a FEATURES "CIickless" Bilateral Audio Switching Four SPST Switches in a 20-Pin Package Ultralow THD+N: 0.0008% @ 1 kHz (2 V rms, R L = 100 kV) Low Charge Injection: 35 pC typ High OFF Isolation: -100 dB typ (RL = 10 kV @ 1 kHz) Low Crosstalk: -94 dB typ (R L = 10 kV @ 1 kHz) Low ON Resistance: 28 V typ Low Supply Current: 900 mA typ Single or Dual Supply Operation: +11 V to +24 V or 65.5 V to 612 V Guaranteed Break-Before-Make TTL and CMOS Compatible Logic Inputs Low Cost-Per-Switch GENERAL DESCRIPTION The SSM2404 integrates four SPST analog switches in a single 20-pin package. Developed specifically for high performance audio applications, distortion and noise are negligible over the full operating range of 20 Hz to 20 kHz. With very low charge injection of 35 pC, "clickless" audio switching is possible, even under the most demanding conditions. Switch control is realized by conventional TTL or CMOS logic. Guaranteed "break-before-make" operation assures that all switches in a large system will open before any switch reaches the ON state. Single or dual supply operation is possible. Additional features include -100 dB OFF isolation, -94 dB crosstalk and 28 ON resistance. Optional current-mode switching permits an extended signal-handling range. Although optimized for large load impedances, the SSM2404 maintains good audio performance even under low load impedance conditions. Quad Audio Switch SSM2404 BLOCK DIAGRAM OF ONE SWITCH CHANNEL V- CONTROL LOGIC INTERFACE AND BREAK-BEFORE-MAKE CONTROL SW1 A RAMP GENERATOR DIGITAL CONTROL SW1 B V+ PIN CONNECTIONS Epoxy Mini-DIP (P Suffix) and SOIC (S Suffix) SW1 A 1 AGND 2 SW1 B 3 SW1 SW1 SW4 20 SW4 A 19 AGND 18 SW4 B 17 V+ DGND 4 SW1 CONTROL 5 16 SW4 CONTROL SW2 CONTROL 6 15 SW3 CONTROL NC* 7 14 V- SW2 B 8 13 SW3 B AGND 9 12 AGND SW2 A 10 11 SW3 A O TOP VIEW (Not to Scale) SSM2404 SW2 SW3 NC = NO CONNECT *CONNECT TO ANALOG GROUND FOR BEST NOISE ISOLATION 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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703 SSM2404-SPECIFICATIONS (VS = 612 V, TA = +258C, unless otherwise noted. Typical specifications apply at TA = +258C.) Parameter Symbol Conditions AUDIO PERFORMANCE Total Harmonic Distortion Plus Noise THD+N @ 1 kHz, with 80 kHz Filter, RL = 100 k, VIN = 2 V rms 20 Hz to 20 kHz 20 Hz to 20 kHz Spectral Noise Density Wideband Noise Density ANALOG SIGNAL SECTION Analog Voltage Range Analog Current Range ON Resistance RON Matching ON Leakage Current OFF Leakage Current Charge Injection ON-State Input Capacitance OFF-State Input Capacitance OFF Isolation Channel-to-Channel Crosstalk CONTROL SECTION Digital Input High Digital Input Low Turn-On Time1 Turn-Off Time2 Break-Before-Make Time Delay Logic Input Current Logic HI Logic LO POWER SUPPLY Supply Voltage Range Positive Supply Current Negative Supply Current Ground Current en en p-p Min Typ Max Units 0.0008 0.8 0.6 % nV/Hz V p-p 12 10 28 45 1 0.1 +20 0.1 +20 35 31 17 -100 -94 V mA % nA nA pC pF pF dB dB VA IA RON RON Match IS(ON) IS(OFF) Q CON COFF ISO(OFF) CT VINH = 2.4 V, IA = 2 mA VINH = 2.4 V, VA = 0 V IA = 10 mA, VA = 10 V dc IA = 10 mA, VA = 0 V VA = 10 V VA = 10 V VINH VINL tON tOFF tON-tOFF DGND = 0 V DGND = 0 V See Test Circuit See Test Circuit 2.4 0 VINH = 2.4 V VINL = 0.8 V -1000 1.3 -1000 1.0 +1000 nA +1000 nA Single Supply Dual Supply All Channels On All Channels On All Channels On +11 5.5 +24 12 5 VS ISY+ ISY- -20 -20 VA = 5 V rms VA = 5 V rms VA = 50 mV rms, f = 1 kHz, RL = 10 k VA = 50 mV rms, f = 1 kHz, RL = 10 k 8 5 3 -1.5 -2.0 0.9 -0.6 -0.3 VS 0.8 50 30 20 V V ms ms ms V V mA mA mA NOTES 1 Turn-on time is measured from the time the logic input reaches the 50% point to the time the output reaches 50% of the final value. 2 Turn-off time is measured from the time the logic input reaches the 50% point to the time the output reaches 50% of the initial value. Specifications subject to change without notice. ABSOLUTE MAXIMUM RATINGS Supply Voltage Single Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +27 V Dual Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.5 V Analog Input Voltage (VA) . . . . . . . . . . . . . . . . . . . . . . . . . . VS Logic Input Voltage (VINL/INH) . . . . . . . . . . . . . . . . . . . . . . VS Maximum Current Through Any Switch . . . . . . . . . . . 20 mA Operating Temperature Range . . . . . . . . . . . . -40C to +85C Storage Temperature Range . . . . . . . . . . . . -65C to +150C Junction Temperature (TJ) . . . . . . . . . . . . . . . . . . . . +150C Lead Temperature (Soldering, 60 sec) . . . . . . . . . . . . +300C Thermal Resistance1 20-Pin Plastic DIP (P): JA = 74, JC = 32 . . . . . . . . . C/W 20-Pin SOIC (S): JA = 90, JC = 27 . . . . . . . . . . . . . . C/W ORDERING GUIDE Model Operating Temperature Range Package Package Option* SSM2404P SSM2404S -40C to +85C -40C to +85C 20-Pin Plastic DIP 20-Pin SOIC N-20 R-20 *N = Plastic DIP, R = SOIC. NOTE 1 JA is specified for worst case mounting conditions, i.e., JA is specified for device in socket for P-DIP package. -2- REV. B SSM2404 VA (IN) = 50mVRMS f = 20Hz TO 100kHz VA (IN) VA (OUT) R L = 10k AND 100k 50 OFF ISOLATION = 20 LOG VA (OUT) VA (IN) OFF Isolation Test Circuit HIGH LOGIC INPUT LOW 1.4V t r 100ns t f 100ns 1.4V Figure 2. Headroom (VS = 12 V, f = 1 kHz, with 80 kHz Filter) LOW DC VOLTAGE VA (IN) CLOSED OPEN VA (OUT) 50% 50% OPEN 1.0 t ON t OFF tON/tOFF Timing Diagram THD + N - % 0.1 +12V V+ VA (IN) 0.01 VA (OUT) SWITCH CONROL 0.001 GND V- 0.0001 100 -12V 1k 10k LOAD RESISTANCE - 100k Figure 3. THD+N vs. Load (VS = 12 V, VA = 2 V rms, f = 1 kHz, with 80 kHz Filter) Test Circuit for tON/tOFF Timing Specification, tON/tOFF Switching Response, and ON/OFF Transition Photos THD + N - % 0.01 0.001 0.0001 0 Figure 1. THD+N vs. Frequency (VS = 12 V, VA = 2 V rms, with 80 kHz Filter) REV. B 4 8 12 SUPPLY VOLTAGE - V Figure 4. THD+N vs. Supply Voltage (VA = 2 V rms, f = 1 kHz, RL = 100 k, with 80 kHz Filter) -3- SSM2404 9.5 OUTPUT VOLTAGE SWING - VRMS 9.0 TA = 25C VS = 12V f = 20kHz 8.5 8.0 7.5 7.0 6.5 6.0 100 1k 10k 100k LOAD RESISTANCE - Figure 8. Output Voltage Swing vs. Load Resistance Figure 5. Frequency Response (VS = 12 V, VA = 1 V rms, RL = 100 k) 10 CH A: 8.00V FS MKR: 0.11V/ Hz 0Hz MKR: 20 000Hz OUTPUT VOLTAGE SWING - VRMS 9 1.00V/DIV 8 7 TA = 25C R L = 100k f = 20kHz 0.1% THD + N 6 5 4 3 2 1 25kHz BW: 150Hz 0 4 6 10 8 12 SUPPLY VOLTAGE - Volts Figure 9. Output Voltage Swing vs. Supply Voltage Figure 6. SSM2404 Spectral Noise Density en [5 Devices (20 Switches) Chained Together] -20 TA = 25C VS = 12V VA = 50mVRMS -30 -40 OFF ISOLATION - dB 10V 100 0V 0V INPUT 90 OUTPUT 10 -50 R L = 100k -60 -70 -80 R L = 10k -90 -100 0% 10V -110 5s -120 10 Figure 7. Square Wave Response (TA = +25C, VS = 12 V, RL = 100 k, f = 20 kHz) 100 1k FREQUENCY - Hz 10k 100k Figure 10. OFF-Isolation vs. Frequency -4- REV. B SSM2404 50 0 CROSSTALK - dB -30 SWITCH LEAKAGE CURRENT - nA TA = 25C VS = 12V VA = 50mVRMS -15 -45 -60 R L = 100k -75 R L = 10k -90 -105 -120 40 VS = 12V VINL = 0.8V RL = -40C TO +85 C 30 20 10 0 -10 -135 -150 10 100 1k FREQUENCY - Hz 10k -20 -10 100k 0 5 10 ANALOG INPUT VOLTAGE - Volts Figure 11. Channel-to-Channel Crosstalk vs. Frequency (Worst Case Conditions, as Measured Between Switches 1 and 4, or 2 and 3) Figure 14. Leakage Current vs. Analog Voltage 50 20 VS = 12V RL = IA = 10mA 40 VS = 12V VA = 5V RL = 18 16 +85C 30 +25C 20 -40C SWITCHING TIME - ms ON RESISTANCE - -5 10 14 12 10 TON 8 6 TOFF 4 2 0 -10 0 -5 5 ANALOG INPUT VOLTAGE - Volts 0 -40 10 Figure 12. ON Resistance vs. Analog Voltage 20 40 TEMPERATURE - C 60 80 100 1.0 TA = 25C VS = 12V RL = 80 70 0.8 60 50 40 VIL = 0.8V 30 20 10 VIH = 2.4V 0.2 0 -0.2 I SY- -0.4 IGND -0.6 -10 -0.8 -1.0 -40 -20 -10 -5 0 5 ANALOG INPUT VOLTAGE - Volts 10 15 VS = 12V VA = GND VINH = 2.4V 0.4 0 -15 I SY+ 0.6 SUPPLY CURRENT - mA SWITCH LEAKAGE CURRENT - mA 0 Figure 15. Switching Time vs. Temperature 90 -20 0 20 40 60 80 TEMPERATURE - C Figure 16. Supply Current vs. Temperature Figure 13. Overvoltage Characteristics REV. B -20 -5- 100 SSM2404 10V 100 5V 90 0 5V 10 0% 0 ANALOG OUTPUT VA (OUT) SSM2404 can also be configured as a 4:1 multiplexer, or by using additional packages, as 8:1 or 16:1 and up. The breakbefore-make feature is guaranteed from part to part allowing such multiple-package applications. LOGIC INPUT VINL/INH As Figure 20 shows, the SSM2404 is easy to use, and no additional devices are needed. The load resistors are recommended for improved OFF-isolation and charge injection. The ON resistance of the switch is only 28 typically, which causes very little signal attenuation even with a load resistor. 5ms/div IN1 Figure 17. tON/tOFF Switching Response 1 2 RL IN4 SW4 19 RL 18 3 OUT1 DGND SW1 CONTROL OUT4 17 +12V 16 SW4 CONTROL 6 15 SW3 CONTROL 7 14 -12V 8 13 4 5 TOP VIEW (Not to Scale) SSM2404 100 90 SW2 CONTROL CLOSED (SWITCH ON) OUT2 RL OUT3 RL 9 OPEN (SWITCH OFF) 20 SW1 SW2 SW3 12 10 IN2 0% 50mV 50s 10 11 R L IS OPTIONAL Figure 18. Switch OFF-to-ON Transition (RL = 5 k) IN3 SW SWITCH CONTROL STATE 0 1 OFF ON Figure 20. Basic Circuit Configuration OPTIMIZING PERFORMANCE 100 90 CLOSED (SWITCH ON) OPEN (SWITCH OFF) 10 0% 50mV As the performance curves show, the switch is optimized for high impedance loads. The distortion performance is at its best when the switch has a load impedance of 100 k or greater as shown in Figure 1. However, even at lower values of load resistances, the 1 kHz distortion performance is still excellent, 0.006% for a 10 k load. The main trade-off with THD is OFF-isolation and crosstalk. This is shown in Figures 10 and 11, again with two different load conditions. As these graphs show, the 10 k load yields approximately a 16 dB improvement in both characteristics. 50s Figure 19. Switch ON-to-OFF Transition (RL = 5 k) APPLICATIONS INFORMATION The SSM2404 integrates four analog CMOS switches with guaranteed "break-before-make" operation to provide high quality audio switching. Each switch has complementary N-channel and P-channel MOSFETs to allow the analog input voltage range to include the positive and negative rails and improve linearity. In addition, the topology permits fully bilateral switching. When using the SSM2404 there is full flexibility in configuring the switches. For example, they can be used individually as shown in Figure 20, or as a double-pole, double-throw (DPDT) switch, which is explained later. The Thus, the optimum operating point depends on the most critical parameters. When THD is critical then high load impedances should be used; however, when crosstalk and OFFisolation are critical, lower impedances on the order of 10 k should be used. An additional benefit of using the smaller load resistor is that any charge injected onto the output will be shunted to ground through the resistor. If improved OFFisolation is needed, the SSM2404 dual audio switch should be considered with its excellent 120 dB OFF-isolation at 20 kHz. It is important that all of the AGND pins be connected to the system analog ground. These pins isolate the input and output of each switch. Without connecting these pins, the OFFisolation will degrade significantly. -6- REV. B SSM2404 voltages of N4 and P4 are changing, the ON resistance of each switch is ramping from its OFF state to 28 and vice versa. The actual rise and fall times are shown in Figures 18 and 19 for a 5 k load. These times are significantly slower than typical switches, minimizing the SSM2404's charge injection and giving it "clickless" performance. DETAILED SWITCH OPERATION A simplified circuit schematic with the functional sections is shown in Figure 21. The TTL interface has an internally regulated 5 V to ensure TTL logic levels regardless of the supply voltage. The logic threshold is with respect to the DGND pin, which can be offset. For example, if DGND is connected to the negative supply, then the SSM2404 will operate with negative rail logic. The interface shifts the control logic down to the negative supply and inverts it to drive N1. DOUBLE-POLE DOUBLE-THROW SWITCH The SSM2404 is ideal as a one-chip solution for a stereo switch. The schematic in Figure 22 shows the typical configuration. This circuit will select one of two stereo sources, channel A or B. The switch controls for the left and right input of each channel are tied together so that both will be turned on or off simultaneously. An inverter is inserted between the channel A and B controls so that only one logic signal is needed. The outputs can be configured many different ways, such as an inverting or noninverting amplifier stage, and the 10 k load resistors are added to improve the OFF-isolation. The performance of this stereo switch is equivalent to each individual switch, yielding a high quality audio switch that is virtually transparent to the signal. V+ 100nA 100nA P1 SW1 A BIAS P2 P3 C1 15pF SW CONTROL DGND -1 C2 15pF TTL INTERFACE N1 N2 N4 P4 -1 V+ SW1 B N3 17 V- BREAK-BEFORE-MAKE SSM2404 RAMP GENERATOR 10 8 SW2 L INA Figure 21. Simplified Schematic 1 N1 in combination with C1 and the 100 nA current source provides the break-before-make operation of the switch. When the switch is on, N1 is off and C1 is charged up to the positive rail. However, when the SW CONTROL is turned off, then the gate of N1 is pulled high. This turns N1 on, providing a low impedance path to quickly discharge C1 to the negative rail, which quickly "breaks" the switch. On the other hand, when the SW CONTROL goes high again, the gate of N1 is pulled low, turning it off. This leaves C1 to be slowly charged up to the positive rail by the 100 nA current source. The difference in the discharge and charging times ensures break-before-make operation, even from device to device. 3 SW1 L INB 6 SWA/SWB 15 4 5 16 SW2 CONTROL AGND SW3 CONTROL 12 DGND 19 SW1 CONTROL SW4 CONTROL 13 SW3 20 R INB 2 9 11 R INA L OUT 10k SWA/SWB CHANNEL SELECTED 0 1 B A 18 SW4 R OUT 10k 14 The voltage on C1 is inverted by P1 to drive the ramp generator differential pair, consisting of P2, P3 and N2, N3. This differential pair steers the 100 nA of tail current to either charge or discharge C2. As discussed above, when the switch is on, C1 is charged up to the positive rail. P1 inverts this, putting a low voltage equivalent to the negative supply on the gate of P2. The BIAS voltage is approximately equal to the midpoint of the two supply voltages. Thus, when P2 is pulled down, it is turned on and P3 is off. All of the 100 nA flows through N2 and is mirrored by N3. Thus, the 100 nA discharges C2 through N3. When C2 is pulled low, the inverter turns N4 on by pulling its gate high, and the second inverter turns P4 on. To turn the switch off the gate of P2 is pulled above the BIAS so that all 100 nA charges C2 through P3. This is then inverted to turn off N4 and P4. V- Figure 22. Double-Pole, Double-Throw Stereo Switch VIRTUAL GROUND SWITCHING The SSM2404 was built on a CMOS process with a 24 V operating limit for the total supply voltage across the part. This leads to a corresponding limit on the analog voltage range. However, to achieve larger signal swings, the SSM2404 should be configured in the virtual ground mode. As shown in Figure 23, the output of the SSM2404 is connected to the inverting input of an amplifier. Since the noninverting input is grounded, the SSM2404 will also be biased at ground, and large voltage swings on the circuit's input will not significantly change the voltage on the switch. The only limitation is that the current through the switch needs to be less than 10 mA, and the voltage range is limited only by the op amp and its supply voltages. The internal ramp has rise and fall times on the order of a few milliseconds which is sped up by the inverters. As the gate REV. B -7- SSM2404 The circuit was tested with an SSM2131 high slew rate audio amplifier and the results are shown in Figures 24 and 25. This configuration yields excellent THD performance that is primarily determined by the amplifier. Also, the headroom is now +24 dBu (0 dBu = 0.775 V rms), which is due to the amplifier's output voltage swing. Thus, even though the SSM2404 has a 12 V limitation on its supplies, it can be used in systems with much higher voltage ranges. For example, the double-pole double-throw switch from Figure 22 can be reconfigured in the virtual ground mode to allow higher voltage swings, as shown in Figure 26. This application realizes the excellent performance of Figures 24 and 25 while providing a low cost switching solution. V+ 17 SSM2404 5k LINB 1 AUDIO IN 1 SW1 A SW1 B 3 LOUT SW1 6 SWA/SWB 15 4 5 5k R2 5k SSM2404 R1 5k 5k SW2 16 +12V 8 10 RINA SSM2131 SW2 CONTROL 2 AGND SW3 CONTROL 9 DGND 12 SW1 CONTROL 19 SW4 CONTROL 13 11 SW3 5k +18V 5k 3 RINB SSM2131 1N914 C1626-20-1/92 5k LINA 18 20 ROUT SW4 AUDIO OUT 14 SSM2131 V- -12V -18V Figure 26. Double-Pole, Double-Throw Stereo Switch Using Virtual Ground Operation Figure 23. Virtual Ground Switching OUTLINE DIMENSIONS Dimensions shown in inches and (mm). Mini-DIP (P Suffix) 11 20 0.280 (7.11) 0.240 (6.10) PIN 1 1 10 1.060 (26.90) 0.925 (23.50) 0.060 (1.52) 0.015 (0.38) 0.210 (5.33) MAX 0.200 (5.05) 0.125 (3.18) Figure 24. Virtual Ground Switch THD+N vs. Frequency (VS = 12 V, VA = 2 V rms, with 80 kHz Filter) 0.150 (3.81) MIN 0.022 (0.558) 0.014 (0.356) 0.100 (2.54) BSC 0.070 (1.77) 0.045 (1.15) 0.325 (8.25) 0.300 (7.62) 0.195 (4.95) 0.115 (2.93) 0.015 (0.381) 0.008 (0.204) SEATING PLANE SOIC (S Suffix) 20 PRINTED IN U.S.A. 0.5118 (13.00) 0.4961 (12.60) 11 0.2992 (7.60) 0.2914 (7.40) PIN 1 0.4193 (10.65) 0.3937 (10.00) 1 10 0.0500 (1.27) BSC 0.0118 (0.30) 0.0040 (0.10) Figure 25. Virtual Ground Switch Headroom (VS = 12 V for SSM2404; VS = 18 V for Op Amp, f = 1 kHz, with 80 kHz Filter) -8- 0.0192 (0.49) 0.0138 (0.35) 0.1043 (2.65) 0.0926 (2.35) 0.0125 (0.32) 0.0091 (0.23) 0.0291 (0.74) X 45 0.0098 (0.25) 0- 8 0.0500 (1.27) 0.0157 (0.40) REV. B