Low-Noise, Differential Audio Preamplifier IC THAT1580 FEATURES APPLICATIONS * Low Noise: -134.8dBu (1nV/Hz) EIN@60dB gain * Low THD+N: 0.0003% @ 3 - 30 dB gain 0.0005% @ 40 dB gain * Low Current: 7.9 mA typ * Wide Bandwidth: 2.7MHz @40dB gain * High Slew Rate: 53 V/s * Wide Output Swing: +29.8 dBu (18V supplies) * Gain adjustable from 0 to >60 dB * Differential output * Small 4 x 4mm QFN16 package * Mates with THAT's family of Digital Preamplifier Controller ICs * Microphone Preamplifiers * Digitally-Controlled Microphone Preamplifiers * Differential Low-Noise Preamplifiers * Differential Summing Amplifiers * Differential Variable-Gain Amplifiers * Moving-Coil Transducer Amplifiers * Line Input Stages * Audio * Sonar * Instrumentation Description The THAT1580 is a versatile, high performance current-feedback amplifier suitable for differential microphone preamp and bus summing applications. The IC comes in a small 4 x 4 mm QFN package, which saves PCB space over discrete and other integrated solutions. Gain is adjusted via three external resistors (RA, RB, and RG), making it possible to optimize noise over a wide range of gains. The 1580 supports the traditional approach to gain control (viz., THAT's 1510 or 1512) by fixing RA and RB, and varying RG to control gain. However, the 1580 also supports varying all three resistors simultaneously with a dual-gang potentiometer or a switched resistor network. This flexible approach enables the designer to optimize noise over a wider range of gains than is possible with fixed RA and RB. The 1580's differential output simplifies connection to differential input devices such as A/D converters. The part operates from as little as 5V up through 18V supplies. Running on 18V supplies, at unity gain, the part accepts >+28.3 dBu input signals and will deliver up to +29.8 dBu (differential) output signals. The 1580 is designed to mate perfectly with THAT's series of Digital Preamplifier Controller ICs. Designed from the ground up in a high-voltage BiCMOS process, the 1580 improves on existing integrated microphone preamps by offering more versatile gain configuration, lower noise at low gains, higher slew rate, and lower distortion. Pin Name N/C* OUT2 OUT1 N/C* N/C* Rg1 IN1 N/C* N/C* IN2 N/C* VV+ N/C* Rg2 N/C* VFigure 1. THAT1580 Block Diagram QFN Pin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Thermal Pad Table 1. Pin Assignments * N/C pins should be left open and not connected to other traces on the PCB THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; Doc 600187 Rev 01 THAT 1580 Low-Noise Differential Audio Preamplifier IC Page 2 of 16 Document 600187 Rev 01 SPECIFICATIONS1,2 Absolute Maximum Ratings3 Supply Voltage (V+) - (V-) Maximum Input Voltage (VIMax) Storage Temperature Range (TSTG) 40 V V+ to V-40 to +125 C Operating Temperature Range (TOP) Output Short-Circuit Duration (tSH) Junction Temperature (TJMAX) -40 to +85 C Continuous +125 C Electrical Characteristics4,5 Parameter Symbol Conditions Min Typ Max Units Supply Voltage V+; - V- Referenced to GND 5 -- 18 V Supply Current I+; -(I-) No Signal -- 7.9 10 mA Power Supply Input Characteristics Input Bias Current -- 6.8 11 A Input Offset Current IB-OFF IB No signal; either input connected to GND No signal -1.1 -- +1.1 A RG Input Bias Current IBRG No signal -20 +1.5 +20 A IBRG-OFF No signal -3.5 -- +3.5 A VOS No signal, Includes IBRG-OFF * RF 0 dB gain +60 dB gain -10 -250 -- -- +10 +250 mV V Common Mode (V-) + 3.7 -- (V+) - 3.2 RG = -- 26 -- dBu (10 + 0.25*G) mV -- mV -- (V+) -1, (V-)+1 -- V RG Input Offset Current Differential Input Offset Voltage Input Common Mode Voltage Range VIN_CM Maximum Differential Input Level VIN-BAL V Output Characteristics Total Differential Output Offset Common Mode Output Voltage Maximum Single Output Voltage Differential Short Circuit Current Maximum Capacitive Load Maximum Differential Output Level G = gain VOSCM -(10 + 0.25*G) -- No signal; IN1, IN2 connected to GND VOUT-SINGLE RL= 2 k -- -640 ISC Cold Start; RL = 0 -- 62 -- mA CL MAX Over entire temperature range -- -- 100 pF VOUT RL= 2 k 28 -- -- dBu GDIFF Differential in to differential out See Figure 16. (RG = R GV + R GF) AC Characteristics Gain Equation Feedback Impedance Differential Gain Power Supply Rejection Ratio Bandwidth -3dB RA, RB 1 + [(R A + RB)/RG] 2 -- -- k GDIFF Programmed by R A, RB, R G 0 -- 70 dB PSRR V+ = -(V-); 5V to 18V 0 dB gain 20 dB gain 40 dB gain 60 dB gain -- -- -- -- 111 122 147 147 -- -- -- -- dB dB dB dB f-3dB Small signal 0 dB gain 20 dB gain 40 dB gain 60 dB gain Small signal; RG= RA = RB = 2 k RA = RB = 5 k RA = RB = 10 k -- -- -- -- 7.3 6.1 2.7 356 -- -- -- -- MHz MHz MHz kHz -- -- -- 8 3 1.3 -- -- -- MHz MHz MHz 1. All specifications are subject to change without notice. 2. Unless otherwise noted, TA=25C, V+ = +15V, V- = -15V. 3. Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only; the functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 4. 0 dBu = 0.775 Vrms 5. Unless otherwise noted, RA = RB = 2.21 k; CL = 10 pF THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. THAT 1580 Low-Noise Differential Audio Preamplifier IC Page 3 of 16 Document 600187 Rev 01 Electrical Characteristics (con't) Parameter 1,3,4,5 Symbol Conditions Min. Typ. Max Units SR VOUT = 50.3VP-P; RL=2k ; CL=100pF All gains 31 53 -- V/s VOUT = 5VRMS ; f=1kHz; BW=22kHz 0 dB gain 6 dB gain 20 dB gain 40 dB gain 60 dB gain -- -- -- -- -- 0.0004 0.0003 0.0003 0.0005 0.005 -- -- -- -- -- % % % % % -- -- -- -- -- 18.3 10.1 3.3 1.4 1 -- -- -- -- -- nV/Hz nV/Hz nV/Hz nV/Hz nV/Hz -- -- dBu dBu -- -- dBu dBu AC Characteristics (continued) Slew Rate Total Harmonic Distortion Equivalent Input Noise Voltage THD + N eN eN Equivalent Input Noise Current Noise Figure Inputs connected to GND; f=1kHz 0 dB gain 6 dB gain 20 dB gain 40 dB gain 60 dB gain Inputs connected to GND; BW=22kHz; 60 dB gain -- -134.4 A-weighted -- -136.6 Rs = 150; BW=22kHz; 60 dB gain -- -129 A-weighted -- -131.2 iN f=1kHz; 60 dB gain -- 1.5 -- pA/Hz NF 60 dB gain; RS = 150 -- 1.5 -- dB -100 [dBu] -105 -110 -115 -120 BW: 22Hz - 22kHz -125 BW: A-weighted -130 [dB] -135 0 Figure 2. Equivalent Input Noise vs Gain and Source Impedance; BW: 22Hz to 22kHz 10 20 30 40 50 60 Figure 3. Equivalent Input Noise vs Gain and Bandwidth; Source Impedance 150 THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. THAT 1580 Low-Noise Differential Audio Preamplifier IC -100 Page 4 of 16 [dBu] Document 600187 Rev 01 10 [MHz] -105 RA = RB = 2k21 -110 RA = RB = 5k -115 1 -120 RA = RB = 10k -125 -130 -135 -140 0 10 20 30 40 50 [dB] 60 [dB] 0.1 0 10 20 30 40 50 60 Figure 4. Equivalent Input Noise vs Gain and Feedback Impedance; BW: 22Hz to 22kHz Figure 5. Bandwidth vs Gain and Feedback Impedance Figure 6. THD + Noise vs Level f = 1 kHz, BW: 22 Hz to 22 kHz Figure 7. THD + Noise vs Frequency; Vout = +27dBu, RL = 10k, BW: 22 Hz to 22 kHz 15 [V] VOUTP 10 5 0 -5 -10 -15 Figure 8. Power Supply Rejection Ratio vs Frequency; Gain = 0dB, 40 dB VOUTN 0 10 20 30 40 50 [mA] 60 Figure 9. Max Output Voltage vs Output Current THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. THAT 1580 Low-Noise Differential Audio Preamplifier IC Page 5 of 16 Document 600187 Rev 01 [mV] -20 Figure 10. Maximum Output Level vs Supply Voltage -15 -10 -5 0 5 10 15 20 Figure 11. Representative Input Offset Voltage Distribution, Gain = 0 dB [uV] -800 -600 -400 -250 0 250 400 600 800 Figure 12. Representative Input Offset Voltage Distribution, Gain = 60 dB [uA] -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 Figure 13. Representative RG Input Bias Current Distribution [uA] -5 -4 -3 -2 -1 0 1 2 3 4 5 Figure 14. Representative RG Input Offset Current Distribution THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. THAT 1580 Low-Noise Differential Audio Preamplifier IC Page 6 of 16 Document 600187 Rev 01 Applications Gain Setting RA Three external resistors (RA, RB, and RG) set the gain of the THAT1580. Gain follows the formula: =1+ ; where AV is the (differential) R1 RM voltage gain of the part (See Figure 15). RG Because all three resistors are external, the designer is free to select them for best noise performance at the desired gain setting(s). Note, however, that as with any current-feedback amplifier, the part's bandwidth will vary with RA(B). The 1580 is stable with RA(B) values of 2k or larger; bandwidth decreases with increasing RA(B). The part's minimum gain is unity (0dB). This occurs with RG open. Maximum gain depends on the required bandwidth. Full audio bandwidth is maintained to beyond 60dB gain. Other integrated mic preamps which include internal resistors for RA and RB (e.g., the THAT 1510 and 1512) allow gain to be varied using one singlegang potentiometer. The 1580 offers a similar hookup, by fixing RA and RB and varying RG. This is shown in the circuit of Figure 16, where RG is made up of fixed (RGF) and variable (RGV) portions. In such applications, designers should take care in specifying the pot's element construction to avoid excess noise. The potentiometer taper will set the circuit's characteristic of gain vs. pot rotation. Typically, reverse log (audio) taper elements offer the desired OUT+ IN1 RG1 OUT1 RG2 OUT2 OUT- IN2 R2 RB Figure 15. Simple THAT1580 Amplifier Circuit behavior in which gain increases with clockwise rotation (and lower values for RGV). Overall gain accuracy depends on the tolerance of the resistors, including especially the pot (RGV) which dominates RG. Theoretically, when RGV is zero, the gain is determined by RA, RB, RGF alone. End resistance ("hop off") will alter the actual gain; reducing RGF by the amount of end resistance may be appropriate, especially if the end resistance is consistent. It will be easier to maintain consistent gain at the high-gain end of the pot travel at higher values for RA and RB, since this makes the value of RG required proportionately larger for any given gain. The circuit of Figure 16 shows 5 k resistors for RA and RB, so for 60 dB gain, RG = 10 . Its noise performance is very good at 60 dB gain (EIN = 1.1 nV/Hz, or -133.9 dBu6 with a zero ohm input RA 5k +15V THAT 1580 C9 100n IN+ IN- C1 22p C3 220p C2 22p RFI PROTECTION IN1 V+ RG 1 R1 1k0 RGV RGF 10k 10 RG 2 IN2 OUT1 OUT2 OUT+ C11 100n V- R2 1k0 -15V C10 100n RB 5k Figure 16. 1580 Typical Application Circuit Using Single-Gang Pot for Gain Control. THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. OUT- THAT 1580 Low-Noise Differential Audio Preamplifier IC Page 7 of 16 termination, and 1.92 nV/Hz, or -129.1 dBu6 with a more realistic 150 input termination). At minimum gain (6 dB) its noise performance is still good (EIN = 19.9 nV/Hz), or -108.8 dBu6 with a zero ohm input termination. Document 600187 Rev 01 amplified by the gain of the device. Too high a source impedance can easily spoil the noise of the device. The 1 k resistors used at R1 and R2 in Figure 22 provide a low source impedance for the 1580 even when the input is open, and provide a 2 k (differential) load for the microphone. Higher source impedances will increase noise seen (and heard!) with open inputs. One disadvantage of the circuit of Figure 16 is that differential dc offset at the 1580 output will vary with gain. At 0 dB gain, the 1580's worst-case differential output offset voltage is ~15 mV, while at 60 dB gain, this is ~465 mV. As well, if the wiper of the pot loses contact with the element, gain will abruptly change to unity, with an attendant change in dc offset as well. To minimize dc offsets, THAT recommends the circuits of Figures 19 and 21, which ac couple RG. One disadvantage of the single-pot approach is that noise at low gains is dominated by the noise of resistors RA and RB. For the circuit of Figure 16, the equivalent input noise at 6 dB gain (the minimum pot setting) is ~19.9 nV/Hz, or -108.8 dBu7. Much lower noise (~11.2 nV/Hz, or -113,8 dBu6) can be achieved if RA and RB are reduced to ~2.5 k, but to achieve 60 dB gain, this requires RG to be = 5 . (This analysis also assumes RGV = 5 k.) Improving Noise Performance An alternative offered by the 1580 (and not by preamps with internal RA and RB) is that all three resistors may be varied at once. See the circuit of Figure 17, which uses a dual-gang potentiometer as the variable element. The 1580 has extremely low input voltage noise. To achieve this feature, the input transistors are large-geometry NPN types, biased at high (~1 mA) collector current. In order to maintain the low voltage-noise performance of the 1580, designers should take care not to present too high a source impedance to the input pins. A high impedance generates its own self-noise when not shunted by the impedance of the source connected to the input pins. In Figure 17, high gain occurs by decreasing RG while simultaneously increasing RA and RB. An advantage of this approach is that RA and RB will naturally be lower for low gains, without requiring such a low value for RG to achieve high gains. In this circuit, 60 dB gain occurs with RG = 8.66 , and EIN is 1.1 nV/Hz, or -133.9 dBu6 with a zero ohm input termination. With a 150 input termination, the EIN, dominated by the 150 resistor, is 1.92 nV/Hz or ~ -129.1 dBu7. Additionally, the input transistors' base current, and any noise in that base current, must be drawn through the bias network (R1 and R2 in Figure 16) connected to IN1 and IN2 (which connect to the bases of the input transistors). Any input current noise will be drawn across the source impedance (as seen by the inputs), which turns it into a voltage that is This circuit's minimum gain is 3 dB, where RGV is fully CCW. At this gain, the input-referred noise is RA 2k5 R3 10k THAT 1580 IN+ C1 22p IN- C3 220p C2 22p RFI PROTECTION RGV1 5k R1 1k0 IN1 CW RGF 8.66 CW RGV2 5k RG1 RG2 IN2 +15V C9 100n V+ OUT1 OUT2 OUT+ C11 100n OUT- V- R2 1k0 -15V C10 100n R4 10k RB 2k5 Figure 17. 1580 Typical Application Circuit Using Dual-Gang Pot for Gain Control. 6 7 All audio-band noise calculations assume a 20 Hz to 20 kHz bandwidth with no weighting. 20 kHz bandwidth, unweighted. Noise figures will generally be 2.2 dB better (lower) with A weighting. THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. THAT 1580 Low-Noise Differential Audio Preamplifier IC Page 8 of 16 ~12.1 nV/Hz, or -113.1 dBu6 with a shorted input, and is essentially the same with a 150 input termination. This is about 4.3 dB better than the circuit of Figure 16 at its minimum gain (6 dB). Note also that at the minimum +3 dB gain and 18 V rails, the circuit of Figure 17 can accept up to +26.8 dBu input signals without clipping. This offers more headroom than the circuit of Figure 16, which has a maximum input of +23.8 dBu with the same rails. Of course, other minimum and maximum gains can be accommodated by varying the resistors at RA, RB, RGV, and RGF. One additional advantage of the dual-gang pot approach is that it allows more even distribution of gain versus pot rotation. See "DeIntegrating IC Preamps", available on THAT's web site. For variable-gain applications where gain accuracy is important, THAT recommends using discrete, switched resistors for RA, RB and RG. With switched resistors, it becomes even easier to vary all three resistors to optimize noise. As with the circuit of Figure 16, RG in Figure 17 is dc coupled. This means that the differential output offset voltage will vary with gain. Also, if the wiper of either half of the gain pot loses contact with the element, gain and output offset will change abruptly. R3 and R4 help this situation by minimizing the change in dc offset generated by the 1580's input bias current (drawn across the combination of R3 in parallel with the series combination of RA and part of RGV1, or the other mirror half). Again, for best dc performance, THAT recommends the circuits of Figures 20 and 21 which ac-couple RG . Document 600187 Rev 01 13 V+ OUT1 -AV 7 10 6 15 12 OUT2 -AV IN1 3 2 IN2 RG1 RG2 V- Figure 18. 1580 Equivalent Circuit with Internal Protection Diodes. DC Offsets and CG Because RG is dc coupled in the circuits of Figure 16 and 17, the differential dc level at the output of the 1580 will vary with gain. In most such applications, the output should be ac-coupled to the next stage, in order to eliminate this varying offset. For applications where gain is variable, THAT recommends that RG be ac-coupled as shown in Figures 19 and 20. (Figure 19 corresponds to Figure 16, while Figure 20 corresponds to Figure 17.) By adding CG in series with RG, dc gain is fixed at unity. This constrains the differential output dc offset to just over 15 mV, and, more importantly, CG prevents the offset from varying with gain. CG must be large enough not to interfere with low- RA 5k THAT 1580 +15V C9 100n IN+ C1 22p IN- C3 220p C2 22p RFI PROTECTION R1 1k0 RGV 10k RGF CG 10 3300u IN1 V+ RG1 OUT1 RG2 OUT2 IN2 OUT+ C11 100n OUT- V- R2 1k0 -15V C10 100n RB 5k Figure 19. 1580 Typical Application Circuit With Single-Gang Pot for Gain Control, AC-Coupled R G. THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. THAT 1580 Low-Noise Differential Audio Preamplifier IC Page 9 of 16 problem when the preamplifier includes a source of +48 V phantom power (see text below) but can be of concern in any situation where the input may be connected to high signal levels, in which the input signal voltage could exceed the supply rails. The phantom power protection networks shown in Figures 21 and 22 are worth considering even if phantom power is not included in the design. frequency response at the smallest values of RG. With the values shown in Figures 19 and 20, the -3 dB corner is about 5 Hz. Both circuits require a CG of 3,300 F to maintain this low-frequency corner. The dc voltage appearing across CG is very small and equal to the 1580's "60 dB Differential Input Offset Voltage", specified at 450 V, maximum. The polarity of this voltage across CG will be completely random. While the manufacturer of the capacitor to be used will have the last word on the subject, THAT understands that most polarized electrolytic types can tolerate at least 1 V of continuous reverse voltage with no impact on performance or reliability. We recommend a 6.3 V aluminum electrolytic for minimum PCB footprint. Phantom Power Phantom power is required for many condenser microphones. THAT recommends the circuits of Figure 21 and 22 when phantom power is included. R3, R4, and D1 ~ D6 are used to limit the current that flows through the 1580 inputs when overloaded. These also protect the 1580 when the circuit inputs (IN+ and IN-) are shorted to ground while phantom power is turned on. This causes C4 and/or C5 to discharge through other circuit components (including the 1580 inputs), often generating transient currents of several amps. R3 and R4 should be at least 10 to limit destructive currents. (Higher values further limit current flow, but introduce additional source impedance and noise.) Take care to ensure that the resistors used can handle the short-term inrush current; many small surface-mount types cannot. With the values shown for C4 and C5, THAT recommends at least 1/4 W resistors. Note, in applications where very low frequency signals at high levels may be present at the input of the preamp, the low frequency will appear across CG, attenuated by the filter composed of RG and CG. However, THAT does not believe this is a significant consideration for most audio applications. Inputs Simple Configurations As shown in Figure 18, the 1580 includes protection diodes at all pins. These diodes reduce the likelihood that accidental electrostatic discharge (ESD) or electrical over stress (EOS) will damage the ICs. Other diodes across the base-emitter junctions of the input transistors prevent excessive reverse biasing of these junctions (which would degrade the noise performance of the input devices). However, while the internal against ESD, they should not protect against excessive input result in significant current flow. Document 600187 Rev 01 D1 through D4 prevent the IC's inputs from significantly exceeding the supply rails. For best results, they should be glass-passivated types (sometimes called "GP") to ensure low leakage. (Leakage manifests itself as noise in addition to offset.) D5 and D6 steer currents around the input stage in the 1580, further preventing damage. diodes are effective be relied upon to voltage, which can This is a particular The series combination of C4 and C5 should be made large to minimize high-pass filtering of the signal based upon the sum of the values of R1+R2. As RA 2k5 R3 10k THAT 1580 IN+ C1 22p IN- C3 220p C2 22p R1 1k0 RGF 8.66 CG 3300u RGV1 5k IN1 CW RG1 CW RG2 RGV2 5k IN2 +15V C9 100n V+ OUT1 OUT2 C11 100n OUT- V- R2 1k0 -15V RFI PROTECTION OUT+ C10 100n R4 10k RB 2k5 Figure 20. 1580 Typical Application Circuit With Dual-Gang Pot for Gain Control, AC-Coupled RG. THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. THAT 1580 Low-Noise Differential Audio Preamplifier IC Page 10 of 16 Document 600187 Rev 01 RA PHANTOM POWER +48V R5 6k81 IN+ C1 22p IN- C3 220p C2 22p 5k +15V R6 6k81 C4 + R3 47u 10 C5 + D2 +15V S1DB D3 -15V R4 S1DB 47u 10 D4 S1DB -15V RFI PROTECTION D5 +15V D1 S1DB THAT 1580 C9 100n 1N4148 IN1 RG1 C6 100p 5% C8 220p R1 1k2 RGV 10k RGF CG 10 3300u C7 100p 5% R2 1k2 RG2 OUT2 V- IN2 OUT+ C11 100n OUT- D6 C10 -15V 100n 1N4148 RFI PROTECTION PHANTOM POWER FAULT PROTECTION V+ OUT1 RB 5k Figure 21. 1580 Typical Phantom Power Application Circuit With Single-Gang Pot for Gain Control, AC-Coupled RG. well, keeping their reactance low relative to the external microphone's source impedance will avoid increasing the effects of low-frequency current noise in the 1580 input stage. series input resistors will limit the noise performance of the preamp. The ultimate floor is set by the impedance of the microphone, but any additional series resistance further degrades performance. As in Figures 16 and 17, Figures 21 and 22 differ in their approach to the gain potentiometer. The single-gang pot shown in Figure 21 may be a little less expensive to implement, but the dual-gang pot of Figure 22 will deliver better noise performance at low gains, for the reasons noted above. Note that Figure 22 features minimum gain of 3 dB, compared to Figure 21 at 6 dB. The low-frequency corners are about the same (~5 Hz) in the two circuits. Additionally, while at one time we recommended Schottky diodes for D1~D4 in Figures 21 and 22, we no longer do so. Schottky diodes appeal because of their fast turn-on behavior and low forward voltage drop. However, aside from their higher cost, our experience is that they tend to leak much more than conventional, glass-passivated power diodes, and that their fast turn-on behavior is unnecessary in practice. Other manufacturers have recommended, and some pro audio products include, a zener diode arrangement instead of the bridge rectifier to V+ and V- as shown in Figures 21 and 22. THAT does not recommend the zener approach, because we find that R3 and R4 must be made much larger (e.g.,51 ) in order to limit peak currents enough to protect reasonably sized zener diodes (e.g. 1/2 W). Such large For further insights into this subject, see the Audio Engineering Society preprint "The 48 Volt Phantom Menace Returns" by Rosalfonso Bortoni and Wayne Kirkwood, presented at the 127th AES Convention, (available on THAT's web site) and subsequently published in the Journal of the Audio Engineering Society. RA 2k5 R10 PHANTOM POWER +48V 10k R5 6k81 IN+ C1 22p IN- C3 220p C2 22p D5 R6 6k81 C4 + R3 47u 10 +15V D1 S1DB C5 + D2 +15V S1DB D3 -15V R4 S1DB 47u 10 D4 S1DB -15V RFI PROTECTION PHANTOM POWER FAULT PROTECTION THAT 1580 1N4148 R1 1k2 R2 1k2 C6 100p 5% C8 220p C7 100p 5% RFI PROTECTION RGV1 5k RGF 8.66 CG 3300u RGV2 5k IN1 CW RG1 CW RG2 IN2 +15V C9 100n OUT1 OUT2 C11 100n OUT- V- D6 1N4148 OUT+ V+ -15V C10 100n R11 10k RB 2k5 Figure 22. 1580 Typical Phantom Power Application Circuit With Dual-Gang Pot for Gain Control, AC-Coupled RG. THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. THAT 1580 Low-Noise Differential Audio Preamplifier IC Page 11 of 16 Document 600187 Rev 01 Outputs Digitally Controlled Gain Each of the two 1580 outputs has a dc offset of 640 mV. This common-mode dc offset must be considered in connecting the 1580 to subsequent circuitry. Most high-performance A/D converters require a specific dc common-mode voltage at their inputs for proper operation. In such cases, drive circuitry should be configured to add the appropriate dc voltage to the 1580 outputs in order to match the converter. In addition to analog-controlled applications, the 1580 has been designed to mate perfectly with THAT's family of Digital Preamplifier Controller ICs to produce an optimized, digitally controlled audio preamplifier. THAT's digital controllers are intended primarily for use in the feedback loop of differential, current-feedback gain stages, such as the 1580. Figure 23 shows a THAT5171 or 5173 Digital Controller connected to the 1580. The controller varies RA, RB and RG (from Figure 15) to produce the desired gain based on the gain command provided via the SPI control interface. The feedback network impedances in these controller ICs have been chosen to minimize noise and distortion within the combined amplifier and controller at each gain step. As well, the 1580 has common-mode gain of unity, regardless of its differential gain. Commonmode inputs are presented at the output, along with the common-mode dc offset of -640 mV. If these common-mode signals are not removed, they may limit the dynamic range of subsequent stages. If a single-ended output is desired, the THAT1246 is a self-contained differential amplifier which offers a convenient way to remove common mode offset, convert to single-ended, and match the headroom of the 1580 output to a single-ended drive. A dual version of this part, the 1280, and low cost versions (1250 single and 1290 dual) are also available. See Design Note 140, "Input and Output Circuits for THAT Preamplifier ICs" for further ideas. The controllers also include a differential servo amplifier which minimizes the differential dc offset at the output. The servo generates a correction voltage at the 1580 inputs which in turn reduces the output offset voltage. The output dc offset is controlled by the servo amplifier inside the controller, making CG unnecessary, and enabling a more compact PCB design. Please refer to the 5171 and 5173 data sheets for more information. The 1580 will drive loads as low as 2 k, making it possible to drive A/D converters through resistive attenuators in low-cost applications. However, in order to provide common mode rejection and to improve distortion performance, THAT recommends active designs to drive high-performance A/D converters. +3.3V +3.3V IN2 DGnd Vdd Vdd BSY RST TRC CT IN1 C16 100n RT DGnd SYSTEM RESET +15V 20k V+ R18 47k RG +15V C14 100n -15V 22u NP C12 R7 1M2 C15 100n RA RB V- SCAP2 SCAP1 SOUT1 SOUT2 GPO2 GPO1 GPO0 GPO3 DOUT DIN SCLK CS To: Host MCU C13 RG2 V- THAT 5171/5173 AGnd Resistor Network with FET Switches R G1 - + Servo + - Control Logic SPI Interface V+ 20k C9 100n IN1 V+ OUT+ OUT1 RG1 RG2 22u NP R8 1M2 IN2 IN+ OUT- OUT2 V- C11 100n -15V C10 100n C8 220p INR2 1k2 R1 1k2 C7 100p C6 100p RFI PROTECTION Figure 23. Basic Application Circuit With THAT 5171/5173 Digital Controller. THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. THAT 1580 Low-Noise Differential Audio Preamplifier IC Page 12 of 16 Document 600187 Rev 01 PCB Layout Information The 1580 QFN package includes an exposed thermal pad on its bottom, as shown in Figure 24. This pad should be soldered to a thermal pad on the PCB as shown in Figure 25. Five thermal vias should be arranged in the configuration shown to conduct heat from the top layer of the PCB to the bottom layer, which should have a similar- or larger-sized plane. The thermal pad can be left electrically floating. However if it is not electrically floating, it should be connected only to V-. For current feedback amplifiers such as the THAT1580, stray capacitance to ground or power planes results in higher gains at high frequencies. This compromises common-mode rejection at high frequencies and, in extreme cases, can even lead to oscillation. Take care to avoid ground and power planes under and near RA, RB, RG, their associated pins and traces. The input signal lines are susceptible to magnetic pickup from power supply currents, which often take the form of half-wave rectified versions of the signal. Voltage fluctuations on the supply lines can couple capacitively as well. For this reason, take care not to run power and input signal lines close and/or parallel to each other. Minimizing RFI To minimize RF pickup, the C1 ~ C3 network at the input of all the applications schematics should be located as close as possible to the input connector, and the ground ends of C1 and C2 tied as closely as possible to the chassis. When using the additional RFI protection network C6 ~ C8 (shown in the phantom power circuits Fig. 21 and 22), these components should be located as close as possible to the 1580's input pins, and the grounded ends of this network should connect to the analog circuit ground. THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. THAT 1580 Low-Noise Differential Audio Preamplifier IC Page 13 of 16 Document 600187 Rev 01 Package and Soldering Information Package Characteristics Parameter Symbol Package Style Thermal Resistance JA Conditions Typ See Fig. 24 for dimensions 16 Pin QFN QFN package soldered to board Environmental Regulation Compliance 8 Units 130 C/W Complies with July 21, 2011 RoHS 2 requirements Soldering Reflow Profile JEDEC JESD22-A113-D (250 C) Moisture Sensitivity Level MSL Above-referenced JEDEC soldering profile 3 BOTTOM VIEW Package Order Number I 16 pin QFN 1580N16-U 9 12 D Table 2. Ordering Information 13 8 J B K 5 16 A MILLIMETERS 4.00 0.10 4.00 0.10 0.90 0.05 0.30 0.05 0.65 0.05 0.40 0.05 0.00 ~ 0.05 0.20 0.05 2.60 0.05 2.60 0.05 C' 0.3 x 45 INCHES 0.157 0.004 0.157 0.004 0.035 0.002 0.012 0.002 0.026 0.002 0.016 0.002 0.000 ~ 0.020 0.008 0.002 0.102 0.002 0.102 0.002 C` 0.012 x 45 Figure 24. QFN-16 Surface Mount Package 1.05 mm (0.041") 0.45 mm (0.018") 0 1.65 mm (0.065") 2.10 mm (0.083") H 0 2.10 mm (0.083") 1.65 mm (0.065") 1.05 mm (0.041") C G 0 F Exposed Thermal Pad E ITEM A B C D E F G H I J K Hole: 0.254 mm (0.010") Pad: 0.30 mm (0.012") 1 0.45 mm (0.018") 4 Figure 25. QFN-16 Thermal Solder Pad 8 PCB used for thermal characterization was two-layer board, 2" x 2", with thermal pad on top and bottom as shown in Figure 23. THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. THAT 1580 Low-Noise Differential Audio Preamplifier IC Page 14 of 16 Document 600187 Rev 01 Revision History Revision ECO Date Changes 00 -- 06/08/15 Initial Release -- 01 2979 07/20/16 Added performance graphs, Added RG Input Current specs, Changed Differential Input Offset Voltage and EIN Voltage specs, Redrawn -- THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. Page THAT 1580 Low-Noise Differential Audio Preamplifier IC Page 15 of 16 Document 600187 Rev 01 Notes THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. THAT 1580 Low-Noise Differential Audio Preamplifier IC Page 16 of 16 Document 600187 Rev 01 Notes THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA Tel: +1 508 478-9200; Fax +1 508 478-0990; Web: www.thatcorp.com Copyright (c) 2016, THAT Corporation; All rights reserved. Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: THAT Corporation: 1580N16-U 1580N16-UR