LT®1795 dual current feedback amplifier with high output current excel
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LT1795 Dual 500mA/50MHz Current Feedback Line Driver Amplifier DESCRIPTIO
LT®1795 dual current feedback amplifier with high output current excellent large signal characteristics. combination high slew rate, 500mA output drive ±15V operation enables device deliver significant power frequencies 1MHz 2MHz range. Short-circuit protection thermal shutdown insure device's ruggedness. LT1795 stable with large capacitive loads easily supply large currents required capacitive loading. shutdown feature switches device into high impedance, current mode, reducing power dissipation when device use. lower bandwidth applications, supply current reduced with single external resistor. LT1795 comes very small, thermally enhanced, 20-lead TSSOP package maximum port density line driver applications.
registered trademarks Linear Technology Corporation.
500mA Output Drive Current 50MHz Bandwidth, 900V/µs Slew Rate, Distortion: -75dBc 1MHz High Input Impedance, Wide Supply Range, ±15V Full Rate, Downstream ADSL Supported Power Enhanced Small Footprint Packages TSSOP-20, S0-20 Wide Power Shutdown Mode Power Saving Adjustable Supply Current Stable with 10,000pF
APPLICATIO
ADSL HDSL2, G.lite Drivers Buffers Test Equipment Amplifiers Video Amplifiers Cable Drivers
TYPICAL APPLICATION
Loss, High Power Central Office ADSL Line Driver
LT1795
12.5
1:2*
LT1795
12.5
1795 TA01
MIDCOM 50215 EQUIVALENT
LT1795
ABSOLUTE
RATI
Supply Voltage ±18V Input Current ±15mA Output Short-Circuit Duration (Note Indefinite Operating Temperature Range 40°C 85°C
PACKAGE/ORDER ATIO
VIEW SHDN SHDNREF
ORDER PART NUMBER LT1795CFE LT1795IFE
COMP COMP
PACKAGE 20-LEAD PLASTIC TSSOP TJMAX 150° 40°C/W (Note
Consult factory Military grade parts.
ELECTRICAL CHARACTERISTICS
denotes specifications which apply over full specified temperature range, otherwise specifications 25°C. ±15V, pulse tested, VSHDN 2.5V, VSHDNREF unless otherwise noted. (Note
SYMBOL PARAMETER Input Offset Voltage
CONDITIONS
Input Offset Voltage Matching
Input Offset Voltage Drift
Noninverting Input Current
Noninverting Input Current Matching
IIN-
Inverting Input Current
Inverting Input Current Matching
Input Noise Voltage Density Input Noise Current Density Input Noise Current Density
10kHz, =1k, 10kHz, =1k, 10kHz, =1k,
(Note
Specified Temperature Range (Note 40°C 85°C Junction Temperature 150°C Storage Temperature Range 65°C 150°C Lead Temperature (Soldering, sec). 300°C
VIEW COMP COMP SHDNREF
ORDER PART NUMBER LT1795CSW LT1795ISW
SHDN
PACKAGE 20-LEAD PLASTIC TJMAX 150° 40°C/W (Note
±4.5 ±1.5 ±0.5 ±1.5
±3.5 ±5.0 ±100
UNITS µV/°C nV/Hz pA/Hz pA/Hz
LT1795
ELECTRICAL CHARACTERISTICS
denotes specifications which apply over full specified temperature range, otherwise specifications 25°C. ±15V, pulse tested, VSHDN 2.5V, VSHDNREF unless otherwise noted. (Note
SYMBOL
PARAMETER Input Resistance Input Capacitance Input Voltage Range (Note
CONDITIONS ±12V, ±15V ±2V, ±15V ±15V ±15V, ±12V ±5V, ±15V, ±12V ±5V, ±15V ±15V ±15V ±15V, VOUT ±10V, ±5V, VOUT ±2V, ±15V, VOUT ±10V, ±5V, VOUT ±2V, ±15V,
±13.5 ±3.5
UNITS
CIN+
CMRR
Common Mode Rejection Ratio Inverting Input Current Common Mode Rejection
µA/V µA/V nA/V µA/V
PSRR
Power Supply Rejection Ratio Noninverting Input Current Power Supply Rejection Inverting Input Current Power Supply Rejection
VOUT
Large-Signal Voltage Gain Transresistance, VOUT/IIN Maximum Output Voltage Swing
±11.5 ±10.0 ±2.5 ±2.0
±12.5 ±11.5
±5V,
IOUT
Maximum Output Current Supply Current Amplifier Supply Current Amplifier, RSHDN 51k, (Note Positive Supply Current, Shutdown Output Leakage Current, Shutdown Channel Separation
±15V, ±15V, VSHDN 2.5V
V/µs V/µs
±15V
±15V, VSHDN 0.4V ±15V, VSHDN 0.4V ±15V, VOUT ±10V, 1MHz, 20VP-P, ±15V, Peaking 1.5dB 910, ±15V, Peaking 1.5dB 820,
HD2,
Harmonic Distortion Differential Mode Slew Rate (Note Slew Rate Small-Signal
Note Absolute Maximum Ratings those values beyond which life device impaired. Note Applies short-circuits ground only. short-circuit between output either supply permanently damage part when operated supplies greater than ±10V. Note LT1795C guaranteed meet specified performance from 70°C designed, characterized expected meet these extended temperature limits, tested 40°C 85°C. LT1795I guaranteed meet extended temperature limits.
Note Thermal resistance varies depending upon amount board metal attached device. maximum dissipation package exceeded, device will into thermal shutdown protected. Note Guaranteed CMRR tests. Note RSHDN connected between SHDN Note Slew rate measured ±10V output signal while operating ±15V supplies with 400.
LT1795
SMALL-SIGNAL BANDWIDTH
30mA Amplifer, ±15V, Peaking 1dB,
1.15k -3dB (MHz)
TYPICAL PERFOR CHARACTERISTICS
Supply Current Ambient Temperature
OUTPUT SATURATION VOLTAGE
SUPPLY CURRENT AMPLIFIER (mA)
OUTPUT SHORT-CIRCUIT CURRENT
±15V
TEMPERATURE (°C)
SHDN Current Voltage
±15V VSHDNREF
DISTORTION (dBc)
CURRENT INTO SHDN (mA)
DISTORTION (dBc)
VOLTAGE APPLIED SHDN
51k, 15mA Amplifer, ±15V, Peaking 1dB,
1.15k -3dB (MHz)
Output Saturation Voltage Junction Temperature
±15V
Output Short-Circuit Current Junction Temperature
±15V SOURCING SINKING
TEMPERATURE (°C)
TEMPERATURE (°C)
LT1795
LT1795
LT1795
Second Harmonic Distortion Frequency
DIFFERENTIAL VOUT 20VP-P ±15V RLOAD AMPLIFIER 10mA -100 15mA 20mA 100k FREQUENCY (Hz)
LT1795
Third Harmonic Distortion Frequency
DIFFERENTIAL VOUT 20VP-P ±15V RLOAD AMPLIFIER
10mA 20mA
15mA -100 100k FREQUENCY (Hz)
LT1795
1795
LT1795 TYPICAL PERFOR CHARACTERISTICS
Second Harmonic Distortion Frequency
DIFFERENTIAL VOUT 20VP-P ±15V RLOAD AMPLIFIER 20mA DISTORTION (dBc) -100 DIFFERENTIAL VOUT 20VP-P ±15V RLOAD AMPLIFIER 10mA 20mA 15mA -100 100k FREQUENCY (Hz)
LT1795
DISTORTION (dBc)
DISTORTION (dBc)
15mA
Third Harmonic Distortion Frequency
DISTORTION (dBc)
DISTORTION (dBc)
DISTORTION (dBc)
DIFFERENTIAL VOUT 20VP-P ±12V RLOAD AMPLIFIER 20mA
15mA 10mA -100 100k FREQUENCY (Hz)
LT1795
Second Harmonic Distortion Frequency
DISTORTION (dBc) -100 20mA 10mA 15mA DIFFERENTIAL VOUT 4VP-P ±12V RLOAD AMPLIFIER
DISTORTION (dBc)
DISTORTION (dBc)
100k FREQUENCY (Hz)
10mA
LT1795
Third Harmonic Distortion Frequency
Second Harmonic Distortion Frequency
DIFFERENTIAL VOUT 20VP-P ±12V RLOAD AMPLIFIER 10mA -100 15mA 20mA 100k FREQUENCY (Hz)
LT1795
100k FREQUENCY (Hz)
LT1795
Second Harmonic Distortion Frequency
DIFFERENTIAL VOUT 20VP-P ±12V RLOAD AMPLIFIER
Third Harmonic Distortion Frequency
DIFFERENTIAL VOUT 20VP-P ±12V RLOAD AMPLIFIER -100 10mA 15mA 100k FREQUENCY (Hz)
LT1795
20mA 10mA 15mA
20mA
-100
100k FREQUENCY (Hz)
LT1795
Third Harmonic Distortion Frequency
DIFFERENTIAL VOUT 4VP-P ±12V RLOAD AMPLIFIER
Second Harmonic Distortion Frequency
DIFFERENTIAL VOUT 4VP-P ±12V RLOAD AMPLIFIER 10mA 20mA 15mA
10mA
15mA
20mA
-100
100k FREQUENCY (Hz)
LT1795
-100
100k FREQUENCY (Hz)
LT1795
LT1795 TYPICAL PERFOR CHARACTERISTICS
Third Harmonic Distortion Frequency
DISTORTION (dBc)
DISTORTION (dBc)
-100
DISTORTION (dBc)
-100
DIFFERENTIAL VOUT 4VP-P ±12V RLOAD AMPLIFIER
10mA 15mA
20mA
-110
100k FREQUENCY (Hz)
Second Harmonic Distortion Frequency
DISTORTION (dBc)
DISTORTION (dBc)
DIFFERENTIAL VOUT 4VP-P RLOAD AMPLIFIER 20mA 15mA 10mA
-100
Slew Rate Supply Current
1200 1000 FALLING -3dB BANDWIDTH (MHz) RISING SLEW RATE (V/µs)
SUPPLY CURRENT AMPLIFIER (mA)
1795
LT1795
Second Harmonic Distortion Frequency
DIFFERENTIAL VOUT 4VP-P RLOAD AMPLIFIER
Third Harmonic Distortion Frequency
-100 15mA 20mA DIFFERENTIAL VOUT 4VP-P RLOAD AMPLIFIER
10mA
10mA 20mA 15mA
100k FREQUENCY (Hz)
LT1795
100k FREQUENCY (Hz)
LT1795
Third Harmonic Distortion Frequency
-100 15mA DIFFERENTIAL VOUT 4VP-P RLOAD AMPLIFIER
10mA
20mA 100k FREQUENCY (Hz)
LT1795
100k FREQUENCY (Hz)
LT1795
-3dB Bandwidth Supply Current
±15V =25°C RLOAD
±15V =25°C RLOAD
SUPPLY CURRENT AMPLIFIER (mA)
1795
LT1795
APPLICATIO ATIO
LT1795 dual current feedback amplifier with high output current drive capability. amplifier designed drive impedance loads such twisted-pair transmission lines with excellent linearity. SHUTDOWN/CURRENT shutdown/current feature used, connect SHDN SHDNREF ground. SHDN SHDNREF pins control biasing amplifiers. pins used either turn amplifiers completely, reducing quiescent current less then 200µA, control quiescent current normal operation.
RSHDN SHDN SHDNREF
1795
Figure RSHDN Connected Between SHDN (Pin 10); SHDNREF (Pin GND. Figure
AMPLIFIER SUPPLY CURRENT, (BOTH AMPLIFIERS)
25°C ±15V
AMPLIFIER SUPPLY CURRENT, (BOTH AMPLIFIERS)
RSHDN
1795
Figure LT1795 Amplifier Supply Current RSHDN. RSHDN Connected Between SHDN, SHDNREF (See Figure
When VSHDN VSHDNREF, device shut down. device will interface directly with CMOS logic when SHDNREF grounded control signal applied SHDN pin. Switching time between active shutdown states about 1.5µs. Figures illustrate SHDN SHDNREF pins used reduce amplifier quiescent current. both cases, external resistor used current. approaches equivalent, however required resistor values different. quiescent current will approximately times current SHDN times current SHDNREF pin. voltage across resistor either condition 1.5V. example, resistor between SHDN will
SHDN SHDNREF RSHDNREF
1795
Figure RSHDNREF Connected Between SHDNREF (Pin GND; SHDN (Pin Figure
RSHDNREF
1795
25°C ±15V
Figure LT1795 Amplifier Supply Current RSHDNREF. RSHDNREF Connected Between SHDNREF GND, SHDN (See Figure
LT1795
APPLICATIO ATIO
quiescent current 33mA with ±15V. ON/OFF control desired addition reduced quiescent current, then circuits Figures employed.
RSHDN (0V) (3.3V/5V) 2N3904 EQUIVALENT
1795
SHDN SHDNREF
INTERNAL LOGIC THRESHOLD ~1.4V
Figure Setting Amplifier Supply Current Level with ON/OFF Control, Version
SHDN RPULLUP >500k SHDNREF RSHDN1 (0V) (3.3V/5V) (0V) (3.3V/5V) RSHDN2
Q1A, Q1B: ROHM IMX1 FMG4A (W/INTERNAL
Figure Setting Multiple Amplifier Supply Current Levels with ON/OFF Control, Version
REXT
(0V) IPROG (3.3V/5V) IPROG 0.5mA REXT (SEE SHDN CURRENT VOLTAGE CHARACTERISTIC)
SHDN CONTROL SHDNREF
1795
INTERNAL LOGIC THRESHOLD 1.4V
Figure Setting Amplifier Supply Current Level with ON/OFF Control, Version
Figure illustrates partial shutdown with direct logic control. keeping output stage slightly biased output impedance remains low, preserving line termination. design equations are:
)OFF (VSHDN )OFF )OFF
VSHDN
where Logic High Level (IS)ON Supply Current Fully (IS)OFF Supply Current Partially VSHDN Shutdown Voltage 1.4V Positive Supply Voltage
1795
(0V) (3.3V/5V)
SHDN INTERNAL LOGIC THRESHOLD 1.4V CONTROL
SHDNREF
1795
Figure Partial Shutdown
THERMAL CONSIDERATIONS LT1795 contains thermal shutdown feature that protects against excessive internal (junction) temperature. junction temperature device exceeds protection threshold, device will begin cycling between normal operation state. cycling harmful part. thermal cycling occurs slow rate, typically 10ms several seconds, which depends power dissipation thermal time constants package heat sinking. Raising ambient tempera-
LT1795
APPLICATIO ATIO
ture until device begins thermal shutdown gives good indication much margin there thermal design. surface mount devices, heat sinking accomplished using heat spreading capabilities board copper traces. TSSOP package, power dissipated through exposed heatsink. package, power dissipated from package primarily through pins 17). These pins should have good thermal connection copper plane, either direct contact plated through holes. copper plane internal external layer. thermal resistance, junction-to-ambient will depend total copper area connected device. example, thermal resistance LT1795 connected inch, double sided copper plane 40°C/W. CALCULATING JUNCTION TEMPERATURE junction temperature calculated from equation: (PD)(JA) where Junction Temperature Ambient Temperature Device Dissipation Thermal Resistance (Junction-to-Ambient) Differential Input Signal Swing differential input swing limited about protection device connected between inputs. normal operation, differential voltage between input pins small, this clamp effect. However, shutdown mode, differential swing same input swing. clamp voltage will then maximum allowable input voltage. POWER SUPPLY BYPASSING obtain maximum output minimum distortion from LT1795, power supply rails should well bypassed. example, with output stage supply-
0.5A current peaks into load, power supply impedance will cause droop 0.5V, reducing available output swing that amount. Surface mount tantalum ceramic capacitors make excellent bypass elements when placed close chip. frequencies above 100kHz, 100nF ceramic capacitors. significant power must delivered below 100kHz, capacitive reactance becomes limiting factor. Larger ceramic tantalum capacitors, such 4.7µF, recommended place unit mentioned above. Inadequate bypassing evidenced reduced output swing "distorted" clipping effects when output driven rails. this observed, check supply pins device ripple directly related output waveform. Significant supply modulation indicates poor bypassing. Capacitance Inverting Input Current feedback amplifiers require resistive feedback from output inverting input stable operation. Take care minimize stray capacitance between output inverting input. Capacitance inverting input ground will cause peaking frequency response (and overshoot transient response), does degrade stability amplifier. Feedback Resistor Selection optimum value feedback resistors function operating conditions device, load impedance desired flatness response. Typical Performance tables give values which result less than peaking various resistive loads operating conditions. this level flatness required, higher bandwidth obtained lower feedback resistor. resistive loads, COMP should left open (see Capacitive Loads section). Capacitive Loads LT1795 includes optional compensation network driving capacitive loads. This network eliminates most output stage peaking associated with capacitive loads, allowing frequency response flattened.
LT1795
APPLICATIONS INFORMATION
Figure shows effect network 200pF load. Without optional compensation, there peak 85MHz caused effect capacitance output stage. Adding 0.01µF bypass capacitor between output COMP pins connects compensation
±15V 200pF COMPENSATION 3.4k COMPENSATION
VOLTAGE GAIN (dB)
3.4k COMPENSATION FREQUENCY (MHz)
1795
Figure
PACKAGE DESCRIPTIO
Dimensions inches (millimeters) unless otherwise noted. Package 20-Lead Plastic Small Outline (Wide 0.300)
(LTC 05-08-1620)
0.496 0.512* (12.598 13.005)
0.291 0.299** (7.391 7.595) 0.010 0.029 (0.254 0.737)
0.009 0.013 (0.229 0.330)
NOTE 0.016 0.050 (0.406 1.270)
NOTE: IDENT, NOTCH CAVITIES BOTTOM PACKAGES MANUFACTURING OPTIONS. PART SUPPLIED WITH WITHOUT OPTIONS *DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH SHALL EXCEED 0.006" (0.152mm) SIDE **DIMENSION DOES INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL EXCEED 0.010" (0.254mm) SIDE
greatly reduces peaking. lower value feedback resistor used, resulting response which flat ±1dB 45MHz. network greatest effect range 1000pF. Although optional compensation works well with capacitive loads, simply reduces bandwidth when connected with resistive loads. instance, with load, bandwidth drops from 48MHz 32MHz when compensation connected. Hence, compensation made optional. disconnect optional compensation, leave COMP open. DEMO BOARD demo board (DC261A) available evaluating performence LT1795. board configured differential line driver/receiver suitable xDSL applications. details, consult your local sales representative.
NOTE
0.394 0.419 (10.007 10.643)
0.093 0.104 (2.362 2.642)
0.037 0.045 (0.940 1.143)
0.050 (1.270) 0.014 0.019 (0.356 0.482)
0.004 0.012 (0.102 0.305)
(WIDE) 1098
LT1795
PACKAGE DESCRIPTIO
Dimensions millimeters (inches) unless otherwise noted.
Package 20-Lead Plastic TSSOP (4.4mm)
(LTC 05-08-1663)
6.40 6.60* (0.252 0.260)
(0.118)
6.25 6.50 (0.246 0.256)
4.30 4.48** (0.169 0.176)
5.12 (0.202)
1.15 (0.453)
0.09 0.18 (0.0035 0.0071)
0.50 0.70 (0.020 0.028)
0.65 (0.0256)
NOTE: DIMENSIONS MILLIMETERS *DIMENSIONS INCLUDE MOLD FLASH. MOLD FLASH SHALL EXCEED 0.152mm (0.006") SIDE **DIMENSIONS INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL EXCEED 0.254mm (0.010") SIDE
0.18 0.30 (0.0071 0.0118)
0.05 0.15 (0.002 0.006)
FE20 TSSOP 0200
Information furnished Linear Technology Corporation believed accurate reliable. However, responsibility assumed use. Linear Technology Corporation makes representation that interconnection circuits described herein will infringe existing patent rights.
LT1795
PLIFIED SCHEMATIC
SHDN
RELATED PARTS
PART NUMBER LT1497 LT1207 LT1886 DESCRIPTION Dual 125mA, 50MHz Current Feedback Amplifier Dual 250mA, 60MHz Current Feedback Amplifier Dual 200mA, 700MHz Voltage Feedback Amplifier COMMENTS 900V/µs Slew Rate Shutdown/Current Function Distortion: -72dBc 200kHz
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, 95035-7417
(408)432-1900 FAX: (408) 434-0507 www.linear-tech.com
SHDNREF
CURRENT SOURCES
COMP OUTPUT
1795
1795fs, sn1795 LT/TP 0200 PRINTED
LINEAR TECHNOLOGY CORPORATION 1999
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