4500
UNITS ns
25 25 5
CL = 100pF (Figures 4, 6), S2 Closed CL = 100pF (Figures 4, 6), S1 Closed CL = 15pF (Figures 4, 6), S1 Closed CL = 15pF (Figures 4, 6), S2 Closed RDIFF = 54, CL1 = CL2 = 100pF, (Figure 3, 7)
q q q q q q
ns ns ns ns ns ns ns ns ns ns ns Mbits/s ns ns ns ns ns
30 30
140 140 13 50 50 50 50
CRL = 15pF (Figures 2, 8), S1 Closed CRL = 15pF (Figures 2, 8), S2 Closed CRL = 15pF (Figures 2, 8), S1 Closed CRL = 15pF (Figures 2, 8), S2 Closed DE = 0, RE = CL = 100pF (Figures 4, 6), S2 Closed CL = 100pF (Figures 4, 6), S1 Closed CL = 15pF (Figures 2, 8), S2 Closed CL = 15pF (Figures 2, 8), S1 Closed
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2.5 50 200 70 70
Note 2: All currents into device pins are positive; all currents out ot device pins are negative. All voltages are referenced to device ground unless otherwise specified. Note 3: All typicals are given for VCC = 3.3V and TA = 25C.
Driver Output Low/High Voltage vs Output Current
150 100 50 0 - 50 -100 -150 0 0.5 2.5 1.0 1.5 2.0 OUTPUT VOLTAGE (V) 3.0 3.5 VCC = 3.3V TA = 25C 2.2 2.1 2.0 1.9
Driver Differential Output Voltage vs Temperature
RL = 100
RL = 54 1.8 1.7 1.6 VCC = 3.3V 1.5 -40 -20 40 20 60 0 TEMPERATURE (C) 80 100
LT1480 * TPC02
LTC1480 * TPC03
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LTC1480 TYPICAL PERFORMANCE CHARACTERISTICS
Driver Skew vs Temperature
7.0 6.5 6.0 VCC = 3.3V
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
TIME (ns)
5.5 5.0 4.5 4.0 3.5 3.0 - 40 - 20
0
40 60 20 TEMPERATURE (C)
Receiver tPLH - tPHL vs Temperature
12 VCC = 3.3V 10
OUTPUT VOLTAGE (V)
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0.4 0.3 0.2 0.1 0 -40 -20
OUTPUT VOLTAGE (V)
TIME (ns)
6 4 2 0 -40 -20
40 20 60 0 TEMPERATURE (C)
PIN FUNCTIONS
RO (Pin 1): Receiver Output. If the receiver output is enabled (RE LOW) and A > B by 200mV, then RO will be HIGH. If A < B by 200mV, then RO will be LOW. RE (Pin 2): Receiver Output Enable. A LOW enables the receiver output, RO. A HIGH input forces the receiver output into a high impedance state. DE (Pin 3): Driver Outputs Enable. A HIGH on DE enables the driver output. A, B and the chip will function as a line driver. A low input will force the driver outputs into a high impedance state and the chip will function as a line receiver. If RE is high and DE is LOW, the part will enter a low power (1A) shutdown state. If RE is low and DE is high, the driver outputs will be fed back to the receiver and the receive output will correspond to the driver input. DI (Pin 4): Driver Input. If the driver outputs are enabled (DE HIGH) then a low on DI forces the outputs A LOW and B HIGH. A HIGH on DI with the driver outputs enabled will force A HIGH and B LOW. GND (Pin 5): Ground. A (Pin 6): Driver Output/Receiver Input. B (Pin 7): Driver Output/Receiver Input. VCC (Pin 8): Positive Supply. 3.0V < VCC < 3.6V.
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80
LT1480 * TPC04
Receiver Output Low Voltage vs Output Current
25 VCC = 3.3V TA = 25C - 16 - 14 - 12 - 10 -8 -6 -4 -2 0
100
Receiver Output High Voltage vs Output Current
VCC = 3.3V TA = 25C
20
15
10
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0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 OUTPUT VOLTAGE (V)
LTC1480 * TPC05
0 3.30 3.05 2.80 2.55 2.30 2.05 1.80 1.55 1.30 OUTPUT VOLTAGE (V)
LT1480 * TPC06
Receiver Output Low Voltage vs Temperature
0.6 0.5 VCC = 3.3V 1 = 8mA
3.0
Receiver Output High Voltage vs Temperature
VCC = 3.3V 1 = 8mA
2.8
2.6
2.4
2.2
80
100
40 20 60 0 TEMPERATURE (C)
80
100
2.0 - 40 - 20
40 20 0 60 TEMPERATURE (C)
80
100
LT1480 * TPC07
LTC1480 * TPC08
LTC1480 * TPC09
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LTC1480
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LTC1480 Transmitting
INPUTS RE X X 0 1 DE 1 1 0 0 DI 1 0 X X 0 1 Z Z* OUTPUTS B A 1 0 Z Z* RE 0 0 0 1
*Shutdown mode
TEST CIRCUITS
A R VOD R B
LTC1480 * F01
3V DE A DI LTC1480 DRIVER B RDIFF CL2 CL1 A
S1
Figure 3. Driver/Receiver Timing Test Circuit
SWITCHI G TI E WAVEFOR S
3V DI 0V t PLH B VO A VO 0V -VO 1/2 VO 10% tr tSKEW 90% VDIFF = V(A) - V(B) tf t SKEW 90% 10%
LTC1480 * F05
1.5V
Figure 5. Driver Propagation Delays
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LTC1480 Receiving
INPUTS DE 0 0 0 0 A-B 0.2V - 0.2V Inputs Open X OUTPUTS RO 1 0 1 Z*
*Shutdown mode
RECEIVER OUTPUT
VOC
TEST POINT
S1
1k VCC
CRL
1k
S2
LTC1480 * F02
Figure 1. Driver DC Test Load
Figure 2. Receiver Timing Test Load
LTC1480 B RECEIVER RE
LTC1480 * F03
RO 15pF
OUTPUT UNDER TEST 500 S2 CL
LTC1480 * F04
VCC
Figure 4. Driver Timing Test Load
f = 1MHz, tr 10ns, tf 10ns t PHL
1.5V 1/2 VO
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LTC1480
SWITCHI G TI E WAVEFOR S
3V DE 0V 3.3V A, B VOL VOH A, B 0V t ZH(SHDN), t ZH t HZ
LTC1480 * F06
1.5V
Figure 6. Driver Enable and Disable Times
VOH RO VOL t PHL VOD2 A-B -VOD2 0V 1.5V OUTPUT f = 1MHz, tr 10ns, tf 10ns INPUT t PLH 0V
LTC1480 * F07
Figure 7. Receiver Propagation Delays
3V RE 0V 3.3V RO VOL VOH RO 0V t ZH(SHDN), tZH t HZ
LTC1480 * F08
1.5V
Figure 8. Receiver Enable and Disable Times
APPLICATIO S I FOR ATIO
CMOS Output Driver
The LTC1480 transceiver provides full RS485 compatibility while operating from a single 3.3V supply. The RS485 specification requires that a transceiver withstand common-mode voltages of up to 12V or -7V at the RS485 line connections. Additionally, the transceiver must be immune to both ESD and latch-up, This rules out traditional CMOS drivers, which include parasitic diodes from their driver outputs to each supply rail (Figure 9). The LTC1480 uses a proprietary process enhancement which adds a pair of Schottky diodes to the output stage (Figure 10), preventing current from flowing when the common-mode
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f = 1MHz, tr 10ns, tf 10ns t ZL(SHDN), t ZL t LZ
1.5V
2.3V
OUTPUT NORMALLY LOW
0.5V
2.3V
OUTPUT NORMALLY HIGH
0.5V
1.5V
f = 1MHz, tr 10ns, tf 10ns t ZL(SHDN), tZL t LZ
1.5V
1.5V
OUTPUT NORMALLY LOW
0.5V
1.5V
OUTPUT NORMALLY HIGH
0.5V
VCC
VCC P1
SD3 P1
D1 OUTPUT N1 D2
D1 OUTPUT
LOGIC
LOGIC N1
SD4 D2
LTC1480 * F10
LTC1480 * F09
Figure 9. Conventional CMOS Output Stage
Figure 10. LTC1480 Output Stage
LTC1480
APPLICATIO S I FOR ATIO
voltage exceeds the supply rails. Latch-up at the output drivers is virtually eliminated and the driver is prevented from loading the line under RS485 specified fault conditions. A proprietary output protection structure protects the transceiver line terminals against ESD strikes of up to 10kV. When two or more drivers are connected to the same transmission line, a potential condition exists whereby more than two drivers are simultaneously active. If one or more drivers is sourcing current while another driver is sinking current, excessive power dissipation may occur within either the sourcing or sinking element. This condition is defined as driver contention, since multiple drivers are competing for one transmission line. The LTC1480 provides a current limiting scheme to prevent driver contention failure. When driver contention occurs, the current drawn is limited to about 70mA preventing excessive power dissipation within the drivers. The LTC1480 has a thermal shutdown feature which protects the part from excessive power dissipation. Under extreme fault conditions, up to 250mA can flow through the part causing rapid internal temperature rise. The thermal shutdown circuit will disable the driver outputs when the internal temperature reaches 150C and turns them back on when the temperature cools to 130C. This cycle will repeat as necessary until the fault condition is removed. Receiver Inputs The LTC1480 features an input common-mode range covering the entire RS485 specified range of -7V to 12V. Differential signals of greater than 200mV within the specified input common-mode range will be converted to a TTL compatible signal at the receiver output. A small amount of input hysteresis is included to minimize the effects of noise on the line signals. If the receiver inputs are floating (unterminated) an internal pull-up of 10A at the A input will force the receiver output to a known high state. Low Power Operation The LTC1480 draws very little supply current whenever the driver outputs are disabled. In shutdown mode the quiescent current is typically less than 1A. With the
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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receiver active and the driver outputs disabled, the LTC1480 will typically draw 300A quiescent current. With the driver outputs enabled but unterminated, quiescent current will rise as one of the two outputs sources current into the internal receiver input resistance. With the minimum receiver input resistance of 12k and the maximum output swing of 3.3V, the quiescent current will rise by a maximum of 275A. Typical quiescent current rise with the driver enabled is about 100A. The quiescent current rises significantly if the driver is enabled when it is externally terminated. With 1/2 termination load (120 between the driver outputs) the quiescent current will jump to at least 13mA as the drivers force a minimum of 1.5V across the termination resistance. With a fully terminated 60 line attached, the current will rise to greater than 25mA with the driver enabled, completely overshadowing the extra 100A drawn by internal receiver inputs. Shutdown Mode Both the receiver output (RO) and the driver outputs (A, B) can be placed in three-state mode by bringing RE HIGH and DE LOW respectively. In addition, the LTC1480 will enter shutdown mode when RE is HIGH and DE is LOW. In shutdown the LTC1480 typically draws only 1A of supply current. In order to guarantee that the part goes into shutdown, RE must be high and DE must be LOW for at least 600ns simultaneously. If this time duration is less than 50ns the part will not enter shutdown mode. Propagation Delay Many digital encoding schemes are dependent upon the difference in the propagation delay times of the driver and receiver. Figure 11 shows the test circuit for the LTC1480 propagation delay. The receiver delay times are:
tPLH - tPHL = 13ns Typ, VCC = 3.3V
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The driver's skew times are: tSKEW = 10ns Typ, VCC = 3.3V 20ns Max, VCC = 3.3V, TA = - 40C to 85C
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LTC1480
APPLICATIO S I FOR ATIO
TTL IN t r, t f < 6ns D
Figure 11. Receiver Propagation Delay Test Circuit
PACKAGE DESCRIPTION
0.300 - 0.325 (7.620 - 8.255)
Dimensions in inches (millimeters) unless otherwise noted. N8 Package 8-Lead Plastic DIP
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 0.125 (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
)
0.045 0.015 (1.143 0.381) 0.100 0.010 (2.540 0.254)
*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)
0.053 - 0.069 (1.346 - 1.752) 0- 8 TYP
0.016 - 0.050 0.406 - 1.270
0.014 - 0.019 (0.355 - 0.483)
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm).
RELATED PARTS
PART NUMBER LTC485 LTC1481 LTC1483 LTC1485 LTC1487 DESCRIPTION 5V Low Power RS485 Interface Transceiver 5V Ultra-Low Power RS485 Transceiver with Shutdown 5V Ultra-Low Power RS485 Low EMI Transceiver with Shutdown 5V Differential Bus Transceiver 5V Ultra-Low Power RS485 with Low EMI Shutdown and High Input Impendance COMMENTS Low power Lowest power Low EMI/lowest power Highest speed High input impendance/low EMI/lowest power
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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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100pF BR R 100 100pF R RECEIVER OUT
LTC1480 * F11
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0.255 0.015* (6.477 0.381)
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2
3
4
N8 0694
S8 Package 8-Lead Plastic SOIC
0.189 - 0.197* (4.801 - 5.004) 8 7 6 5
0.004 - 0.010 (0.101 - 0.254) 0.228 - 0.244 (5.791 - 6.197) 0.050 (1.270) BSC 1 2 3 4
0.150 - 0.157* (3.810 - 3.988)
SO8 0294
LT/GP 0695 10K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1995

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