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19-1284; Rev 0; 10/97
Low-Cost, High-Speed, Single-Supply, Gain of +2 Buffers with Rail-to-Rail Outputs in SOT23
_______________General Description
The MAX4014/MAX4017/MAX4019/MAX4022 are precision, closed-loop, gain of +2 (or -1) buffers featuring high slew rates, high output current drive, and low differential gain and phase errors. These single-supply devices operate from +3.15V to +11V, or from 1.575V to 5.5V dual supplies. The input voltage range extends 100mV beyond the negative supply rail and the outputs swing Rail-to-Rail(R). These devices require only 5.5mA of quiescent supply current while achieving a 200MHz -3dB bandwidth and a 600V/s slew rate. In addition, the MAX4019 has a disable feature that reduces the supply current to 400A. Input voltage noise for these parts is only 10nV/Hz and input current noise is only 1.3pA/Hz. This buffer family is ideal for low-power/low-voltage applications that require wide bandwidth, such as video, communications, and instrumentation systems. For space-sensitive applications, the MAX4014 comes in a tiny 5-pin SOT23 package.
____________________________Features
o Internal Precision Resistors for Closed-Loop Gains of +2 or -1 o High Speed: 200MHz -3dB Bandwidth 30MHz 0.1dB Gain Flatness (6MHz min) 600V/s Slew Rate o Single 3.3V/5.0V Operation o Outputs Swing Rail-to-Rail o Input Voltage Range Extends Beyond VEE o Low Differential Gain/Phase: 0.04%/0.02 o Low Distortion at 5MHz: -78dBc Spurious-Free Dynamic Range -75dB Total Harmonic Distortion o High Output Drive: 120mA o Low, 5.5mA Supply Current o 400A Shutdown Supply Current o Space-Saving SOT23-5, MAX, or QSOP Packages
MAX4014/MAX4017/MAX4019/MAX4022
_____________________Selector Guide
PART MAX4014 MAX4017 MAX4019 MAX4022 NO. OF AMPS 1 2 3 4 ENABLE No No Yes No PIN-PACKAGE 5-Pin SOT23 8-Pin SO/MAX 14-Pin SO, 16-Pin QSOP 14-Pin SO, 16-Pin QSOP
______________Ordering Information
PART MAX4014EUK MAX4017ESA MAX4017EUA MAX4019ESD MAX4019EEE MAX4022ESD MAX4022EEE TEMP. RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C PINPACKAGE 5 SOT23-5 8 SO 8 MAX 14 SO 16 QSOP 14 SO 16 QSOP SOT TOP MARK ABZQ -- -- -- -- -- --
________________________Applications
Portable/Battery-Powered Instruments Video Line Driver Analog-to-Digital Converter Interface CCD Imaging Systems Video Routing and Switching Systems
__________Typical Operating Circuit
IN+ 75 VOUT
75
MAX4014
IN500 500
Rail-to-Rail is a registered trademark of Nippon Motorola Ltd.
GAIN OF +2 VIDEO/RF CABLE DRIVER
________________________________________________________________ Maxim Integrated Products
1
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Low-Cost, High-Speed, Single-Supply, Gain of +2 Buffers with Rail-to-Rail Outputs in SOT23 MAX4014/MAX4017/MAX4019/MAX4022
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC to VEE) ..................................................12V IN_-, IN_+, OUT_, EN_ ....................(VEE - 0.3V) to (VCC + 0.3V) Output Short-Circuit Duration to VCC or VEE ..............Continuous Continuous Power Dissipation (TA = +70C) 5-pin SOT23 (derate 7.1mW/C above+70C)..............571mW 8-pin SO (derate 5.9mW/C above +70C)...................471mW 8-pin MAX (derate 4.1mW/C above +70C) ..............330mW 14-pin SO (derate 8.3mW/C above +70C).................667mW 16-pin QSOP (derate 8.3mW/C above +70C)............667mW Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10sec) .............................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or at any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS
(VCC = +5V, VEE = 0V, IN_- =0V, EN_ = 5V, RL = to ground, VOUT = VCC / 2, noninverting configuration, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER Input Voltage Range Input Offset Voltage Input Offset Voltage Drift Input Offset Voltage Matching Input Bias Current Input Resistance Voltage Gain Output Resistance Output Current Short-Circuit Output Current IB RIN AV ROUT IOUT ISC SYMBOL VIN VOS TCVOS Any channels for MAX4017/MAX4019/MAX4022 IN_+ (Note 2) IN_+, over input voltage range RL 50, (VEE + 0.5V) VOUT (VCC - 2.0V) f = DC RL = 20 to VCC or VEE Sinking or sourcing RL = 50 Output Voltage Swing VOUT RL =150 RL = 2k Power-Supply Rejection Ratio (Note 3) Operating Supply-Voltage Range Disabled Output Resistance EN_ Logic-Low Threshold EN_ Logic-High Threshold EN_ Logic Input Low Current EN_ Logic Input High Current Quiescent Supply Current (per Buffer) VIL VIH IIL IIH ICC VCC - VOH VOL - VEE VCC - VOH VOL - VEE VCC - VOH VOL - VEE 46 54 3.15 1 VCC - 2.6 VCC - 1.5 (VEE + 0.2V) EN_ VCC EN_ = VEE 0.5 200 0.5 5.5 0.4 550 10 8.0 0.7 80 1.9 IN_+ IN_RL = 50 CONDITIONS MIN VEE - 0.1 VEE - 0.1 4 8 1 5.4 3 2 25 120 150 1.60 0.04 0.75 0.04 0.06 0.06 57 66 45 11.0 V k V V A A mA dB 2.00 0.50 1.50 0.50 V 2.1 20 TYP MAX VCC - 2.25 VCC + 0.1 20 UNITS V mV V/C mV A M V/V m mA mA
VCC = 5V, VEE = 0V, VOUT = 2V PSRR VCC = 5V, VEE = -5V, VOUT = 0V VCC = 3.3V, VEE = 0V, VOUT = 0.9V VCC to VEE ROUT(OFF) MAX4019, EN_ = 0V, 0V VOUT 5V MAX4019 MAX4019 MAX4019
MAX4019, EN_ = VCC Enabled (EN_ = VCC) MAX4019, disabled (EN_ = VEE)
2
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Low-Cost, High-Speed, Single-Supply, Gain of +2 Buffers with Rail-to-Rail Outputs in SOT23 MAX4014/MAX4017/MAX4019/MAX4022
AC ELECTRICAL CHARACTERISTICS
(VCC = +5V, VEE = 0V, IN_- = 0V, EN_ = 5V, RL = 100 to ground, noninverting configuration, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Small-Signal -3dB Bandwidth Large-Signal -3dB Bandwidth Bandwidth for 0.1dB Gain Flatness Slew Rate Settling Time to 0.1% Rise/Fall Time Spurious-Free Dynamic Range SYMBOL BWSS BWLS BW0.1dB SR tS tR, tF SFDR VOUT = 2Vp-p VOUT = 20mVp-p (Note 4) VOUT = 2V step VOUT = 2V step VOUT = 100mVp-p fC = 5MHz, VOUT = 2Vp-p Second harmonic Harmonic Distortion HD VOUT = 2Vp-p, fC = 5MHz f = 10.0MHz fC = 10MHz, AVCL = +2V/V DP DG en in CIN COUT(OFF) ZOUT tON tOFF MAX4019, EN_ = 0V f = 10MHz MAX4019 MAX4019 MAX4017/MAX4019/MAX4022, f = 10MHz, VOUT = 20mVp-p XTALK MAX4017/MAX4019/MAX4022, f = 10MHz, VOUT = 2Vp-p NTSC, RL = 150 NTSC, RL = 150 f = 10kHz f = 10kHz Third harmonic Total harmonic distortion 6 CONDITIONS VOUT = 20mVp-p MIN TYP 200 140 30 600 45 1 -78 -78 -82 -75 35 11 0.02 0.04 10 1.3 1 2 6 100 1 0.1 -95 dBm dBm degrees % nV/Hz pA/Hz pF pF ns s dB dB dBc MAX UNITS MHz MHz MHz V/s ns ns dBc
Third-Order Intercept Input 1dB Compression Point Differential Phase Error Differential Gain Error Input Noise Voltage Density Input Noise Current Density Input Capacitance Disabled Output Capacitance Output Impedance Buffer Enable Time Buffer Disable Time Buffer Gain Matching Buffer Crosstalk
IP3
Note 1: The MAX4014EUK is 100% production tested at TA = +25C. Specifications over temperature limits are guaranteed by design. Note 2: Tested with VOUT = +2.5V. Note 3: PSRR for single +5V supply tested with VEE = 0V, VCC = +4.5V to +5.5V; for dual 5V supply with VEE = -4.5V to -5.5V, VCC = +4.5V to +5.5V; and for single +3V supply with VEE = 0V, VCC = +3.15V to +3.45V. Note 4: Guaranteed by design.
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Low-Cost, High-Speed, Single-Supply, Gain of +2 Buffers with Rail-to-Rail Outputs in SOT23 MAX4014/MAX4017/MAX4019/MAX4022
__________________________________________Typical Operating Characteristics
(VCC = +5V, VEE = 0V, AVCL = +2, RL = 150 to VCC / 2, TA = +25C, unless otherwise noted.)
SMALL-SIGNAL GAIN vs. FREQUENCY
MAX4014-01
GAIN FLATNESS vs. FREQUENCY
MAX4014-02
LARGE-SIGNAL GAIN vs. FREQUENCY
7 6 GAIN (dB) 5 4 3 2 1 0
MAX4014-03
8 7 6 GAIN (dB) 5 4 3
6.8 6.7 6.6 6.5 GAIN (dB) 6.4 6.3 6.2 6.1
8
2 1 100k 1M 10M FREQUENCY (Hz) 100M 1G
6.0 5.9 100k 1M 10M FREQUENCY (Hz) 100M 1G
100k
1M
10M FREQUENCY (Hz)
100M
1G
MAX4017/19/22 CROSSTALK vs. FREQUENCY
MAX4014-04
CLOSED-LOOP OUTPUT IMPEDANCE vs. FREQUENCY
MAX4014-05
HARMONIC DISTORTION vs. FREQUENCY
-10 HARMONIC DISTORTION (dBc) -20 -30 -40 -50 -60 -70 -80 -90 2ND HARMONIC VOUT = 2Vp-p
MAX4014-06
50 30 10 CROSSTALK (dB)
1000
0
100 IMPEDANCE ()
-10 -30 -50 -70 -90 -110 -130 -150 100k 1M 10M FREQUENCY (Hz) 100M 1G
10
1
3RD HARMONIC
0.1 0.1M 1M 10M 100M FREQUENCY (Hz)
-100 100k 1M 10M 100M FREQUENCY (Hz)
HARMONIC DISTORTION vs. LOAD
MAX4014-07
HARMONIC DISTORTION vs. OUTPUT SWING
MAX4014-08
MAX4019 OFF ISOLATION vs. FREQUENCY
0 -10 OFF ISOLATION (dB) -20 -30 -40 -50 -60 -70
MAX4014-09
0 -10 HARMONIC DISTORTION (dBc) -20 -30 -40 -50 -60 -70 -80 -90 -100 0 200 400 600 LOAD () 800 3rd HARMONIC 2rd HARMONIC f = 5MHz VOUT = 2Vp-p
0 -10 HARMONIC DISTORTION (dBc) -20 -30 -40 -50 -60 -70 -80 -90 -100 3RD HARMONIC 0.5 1.0 1.5 OUTPUT SWING (Vp-p) 2ND HARMONIC f = 5MHz
10
-80 -90 2.0 100k 1M 10M FREQUENCY (Hz) 100M
1000
4
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Low-Cost, High-Speed, Single-Supply, Gain of +2 Buffers with Rail-to-Rail Outputs in SOT23
__________________________________________Typical Operating Characteristics
(VCC = +5V, VEE = 0V, AVCL = +2, RL = 150 to VCC / 2, TA = +25C, unless otherwise noted.)
POWER-SUPPLY REJECTION vs. FREQUENCY
MAX4014-10
MAX4014/MAX4017/MAX4019/MAX4022
CURRENT NOISE DENSITY vs. FREQUENCY
MAX4014-11
VOLTAGE NOISE DENSITY vs. FREQUENCY
MAX4014-12
20 10
POWER-SUPPLY REJECTION (dB)
10
100
0 NOISE (pA/ Hz) NOISE (nV/Hz) 1 100k 1M 10M FREQUENCY (Hz) 100M 1 10 100 1k 10k 100k 1M 10M FREQUENCY (Hz) -10 -20 -30 -40 -50 -60 -70 -80 1 1 10 100 1k 10k 100k 1M 10M FREQUENCY (Hz)
10
OUTPUT SWING vs. LOAD RESISTANCE
MAX4014-13
OUTPUT SWING vs. LOAD RESISTANCE (RL)
MAX4014-14
BANDWIDTH vs. LOAD RESISTANCE
350 300 BANDWIDTH (MHz) 250 200 150 100 50 0
MAX4014-15
5
4.5 4.0 OUTPUT SWING (Vp-p) 3.5 3.0 2.5 2.0 1.5
400
OUTPUT SWING (Vp-p)
4
3
2 10 100 1k 10k 100k 1M LOAD RESISTANCE ()
1.0 25 50 75 100 125 LOAD RESISTANCE () 150
0
100
200 300 400 500 LOAD RESISTANCE ()
600
POWER-SUPPLY CURRENT (PER AMPLIFIER) vs. TEMPERATURE
MAX4014-16
INPUT BIAS CURRENT vs. TEMPERATURE
MAX4014-17
INPUT OFFSET CURRENT vs. TEMPERATURE
MAX4014-18
7 POWER-SUPPLY CURRENT (mA)
6.0
0.20
6
5.5
INPUT OFFSET CURRENT (A) -50 -25 0 25 50 TEMPERATURE (C) 75 100
INPUT BIAS CURRENT (A)
0.16
0.12
5
5.0
0.08
4
4.5
0.04
3 -50 -25 0 25 50 TEMPERATURE (C) 75 100
4.0
0 -50 -25 0 25 50 TEMPERATURE (C) 75 100
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Low-Cost, High-Speed, Single-Supply, Gain of +2 Buffers with Rail-to-Rail Outputs in SOT23 MAX4014/MAX4017/MAX4019/MAX4022
__________________________________________Typical Operating Characteristics
(VCC = +5V, VEE = 0V, AVCL = +2, RL = 150 to VCC / 2, TA = +25C, unless otherwise noted.)
POWER-SUPPLY CURRENT (PER AMPLIFIER) vs. POWER-SUPPLY VOLTAGE
MAX4014-19
INPUT OFFSET VOLTAGE vs. TEMPERATURE
MAX4014-20
VOLTAGE SWING vs. TEMPERATURE
RL = 150 TO VCC / 2 4.8 VOLTAGE SWING (Vp-p)
MAX4014-21
10 POWER-SUPPLY CURRENT (mA) 8
5
5.0
INPUT OFFSET VOLTAGE (mV)
4
6
3
4.6
4
2
4.4
2
1
4.2
0 3 4 5 6 7 8 9 10 POWER-SUPPLY VOLTAGE (V) 11
0 -50 -25 0 25 50 TEMPERATURE (C) 75 100
4.0 -50 -25 0 25 50 TEMPERATURE (C) 75 100
DIFFERENTIAL GAIN AND PHASE
0.01 0.00 -0.01 -0.02 -0.03 -0.04 -0.05 0 0.010 0.005 0.000 -0.005 -0.010 -0.015 -0.020 -0.025 0 IRE IRE DIFF. PHASE (deg) DIFF. GAIN (%)
MAX4014-22
SMALL-SIGNAL PULSE RESPONSE
MAX4014-23
SMALL-SIGNAL PULSE RESPONSE (CL = 5pF)
MAX4014-24
IN VOLTAGE (25mV/div) VOLTAGE (25mV/div)
IN
100
OUT
OUT
100
TIME (20ns/div) VCM = 1.25V, RL = 100 to GROUND
TIME (20ns/div)
LARGE-SIGNAL PULSE RESPONSE
MAX4014-25
LARGE-SIGNAL PULSE RESPONSE (CL = 5pF)
MAX4014-26
ENABLE RESPONSE TIME
MAX4014-27
5.0V (ENABLE) IN VOLTAGE (500mV/div) VOLTAGE (500mV/div) IN 0V (DISABLE) EN_
OUT
OUT OUT
1V
0V TIME (20ns/div) VCM = 0.9V, RL = 100 to GROUND TIME (20ns/div) VCM = 1.75V, RL = 100 to GROUND VIN = 0.5V TIME (1s/div)
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Low-Cost, High-Speed, Single-Supply, Gain of +2 Buffers with Rail-to-Rail Outputs in SOT23
______________________________________________________________Pin Description
PIN MAX4014 SOT23-5 -- 1 2 3 4 5 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- MAX4017 SO/MAX -- -- 4 -- -- 8 1 2 3 7 6 5 -- -- -- -- -- -- -- -- -- MAX4019 SO -- -- 11 -- -- 4 7 6 5 8 9 10 14 13 12 -- -- -- 1 3 2 QSOP 8, 9 -- 13 -- -- 4 7 6 5 10 11 12 16 15 14 -- -- -- 1 3 2 MAX4022 SO -- -- 11 -- -- 4 1 2 3 7 6 5 8 9 10 14 13 12 -- -- -- QSOP 8, 9 -- 13 -- -- 4 1 2 3 7 6 5 10 11 12 16 15 14 -- -- -- N.C. OUT VEE IN+ INVCC OUTA INAINA+ OUTB INBINB+ OUTC INCINC+ OUTD INDIND+ ENA ENB ENC No Connect. Not internally connected. Tie to ground or leave open. Amplifier Output Negative Power Supply or Ground (in single-supply operation) Noninverting Input Inverting Input Positive Power Supply Amplifier A Output Amplifier A Inverting Input Amplifier A Noninverting Input Amplifier B Output Amplifier B Inverting Input Amplifier B Noninverting Input Amplifier C Output Amplifier C Inverting Input Amplifier C Noninverting Input Amplifier D Output Amplifier D Inverting Input Amplifier D Noninverting Input Enable Input for Amplifier A Enable Input for Amplifier B Enable Input for Amplifier C NAME FUNCTION
MAX4014/MAX4017/MAX4019/MAX4022
_______________________________________________________________________________________
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Low-Cost, High-Speed, Single-Supply, Gain of +2 Buffers with Rail-to-Rail Outputs in SOT23 MAX4014/MAX4017/MAX4019/MAX4022
_______________Detailed Description
The MAX4014/MAX4017/MAX4019/MAX4022 are single-supply, rail-to-rail output, voltage-feedback, closedloop buffers that employ current-feedback techniques to achieve 600V/s slew rates and 200MHz bandwidths. These buffers use internal 500 resistors to provide a preset closed-loop gain of +2V/V in the noninverting configuration or -1V/V in the inverting configuration. Excellent harmonic distortion and differential gain/phase performance make these buffers an ideal choice for a wide variety of video and RF signal-processing applications. Local feedback around the buffer' s output stage ensures low output impedance, which reduces gain sensitivity to load variations. This feedback also produces demand-driven current bias to the output transistors for 120mA drive capability, while constraining total supply current to less than 7mA. +2V/V, ground the inverting terminal. Use the noninverting terminal as the signal input of the buffer (Figure 1a). Grounding the noninverting terminal and using the inverting terminal as the signal input configures the buffer for a gain of -1V/V (Figure 1b). Since the inverting input exhibits a 500 input impedance, terminate the input with a 56 resistor when the device is configured for an inverting gain in 50 applications (terminate with 88 in 75 applications). Terminate the input with a 49.9 resistor in the noninverting case. Output terminating resistors should directly match cable impedances in either configuration.
Layout Techniques
Maxim recommends using microstrip and stripline techniques to obtain full bandwidth. To ensure that the PC board does not degrade the buffer's performance, design it for a frequency greater than 1GHz. Pay careful attention to inputs and outputs to avoid large parasitic capacitance. Whether or not you use a constant-impedance board, observe the following guidelines when designing the board: * Don't use wire-wrapped boards. They are too inductive. * Don't use IC sockets. They increase parasitic capacitance and inductance. * Use surface-mount instead of through-hole components for better high-frequency performance. * Use a PC board with at least two layers; it should be as free from voids as possible. * Keep signal lines as short and as straight as possible. Do not make 90 turns; round all corners.
__________Applications Information
Power Supplies
These devices operate from a single +3.15V to +11V power supply or from dual supplies of 1.575V to 5.5V. For single-supply operation, bypass the VCC pin to ground with a 0.1F capacitor as close to the pin as possible. If operating with dual supplies, bypass each supply with a 0.1F capacitor.
Selecting Gain Configuration
Each buffer in the MAX4014 family can be configured for a voltage gain of +2V/V or -1V/V. For a gain of
IN RTIN
IN+ OUT *R OUT *R RS
IN+ OUT *R OUT *R 500 IN 500 500 INRTIN IN500
MAX40_ _
MAX40_ _
*RL = 2R
*RL = 2R
Figure 1a. Noninverting Gain Configuration (AV = +2V/V)
Figure 1b. Inverting Gain Configuration (AV = -1V/V)
8
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Low-Cost, High-Speed, Single-Supply, Gain of +2 Buffers with Rail-to-Rail Outputs in SOT23 MAX4014/MAX4017/MAX4019/MAX4022
20 0 INPUT CURRENT (A) INPUT CURRENT (A) -20 -40 -60 -80 -100 -120 -140 -160 0 100 200 300 400 500 VIL (mV ABOVE VEE) 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 0 100 200 300 400 500 VIL (mV ABOVE VEE)
Figure 2. Enable Logic-Low Input Current vs. Enable LogicLow Threshold
Figure 4. Enable Logic-Low Input Current vs. Enable LogicLow Threshold with 10k Series Resistor
ENABLE 10k
IN+
EN_
MAX40_ _
OUT
IN500 500
the output-drive capability, since the buffers have a fixed voltage gain of +2 or -1. For example, a 50 load can typically be driven from 40mV above VEE to 1.6V below VCC, or 40mV to 3.4V when operating from a single +5V supply. If the buffer is operated in the noninverting, gain of +2 configuration with the inverting input grounded, the effective input voltage range becomes 20mV to 1.7V, instead of the -100mV to 2.75V indicated by the Electrical Characteristics. Beyond the effective input range, the buffer output is a nonlinear function of the input, but it will not undergo phase reversal or latchup.
Figure 3. Circuit to Reduce Enable Logic-Low Input Current
Enable
The MAX4019 has an enable feature (EN_) that allows the buffer to be placed in a low-power state. When the buffers are disabled, the supply current will not exceed 550A per buffer. As the voltage at the EN_ pin approaches the negative supply rail, the EN_ input current rises. Figure 2 shows a graph of EN_ input current versus EN_ pin voltage. Figure 3 shows the addition of an optional resistor in series with the EN pin, to limit the magnitude of the current increase. Figure 4 displays the resulting EN pin input current to voltage relationship.
Input Voltage Range and Output Swing
The input range for the MAX4014 family extends from (VEE - 100mV) to (VCC - 2.25V). Input ground sensing increases the dynamic range for single-supply applications. The outputs drive a 2k load to within 60mV of the power-suply rails. With heavier loads, the output swing is reduced as shown in the Electrical Characteristics and the Typical Operating Characteristics. As the load increases, the input range is effectively limited by
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9
Low-Cost, High-Speed, Single-Supply, Gain of +2 Buffers with Rail-to-Rail Outputs in SOT23 MAX4014/MAX4017/MAX4019/MAX4022
IN+
MAX4014 MAX4017 MAX4019 MAX4022
OUT
500
500
RISO
MAX40_ _
VOUT CL
VIN RTIN 50 IN500 500
Figure 5. Input Protection Circuit
Figure 7. Driving a Capacitive Load through an Isolation Resistor
conditions, the input protection diodes will be forward biased, lowering the disabled output resistance to 500.
6 5 4 3 GIAN (dB) 2 1 0 -1 -2 -3 -4 100k 1M 10M FREQUENCY (Hz) 100M 1G CL = 5pF CL = 10pF CL = 15pF
Output Capacitive Loading and Stability
The MAX4014/MAX4017/MAX4019/MAX4022 provide maximum AC performance with no load capacitance. This is the case when the load is a properly terminated transmission line. However, they are designed to drive up 25pF of load capacitance without oscillating, but with reduced AC performance. Driving large capacitive loads increases the chance of oscillations occurring in most amplifier circuits. This is especially true for circuits with high loop gains, such as voltage followers. The buffer's output resistance and the load capacitor combine to add a pole and excess phase to the loop response. If the frequency of this pole is low enough to interfere with the loop response and degrade phase margin sufficiently, oscillations can occur. A second problem when driving capacitive loads results from the amplifier's output impedance, which looks inductive at high frequencies. This inductance forms an L-C resonant circuit with the capacitive load, which causes peaking in the frequency response and degrades the amplifier's gain margin. Figure 6 shows the frequency response of the MAX4014/ MAX4017/MAX4019/MAX4022 under different capacitive loads. To drive loads with greater than 25pF of capacitance or to settle out some of the peaking, the output requires an isolation resistor like the one shown in
Figure 6. Small-Signal Gain vs. Frequency with Load Capacitance and No Isolation Resistor
Disabled Output Resistance
The MAX4014/MAX4017/MAX4019/MAX4022 include internal protection circuitry that prevents damage to the precision input stage from large differential input voltages, as shown in Figure 5. This protection circuitry consists of five back-to-back Schottky diodes between IN_+ and IN_-. These diodes lower the disabled output resistance from 1k to 500 when the output voltage is 3V greater or less than the voltage at IN_+. Under these
10
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Low-Cost, High-Speed, Single-Supply, Gain of +2 Buffers with Rail-to-Rail Outputs in SOT23 MAX4014/MAX4017/MAX4019/MAX4022
30 ISOLATION RESISTANCE, RISO () 25 20 15 10 5 0 0 50 100 150 200 CAPACITIVE LOAD (pF) 250 GIAN (dB) 3 2 1 0 -1 -2 -3 -4 -5 -6 -7 100k 1M 10M FREQUENCY (Hz) 100M 1G CL = 68pF CL = 120pF RISO = 27 CL = 47pF
Figure 8. Capacitive Load vs. Isolation Resistance
Figure 9. Small-Signal Gain vs. Frequency with Load Capacitance and 27 Isolation Resistor
Figure 7. Figure 8 is a graph of the optimal isolation resistor versus load capacitance. Figure 9 shows the frequency response of the MAX4014/MAX4017/MAX4019/ MAX4022 when driving capacitive loads with a 27 isolation resistor.
Coaxial cables and other transmission lines are easily driven when properly terminated at both ends with their characteristic impedance. Driving back-terminated transmission lines essentially eliminates the lines' capacitance.
______________________________________________________________________________________
11
Low-Cost, High-Speed, Single-Supply, Gain of +2 Buffers with Rail-to-Rail Outputs in SOT23 MAX4014/MAX4017/MAX4019/MAX4022
__________________________________________________________Pin Configurations
TOP VIEW
OUT 1
5
VCC
OUTA 1 INA- 2
8 7
VCC OUTB
ENA 1 ENC 2 3
14 OUTC 13 INC-
VEE 2
MAX4014
MAX4017
INA+ 4 IN3 6 5 INBINB+ VEE 4
ENB
MAX4019
12 INC+ 11 VEE 10 INB+ 9 8 INBOUTB
VCC 4 INA+ 5 INA- 6
IN+ 3
SOT23-5
SO/MAX
OUTA 7
SO
ENA 1 ENC 2 ENB 3 VCC 4 INA+ 5 INA- 6 OUTA 7 N.C. 8
16 OUTC 15 INC14 INC+
OUTA 1 INAINA+ 2 3
14 OUTD 13 IND12 IND+
OUTA 1 INA- 2 INA+ 3 VCC 4 INB+ 5 INB- 6 OUTB 7 N.C. 8
16 OUTD 15 IND14 IND+
MAX4019
13 VEE 12 INB+ 11 INB10 OUTB 9 N.C.
VCC 4 INB+ 5 INB- 6 OUTB 7
MAX4022
11 VEE 10 INC+ 9 8 INCOUTC
MAX4022
13 VEE 12 INC+ 11 INC10 OUTC 9 N.C.
SO QSOP QSOP
___________________Chip Information
PART NUMBER MAX4014 MAX4017 MAX4019 MAX4022 NO. OF TRANSISTORS 95 190 299 362
SUBSTRATE CONNECTED TO VEE
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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