Final Electrical Specifications LT6600-2.5 Very Low Noise, Differential Amplifier and 2.5MHz Lowpass Filter U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Programmable Differential Gain via Two External Resistors Adjustable Output Common Mode Voltage Operates and Specified with 3V, 5V, ±5V Supplies 0.5dB Ripple 4th Order Lowpass Filter with 2.5MHz Cutoff 86dB S/N with 3V Supply and 1VRMS Output Low Distortion, 1VRMS, 800Ω Load 1MHz: 95dBc 2nd, 88dBc 3rd Fully Differential Inputs and Outputs Compatible with Popular Differential Amplifier Pinouts SO-8 Package U APPLICATIO S ■ ■ ■ ■ June 2003 High Speed ADC Antialiasing and DAC Smoothing in Networking or Cellular Base Station Applications High Speed Test and Measurement Equipment Medical Imaging Drop-in Replacement for Differential Amplifiers , LTC and LT are registered trademarks of Linear Technology Corporation. The LT®6600-2.5 combines a fully differential amplifier with a 4th order 2.5MHz lowpass filter approximating a Chebyshev frequency response. Most differential amplifiers require many precision external components to tailor gain and bandwidth. In contrast, with the LT6600-2.5, two external resistors program differential gain, and the filter’s 2.5MHz cutoff frequency and passband ripple are internally set. The LT6600-2.5 also provides the necessary level shifting to set its output common mode voltage to accommodate the reference voltage requirements of A/Ds. Using a proprietary internal architecture, the LT6600-2.5 integrates an antialiasing filter and a differential amplifier/ driver without compromising distortion or low noise performance. At unity gain the measured in band signal-to-noise ratio is an impressive 86dB. At higher gains the input referred noise decreases so the part can process smaller input differential signals without significantly degrading the output signal-to-noise ratio. The LT6600-2.5 also features low voltage operation. The differential design provides outstanding performance for a 4VP-P signal level while the part operates with a single 3V supply. The LT6600-2.5 is available in an SO-8 package. For similar devices with higher cutoff frequency, refer to the LT6600-10 and LT6600-20 data sheets. U TYPICAL APPLICATIO Amplitude Response 12 0.1µF 1580Ω –24 1 7 0.01µF VIN+ – 3 4 VOUT+ 2 LT6600-2.5 8 1580Ω –12 + 6 5 VOUT – GAIN (dB) VIN– VS = ±2.5V 0 5V –36 –48 –60 –72 660025 TA01a –84 –96 100k 1M 10M FREQUENCY (Hz) 50M 660025 TA01b 660025i Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 1 LT6600-2.5 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) Total Supply Voltage ................................................ 11V Operating Temperature Range (Note 6) ...–40°C to 85°C Specified Temperature Range (Note 7) ....–40°C to 85°C Junction Temperature ........................................... 150°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C ORDER PART NUMBER TOP VIEW IN – 1 8 IN + VOCM 2 7 VMID V+ 3 6 V– OUT + 4 5 OUT – LT6600CS8-2.5 LT6600IS8-2.5 S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO 660025 600I25 TJMAX = 150°C, θJA = 100°C/W Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Unless otherwise specified VS = 5V (V+ = 5V, V – = 0V), RIN = 1580Ω, and RLOAD = 1k. PARAMETER Filter Gain, VS = 3V RIN = 1580Ω Filter Gain, VS = 5V RIN = 1580Ω Filter Gain, VS = ±5V Filter Gain, RIN = 402Ω Filter Gain Temperature Coefficient (Note 2) Noise Distortion (Note 4) Differential Output Swing Input Bias Current CONDITIONS VIN = 2VP-P, fIN = DC to 260kHz VIN = 2VP-P, fIN = 700kHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 1.9MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 2.2MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 2.5MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 7.5MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 12.5MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = DC to 260kHz VIN = 2VP-P, fIN = 700kHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 1.9MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 2.2MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 2.5MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 7.5MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 12.5MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = DC to 260kHz VIN = 2VP-P, fIN = DC to 260kHz, VS = 3V VIN = 2VP-P, fIN = DC to 260kHz, VS = 5V VIN = 2VP-P, fIN = DC to 260kHz, VS = ±5V fIN = 260kHz, VIN = 2VP-P Noise BW = 10kHz to 2.5MHz 1MHz, 1VRMS, RL = 800Ω 2nd Harmonic 3rd Harmonic Measured Between Pins 4 and 5 VS = 5V VS = 3V Average of Pin 1 and Pin 8 ● ● ● ● MIN – 0.5 – 0.15 – 0.2 – 0.6 – 2.1 ● ● ● ● ● ● – 0.5 – 0.15 – 0.2 – 0.6 – 2.1 ● ● – 0.6 11.3 11.3 11.2 ● ● ● 8.8 5.1 – 35 TYP 0.1 0 0.2 0.1 0.9 – 34 – 51 –0.1 0 0.2 0.1 –0.9 – 34 – 51 – 0.1 11.8 11.8 11.7 780 51 95 88 9.3 5.5 – 15 MAX 0.4 0.1 0.6 0.5 0 – 31 0.4 0.1 0.6 0.5 0 –31 0.4 12.3 12.3 12.2 UNITS dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB ppm/C µVRMS dBc dBc VP-P DIFF VP-P DIFF µA 660025i 2 LT6600-2.5 ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Unless otherwise specified VS = 5V (V+ = 5V, V – = 0V), RIN = 1580Ω, and RLOAD = 1k. PARAMETER Input Referred Differential Offset CONDITIONS RIN = 1580Ω RIN = 402Ω Differential Offset Drift Input Common Mode Voltage (Note 3) Output Common Mode Voltage (Note 5) Differential Input = 500mVP-P, RIN = 402Ω Differential Input = 2VP-P, Pin 7 at Mid-Supply Output Common Mode Offset (with Respect to Pin 2) Common Mode Rejection Ratio Voltage at VMID (Pin 7) VMID Input Resistance VOCM Bias Current VOCM = VMID= VS/2 Power Supply Current Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: This is the temperature coefficient of the internal feedback resistors assuming a temperature independent external resistor (RIN). Note 3: The input common mode voltage is the average of the voltages applied to the external resistors (RIN). Specification guaranteed for RIN ≥ 402Ω. Note 4: Distortion is measured differentially using a single-ended stimulus. The input common mode voltage, the voltage at Pin 2, and the voltage at Pin 7 are equal to one half of the total power supply voltage. MIN VS = 3V VS = 5V VS = ±5V VS = 3V VS = 5V VS = ±5V ● ● ● VS = 3V VS = 5V VS = ±5V VS = 3V VS = 5V VS = ±5V VS = 3V VS = 5V VS = ±5V ● ● ● ● ● ● 0.0 0.0 –2.5 1.0 1.5 –1.0 –25 –30 –55 VS = 5V VS = 3V ● 2.46 ● 4.3 –15 –10 VS = 5V VS = 3V VS = 3V, VS = 5V VS = 3V, VS = 5V VS = ±5V ● ● ● ● ● ● ● ● ● ● TYP 5 5 5 3 3 3 10 10 5 –10 63 2.51 1.5 5.7 –3 –3 26 28 MAX 25 30 35 13 16 20 1.5 3.0 1.0 1.5 3.0 2.0 45 45 35 2.55 7.7 30 33 36 UNITS mV mV mV mV mV mV µV/°C V V V V V V mV mV mV dB V V kΩ µA µA mA mA mA Note 5: Output common mode voltage is the average of the voltages at Pins 4 and 5. The output common mode voltage is equal to the voltage applied to Pin 2. Note 6: Both the LT6600CS8-2.5 and LT6600IS8-2.5 are guaranteed functional over the operating temperature range of –40°C to 85°C. Note 7: The LT6600CS8-2.5 is guaranteed to meet specified performance from 0°C to 70°C and is designed, characterized and expected to meet specified performance from –40°C and 85°C, but is not tested or QA sampled at these temperatures. The LT6600IS8-2.5 is guaranteed to meet specified performance from –40°C to 85°C. 660025i 3 LT6600-2.5 U U U PI FU CTIO S IN – and IN + (Pins 1, 8): Input Pins. Signals can be applied to either or both input pins through identical external resistors, RIN. The DC gain from differential inputs to the differential outputs is 1580Ω/RIN. VOCM (Pin 2): Is the DC Common Mode Reference Voltage for the 2nd Filter Stage. Its value programs the common mode voltage of the differential output of the filter. Pin 2 is a high impedance input, which can be driven from an external voltage reference, or Pin 2 can be tied to Pin 7 on the PC board. Pin 2 should be bypassed with a 0.01µF ceramic capacitor unless it is connected to a ground plane. V+ and V – (Pins 3, 6): Power Supply Pins. For a single 3.3V or 5V supply (Pin 6 grounded) a quality 0.1µF ceramic bypass capacitor is required from the positive supply pin (Pin 3) to the negative supply pin (Pin 6). The bypass should be as close as possible to the IC. For dual supply applications, bypass Pin 3 to ground and Pin 6 to ground with a quality 0.1µF ceramic capacitor. OUT+ and OUT – (Pins 4, 5): Output Pins. Pins 4 and 5 are the filter differential outputs. Each pin can drive a 100Ω and/or 50pF load to AC ground. VMID (Pin 7): The VMID pin is internally biased at midsupply, see block diagram. For single supply operation, the VMID pin should be bypassed with a quality 0.01µF ceramic capacitor to Pin 6. For dual supply operation, Pin 7 can be bypassed or connected to a high quality DC ground. A ground plane should be used. A poor ground will increase noise and distortion. Pin 7 sets the output common mode voltage of the 1st stage of the filter. It has a 5.5kΩ impedance, and it can be overridden with an external low impedance voltage source. 660025i 4 LT6600-2.5 W BLOCK DIAGRA VIN+ RIN IN + VMID 8 7 V+ V– OUT – 6 5 11k PROPRIETARY LOWPASS FILTER STAGE 1580Ω 11k 800Ω V– OP AMP + 800Ω + – – VOCM – VOCM + – + 800Ω 800Ω 1580Ω 1 VIN– RIN IN – 2 3 4 VOCM V+ OUT + 660025 BD 660025i 5 LT6600-2.5 U W U U APPLICATIO S I FOR ATIO output voltage is 1.65V, and the differential output voltage is 2VP-P for frequencies below 2.5MHz. The common mode output voltage is determined by the voltage at pin 2. Since pin 2 is shorted to pin 7, the output common mode is the mid-supply voltage. In addition, the common mode input voltage can be equal to the mid-supply voltage of Pin␣ 7. Interfacing to the LT6600-2.5 The LT6600-2.5 requires two equal external resistors, RIN, to set the differential gain to 1580Ω/RIN. The inputs to the filter are the voltages VIN+ and VIN– presented to these external components, Figure 1. The difference between VIN+ and VIN– is the differential input voltage. The average of VIN+ and VIN– is the common mode input voltage. Similarly, the voltages VOUT+ and VOUT– appearing at Pins 4 and 5 of the LT6600-2.5 are the filter outputs. The difference between VOUT+ and VOUT– is the differential output voltage. The average of VOUT+ and VOUT– is the common mode output voltage. Figure 2 shows how to AC couple signals into the LT6600-2.5. In this instance, the input is a single-ended signal. AC coupling allows the processing of single-ended or differential signals with arbitrary common mode levels. The 0.1µF coupling capacitor and the 1580Ω gain setting resistor form a high pass filter, attenuating signals below 1kHz. Larger values of coupling capacitors will proportionally reduce this highpass 3dB frequency. Figure 1 illustrates the LT6600-2.5 operating with a single 3.3V supply and unity passband gain; the input signal is DC coupled. The common mode input voltage is 0.5V, and the differential input voltage is 2VP-P. The common mode 3.3V 0.1µF V 3 – 1580Ω 1 VIN VIN+ 1 0 t VIN– + 4 VOUT+ LT6600-2.5 2 0.01µF + VIN 3 – 7 2 V 3 8 –5 + 1580Ω VOUT– 6 2 VOUT+ 1 VOUT– t 0 660025 F01 Figure 1 3.3V 0.1µF V 0.1µF 2 1580Ω 1 7 1 VIN+ 0 0.1µF t 2 0.01µF VIN –1 – + 4 LT6600-2.5 8 + V 3 – + 1580Ω 5 3 VOUT+ 2 VOUT– 1 6 VOUT+ VOUT– 0 660025 F02 Figure 2 5V 0.1µF V – 3 402Ω 1 VIN 7 2 1 0 VIN+ VIN– 2 0.01µF 500mVP-P (DIFF) 8 + VIN t – + 4 LT6600-2.5 – + 402Ω + – V 3 6 2V 5 3 VOUT+ VOUT+ 2 VOUT– 1 0 VOUT– t 660025 F03 Figure 3 660025i 6 LT6600-2.5 U U W U APPLICATIO S I FOR ATIO In Figure 3 the LT6600-2.5 is providing 12dB of gain. The common mode output voltage is set to 2V. Use Figure 4 to determine the interface between the LT6600-2.5 and a current output DAC. The gain, or “transimpedance,” is defined as A = VOUT/IIN. To compute the transimpedance, use the following equation: A= 1580 • R1 (Ω ) (R1+ R2) By setting R1 + R2 = 1580Ω, the gain equation reduces to A = R1(Ω). The voltage at the pins of the DAC is determined by R1, R2, the voltage on Pin 7 and the DAC output current. Consider Figure 4 with R1 = 49.9Ω and R2 = 1540Ω. The voltage at Pin 7 is 1.65V. The voltage at the DAC pins is given by: R1 R1 • R2 VDAC = VPIN7 • + IIN • R1 + R2 + 1580 R1 + R2 = 26mV + IIN • 48.3Ω IIN is IIN+ or IIN–. The transimpedance in this example is 49.6Ω. Evaluating the LT6600-2.5 The low impedance levels and high frequency operation of the LT6600-2.5 require some attention to the matching networks between the LT6600-2.5 and other devices. The previous examples assume an ideal (0Ω) source impedance and a large (1kΩ) load resistance. Among practical examples where impedance must be considered is the evaluation of the LT6600-2.5 with a network analyzer. Figure 5 is a laboratory setup that can be used to characterize the LT6600-2.5 using single-ended instruments with 50Ω source impedance and 50Ω input impedance. For a 12dB gain configuration the LT6600-2.5 requires a 402Ω source resistance yet the network analyzer output is calibrated for a 50Ω load resistance. The 1:1 transformer, 53.6Ω and 388Ω resistors satisfy the two constraints above. The transformer converts the single-ended source into a differential stimulus. Similarly, the output of the LT6600-2.5 will have lower distortion with larger load resistance yet the analyzer input is typically 50Ω. The 4:1 turns (16:1 impedance) transformer and the two 402Ω resistors of Figure 5, present the output of the LT6600-2.5 with a 1600Ω differential load, or the equivalent of 800Ω to ground at each output. The impedance seen by the network analyzer input is still 50Ω, reducing reflections in the cabling between the transformer and analyzer input. Differential and Common Mode Voltage Ranges The rail-to-rail output stage of the LT6600-2.5 can process large differential signal levels. On a 3V supply, the output signal can be 5.1VP-P. Similarly, a 5V supply can support signals as large as 8.8VP-P. To prevent excessive power dissipation in the internal circuitry, the user must limit differential signal levels to 9VP-P. The two amplifiers inside the LT6600-2.5 have independent control of their output common mode voltage (see the “Block Diagram” section). The following guidelines will optimize the performance of the filter. Pin 7 can be allowed to float; Pin 7 must be bypassed to an AC ground with a 0.01µF capacitor or some instability may be observed. Pin 7 can be driven from a low impedance 2.5V 0.1µF CURRENT OUTPUT DAC 3.3V NETWORK ANALYZER SOURCE 0.1µF IIN– R1 R2 7 0.01µF 3 – + 4 VOUT+ 7 50Ω 53.6Ω 2 8 2 LT6600-2.5 IIN+ R1 1 COILCRAFT TTWB-1010 1:1 388Ω 1 8 R2 – + 5 VOUT– 388Ω 3 – + 4 COILCRAFT TTWB-16A 4:1 402Ω LT6600-2.5 – + 6 5 NETWORK ANALYZER INPUT 50Ω 402Ω 0.1µF 660025 F05 6 660025 F04 – 2.5V Figure 4 Figure 5 660025i 7 LT6600-2.5 U W U U APPLICATIO S I FOR ATIO source, provided it remains at least 1.5V above V – and at least 1.5V below V +. An internal resistor divider sets the voltage of Pin 7. While the internal 11k resistors are well matched, their absolute value can vary by ±20%. This should be taken into consideration when connecting an external resistor network to alter the voltage of Pin 7. Pin 2 can be shorted to Pin 7 for simplicity. If a different common mode output voltage is required, connect Pin 2 to a voltage source or resistor network. For 3V and 3.3V supplies the voltage at Pin 2 must be less than or equal to the mid supply level. For example, voltage (Pin 2) ≤ 1.65V on a single 3.3V supply. For power supply voltages higher than 3.3V the voltage at Pin 2 can be set above mid supply. The voltage on Pin 2 should not exceed 1V below the voltage on Pin 7. The voltage on Pin 2 should not be more than 2V above the voltage on Pin 7. Pin 2 is a high impedance input. The LT6600-2.5 was designed to process a variety of input signals including signals centered around the mid-supply voltage and signals that swing between ground and a positive voltage in a single supply system (Figure 1). The range of allowable input common mode voltage (the average of VIN+ and VIN– in Figure 1) is determined by the power supply level and gain setting (see “Electrical Characteristics”). Common Mode DC Currents In applications like Figure 1 and Figure 3 where the LT6600-2.5 not only provides lowpass filtering but also level shifts the common mode voltage of the input signal, DC currents will be generated through the DC path between input and output terminals. Minimize these currents to decrease power dissipation and distortion. Consider the application in Figure 3. Pin 7 sets the output common mode voltage of the 1st differential amplifier inside the LT6600-2.5 (see the “Block Diagram” section) at 2.5V. Since the input common mode voltage is near 0V, there will be approximately a total of 2.5V drop across the series combination of the internal 1580Ω feedback resistor and the external 402Ω input resistor. The resulting 1.25mA common mode DC current in each input path, must be absorbed by the sources VIN+ and VIN–. Pin 2 sets the common mode output voltage of the 2nd differential amplifier inside the LT6600-2.5, and therefore sets the common mode output voltage of the filter. Since, in the example of Figure 3, Pin 2 differs from Pin 7 by 0.5V, an additional 625µA (312µA per side) of DC current will flow in the resistors coupling the 1st differential amplifier output stage to filter output. Thus, a total of 3.125mA is used to translate the common mode voltages. A simple modification to Figure 3 will reduce the DC common mode currents by 36%. If Pin 7 is shorted to Pin 2 the common mode output voltage of both op amp stages will be 2V and the resulting DC current will be 2mA. Of course, by AC coupling the inputs of Figure 3, the common mode DC current can be reduced to 625µA. Noise The noise performance of the LT6600-2.5 can be evaluated with the circuit of Figure 6. Given the low noise output of the LT6600-2.5 and the 6dB attenuation of the transformer coupling network, it will be necessary to measure the noise floor of the spectrum analyzer and subtract the instrument noise from the filter noise measurement. Example: With the IC removed and the 25Ω resistors grounded, Figure 6, measure the total integrated noise (eS) of the spectrum analyzer from 10kHz to 2.5MHz. With the IC inserted, the signal source (VIN) disconnected, and the input resistors grounded, measure the total integrated noise out of the filter (eO). With the signal source connected, set the frequency to 100kHz and adjust the amplitude until VIN measures 100mVP-P. Measure the output amplitude, VOUT, and compute the passband gain 2.5V 0.1µF VIN RIN 1 7 2 8 RIN 3 – + 4 COILCRAFT TTWB-1010 25Ω 1:1 LT6600-2.5 SPECTRUM ANALYZER INPUT 50Ω – + 6 5 0.1µF 25Ω 66002 F06 – 2.5V Figure 6 660025i 8 LT6600-2.5 U W U U APPLICATIO S I FOR ATIO 50 NOISE SPECTRAL DENSITY (nVRMS/√Hz) eIN = (eO )2 – (eS )2 A Table 1 lists the typical input referred integrated noise for various values of RIN. Figure 7 is plot of the noise spectral density as a function of frequency for an LT6600-2.5 with RIN = 1580Ω using the fixture of Figure 6 (the instrument noise has been subtracted from the results). RIN 40 80 SPECTRAL DENSITY 30 60 20 40 10 20 INTEGRATED 0 0.01 0 0.1 1 10 FREQUENCY (MHz) 66002 F07 Figure 7. Input Referred Noise, Gain = 1 Table 1. Noise Performance PASSBAND GAIN (V/V) 100 INTEGRATED NOISE (µVRMS) A = VOUT/VIN. Now compute the input referred integrated noise (eIN) as: INPUT REFERRED INTEGRATED NOISE 10kHz TO 2.5MHz INPUT REFERRED INTEGRATED NOISE 10kHz TO 5MHz 4 402Ω 18µVRMS 23µVRMS 2 806Ω 29µVRMS 39µVRMS 1 1580Ω 51µVRMS 73µVRMS The noise at each output is comprised of a differential component and a common mode component. Using a transformer or combiner to convert the differential outputs to single-ended signal rejects the common mode noise and gives a true measure of the S/N achievable in the system. Conversely, if each output is measured individually and the noise power added together, the resulting calculated noise level will be higher than the true differential noise. Power Dissipation The LT6600-2.5 amplifiers combine high speed with largesignal currents in a small package. There is a need to ensure that the dies’s junction temperature does not exceed 150°C. The LT6600-2.5 package has Pin 6 fused to the lead frame to enhance thermal conduction when connecting to a ground plane or a large metal trace. Metal trace and plated through-holes can be used to spread the heat generated by the device to the backside of the PC board. For example, on a 3/32" FR-4 board with 2oz copper, a total of 660 square millimeters connected to Pin 6 of the LT6600-2.5 (330 square millimeters on each side of the PC board) will result in a thermal resistance, θJA, of Table 2. LT6600-2.5 SO-8 Package Thermal Resistance COPPER AREA TOPSIDE (mm2) BACKSIDE (mm2) BOARD AREA (mm2) THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 1100 330 1100 2500 65°C/W 330 2500 85°C/W 35 35 2500 95°C/W 35 0 2500 100°C/W 0 0 2500 105°C/W about 85°C/W. Without extra metal trace connected to the V – pin to provide a heat sink, the thermal resistance will be around 105°C/W. Table 2 can be used as a guide when considering thermal resistance. Junction temperature, TJ, is calculated from the ambient temperature, TA, and power dissipation, PD. The power dissipation is the product of supply voltage, VS, and supply current, IS. Therefore, the junction temperature is given by: TJ = TA + (PD • θJA) = TA + (VS • IS • θJA) where the supply current, IS, is a function of signal level, load impedance, temperature and common mode voltages. For a given supply voltage, the worst-case power dissipation occurs when the differential input signal is maximum, the common mode currents are maximum (see Applications Information regarding Common Mode DC 660025i 9 LT6600-2.5 U W U U APPLICATIO S I FOR ATIO Currents), the load impedance is small and the ambient temperature is maximum. To compute the junction temperature, measure the supply current under these worstcase conditions, estimate the thermal resistance from Table 2, then apply the equation for TJ. For example, using the circuit in Figure 3 with DC differential input voltage of 1V, a differential output voltage of 4V, no load resistance and an ambient temperature of 85°C, the supply current (current into Pin 3) measures 37.6mA. Assuming a PC board layout with a 35mm2 copper trace, the θJA is 100°C/W. The resulting junction temperature is: TJ = TA + (PD • θJA) = 85 + (5 • 0.0376 • 100) = 104°C When using higher supply voltages or when driving small impedances, more copper may be necessary to keep TJ below 150°C. 660025i 10 LT6600-2.5 U PACKAGE DESCRIPTIO S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 .050 BSC 8 .245 MIN 7 6 5 .160 ±.005 .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) .030 ±.005 TYP 1 RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 0°– 8° TYP .016 – .050 (0.406 – 1.270) NOTE: 1. DIMENSIONS IN .053 – .069 (1.346 – 1.752) .014 – .019 (0.355 – 0.483) TYP INCHES (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm) 2 3 4 .004 – .010 (0.101 – 0.254) .050 (1.270) BSC SO8 0303 660025i 11 LT6600-2.5 RELATED PARTS PART NUMBER ® LTC 1565-31 DESCRIPTION COMMENTS 650kHz Linear Phase Lowpass Filter Continuous Time, SO8 Package, Fully Differential LTC1566-1 Low Noise, 2.3MHz Lowpass Filter Continuous Time, SO8 Package LT1567 Very Low Noise, High Frequency Filter Building Block 1.4nV/√Hz Op Amp, MSOP Package, Fully Differential LT1568 Very Low Noise, 4th Order Building Block Lowpass and Bandpass Filter Designs Up to 10MHz, Differential Outputs LT6600-10 Very Low Noise Differential Amplifier and 10MHz Lowpass Filter 82dB S/N with 3V Supply, SO-8 Package LT6600-20 Very Low Noise Differential Amplifier and 20MHz Lowpass Filter 76dB S/N with 3V Supply, SO-8 Package 660025i 12 Linear Technology Corporation LT/TP 0603 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2003