LT6657 1.5ppm/°C Drift, Low Noise, Buffered Reference Features Description Low Drift nn A Grade: 1.5ppm/°C Max nn B Grade: 3ppm/°C Max nn Low Noise: nn 0.5ppm P-P (0.1Hz to 10Hz) nn 0.8ppm RMS (10Hz to 1kHz) nn Wide Supply Range to 40V nn Sources and Sinks 10mA Min nn Line Regulation: 0.2ppm/V nn Load Regulation: 0.7ppm/mA nn Reverse Supply Protection nn Reverse Output Protection nn Low Power Shutdown: <4µA Max nn Thermal Protection nn Can Operate in Shunt Mode nn Configurable as a Negative Reference nn Available Output Voltage Options: 2.5V, 3V, 5V nn MSOP-8 Package The LT®6657 is a precision voltage reference that combines robust operating characteristics with extremely low drift and low noise. With advanced curvature compensation, this bandgap reference achieves 1.5ppm/°C drift with predictable temperature behavior, and an initial voltage accuracy of 0.1%. It also offers 0.5ppmP-P noise and very low temperature cycling hysteresis. Applications The LT6657 is fully specified over the temperature range of –40°C to 125°C. It is available in the 8-lead MSOP package. High Temperature Industrial nn High Resolution Data Acquisition Systems nn Instrumentation and Process Control nn Automotive Control and Monitoring nn Medical Equipment nn Shunt and Negative Voltage References L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. nn The LT6657 is a low dropout reference that can be powered from as little as 50mV above the output voltage, up to 40V. The buffered output supports ±10mA of output drive with low output impedance and precise load regulation. The high sink current capability allows operation as a negative voltage reference with the same precision as a positive reference. This part is safe under reverse battery conditions, and includes current protection when the output is short-circuited and thermal shutdown for overload conditions. A shutdown is included to allow power reduction while enabling a quick turn-on. nn Typical Application Basic Connection 2 (VOUT + 50mV) < VIN < 40V CIN 0.1µF 3 IN LT6657 OUT 6 VOUT COUT 1µF SHDN GND 4 6657 TA01a OUTPUT VOLTAGE CHANGE (NORMALIZED) (PPM) Output Voltage Temperature Drift 200 THREE TYPICAL PARTS 100 1ppm/°C BOX 0 –100 –200 –45 –20 30 80 5 55 TEMPERATURE (°C) 105 130 6657 TA01b 6657fb For more information www.linear.com/LT6657 1 LT6657 Absolute Maximum Ratings Pin Configuration (Note 1) Input Voltage VIN (to GND)........................... –40V to 40V Shutdown Voltage SHDN............................. –20V to 40V Output Voltage VOUT...................................... –3V to 30V Input-to-Output Differential Voltage (Note 2)...........±40V Output Short-Circuit Duration........................... Indefinite Operating Junction Temperature Range................................................. –40°C to 150°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering 10 sec) (Note 3)............................................................. 300°C TOP VIEW DNC VIN SHDN GND 8 7 6 5 1 2 3 4 DNC DNC VOUT DNC MS8 PACKAGE 8-LEAD PLASTIC MSOP TJMAX = 150°C, θJA = 273°C/W DNC: CONNECTED INTERNALLY DO NOT CONNECT EXTERNAL CIRCUITRY TO THESE PINS Order Information http://www.linear.com/product/LT6657#orderinfo TUBE TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION LT6657AHMS8-2.5#PBF LT6657AHMS8-2.5#TRPBF LTGKN 8-Lead Plastic MSOP SPECIFIED TEMPERATURE RANGE –40°C to 125°C LT6657BHMS8-2.5#PBF LT6657BHMS8-2.5#TRPBF LTGKN 8-Lead Plastic MSOP –40°C to 125°C LT6657AHMS8-3#PBF LT6657AHMS8-3#TRPBF LTGYG 8-Lead Plastic MSOP –40°C to 125°C LT6657BHMS8-3#PBF LT6657BHMS8-3#TRPBF LTGYG 8-Lead Plastic MSOP –40°C to 125°C LT6657AHMS8-5#PBF LT6657AHMS8-5#TRPBF LTGYH 8-Lead Plastic MSOP –40°C to 125°C LT6657BHMS8-5#PBF LT6657BHMS8-5#TRPBF LTGYH 8-Lead Plastic MSOP –40°C to 125°C *Temperature grades are identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges. Parts ending with PBF are RoHS and WEEE compliant. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. † This product is only offered in trays. For more information go to: http://www.linear.com/packaging/ Available Options OUTPUT VOLTAGE INITIAL ACCURACY TEMPERATURE COEFFICIENT ORDER PART NUMBER** SPECIFIED TEMPERATURE RANGE 2.5V 0.1% 0.1% 1.5ppm/°C 3ppm/°C LT6657AHMS8-2.5 LT6657BHMS8-2.5 –40°C to 125°C –40°C to 125°C 3V 0.1% 0.1% 1.5ppm/°C 3ppm/°C LT6657AHMS8-3 LT6657BHMS8-3 –40°C to 125°C –40°C to 125°C 5V 0.1% 0.1% 1.5ppm/°C 3ppm/°C LT6657AHMS8-5 LT6657BHMS8-5 –40°C to 125°C –40°C to 125°C ** See the Order Information section for complete part number listing. 6657fb 2 For more information www.linear.com/LT6657 LT6657 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. The test conditions are VIN = VOUT + 0.5V, VSHDN = 1.6V, IOUT = 0, COUT = 1µF, unless otherwise noted. PARAMETER CONDITIONS MIN Output Voltage Accuracy –0.1 Output Voltage Temperature Coefficient (Note 4) LT6657A LT6657B Line Regulation (Note 5) VOUT + 0.5V ≤ VIN ≤ 40V l l TYP MAX 0 0.1 % 0.5 1 1.5 3 ppm/°C ppm/°C 0.2 2 4 ppm/V ppm/V 0.7 2 4 ppm/mA ppm/mA 0.9 3 6 ppm/mA ppm/mA 0.9 6 ppm/mA 20 50 70 mV mV 65 100 140 mV mV 330 450 500 mV mV –230 –150 –50 mV mV 0.7 2 V µA l Load Regulation (Note 5) IOUT (Source) = 10mA l IOUT (Sink) = 10mA l Shunt Configuration VOUT Is Shorted to VIN ISHUNT 2.5 to 11mA Minimum VIN – VOUT VIN – VOUT, ΔVOUT = 0.1% l IOUT = 0mA l IOUT (Source) = 1mA l IOUT (Source) = 10mA l IOUT (Sink) = 10mA l Shutdown Pin (SHDN) Supply Current in Shutdown 1.6 UNITS Logic High Input Voltage Logic High Input Current, SHDN = 1.6V l l Logic Low Input Voltage Logic Low Input Current, SHDN = 0.8V l l 0.2 0.8 1 V µA SHDN = 0.4V l 0.01 4 µA SHDN = 0.8V l 2.0 20 µA 1.2 1.8 2.3 mA mA Supply Current No Load Output Short-Circuit Current Short VOUT to GND Short VOUT to VIN 15 16 mA mA Output Voltage Noise (Note 6) 0.1Hz ≤ f ≤ 10Hz 10Hz ≤ f ≤ 1kHz 0.5 0.8 ppmP-P ppmRMS Turn-On Time 0.1% Settling, CL = 1µF 180 µsec 30 ppm/√kHr 20 24 30 35 40 ppm ppm ppm ppm ppm l Long-Term Drift of Output Voltage (Note 7) Hysteresis (Note 8) ΔT = 0°C to 50°C ΔT = 0°C to 70°C ΔT = –40°C to 85°C ΔT = –40°C to 125°C ΔT = –55°C to 125°C Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: With VIN at 40V, VOUT may not be pulled below 0V. The total VIN to VOUT differential voltage must not exceed ±40V. Note 3: The stated temperature is typical for soldering of the leads during manual rework. For detailed IR reflow recommendations, refer to the Application information section. Note 4: Temperature coefficient is measured by dividing the maximum change in output voltage by the specified temperature range. 6657fb For more information www.linear.com/LT6657 3 LT6657 Electrical Characteristics Note 5: Line and load regulation are measured on a pulse basis for specified input voltage or load current ranges. Output voltage change due to die temperature change must be taken into account separately. Note 6: Peak-to-peak noise is measured with a 2-pole highpass filter at 0.1Hz and 3-pole lowpass filter at 10Hz. The unit is enclosed in a still-air environment to eliminate thermocouple effects on the leads, and the test time is 10 seconds. Due to the statistical nature of noise, repeating noise measurements will yield larger and smaller peak values in a given measurement interval. By repeating the measurement for 1000 intervals, each 10 seconds long, it is shown that there are time intervals during which the noise is higher than in a typical single interval, as predicted by statistical theory. In general, typical values are considered to be those for which at least 50% of the units may be expected to perform similarly or better. For the 1000 interval test, a typical unit will exhibit noise that is less than the typical value listed in the Electrical Characteristics table in more than 50% of its measurement intervals. See Application Note 124 for noise testing details. RMS noise is measured with a spectrum analyzer in a shielded environment. Note 7: Long term stability typically has a logarithmic characteristic and therefore change after 1000 hours tend to be much smaller than before that time. Total drift in the second thousand hours is normally less than one third of the first thousand hours with a continuing trend toward reduced drift with time. Long-term stability will also be affected by differential stresses between the IC and the board material created during board assembly. Note 8 : Hysteresis in output voltage is created by mechanical stress that depends on whether the IC was previously at a different temperature. Output voltage is always measured at 25°C, but the IC is cycled 25°C to cold to 25°C, or 25°C to hot to 25°C before successive measurements. Hysteresis measures the maximum output change for the averages of three hot or cold temperature cycles, preconditioned by one cold and one hot cycles. For instruments that are stored at well controlled temperatures (within 30 degrees of the operational temperature), hysteresis is usually not a significant error source. 6657fb 4 For more information www.linear.com/LT6657 LT6657 Typical Performance Characteristics VIN = VOUT + 0.5V, VSHDN = 1.6V, IOUT = 0, COUT = 1µF, unless otherwise noted. 2.5V Output Voltage Temperature Drift 2.5008 The test conditions are TA = 25°C, 2.5V Low Frequency 0.1Hz to 10Hz Noise 2.5V Output Voltage Noise Spectrum 110 THREE TYPICAL PARTS COUT = 1µF Cer COUT = 5µF Cer COUT = 47µF Tant 2.5000 2.4996 2.4992 –50 –25 0 NOISE VOLTAGE (nV/√Hz) OUTPUT NOISE (500nV/DIV) OUTPUT VOLTAGE (V) 100 2.5004 90 80 70 60 25 50 75 100 125 150 TEMPERATURE (°C) TIME (1s/DIV) 50 0.01 6657 G02 0.1 1 10 FREQUENCY (kHz) 100 6657 G03 6657 G01 2.5V Integrated Noise 10Hz to 10kHz 2.0 COUT = 1µF VSHDN = VIN 1 1.0 0.5 125°C 25°C –40°C –55°C 0.0 –0.5 –40 –30 –20 –10 0 10 20 INPUT VOLTAGE (V) 10 6657 G04 30 MS8 PACKAGE PART SELF HEATING IS INCLUDED 10 0 –10 –20 –30 0.1 125°C 25°C –40°C –55°C 1 OUTPUT CURRENT (mA) 2.5000 2.4995 2.4990 10 6657 G07 0 10 30 20 INPUT VOLTAGE (V) 40 6657 G06 2.5V Minimum VIN to VOUT Differential (Sourcing) 2.5V Load Regulation (Sinking) OUTPUT VOLTAGE CHANGE (ppm) 20 40 125°C 25°C –40°C 6657 G05 2.5V Load Regulation (Sourcing) 30 30 PART SELF HEATING IS INCLUDED 2.5005 20 10 MS8 PACKAGE PART SELF HEATING IS INCLUDED OUTPUT CURRENT (mA) 0.1 1 FREQUENCY (kHz) OUTPUT VOLTAGE (V) 10 0.1 0.01 OUTPUT VOLTAGE CHANGE (ppm) 2.5V Line Regulation 2.5010 1.5 INPUT CURRENT (mA) INTEGRATED NOISE (µVRMS) 100 2.5V Supply Current vs Input Voltage 10 0 –10 –20 –30 0.1 125°C 25°C –40°C –55°C 1 OUTPUT CURRENT (mA) 10 6657 G08 1 0.1 125°C 25°C –40°C –55°C 0 100 200 300 400 INPUT-OUTPUT VOLTAGE (mV) 500 6657 G09 6657fb For more information www.linear.com/LT6657 5 LT6657 Typical Performance Characteristics VIN = VOUT + 0.5V, VSHDN = 1.6V, IOUT = 0, COUT = 1µF, unless otherwise noted. 2.5V Minimum VIN to VOUT Differential (Sinking) 2.5V Power Supply Rejection Ratio vs Frequency 120 1 VIN < VOUT 0.1 0 –300 –250 –200 –150 –100 –50 INPUT-OUTPUT VOLTAGE (mV) 100 80 60 40 1 10 100 FREQUENCY (kHz) 0 GROUND PIN CURRENT CURRENTS GOING INTO THE PART ARE POSITIVE –12 –10 –5 0 5 LOAD CURRENT (mA) 1.35 1.30 1.25 1.15 1.10 1.05 5.0016 OUTPUT VOLTAGE (V) SUPPLY CURRENT IN SHUTDOWN (µA) 1.0 0.0 0 20 30 INPUT VOLTAGE (V) 40 6657 G16 0 –5 –10 –15 –20 0 50 100 TEMPERATURE (°C) 150 –30 –10 125°C 25°C –40°C –55°C 0 40 10 20 30 SHUTDOWN VOLTAGE (V) 6657 G15 5V Output Voltage Temperature Drift 4.0 2.0 5 6657 G14 2.5V Supply Current in Shutdown vs Input Voltage 3.0 10 –25 1.00 –50 10 125°C 25°C –40°C –55°C 1k Shutdown Pin Current vs Shutdown Voltage VTH(RISING) VTH(FALLING) 6657 G13 VSHDN = 0.4V 10 100 FREQUENCY (kHz) 5V Low Frequency 0.1Hz to 10Hz Noise THREE TYPICAL PARTS OUTPUT NOISE (500nV/DIV) –8 1 6657 G12 SHUTDOWN CURRENT (µA) SHUTDOWN VOLTAGE THRESHOLDS (V) SUPPLY AND GROUND CURRENTS (mA) 1.40 SUPPLY PIN CURRENT –4 0.1 1000 Shutdown Voltage Thresholds vs Temperature 125°C 25°C –40°C –55°C 4 1 6657 G11 Supply and Ground Currents vs Load Current 8 COUT = 1µF COUT = 10µF COUT = 100µF 20 6657 G10 12 10 COUT = 1µF COUT = 10µF 0 0.1 50 2.5V Output Impedance vs Frequency OUTPUT IMPEDANCE (Ω) 125°C 25°C –40°C –55°C POWER SUPPLY REJECTION RATIO (dB) OUTPUT CURRENT (mA) 10 The test conditions are TA = 25°C, 5.0008 5.0000 4.9992 4.9984 –50 –30 –10 10 30 50 70 90 110 130 150 TEMPERATURE (°C) 6657 G17 TIME (1s/DIV) 6657 G18 6657fb 6 For more information www.linear.com/LT6657 LT6657 Typical Performance Characteristics The test conditions are TA = 25°C, VIN = VOUT + 0.5V, VSHDN = 1.6V, IOUT = 0, COUT = 1µF, unless otherwise noted. 5V Output Voltage Noise Spectrum 250 200 150 100 50 0.01 0.1 2.0 1 10 FREQUENCY (kHz) 1.5 10 1 0.1 0.01 100 0.1 1 FREQUENCY (kHz) 5.0000 4.9995 0 10 20 30 INPUT VOLTAGE (V) 10 0 –10 –30 0.1 40 6657 G22 1 OUTPUT CURRENT (mA) 0 –10 125°C 25°C –40°C –55°C 100 200 300 400 INPUT–OUTPUT VOLTAGE (mV) 500 6657 G25 OUTPUT CURRENT (mA) 1 125°C 25°C –40°C –55°C –20 –30 0.1 10 1 OUTPUT CURRENT (mA) 10 6657 G24 5V Output Impedance vs Frequency 10 0 10 5V Minimum VIN to VOUT Differential (Sinking) 10 OUTPUT CURRENT (mA) 125°C 25°C –40°C –55°C MS8 PACKAGE PART SELF HEATING IS INCLUDED 20 6657 G23 5V Minimum VIN to VOUT Differential (Sourcing) 0.1 MS8 PACKAGE PART SELF HEATING IS INCLUDED –20 40 5V Load Regulation (Sinking) 100 125°C 25°C –40°C –55°C OUTPUT IMPEDANCE (Ω) 4.9990 20 30 30 OUTPUT VOLTAGE CHANGE (ppm) 125°C 25°C –40°C 125°C 25°C –40°C –55°C 6657 G21 5V Load Regulation (Sourcing) 30 OUTPUT VOLTAGE CHANGE (ppm) OUTPUT VOLTAGE (V) 5.0005 0.5 –0.5 –40 –30 –20 –10 0 10 20 INPUT VOLTAGE (V) 10 6657 G20 5V Line Regulation PART SELF HEATING IS INCLUDED 1.0 0 6657 G19 5.0010 VSHDN = VIN COUT = 1µF INTEGRATED NOISE (µVRMS) 300 NOISE VOLTAGE (nV/√Hz) 100 COUT = 1µF Cer COUT = 5µF Cer COUT = 47µF Tant 5V Supply Current vs Input Voltage INPUT CURRENT (mA) 350 5V Integrated Noise 10Hz to 10kHz 1 VIN < VOUT 0.1 –350 –300 –250 –200 –150 –100 –50 0 INPUT–OUTPUT VOLTAGE (mV) 50 6657 G26 COUT = 1µF COUT = 10µF COUT = 100µF 10 1 0.1 1 10 100 FREQUENCY (kHz) 1k 6657 G27 6657fb For more information www.linear.com/LT6657 7 LT6657 Pin Functions SHDN (Pin 3): Shutdown Input. This active low input disables the part to reduce supply current < 2µA. This pin must be driven externally and should be tied to VIN if unused. It may be driven to logic high or to VIN during normal operation. VOUT (Pin 6): Reference Output Voltage. This pin can source and sink current to a load. An output capacitor of 1µF or higher is required for stability. DNC (Pins 1, 5, 7, 8): Internal Functions. Do Not Connect or electrically stress these pins. These pins must be left floating and leakage currents from these pins should be kept to a minimum. Allow additional routing clearance. VIN (Pin 2): Input Voltage Supply. Bypass VIN with a local 0.1µF or larger capacitor to GND. GND (Pin 4): Device Ground. This pin must be connected to a noise-free ground plane. A star-ground with related circuits will give the best results. Be careful of trace impedance, as the GND pin carries supply return current. Block Diagram VIN 3 SHDN 2 BIAS + BANDGAP – VOUT ERROR AMP 6 RF RG GND 4 6657 BD 6657fb 8 For more information www.linear.com/LT6657 LT6657 Applications Information Line and Load Regulation The line regulation of the LT6657 is typically well below 1ppm/V. A 10V change in input voltage causes a typical output shift of only 2ppm. Load regulation is also less than 1ppm/mA in an MS8 package. A 5mA change in load current shifts output voltage by only 4ppm. These electrical effects are measured with low duty cycle pulses. To realize such excellent load regulation the IR drops on the VOUT and GND lines need to be minimized. One ounce copper foil printed circuit board has 0.5mΩ/square. Just 1mΩ of added trace resistance introduces an error of 1µV for each 1mA passing through it. This will add a 0.4ppm/ mA to the load regulation with a 2.5V reference. These externally created errors have the same order of magnitude as the typical load regulation values for the LT6657. Minimizing wire resistance and using a separate ground return for the load will maintain excellent load regulation. When sourcing current, the ground connection pin can be used as kelvin sensing for improved output regulation. Additional output changes due to die temperature change must be taken into account separately. These added effects may be estimated from: Line_Reg (in ppm) = (IIN + IOUT) • θJA • TC • VIN Load_Reg (in ppm) = (VIN – VOUT) • θJA • TC • IOUT Where voltages are in V, currents are in mA, package thermal resistance θJA is in °C/mW, and temperature coefficient, TC, is in ppm/°C. For example, with typical quiescent current IIN = 1.2mA, IOUT = 1mA, VIN – VOUT = 1V, the added line-regulation is typically 0.66ppm/V and added load-regulation is typically 0.3ppm/mA for a TC of 1ppm/°C and MSOP-8 package with θJA = 0.3°C/mW thermal resistance. Bypass and Load Capacitors The LT6657 voltage reference requires a 0.1µF or larger input capacitor placed close to the part to improve power supply rejection. A long input wire with large series inductance can create ringing response to large load transients. The output requires a capacitor of 1µF or higher placed near the part. Frequency stability, turn-on time and settling behavior are directly affected by the value and type of the output capacitor. Equivalent resistance in series with the output capacitor (ESR) introduces a zero in the output buffer transfer function and can cause instability. It is recommended to keep the ESR less than 0.5Ω to maintain sufficient phase margin. Both capacitance and ESR are frequency dependent. At higher frequencies, capacitance drops and ESR increases. To ensure stability above 100kHz, the output capacitor must also have suitable characteristics above 100kHz. The following paragraphs describe capacitors with suitable performance. For applications requiring a large output capacitor, a low ESR ceramic capacitor in parallel with a bulk tantalum capacitor provides an optimally damped response. For example, a 47µF tantalum capacitor with larger ESR in parallel with a 10µF ceramic capacitor with ESR smaller than 0.5Ω improves transient response and increases phase margin. Give extra consideration to the use of ceramic capacitors such as X7R types. These capacitors are small, come in appropriate values and are relatively stable over a wide temperature range. However, for low noise requirements, X7R capacitors may not be suitable as they may exhibit a piezoelectric effect. Mechanical vibrations cause a charge displacement in the ceramic dielectric and the resulting perturbations can appear as noise. For very low noise applications, film capacitors should be considered for their lack of piezoelectric effects. Film capacitors such as polyester, polycarbonate and polypropylene have good temperature stability. Additional care must be taken as polypropylene have an upper limit of 85°C to 105°C. Above these temperatures the working voltage often needs to be derated per manufacturer specifications. Another type of film capacitor is polyphenylene sulfide (PPS). These capacitors work over a wide temperature range, are stable and have large capacitance values beyond 1µF. In voltage reference applications, film capacitor lifetime is affected by temperature and applied voltage. Capacitor lifetime is degraded by operating near or exceeding the rated voltage, at high temperature, with AC ripple or some combination of these. Most voltage reference applications present AC ripple only during transient events. 6657fb For more information www.linear.com/LT6657 9 LT6657 Applications Information Turn-On and Line Transient Response The turn-on time is slew-limited and determined by the short-circuit current, the output capacitor, and the output voltage value as determined by the equation: tON = VOUT Increasing the output load speeds up the response (Figure 3). VIN 0.2V/DIV 3V/DC C • OUT ISC For example, the LT6657-2.5V, with a 1µF output capacitor and a typical current limit of 15mA the turn-on time would be: 1µF tON = 2.5V • = 167µs 15mA The resulting turn-on time is shown in Figure 1. VOUT 2mV/DIV 2.5V/DC COUT = 1µF, IOUT = 1mA SOURCING 6657 F03 50µs/DIV Figure 3. Line Transient Response with VIN = 0.4VP-P A larger output capacitor lowers the amplitude response with a longer time response trade-off (Figure 4). VIN 1V/DIV VIN 0.5V/DIV 3V/DC GND VOUT 1V/DIV GND VOUT 2mV/DIV 2.5V/DC COUT = 1µF 50µs/DIV 6657 F01 COUT = 10µF, IOUT = 0mA Figure 1. 2.5V Turn-On Characteristics Line transient response with a 1µF output capacitor and no output current is shown in Figure 2. The peak voltage output response is less than 1mV. 6657 F04 50µs/DIV Figure 4. Line Transient Response with VIN = 1VP-P Load Transient Response The test circuit of Figure 5 is used to measure load transient response with various currents. VIN 0.2V/DIV 3V/DC 2 VIN = 3V 3 VOUT 2mV/DIV 2.5V/DC CIN 0.1µF COUT = 1µF, IOUT = 0mA 50µs/DIV LT6657 SHDN OUT 6 VOUT 1k VGEN COUT 1µF GND 6657 F05 4 6657 F02 Figure 2. Line Transient Response with VIN = 0.4VP-P IN Figure 5. Transient Load Test Circuit 6657fb 10 For more information www.linear.com/LT6657 LT6657 Applications Information Figure 6 and 7 shows the load transient response to a 5mA current step both sourcing and sinking. IOUT 5mA 4mA IOUT 0mA VOUT 2mV/DIV/AC 2.5VDC 5mA COUT = 1µF VOUT 10mV/DIV/AC 2.5V/DC 50µs/DIV 6657 F09 Figure 9. Output Response with a 4mA to 5mA Load Step Sinking COUT = 1µF 50µs/DIV 6657 F06 Figure 6. Output Response with a 5mA Load Step Sourcing Figures 10 and 11 show the load transient response to an even smaller 0.5mA current step both sourcing and sinking. IOUT 0mA IOUT 5mA 0.5mA 0mA VOUT 2mV/DIV/AC 2.5V/DC VOUT 10mV/DIV/AC 2.5VDC COUT = 1µF COUT = 1µF 50µs/DIV 50µs/DIV 6657 F07 6657 F10 Figure 10. Output Response with a 0.5mA Load Step Sourcing Figure 7. Output Response with a 5mA Load Step Sinking Figure 8 and 9 shows the load transient response to a smaller 4mA to 5mA current step while sourcing and sinking. IOUT 0.5mA 0mA IOUT 4mA VOUT 2mV/DIV/AC 2.5V/DC 5mA COUT = 1µF VOUT 2mV/DIV/AC 2.5V/DC 50µs/DIV 6657 F11 Figure 11. Output Response with a 0.5mA Load Step Sinking COUT = 1µF 50µs/DIV 6657 F08 Figure 8. Output Response with a 4mA to 5mA Load Step Sourcing 6657fb For more information www.linear.com/LT6657 11 LT6657 Applications Information LT6657 Sinking Current Dropout Description The LT6657 output stage can source and sink current of equal magnitude. When sourcing current it performs as a conventional low dropout regulating device. When sinking current, it can maintain a regulated output with an input voltage equal to, more positive than, or also slightly less than the output voltage. The specification for dropout voltage while sinking is expressed in negative voltage values for VIN – VOUT. A typical unit will maintain a regulated output voltage while sinking current with an input voltage 250mV (50mV guaranteed) below the output voltage. Lower input voltage will cause the output to drop out of regulation. This allows shunt reference applications where the output and input can be tied together and sink current from the output to ground. Positive or Negative Shunt Mode Operation In addition to the series mode operation, the LT6657 can be operated in shunt mode. In this mode the reference is wired as a two terminal circuit which can be used both as a positive or a negative voltage reference, as shown in Figures 12 and 13. RSHUNT is chosen using the following formula: RSHUNT = VDD – VOUT ISHUNT _ MAX where: ISHUNT_MAX = 2.5mA + IOUT_MAX 2 3 –VDD ISHUNT RSHUNT IN LT6657 SHDN OUT 6 IOUT +VOUT COUT 1µF GND 4 IOUT –VOUT 6657 F13 Figure 13. Negative Shunt Mode Operation The ISHUNT current has to be operated above 2.5mA to obtain the same performance as the series mode operation. In shunt mode operation IOUT_MAX is less than or equal to 8.5mA. A COUT of 1µF or more is required on the output for stability. Shutdown Mode When the SHDN pin is pulled below 0.8V with respect to ground, the LT6657 enters a low power state and turns the output off. Quiescent current is typically 2µA. If SHDN is set less than 0.4V the quiescent current drops to 0.01µA typical. The SHDN pin turn-on threshold is 1.26V and it has approximately 150mV hysteresis for the turn-off threshold. The turn-on logic high voltage is 1.6V. Drive the SHDN with either logic or an open-collector/drain with a pull-up resistor. The resistor supplies the pull-up current to the open-collector/drain logic, normally several microamperes, plus the SHDN pin current, typically less than 5µA at 6V. If unused, connect the SHDN input pin to VIN. Power Dissipation VDD RSHUNT 2 3 IN LT6657 SHDN OUT 6 IOUT COUT 1µF GND 4 6657 F12 +VOUT Power dissipation for LT6657 depends on VIN, load current and the package type. The MSOP-8 package has a thermal resistance of θJA = 273°C/W. Although the maximum junction temperature is 150°C ,for best performance it is recommended to limit the change in junction temperature as much as possible. The plot in Figure 12. Positive Shunt Mode Operation 6657fb 12 For more information www.linear.com/LT6657 LT6657 Applications Information Figure 14 shows the maximum ambient temperature limits for different VIN and load condition using a maximum junction temperature of 125°C in the MSOP-8 package. If the load current exceeds 10mA the parts could begin to current limit. In this case, the output voltage is no longer regulated and the part could dissipate much more power and operate hotter than the graph shows. MAXIMUM AMBIENT OPERATING TEMPERATURE (°C) 125 VOUT = 2.5V 115 105 95 85 75 65 55 45 10mA SINK MS8 10mA SOURCE MS8 0 5 10 15 20 25 VIN (V) 30 35 40 6657 F14 Figure 14. Maximum Ambient Operating Temperature With a large input voltage and sourcing current, an internal thermal shutdown protection circuit limits the maximum power dissipation. When sinking current, there is no need for thermal shutdown protection because the power dissipation is much smaller and the sinking current limit will give some load protection. Noise Performance and Specification The LT6657 offers exceptional low noise for a bandgap reference; only 0.5ppmP-P in the 0.1Hz to 10Hz bandwidth. As a result system noise performance may be dominated by system design and physical layout. Care is required to achieve the best possible noise performance. The use of dissimilar metals in component leads and PC board traces creates thermocouples. Variations in thermal resistance, caused by uneven air flow over the circuit board create differential lead temperature, thereby creating a thermoelectric voltage noise at the output of the reference. Minimizing the number of thermocouples, as well as limiting airflow, can substantially reduce these errors. Additional information can be found in Linear Technology Application Note 82. Position the input and load capacitors close to the part. Although the LT6657 has 130dB DC PSRR, the power supply should be as stable as possible to guarantee optimal performance. A plot of the 0.1Hz to 10Hz low frequency noise is shown in the Typical Performance Characteristics section. Noise performance can be further improved by wiring several LT6657s in parallel as shown in the Typical Applications Section. With this technique the noise is reduced by √N, where N is the number of LT6657s used. Noise in any frequency band is a random function based on physical properties such as thermal noise, shot noise, and flicker noise. The most precise way to specify a random error such as noise is in terms of its statistics, for example as an RMS value. This allows for relatively simple maximum error estimation, generally involving assumptions about noise bandwidth and crest factor. Unlike wideband noise, low frequency noise, typically specified in a 0.1Hz to 10Hz band, has traditionally been specified in terms of expected error, illustrated as peak-to-peak error. Low frequency noise is generally measured with an oscilloscope over a 10 second time frame. This is a pragmatic approach, given that it can be difficult to measure noise accurately at low frequencies, and that it can also be difficult to agree on the statistical characteristics of the noise, since flicker noise dominates the spectral density. While practical, a random sampling of 10 second intervals is an inadequate method for representation of low frequency noise, especially for systems where this noise is a dominant limit of system performance. Given the random nature of noise, the output voltage may be observed over many time intervals, each giving different results. Noise specifications that were determined using this method are prone to subjectivity, and will tend toward a mean statistical value, rather than the maximum noise that is likely to be produced by the device in question. Because the majority of voltage reference data sheets express low frequency noise as a typical number, and as it tends to be illustrated with a repeatable plot near the mean of a distribution of peak-to-peak values, the LT6657 data sheet provides a similarly defined typical specification in order to allow a reasonable direct comparison against similar products. Data produced with this method generally 6657fb For more information www.linear.com/LT6657 13 LT6657 Applications Information 15V + 1µF 10k A1 LT1012 Q3 2N2907 – T 4 A = 10 LOW NOISE PRE-AMP = TANTALUM,WET SLUG ILEAK < 5nA SEE TEXT/APPENDIX B 100k 1k* 1µF 200Ω* 450Ω* 900Ω* LT6657 2.5V OUT T 100k + SHIELD Q1 + 1300µF SHDN 15V –15V –15V – VIN IN 1N4697 10V 0.15µF A2 LT1097 5 Q2 0.022µF 100k* **1.2k – INPUT 750Ω* 1µF REFERENCE UNDER TEST 10Ω* –15V SHIELDED CAN AC LINE GROUND 0.1µF 6657 F16 A = 100 AND 0.1Hz TO 10Hz FILTER 0.1µF 1µF + 124k* A3 LT1012 – 124k* – A4 LT1012 ADC/DVM SYSTEM + 0.1µF 1M* 330µF 16V 10k* 330Ω* 330µF 16V 100Ω* OUT + + IN 330µF 16V 330µF 16V + + 2k 10k TO ADC/DVM SYSTEM Figure 15. LT6657 Noise Test Circuitry (from AN124) suggests that in a series of 10 second output voltage measurements, at least half the observations should have a peak-to-peak value that is below this number. For example, the LT6657-2.5 measures less than 0.5ppmP-P in at least 50% of the 10 second observations. As mentioned above, the statistical distribution of noise is such that if observed for long periods of time, the peak error in output voltage due to noise may be much larger than that observed in a smaller interval. The likely maximum error due to noise is often estimated using the RMS value, multiplied by an estimated crest factor, assumed to be in the range of 6 to 8.4. This maximum possible value will only be observed if the output voltage is measured for very long periods of time. Therefore, in addition to the common method, a more thorough approach to measuring noise has been used for the LT6657 (described in detail in Linear Technology’s AN124) that allows more information to be obtained from the result. In particular, this method characterizes the noise over a significantly greater length of time, resulting in a more complete description of low frequency noise. The reference noise is measured at the output of the circuit shown in Figure 15 with an ADC/DVM system. Peak-to-peak voltage is then calculated for 10 6657fb 14 For more information www.linear.com/LT6657 LT6657 Applications Information 1.2 AVERAGE VP-P = 1.24µV 5000 1 4000 0.8 3000 0.6 2000 0.4 1000 0.2 0 0.8 1 1.2 1.6 1.4 PEAK-TO-PEAK NOISE (µVP-P) CUMULATIVE PROBABILITY NUMBER OF OBSERVATIONS 6000 0 1.8 6657 F16 Figure 16. LT6657 Low Frequency Noise Histogram This method of testing low frequency noise is more practical than common methods. The results yield a comprehensive statistical description, rather than a single observation. In addition, the direct measurement of output voltage over time gives an actual representation of peak noise, rather than an estimate based on statistical assumptions such as crest factor. Hysteresis Thermal hysteresis is a measure of change of output voltage as a result of temperature cycling. Figure 17 illustrates the typical hysteresis based on data taken from the LT6657-2.5. A proprietary design technique minimizes thermal hysteresis. The LT6657 is capable of dissipating relatively high power. For example, with a 40V input voltage and 5mA source load current applied to the LT6657-2.5, the power dissipation is PD = 40V • 1.4mA + 37.5V • 5mA = 244mW, which causes an increase in the die temperature of 73°C in MSOP-8 package. This could increase the junction temperature above 125°C and may cause the output to shift due to thermal hysteresis each time the device is powered up. 20 COLD: 25°C TO –40°C TO 25°C HOT: 25°C TO 125°C TO 25°C MS8 16 NUMBER OF UNITS second intervals over hundreds of intervals. The results are then summarized in terms of the fraction of measurement intervals for which observed noise is below a specified level. For example, the LT6657-2.5 measures less than 0.55ppmP-P in 80% of the measurement intervals, and less than 0.59ppmP-P in 95% of observation intervals. The preamplifier and filter are shown in Figure 15. This statistical variation in noise is illustrated in Figure 16. 12 8 4 0 –150 –100 –50 0 100 50 CHANGE IN OUTPUT VOLTAGE (ppm) 150 6657 F17 Figure 17. ∆VOUT Due to Thermal Hysteresis 6657fb For more information www.linear.com/LT6657 15 LT6657 Applications Information Long-Term Drift PC Board Layout Stress The LT6657 drift data was taken on parts that were soldered into PC boards similar to a real world application. The boards were then placed into a constant temperature oven with TA = 35°C, their outputs scanned regularly and measured with an 8.5 digit DVM. Typical long-term drift is illustrated in Figure 18a and 18b. The LT6657 is a very stable reference over temperature with less than 1.5ppm/°C error as shown in the Electrical Characteristics table. The mechanical stress caused by soldering parts to a printed circuit board may cause the output voltage to shift and the die temperature coefficient to change. The PC Board can affect all aspects of stability, including long term stability, thermal hysteresis and humidity stability. See Linear’s AN82 for more detailed information. LONG TERM DRIFT (ppm) 80 40 IR Reflow Shift 0 –40 –80 0 200 400 600 TIME (HOURS) 800 1000 6657 F18a Figure 18a. Long-Term Drift MS8 40 300 0 –40 –80 380s 0 500 1000 1500 2000 TIME (HOURS) 2500 3000 150 RAMP DOWN tP 30s T = 150°C tL 130s RAMP TO 150°C 75 40s 120s 6657 F18b 0 Figure 18b. Long-Term Drift MS8 Burn-In 150°C/24H Figure 18. TP = 260°C TL = 217°C TS(MAX) = 200°C TS = 190°C 225 TEMPERATURE (°C) LONG TERM DRIFT (ppm) 80 The mechanical stress of soldering a part to a board can cause the output voltage to shift. Moreover, the heat of an IR reflow or convection soldering oven can also cause the output voltage to shift. The materials that make up a semiconductor device and its package have different rates of expansion and contraction. After a part undergoes the extreme heat of a lead-free IR reflow profile, like the one shown in Figure 19, the output voltage shifts. After the device expands, due to the heat, and then contracts, the stresses on the die move. This shift is similar to, but larger than thermal hysteresis. 0 2 6 4 MINUTES 8 10 6657 F19 Figure 19. Lead-Free Reflow Profile 6657fb 16 For more information www.linear.com/LT6657 LT6657 Applications Information Experimental results of IR reflow shift are shown in Figure 20 for MS8. These results show only shift due to reflow and not mechanical stress. 9 8 MS8 1 CYCLE 3 CYCLES NUMBER OF UNITS 7 6 5 4 3 2 1 0 –300 –200 –100 0 200 100 CHANGE IN OUTPUT VOLTAGE (ppm) 300 6657 F20 Figure 20. ∆VOUT Due to IR Reflow (MS8 Package), Peak Temperature = 260°C 6657fb For more information www.linear.com/LT6657 17 LT6657 Typical Applications Extended Supply Range Reference Boosted Output Current Reference 40V TO 100V VOUT + 1.5V < VIN < 40V 270k 220Ω 2N3440 4.7µF 2N2905 IN BZX84C12 LT6657 OUT SHDN IN 1µF LT6657 0.1µF 0.1µF IOUT UP TO 300mA OUT SHDN 6657 TA02 GND GND 1µF 6657 TA03 Boosted Output Current with Current Limit Negative Shunt Mode Reference VOUT + 2V < VIN < 40V 1 LED1* 4.7µF 220Ω IN 10Ω LT6657 OUT SHDN 2 2N2905 –VDD RSHUNT ISHUNT IOUT 1µF GND IOUT –VOUT 6657 TA05 IN LT6657 SHDN 0.1µF V –V RSHUNT = DD OUT ISHUNT _MAX IOUT UP TO 100mA OUT ISHUNT _MAX = 2.5mA + IOUT _MAX 1µF IOUT _MAX < 8.5mA GND 6657 TA04 *LED CANNOT BE OMMITTED THE LED CLAMPS THE VOLTAGE DROP ACROSS THE 220Ω AND LIMITS OUTPUT CURRENT Sinking Current from External Circuitry VEXT (>VOUT) RLOAD (VOUT – 230mV) TO 40V IN LT6657 VOUT OUT SHDN 0.1µF 1µF GND 6657 TA06 6657fb 18 For more information www.linear.com/LT6657 LT6657 Typical Applications Low Noise Statistical Averaging Reference eNOUT = eN/√N Where N is the Number of LT6657s in Parallel 3V TO 40V IN LT6657 20Ω OUT VOUT = 2.5V SHDN 0.1µF 1µF 1µF GND IN LT6657 20Ω OUT SHDN 0.1µF 1µF GND IN LT6657 20Ω OUT SHDN 0.1µF GND 1µF IN 6657 TA07a LT6657 20Ω OUT SHDN 0.1µF 1µF GND Low Frequency Noise (0.1Hz to 10Hz) with Four LT6657s in Parallel 9000 1 7000 6000 0.8 5000 0.6 4000 3000 0.4 2000 0.2 1000 0 0.4 CUMULATIVE PROBABILITY NUMBER OF OBSERVATIONS 8000 1.2 AVERAGE VP-P = 0.63µV 0.5 0.6 0.8 0.9 0.7 PEAK-TO-PEAK NOISE (µVP-P) 0 1.0 6657 TA07b 6657fb For more information www.linear.com/LT6657 19 LT6657 Package Description Please refer to http://www.linear.com/product/LT6657#packaging for the most recent package drawings. MS8 Package 8-Lead Plastic MSOP (Reference LTC DWG # 05-08-1660 Rev G) 0.889 ±0.127 (.035 ±.005) 5.10 (.201) MIN 3.20 – 3.45 (.126 – .136) 3.00 ±0.102 (.118 ±.004) (NOTE 3) 0.65 (.0256) BSC 0.42 ± 0.038 (.0165 ±.0015) TYP 8 7 6 5 0.52 (.0205) REF RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 3.00 ±0.102 (.118 ±.004) (NOTE 4) 4.90 ±0.152 (.193 ±.006) DETAIL “A” 0° – 6° TYP GAUGE PLANE 0.53 ±0.152 (.021 ±.006) DETAIL “A” 1 2 3 4 1.10 (.043) MAX 0.86 (.034) REF 0.18 (.007) SEATING PLANE 0.22 – 0.38 (.009 – .015) TYP 0.65 (.0256) NOTE: BSC 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 0.1016 ±0.0508 (.004 ±.002) MSOP (MS8) 0213 REV G 6657fb 20 For more information www.linear.com/LT6657 LT6657 Revision History REV DATE DESCRIPTION A 03/16 Conditions Added for Electrical Characteristic, Minimum VIN – VOUT PAGE NUMBER B 06/16 3 Added 3V, 5V options 1, 2, 6, 7 Changed CL, CLOAD to COUT 9, 10, 11 Corrected Graphs G03, G12 5, 6 6657fb 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. For more information www.linear.com/LT6657 21 LT6657 Typical Application Low Noise Precision 20-Bit Analog-to-Digital Converter Application SNR = 97dB SINAD = 97dB THD = –117dB SFDR = 120dB 2 VIN = 5V 0.1µF 3 IN OUT 6 LT6657 47µF 10V X7R 1µF SHDN 0.1µF GND 4 +3.3V 10µF 6.3V 2 + 4 10Ω V– 6800pF –3.6V NPO 0.1µF 4 3300pF 1206 NPO VIN– 5 + – LT6203 10Ω IN+ LTC2378-20 6800pF NPO 5 IN– GND GND GND GND VIN+ 10µF 6.3V 9 CNV 13 SCK SCK 14 SDO SDO 11 BUSY BUSY RDL/SDI 12 RD 3 6 10 16 1 V+ 8V LT6203 3 5 – 1 0.1µF VDD 2 OVDD 15 REF 7 8 REF/DGC +2.5V 7 6657 TA08 1k 6 Related Parts PART NUMBER DESCRIPTION COMMENTS LT1236 Precision Low Drift, Low Noise Reference 0.05% Max, 5ppm/°C Max, 1ppm (Peak-to-Peak) Noise LT1460 Micropower Series References 0.075% Max, 10ppm/°C Max, 20mA Output Current LT1461 Micropower Series Low Dropout 0.04% Max, 3ppm/°C Max, 50mA Output Current LT1790 Micropower Precision Series References 0.05% Max, 10ppm/°C Max, 60µA Supply, SOT23 Package LT6660 Tiny Micropower Series Reference 0.2% Max, 20ppm/°C Max, 20mA Output Current, 2mm × 2mm DFN LT6650 Micropower Reference with Buffer Amplifier 0.5% Max, 5.6µA Supply, SOT23 Package LTC6652 High Precision, Buffered Voltage Reference Family 0.05% Max Initial Error, 5ppm/°C Max Drift, Shutdown Current <2µA, –40°C to 125°C Operation LT6654 Low Noise, High Voltage, High Output Drive Voltage Reference Family 1.6ppm Peak-to-Peak Noise (0.1Hz to 10Hz), Sink/Source ±10mA, 10ppm/°C Max Drift, –40°C to 125°C Operation LTC6655 Precision, Very Low Noise and Temperature Drift, Voltage Reference Family 0.25ppm Peak-to-Peak Noise (0.1Hz to 10Hz), Sink/Source ±5mA, 0.025% Max, 2ppm/°C Max Drift, –40°C to 125°C Operation LT6656 Ultra Low Current Series Voltage Reference Family Supply current < 1µA, 0.05% Max, 10ppm/°C, Sink/Source ±5mA 6657fb 22 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LT6657 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LT6657 LT 0616 REV B • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2015