OUT 5 V S 6 PD 7 FB 8 FB PD FEATURES High speed 85 MHz, db bandwidth (G =, RL = kω, LFCSP) 75 MHz, db bandwidth (G =, RL = kω, SOIC) 8 V/µs slew rate Low distortion: 88 dbc @ MHz (G =, RL = kω) Low power: 5 ma/amplifier @ V Low noise: 4.4 nv/ Hz Wide supply voltage range: 5 V to V Power-down feature Available in mm mm 8-lead LFCSP (single), 8-lead SOIC (single), and 4 mm 4 mm 6-lead LFCSP (dual) APPLICATIONS Instrumentation IF and baseband amplifiers Active filters ADC drivers DAC buffers Ultralow Distortion, Low Power, Low Noise, High Speed Op Amp ADA4857-/ADA4857- CONNECTION DIAGRAMS PD FB IN IN 4 ADA4857- TOP VIEW (Not to Scale) NC = NO CONNECT 8 V S 7 OUT 6 NC 5 V S Figure. 8-Lead LFCSP (CP) FB IN IN V S 4 ADA4857- TOP VIEW (Not to Scale) NC = NO CONNECT 8 PD 7 V S 6 OUT 5 NC Figure. 8-Lead SOIC (R) 74-74- V S OUT 6 5 4 ADA4857- TOP VIEW (Not to Scale) IN IN NC V S 4 V S NC IN 9 IN GENERAL DESCRIPTION The ADA4857 is a unity-gain stable, high speed, voltage feedback amplifier with low distortion, low noise, and high slew rate. With a spurious-free dynamic range (SFDR) of 88 dbc @ MHz, the ADA4857 is an ideal solution for a variety of applications, including ultrasounds, ATE, active filters, and ADC drivers. The Analog Devices, Inc., proprietary next-generation XFCB process and innovative architecture enables such high performance amplifiers. NC = NO CONNECT Figure. 6-Lead LFCSP (CP) The ADA4857 has 85 MHz bandwidth, 8 V/µs slew rate, and settles to.% in 5 ns. With a wide supply voltage range (5 V to V), the ADA4857 is an ideal candidate for systems that require high dynamic range, precision, and speed. The ADA4857- amplifier is available in a mm mm, 8-lead LFCSP and a standard 8-lead SOIC. The ADA4857- is available in a 4 mm 4 mm, 6-lead LFCSP. The LFCSP features an exposed paddle that provides a low thermal resistance path to the printed circuit board (PCB). This path enables more efficient heat transfer and increases reliability. The ADA4857 works over the extended industrial temperature range ( 4 C to 5 C). 74- Rev. B Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 96, Norwood, MA 6-96, U.S.A. Tel: 78.9.47 www.analog.com Fax: 78.46. 8 Analog Devices, Inc. All rights reserved.
ADA4857-/ADA4857- TABLE OF CONTENTS Features... Applications... Connection Diagrams... General Description... Revision History... Specifications... ±5 V Supply... 5 V Supply... 4 Absolute Maximum Ratings... 6 Thermal Resistance... 6 Maximum Power Dissipation... 6 ESD Caution... 6 Pin Configurations and Function Descriptions... 7 Typical Performance Characteristics... 9 Test Circuits... 5 Applications Information... 6 Power-Down Operation... 6 Capacitive Load Considerations... 6 Recommended Values for Various Gains... 6 Active Low-Pass Filter (LPF)... 7 Noise... 8 Circuit Considerations... 8 PCB Layout... 8 Power Supply Bypassing... 8 Grounding... 8 Outline Dimensions... 9 Ordering Guide... REVISION HISTORY 8/ Rev. A to Rev. B Changes to Table Conditions... Changes to Table Conditions... 4 Changes to Typical Performance Characteristics Conditions... 9 Changes to Figure 8... Changes to Figure 4... 5 Changes to Table 9... 6 Changes to Ordering Guide... /8 Rev. to Rev. A Changes to Table 5... 7 Changes to Table 7... 8 Changes to Figure... Added Figure 44; Renumbered Sequentially... 5 Changes to Layout... 5 Changes to Table 8... 6 Added Active Low-Pass Filter (LFP) Section... 7 Added Figure 48 and Figure 49; Renumbered Sequentially... 7 Changes to Grounding Section... 8 Exposed Paddle Notation Added to Outline Dimensions... 9 Changes to Ordering Guide... 5/8 Revision : Initial Version Rev. B Page of
ADA4857-/ADA4857- SPECIFICATIONS ±5 V SUPPLY TA = 5 C, G =, RG = RF = 499 Ω, RS = Ω for G = (SOIC), RL = kω to ground, PD = no connect, unless otherwise noted. Table. Parameter Conditions Min Typ Max Unit DYNAMIC PERFORMANCE db Bandwidth (LFCSP/SOIC) G =, VOUT =. V p-p 65 85/75 MHz G =, VOUT = V p-p 6/55 MHz G =, VOUT =. V p-p 4/5 MHz Full Power Bandwidth G =, VOUT = V p-p, THD < 4 dbc MHz Bandwidth for. db Flatness (LFCSP/SOIC) G =, VOUT = V p-p, RL = 5 Ω 75/9 MHz Slew Rate (% to 9%) G =, VOUT = 4 V step 8 V/µs Settling Time to.% G =, VOUT = V step 5 ns NOISE/HARMONIC PERFORMANCE Harmonic Distortion f = MHz, G =, VOUT = V p-p (HD) 8 dbc f = MHz, G =, VOUT = V p-p (HD) 8 dbc f = MHz, G =, VOUT = V p-p (HD) 88 dbc f = MHz, G =, VOUT = V p-p (HD) 9 dbc f = 5 MHz, G =, VOUT = V p-p (HD) 65 dbc f = 5 MHz, G =, VOUT = V p-p (HD) 6 dbc Input Voltage Noise f = khz 4.4 nv/ Hz Input Current Noise f = khz.5 pa/ Hz DC PERFORMANCE Input Offset Voltage ± ±4.5 mv Input Offset Voltage Drift. µv/ C Input Bias Current. µa Input Bias Current Drift 4.5 na/ C Input Bias Offset Current 5 na Open-Loop Gain VOUT =.5 V to.5 V 57 db PD (POWER-DOWN) PIN PD Input Voltage Chip powered down (VCC ) V Chip enabled (VCC 4.) V Turn-Off Time 5% off PD to <% of final VOUT, VIN = V, G = 55 µs Turn-On Time 5% off PD to <% of final VOUT, VIN = V, G = ns PD Pin Leakage Current Chip enabled 58 µa Chip powered down 8 µa INPUT CHARACTERISTICS Input Resistance Common mode 8 MΩ Differential mode 4 MΩ Input Capacitance Common mode pf Input Common-Mode Voltage Range ±4 V Common-Mode Rejection Ratio VCM = ± V 78 86 db OUTPUT CHARACTERISTICS Output Overdrive Recovery Time VIN = ±.5 V, G = ns Output Voltage Swing RL = kω ±4 V RL = Ω ±.7 V Output Current 5 ma Short-Circuit Current Sinking and sourcing 5 ma Capacitive Load Drive % overshoot, G = pf Rev. B Page of
ADA4857-/ADA4857- Parameter Conditions Min Typ Max Unit POWER SUPPLY Operating Range 4.5.5 V Quiescent Current 5 5.5 ma Quiescent Current (Power Down) PD VCC V 5 45 µa Positive Power Supply Rejection VS = 4.5 V to 5.5 V, VS = 5 V 59 6 db Negative Power Supply Rejection VS = 5 V, VS = 4.5 V to 5.5 V 65 68 db 5 V SUPPLY TA = 5 C, G =, RF = RG = 499 Ω, RS = Ω for G = (SOIC), RL = kω to midsupply, PD = no connect, unless otherwise noted. Table. Parameter Conditions Min Typ Max Unit DYNAMIC PERFORMANCE db Bandwidth (LFCSP/SOIC) G =, VOUT =. V p-p 595 8/75 MHz G =, VOUT = V p-p 5/4 MHz G =, VOUT =. V p-p 6/ MHz Full Power Bandwidth G =, VOUT = V p-p, THD < 4 dbc 95 MHz Bandwidth for. db Flatness (LFCSP/SOIC) G =, VOUT = V p-p, RL = 5 Ω 5/4 MHz Slew Rate (% to 9%) G =, VOUT = V step 5 V/µs Settling Time to.% G =, VOUT = V step 5 ns NOISE/HARMONIC PERFORMANCE Harmonic Distortion f = MHz, G =, VOUT = V p-p (HD) 9 dbc f = MHz, G =, VOUT = V p-p (HD) 9 dbc f = MHz, G =, VOUT = V p-p (HD) 8 dbc f = MHz, G =, VOUT = V p-p (HD) 7 dbc f = 5 MHz, G =, VOUT = V p-p (HD) 69 dbc f = 5 MHz, G =, VOUT = V p-p (HD) 55 dbc Input Voltage Noise f = khz 4.4 nv/ Hz Input Current Noise f = khz.5 pa/ Hz DC PERFORMANCE Input Offset Voltage ± ±4. mv Input Offset Voltage Drift 4.6 µv/ C Input Bias Current.7. µa Input Bias Current Drift 4.5 na/ C Input Bias Offset Current 5 na Open-Loop Gain VOUT =.5 V to.75 V 57 db PD (POWER-DOWN) PIN PD Input Voltage Chip powered down (VCC ) V Chip enabled (VCC 4.) V Turn-Off Time 5% off PD to <% of final VOUT, VIN = V, G = 8 µs Turn-On Time 5% off PD to <% of final VOUT, VIN = V, G = ns PD Pin Leakage Current Chip enable 8 µa Chip powered down µa INPUT CHARACTERISTICS Input Resistance Common mode 8 MΩ Differential mode 4 MΩ Input Capacitance Common mode pf Input Common-Mode Voltage Range to 4 V Common-Mode Rejection Ratio VCM = V to V 76 84 db Rev. B Page 4 of
ADA4857-/ADA4857- Parameter Conditions Min Typ Max Unit OUTPUT CHARACTERISTICS Overdrive Recovery Time G = 5 ns Output Voltage Swing RL = kω to 4 V RL = Ω. to.9 V Output Current 5 ma Short-Circuit Current Sinking and sourcing 75 ma Capacitive Load Drive % overshoot, G = pf POWER SUPPLY Operating Range 4.5.5 V Quiescent Current 4.5 5 ma Quiescent Current (Power Down) PD VCC V 5 5 µa Positive Power Supply Rejection VS = 4.5 V to 5.5 V, VS = V 58 6 db Negative Power Supply Rejection VS = 5 V, VS =.5 V to.5 V 65 68 db Rev. B Page 5 of
ADA4857-/ADA4857- ABSOLUTE MAXIMUM RATINGS Table. Parameter Rating Supply Voltage V Power Dissipation See Figure 4 Common-Mode Input Voltage VS.7 V to VS.7 V Differential Input Voltage ±VS Exposed Paddle Voltage VS Storage Temperature Range 65 C to 5 C Operating Temperature Range 4 C to 5 C Lead Temperature (Soldering, sec) C Junction Temperature 5 C Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. THERMAL RESISTANCE θja is specified for the worst-case conditions, that is, θja is specified for device soldered in circuit board for surface-mount packages. Table 4. Package Type θja θjc Unit 8-Lead SOIC 5 5 C/W 8-Lead LFCSP 94.5 4.8 C/W 6-Lead LFCSP 68. 9 C/W MAXIMUM POWER DISSIPATION The maximum safe power dissipation for the ADA4857 is limited by the associated rise in junction temperature (TJ) on the die. At approximately 5 C, which is the glass transition temperature, the properties of the plastic change. Even temporarily exceeding this temperature limit may change the stresses that the package exerts on the die, permanently shifting the parametric performance of the ADA4857. Exceeding a junction temperature of 75 C for an extended period can result in changes in silicon devices, potentially causing degradation or loss of functionality. The power dissipated in the package (PD) is the sum of the quiescent power dissipation and the power dissipated in the die due to the ADA4857 drive at the output. The quiescent power is the voltage between the supply pins (VS) times the quiescent current (IS). PD = Quiescent Power (Total Drive Power Load Power) P D = ( V I ) S S V V S OUT R L V R OUT RMS output voltages should be considered. If RL is referenced to VS, as in single-supply operation, the total drive power is VS IOUT. If the rms signal levels are indeterminate, consider the worst case, when VOUT = VS/4 for RL to midsupply. P D = ( V I ) S S ( V /4) S R L In single-supply operation with RL referenced to VS, the worst case is VOUT = VS/. Airflow increases heat dissipation, effectively reducing θja. In addition, more metal directly in contact with the package leads and exposed paddle from metal traces, through holes, ground, and power planes reduces θja. Figure 4 shows the maximum power dissipation in the package vs. the ambient temperature for the SOIC and LFCSP packages on a JEDEC standard 4-layer board. θja values are approximations. MAXIMUM POWER DISSIPATION (W)..5..5..5 ADA4857- (LFCSP) 4 5 6 7 8 9 AMBIENT TEMPERATURE ( C) L ADA4857- (LFCSP) ADA4857- (SOIC) Figure 4. Maximum Power Dissipation vs. Temperature for a 4-Layer Board 74-4 ESD CAUTION Rev. B Page 6 of
ADA4857-/ADA4857- PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS PD FB IN IN 4 ADA4857- TOP VIEW (Not to Scale) NC = NO CONNECT 8 V S 7 OUT 6 NC 5 V S 74-5 FB IN ADA4857- IN TOP VIEW (Not to Scale) V S 4 NC = NO CONNECT 8 7 6 5 PD V S OUT NC 74-6 Figure 5. 8-Lead LFCSP Pin Configuration Figure 6. 8-Lead SOIC Pin Configuration Table 5. 8-Lead LFCSP Pin Function Descriptions Pin No. Mnemonic Description PD Power Down. FB Feedback. IN Inverting Input. 4 IN Noninverting Input. 5 VS Negative Supply. 6 NC No Connect. 7 OUT Output. 8 VS Positive Supply. EP GND or VS Exposed Pad. The exposed pad may be connected to GND or VS. Table 6. 8-Lead SOIC Pin Function Descriptions Pin No. Mnemonic Description FB Feedback IN Inverting Input IN Noninverting Input 4 VS Negative Supply 5 NC No Connect 6 OUT Output 7 VS Positive Supply 8 PD Power Down Rev. B Page 7 of
ADA4857-/ADA4857- V S OUT OUT 5 V S 6 PD 7 FB 8 6 5 4 FB PD IN IN NC V S 4 ADA4857- TOP VIEW (Not to Scale) V S NC IN 9 IN NC = NO CONNECT Figure 7. 6-Lead LFCSP Pin Configuration 74-7 Table 7. 6-Lead LFCSP Pin Function Descriptions Pin No. Mnemonic Description IN Inverting Input. IN Noninverting Input., NC No Connect. 4 VS Negative Supply. 5 OUT Output. 6 VS Positive Supply. 7 PD Power Down. 8 FB Feedback. 9 IN Inverting Input. IN Noninverting Input. VS Negative Supply. OUT Output. 4 VS Positive Supply. 5 PD Power Down. 6 FB Feedback. EP GND or Vs Exposed Pad. The exposed pad may be connected to GND or VS. Rev. B Page 8 of
ADA4857-/ADA4857- TYPICAL PERFORMANCE CHARACTERISTICS T = 5 C, G =, RF = Ω, and, RG open, RS = Ω for SOIC, (for G =, RF = RG = 499 Ω), unless otherwise noted. NORMALIZED CLOSED-LOOP GAIN (db) 5 7 G = G = 5 8 9 R L = kω V OUT =.V p-p G = G = Figure 8. Small Signal Frequency Responses for Various Gains (LFCSP) 74-8 NORMALIZED CLOSED-LOOP GAIN (db) 5 7 G = G = 5 8 9 R L = kω V OUT = V p-p G = G = Figure. Large Signal Frequency Responses for Various Gains (LFCSP) 74- CLOSED-LOOP GAIN (db) 5 7 8 G = 9 R L = kω V OUT =.V p-p Figure 9. Small Signal Frequency Response for Various Supply Voltages (LFCSP) 5V ±5V 74-9 CLOSED-LOOP GAIN (db) 9 8 7 6 5 4 NO CAP LOAD G = 5 R L = kω V OUT =.V p-p 7 pf Figure. Small Signal Frequency Response for Various Capacitive Loads (LFCSP) 5pF 74- CLOSED-LOOP GAIN (db) 5 7 8 G = 5 C 9 R L = kω V OUT =.V p-p 5 C C Figure. Small Signal Frequency Response for Various Temperatures (LFCSP) 74- CLOSED-LOOP GAIN (db) 5 7 4V p-p 8 G = 9 R L = Ω V p-p Figure. Large Signal Frequency Response vs. VOUT (LFCSP) 74- Rev. B Page 9 of
ADA4857-/ADA4857- CLOSED-LOOP GAIN (db) 9 8 7 6 5 4 R L = Ω 5 G = V OUT =.V p-p 7 R L = kω Figure 4. Small Signal Frequency Response for Various Resistive Loads (LFCSP) 74-4 CLOSED-LOOP GAIN (db) 5 7 R L = Ω 8 G = 9 V OUT = V p-p R L = kω Figure 7. Large Signal Frequency Response for Various Resistive Loads (LFCSP) 74-7 NORMALIZED CLOSED-LOOP GAIN (db) 5 7 G = G = 5 8 V S = 5V 9 R L = kω V OUT =.V p-p G = G = Figure 5. Small Signal Frequency Response for Various Gains (LFCSP) 74-5 NORMALIZED CLOSED-LOOP GAIN (db) 5 7 V IN G = R T R S Ω G = G = 5 V S V S R L V OUT 8 9 R L = kω V OUT =.V p-p G = G = Figure 8. Small Signal Frequency Response for Various Gains (SOIC), RS = Ω for G = 74-8 5 V OUT = V p-p R L = kω 5 G = V OUT = V p-p DISTORTION (dbc) 7 8 9 G =, HD G =, HD G =, HD DISTORTION (dbc) 7 8 9 R L = Ω, HD R L = Ω, HD R L = kω, HD G =, HD. Figure 6. Harmonic Distortion vs. Frequency and Gain (LFCSP) 74-6 R L = kω, HD. Figure 9. Harmonic Distortion vs. Frequency and Load (LFCSP) 74-9 Rev. B Page of
ADA4857-/ADA4857- DISTORTION (dbc) 5 7 8 9 G = R L = kω HD, f = MHz HD, f = MHz HD, f = MHz HD, f = MHz 4 5 6 7 8 OUTPUT VOLTAGE (V p-p) 74- SETTLING TIME (%).5.4.......4.5 INPUT OUTPUT TIME (5ns/DIV) V OUT = V p-p G = V S = ±5 74- Figure. Harmonic Distortion vs. Output Voltage Figure. Short-Term Settling Time (LFCSP) 6. 6. G = R L = 5Ω 6. 6. G = R L = 5Ω CLOSED-LOOP GAIN (db) 6. 6. 5.9 5.8 V OUT =.V p-p V OUT = V p-p CLOSED-LOOP GAIN (db) 6. 6. 5.9 5.8 V OUT =.V p-p V OUT = V p-p 5.7 Figure.. db Flatness vs. Frequency for Various Output Voltages (SOIC) 74-5.7 Figure 4.. db Flatness vs. Frequency for Various Output Voltages (LFCSP) 74-4 OUTPUT VOLTAGE (V).5..5..5.5. 4V p-p V p-p R L = kω G = OUTPUT VOLTAGE (V).5..5..5.5. 4V p-p V p-p R L = kω G =.5.5..5 TIME (ns/div) Figure. Large Signal Transient Response for Various Output Voltages (SOIC) 74-..5 TIME (ns/div) Figure 5. Large Signal Transient Response for Various Output Voltages (LFCSP) 74-5 Rev. B Page of
ADA4857-/ADA4857-.5..5 R L = kω G =..6. G = OUTPUT VOLTAGE (V)..5.5. C L =.5pF OUTPUT VOLTAGE (V).8.4.4.8 R L = kω.5 C L = pf..5 TIME (ns/div) Figure 6. Small Signal Transient Response for Various Capacitive Loads (LFCSP) 74-6. R L = Ω.6. TIME (ns/div) Figure 9. Large Signal Transient Response for Various Load Resistances (SOIC) 74-9.5..5 R L = kω G =..6. R L = kω G = OUTPUT VOLTAGE (V)..5.5. V S = ±.5V OUTPUT VOLTAGE (V).8.4.4.8.5..5 TIME (ns/div) Figure 7. Small Signal Transient Response for Various Supply Voltages (LFCSP) 74-7. R L = Ω.6. TIME (ns/div) Figure. Large Signal Transient Response for Various Load Resistances (LFCSP) 74- CLOSED-LOOP OUTPUT IMPEDANCE (Ω) G = 5 G = CLOSED-LOOP INPUT IMPEDANCE (kω). G =.. Figure 8. Closed-Loop Output Impedance vs. Frequency for Various Gains 74-8. Figure. Closed-Loop Input Impedance vs. Frequency 74- Rev. B Page of
ADA4857-/ADA4857- OPEN-LOOP GAIN (db) 8 7 6 5 4 GAIN PHASE R L = kω 8 OPEN-LOOP PHASE (Degrees) PD ISOLATION (db) 5 7 8 G = R L = kω PD = V LFCSP SOIC 9. 8 74-. 74-5 Figure. Open-Loop Gain and Phase vs. Frequency Figure 5. PD Isolation vs. Frequency 8 6 G = 8 6 G = OUTPUT VOLTAGE (V) 4 8 INPUT OUTPUT R L = Ω OUTPUT R L = kω TIME (4ns/DIV) 74- OUTPUT VOLTAGE (V) 4 8 INPUT OUTPUT R L = kω OUTPUT R L = Ω TIME (ns/div) 74-6 Figure. Input Overdrive Recovery for Various Resistive Loads Figure 6. Output Overdrive Recovery for Various Resistive Loads R L = kω 5 R L = kω PSRR (db) CMRR (db) 5 PSRR 7 7 PSRR 8. Figure 4. Power Supply Rejection Ratio (PSRR) vs. Frequency 74-4 8 9. Figure 7. Common-Mode Rejection Ratio (CMRR) vs. Frequency 74-7 Rev. B Page of
ADA4857-/ADA4857- CURRENT NOISE (pa/ Hz) VOLTAGE NOISE (nv/ Hz) k k k M FREQUENCY (Hz) 74-5 k k k M FREQUENCY (Hz) 74-4 Figure 8. Input Current Noise vs. Frequency Figure 4. Input Voltage Noise vs. Frequency 5 N = 8 MEAN: 5. SD:..5. 4.5 PD INPUT COUNT VOLTAGE (V)..5. 4.85 4.9 4.95 5. 5.5 SUPPLY CURRENT (ma) 5. 5.5 74-4.5.5 OUTPUT TIME (µs/div) 74-4 Figure 9. Supply Current Figure 4. Disable/Enable Switching Speed Rev. B Page 4 of
ADA4857-/ADA4857- TEST CIRCUITS µf V S µf V S.µF.µF kω kω.µf.µf IN R L V R S V OUT 49.9Ω µf.µf V S Figure 4. Noninverting Load Configuration 74-47 V IN kω V OUT R L 5.6Ω kω µf.µf V S Figure 45. Common-Mode Rejection 74-46 V S V S AC 49.9Ω µf.µf V OUT V OUT µf V S.µF R L 74-45 AC V S 49.9Ω R L 74-48 Figure 4. Positive Power Supply Rejection Figure 46. Negative Power Supply Rejection µf V S µf V S R G R F.µF V IN 49.9Ω µf.µf V S.µF V OUT C L R L Figure 44. Typical Capacitive Load Configuration (LFCSP) 74-5 V IN R G R F.µF.µF 4Ω V R OUT SNUB C L R L 49.9Ω µf.µf V S Figure 47. Typical Capacitive Load Configuration (SOIC) 74-49 Rev. B Page 5 of
ADA4857-/ADA4857- APPLICATIONS INFORMATION POWER-DOWN OPERATION The PD pin is used to power down the chip, which reduces the quiescent current and the overall power consumption. It is low enabled, which means that the chip is on with full power when the PD pin input voltage is low (see Table 8). Note that PD does not put the output in a high-z state, which means that the ADA4857 should not be used as a multiplexer. Table 8. PD Operation Table Guide Supply Voltage Condition ±5 V ±.5 V 5 V Enabled.8 V.7 V.8 V Powered down V.5 V V CAPACITIVE LOAD CONSIDERATIONS When driving a capacitive load using the SOIC package, RSNUB is used to reduce the peaking (see Figure 47). An optimum resistor value of 4 Ω is found to maintain the peaking within db for any capacitive load up to 4 pf. RECOMMENDED VALUES FOR VARIOUS GAINS Table 9 provides a useful reference for determining various gains and associated performance. RF and RG are kept low to minimize their contribution to the overall noise performance of the amplifier. Table 9. Various Gain and Recommended Resistor Values Associated with Conditions; VS = ±5 V, TA = 5 C, RL = kω, RT = 49.9 Ω Gain RS (Ω) (CSP/SOIC) RF (Ω) RG (Ω) db SS BW (MHz) (CSP/SOIC) Slew Rate (V/μs), VOUT = V Step ADA4857 Voltage Noise (nv/ Hz), RTO / N/A 85/75 5 4.4 4.49 / 499 499 6/ 68 8.8 9.89 5 / 499 4 9/89 56..49 / 499 56. 4/4 4.47 45. Total System Noise (nv/ Hz), RTO Rev. B Page 6 of
ACTIVE LOW-PASS FILTER (LPF) Active filters are used in many applications such as antialiasing filters and high frequency communication IF strips. With a 4 MHz gain bandwidth product and high slew rate, the ADA4857- is an ideal candidate for active filters. Figure 48 shows the frequency response of 9 MHz and 45 MHz LPFs. In addition to the bandwidth requirements, the slew rate must be capable of supporting the full power bandwidth of the filter. In this case, a 9 MHz bandwidth with a V p-p output swing requires at least 8 V/μs. The circuit shown in Figure 49 is a 4-pole, Sallen-Key LPF. The filter comprises two identical cascaded Sallen-Key LPF sections, each with a fixed gain of G =. The net gain of the filter is equal to G = 4 or db. The actual gain shown in Figure 48 is db. This does not take into account the output voltage being divided in half by the series matching termination resistor, RT, and the load resistor. Setting the resistors equal to each other greatly simplifies the design equations for the Sallen-Key filter. To achieve 9 MHz, the value of R should be set to 8 Ω. However, if the value of R is doubled, the corner frequency is cut in half to 45 MHz. This would be an easy way to tune the filter by simply multiplying the value of R (8 Ω) by the ratio of 9 MHz and the new corner frequency in megahertz. ADA4857-/ADA4857- Figure 48 shows the output of each stage is of the filter and the two different filters corresponding to R = 8 Ω and R = 65 Ω. Resistor values are kept low for minimal noise contribution, offset voltage, and optimal frequency response. Due to the low capacitance values used in the filter circuit, the PCB layout and minimization of parasitics is critical. A few picofarads can detune the corner frequency, fc of the filter. The capacitor values shown in Figure 49 actually incorporate some stray PCB capacitance. Capacitor selection is critical for optimal filter performance. Capacitors with low temperature coefficients, such as NPO ceramic capacitors and silver mica, are good choices for filter elements. MAGNITUDE (db) 5 9 6 9 5 8 7 6 9 R L = Ω OUT, f = 9MHz OUT, f = 45MHz. 5 OUT, f = 9MHz OUT, f = 45MHz Figure 48. Low-Pass Filter Response 74-74 C.9pF C.9pF 5V µf 5V µf IN R T 49.9Ω R R C 5.6pF U.µF µf R OUT R C4 5.6pF U.µF µf R T 49.9Ω OUT R 48Ω 5V.µF R 48Ω R4 48Ω 5V.µF R 48Ω 74-75 Figure 49. 4-Pole, Sallen-Key Low-Pass Filter (ADA4857-) Rev. B Page 7 of
ADA4857-/ADA4857- NOISE To analyze the noise performance of an amplifier circuit, identify the noise sources and determine if the source has a significant contribution to the overall noise performance of the amplifier. To simplify the noise calculations, noise spectral densities were used rather than actual voltages to leave bandwidth out of the expressions (noise spectral density, which is generally expressed in nv/ Hz, is equivalent to the noise in a Hz bandwidth). The noise model shown in Figure 5 has six individual noise sources: the Johnson noise of the three resistors, the op amp voltage noise, and the current noise in each input of the amplifier. Each noise source has its own contribution to the noise at the output. Noise is generally referred to input (RTI), but it is often easier to calculate the noise referred to the output (RTO) and then divide by the noise gain to obtain the RTI noise. B A V N, R 4kTR V N, R 4kTR R R RTI NOISE = I N I N V N V N, R 4kTR R V N 4kTR 4kTR R R R I N R I R R N 4kTR R R RTO NOISE = NG RTI NOISE Figure 5. Op Amp Noise Analysis Model GAIN FROM A TO OUTPUT = NOISE GAIN = R NG = R V OUT GAIN FROM B TO OUTPUT = R R All resistors have Johnson noise that is calculated by (4kBTR) R R R where: k is Boltzmann s Constant (.8 J/K). B is the bandwidth in Hertz. T is the absolute temperature in Kelvin. R is the resistance in ohms. A simple relationship that is easy to remember is that a 5 Ω resistor generates a Johnson noise of nv/ Hz at 5 C. In applications where noise sensitivity is critical, care must be taken not to introduce other significant noise sources to the amplifier. Each resistor is a noise source. Attention to the following areas is critical to maintain low noise performance: design, layout, and component selection. A summary of noise performance for the amplifier and associated resistors can be seen in Table 9. 74-7 CIRCUIT CONSIDERATIONS Careful and deliberate attention to detail when laying out the ADA4857 board yields optimal performance. Power supply bypassing, parasitic capacitance, and component selection all contribute to the overall performance of the amplifier. PCB LAYOUT Because the ADA4857 can operate up to 85 MHz, it is essential that RF board layout techniques be employed. All ground and power planes under the pins of the ADA4857 should be cleared of copper to prevent the formation of parasitic capacitance between the input pins to ground and the output pins to ground. A single mounting pad on the SOIC footprint can add as much as. pf of capacitance to ground if the ground plane is not cleared from under the mounting pads. The low distortion pinout of the ADA4857 increases the separation distance between the inputs and the supply pins, which improves the second harmonics. In addition, the feedback pin reduces the distance between the output and the inverting input of the amplifier, which helps minimize the parasitic inductance and capacitance of the feedback path, reducing ringing and peaking. POWER SUPPLY BYPASSING Power supply bypassing for the ADA4857 was optimized for frequency response and distortion performance. Figure 4 shows the recommended values and location of the bypass capacitors. The. µf bypassing capacitors should be placed as close as possible to the supply pins. Power supply bypassing is critical for stability, frequency response, distortion, and PSR performance. The capacitor between the two supplies helps improve PSR and distortion performance. The µf electrolytic capacitors should be close to the. µf capacitors; however, it is not as critical. In some cases, additional paralleled capacitors can help improve frequency and transient response. GROUNDING Ground and power planes should be used where possible. Ground and power planes reduce the resistance and inductance of the power planes and ground returns. The returns for the input, output terminations, bypass capacitors, and RG should all be kept as close to the ADA4857 as possible. The output load ground and the bypass capacitor grounds should be returned to the same point on the ground plane to minimize parasitic trace inductance, ringing, and overshoot and to improve distortion performance. The ADA4857 LFSCP packages feature an exposed paddle. For optimum electrical and thermal performance, solder this paddle to the ground plane or the power plane. For more information on high speed circuit design, see A Practical Guide to High-Speed Printed-Circuit-Board Layout at www.analog.com. Rev. B Page 8 of
ADA4857-/ADA4857- OUTLINE DIMENSIONS.5. SQ.75.6 MAX.6 MAX.5 BSC PIN INDICATOR TOP VIEW.95.75 SQ.55 5 8 EXPOSED PAD (BOTTOM VIEW).6.45. MAX.7 MAX.5.4..9 MAX.65 TYP.85 NOM.5 MAX. NOM SEATING PLANE...8. REF 4.89.74.59 PIN INDICATOR FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. Figure 5. 8-Lead Lead Frame Chip Scale Package [LFCSP_VD] mm mm Body, Very Thin, Dual Lead (CP-8-) Dimensions shown in millimeters 748-B 5. (.968) 4.8 (.89) 4. (.574).8 (.497) 8 5 4 6. (.44) 5.8 (.84).5 (.98). (.4) COPLANARITY. SEATING PLANE.7 (.5) BSC.75 (.688).5 (.5).5 (.). (.) 8.5 (.98).7 (.67).5 (.96).5 (.99).7 (.5).4 (.57) 45 COMPLIANT TO JEDEC STANDARDS MS--AA CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN. Figure 5. 8-Lead Standard Small Outline Package [SOIC_N] (R-8) Dimensions shown in millimeters and (inches) 47-A Rev. B Page 9 of
ADA4857-/ADA4857- PIN INDICATOR..85.8 MAX SEATING PLANE 4. BSC SQ TOP VIEW.8 MAX.65 TYP.5..5.75 BSC SQ. REF.5 MAX. NOM.6 MAX.65 BSC.75.6.5 COPLANARITY.8 9 8.6 MAX (BOTTOM VIEW).95 BSC 6 5 4 PIN INDICATOR.5. SQ.95.5 MIN FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. COMPLIANT TO JEDEC STANDARDS MO--VGGC Figure 5. 6-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 4 mm 4 mm Body, Very Thin Quad (CP-6-4) Dimensions shown in millimeters 788-A ORDERING GUIDE Model Temperature Range Package Description Package Option Ordering Quantity Branding ADA4857-YCPZ-R C to 5 C 8-Lead LFCSP_VD CP-8-5 H5 ADA4857-YCPZ-RL C to 5 C 8-Lead LFCSP_VD CP-8-5, H5 ADA4857-YCPZ-R7 C to 5 C 8-Lead LFCSP_VD CP-8-,5 H5 ADA4857-YRZ C to 5 C 8-Lead SOIC_N R-8 98 ADA4857-YRZ-R7 C to 5 C 8-Lead SOIC_N R-8,5 ADA4857-YRZ-RL C to 5 C 8-Lead SOIC_N R-8, ADA4857-YR-EBZ Evaluation Board ADA4857-YCP-EBZ Evaluation Board ADA4857-YCPZ-R C to 5 C 6-Lead LFCSP_VQ CP-6-4 5 ADA4857-YCPZ-RL C to 5 C 6-Lead LFCSP_VQ CP-6-4 5, ADA4857-YCPZ-R7 C to 5 C 6-Lead LFCSP_VQ CP-6-4,5 ADA4857-YCP-EBZ Evaluation Board Z = RoHS Compliant Part. 8 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D74--8/(B) Rev. B Page of