LT1461 Micropower Precision Low Dropout Series Voltage Reference Family U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Trimmed to High Accuracy: 0.04% Max Low Drift: 3ppm/°C Max Low Supply Current: 50µA Max Temperature Coefficient Guaranteed to 125°C High Output Current: 50mA Min Low Dropout Voltage: 300mV Max Excellent Thermal Regulation Power Shutdown Thermal Limiting Operating Temperature Range: – 40°C to 125°C Voltage Options: 2.5V, 3V, 3.3V, 4.096V and 5V U APPLICATIO S ■ ■ ■ ■ A/D and D/A Converters Precision Regulators Handheld Instruments Power Supplies The LT ®1461 is a family of low dropout micropower bandgap references that combine very high accuracy and low drift with low supply current and high output drive. These series references use advanced curvature compensation techniques to obtain low temperature coefficient and trimmed precision thin-film resistors to achieve high output accuracy. The LT1461 family draws only 35µA of supply current, making them ideal for low power and portable applications, however their high 50mA output drive makes them suitable for higher power requirements, such as precision regulators. In low power applications, a dropout voltage of less than 300mV ensures maximum battery life while maintaining full reference performance. Line regulation is nearly immeasurable, while the exceedingly good load and thermal regulation will not add significantly to system error budgets. The shutdown feature can be used to switch full load currents and can be used for system power down. Thermal shutdown protects the part from overload conditions. The LT1461 is available in 2.5V, 3V, 3.3V 4.096V and 5V options. , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATIO LT1461-2.5 Load Regulation, PDISS = 200mW Basic Connection (VOUT + 0.3V) ≤ VIN ≤ 20V VOUT LT1461 CIN 1µF CL 2µF 1461 TA01 0mA IOUT 20mA VOUT LOAD REG 1mV/DIV 10ms/DIV 1461 TA02 1 LT1461 W W W AXI U U ABSOLUTE RATI GS (Note 1) Input Voltage ........................................................... 20V Output Short-Circuit Duration ......................... Indefinite Operating Temperature Range (Note 2) ........................................... – 40°C to 125°C Storage Temperature Range (Note 3) ... – 65°C to 150°C Specified Temperature Range Commercial ............................................ 0°C to 70°C Industrial ........................................... – 40°C to 85°C High ................................................. – 40°C to 125°C Lead Temperature (Soldering, 10 sec).................. 300°C U U W PACKAGE/ORDER I FOR ATIO ORDER PART NUMBER TOP VIEW DNC* 1 8 DNC* VIN 2 7 DNC* SHDN 3 6 VOUT GND 4 5 DNC* S8 PACKAGE 8-LEAD PLASTIC SO *DNC: DO NOT CONNECT TJMAX = 150°C, θJA = 190°C/ W (Note 3) LT1461ACS8-2.5 LT1461BCS8-2.5 LT1461CCS8-2.5 LT1461AIS8-2.5 LT1461BIS8-2.5 LT1461CIS8-2.5 LT1461DHS8-2.5 LT1461ACS8-3 LT1461BCS8-3 LT1461CCS8-3 LT1461AIS8-3 LT1461BIS8-3 LT1461CIS8-3 LT1461DHS8-3 LT1461ACS8-3.3 LT1461BCS8-3.3 LT1461CCS8-3.3 LT1461AIS8-3.3 LT1461BIS8-3.3 LT1461CIS8-3.3 LT1461DHS8-3.3 LT1461ACS8-4 LT1461BCS8-4 LT1461CCS8-4 LT1461AIS8-4 LT1461BIS8-4 LT1461CIS8-4 LT1461DHS8-4 S8 PART MARKING LT1461ACS8-5 LT1461BCS8-5 LT1461CCS8-5 LT1461AIS8-5 LT1461BIS8-5 LT1461CIS8-5 LT1461DHS8-5 461A25 461B25 461C25 61AI25 61BI25 61CI25 61DH25 1461A3 1461B3 1461C3 461AI3 461BI3 461CI3 461DH3 461A33 461B33 461C33 61AI33 61BI33 61CI33 61DH33 1461A4 1461B4 1461C4 461AI4 461BI4 461CI4 461DH4 1461A5 1461B5 1461C5 461AI5 461BI5 461CI5 461DH5 Consult factory for Military grade parts. U AVAILABLE OPTIO S OUTPUT VOLTAGE INITIAL ACCURACY TEMPERATURE COEFFICIENT TEMPERATURE RANGE 2.5V 3.0V 3.3V 4.096V 5.0V 0.04% Max 0.04% Max 3ppm/°C Max 3ppm/°C Max 0°C to 70°C – 40°C to 85°C LT1461ACS8-2.5 LT1461AIS8-2.5 LT1461ACS8-3 LT1461AIS8-3 LT1461ACS8-3.3 LT1461AIS8-3.3 LT1461ACS8-4 LT1461AIS8-4 LT1461ACS8-5 LT1461AIS8-5 0.06% Max 0.06% Max 7ppm/°C Max 7ppm/°C Max 0°C to 70°C – 40°C to 85°C LT1461BCS8-2.5 LT1461BIS8-2.5 LT1461BCS8-3 LT1461BIS8-3 LT1461BCS8-3.3 LT1461BIS8-3.3 LT1461BCS8-4 LT1461BIS8-4 LT1461BCS8-5 LT1461BIS8-5 0.08% Max 0.08% Max 12ppm/°C Max 12ppm/°C Max 0°C to 70°C – 40°C to 85°C LT1461CCS8-2.5 LT1461CIS8-2.5 LT1461CCS8-3 LT1461CIS8-3 LT1461CCS8-3.3 LT1461CIS8-3.3 LT1461CCS8-4 LT1461CIS8-4 LT1461CCS8-5 LT1461CIS8-5 0.15% Max 20ppm/°C Max –40°C to 125°C LT1461DHS8-2.5 LT1461DHS8-3 LT1461DHS8-3.3 LT1461DHS8-4 LT1461DHS8-5 2 LT1461 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the specified temperature range, otherwise specifications are at TA = 25°C. VIN – VOUT = 0.5V, Pin 3 = 2.4V, CL = 2µF, unless otherwise specified. PARAMETER CONDITIONS Output Voltage (Note 4) LT1461ACS8/LT1461AIS8 LT1461BCS8/LT1461BIS8 LT1461CCS8/LT1461CIS8 LT1461DHS8 MIN Output Voltage Temperature Coefficient (Note 5) LT1461ACS8/LT1461AIS8 LT1461BCS8/LT1461BIS8 LT1461CCS8/LT1461CIS8 LT1461DHS8 Line Regulation (VOUT + 0.5V) ≤ VIN ≤ 20V TYP – 0.04 – 0.06 – 0.08 – 0.15 ppm/°C ppm/°C ppm/°C ppm/°C 2 8 12 ppm/V ppm/V 15 50 ppm/V 12 ● 30 40 ppm/mA ppm/mA LT1461DHS8, 0 ≤ IOUT ≤ 10mA ● 50 ppm/mA VIN – VOUT, VOUT Error = 0.1% IOUT = 0mA IOUT = 1mA IOUT = 10mA IOUT = 50mA, I and C Grades Only ● ● ● 0.3 0.4 2.0 V V V V ● VIN = VOUT + 2.5V 0 ≤ IOUT ≤ 50mA Output Current Short VOUT to GND Shutdown Pin Logic High Input Voltage Logic High Input Current, Pin 3 = 2.4V ● ● Logic Low Input Voltage Logic Low Input Current, Pin 3 = 0.8V ● ● Supply Current 0.06 0.13 0.20 1.50 100 No Load RL = 1k mA 2.4 2 15 V µA 0.5 0.8 4 V µA 35 50 70 µA µA 25 35 55 µA µA ● Shutdown Current % % % % 3 7 12 20 LT1461DHS8 Dropout Voltage UNITS 0.04 0.06 0.08 0.15 1 3 5 7 ● ● ● ● ● Load Regulation Sourcing (Note 6) MAX ● Output Voltage Noise (Note 7) 0.1Hz ≤ f ≤ 10Hz 10Hz ≤ f ≤ 1kHz 8 9.6 ppmP-P ppmRMS Long-Term Drift of Output Voltage, SO-8 Package (Note 8) See Applications Information 60 ppm/√kHr Thermal Hysteresis (Note 9) ∆T = 0°C to 70°C ∆T = – 40°C to 85°C ∆T = – 40°C to 125°C 40 75 120 ppm ppm ppm Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT1461 is guaranteed functional over the operating temperature range of – 40°C to 125°C. Note 3: If the part is stored outside of the specified temperature range, or the junction temperature exceeds the specified temperature range, the output may shift due to hysteresis. Note 4: ESD (Electrostatic Discharge) sensitive device. Extensive use of ESD protection devices are used internal to the LT1461, however, high electrostatic discharge can damage or degrade the device. Use proper ESD handling precautions. Note 5: Temperature coefficient is calculated from the minimum and maximum output voltage measured at TMIN, Room and TMAX as follows: TC = (VOMAX – VOMIN)/(TMAX – TMIN) Incremental slope is also measured at 25°C. Note 6: Load regulation is measured on a pulse basis from no load to the specified load current. Output changes due to die temperature change must be taken into account separately. Note 7: Peak-to-peak noise is measured with a single pole highpass filter at 0.1Hz and a 2-pole lowpass filter at 10Hz. The unit is enclosed in a stillair environment to eliminate thermocouple effects on the leads. The test time is 10 seconds. RMS noise is measured with a single pole highpass filter at 10Hz and a 2-pole lowpass filter at 1kHz. The resulting output is full-wave rectified and then integrated for a fixed period, making the final reading an average as opposed to RMS. A correction factor of 1.1 is used to convert from average to RMS and a second correction of 0.88 is used to correct for the nonideal bandpass of the filters. 3 LT1461 ELECTRICAL CHARACTERISTICS Note 8: Long-term drift typically has a logarithmic characteristic and therefore, changes 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 that of the first thousand hours with a continuing trend toward reduced drift with time. Long-term drift will also be affected by differential stresses between the IC and the board material created during board assembly. See the Applications Information section. Note 9: Hysteresis in output voltage is created by package stress that depends on whether the IC was previously at a higher or lower temperature. Output voltage is always measured at 25°C, but the IC is cycled hot or cold before successive measurements. Hysteresis is roughly proportional to the square of the temperature change. Hysteresis is not normally a problem for operational temperature excursions where the instrument might be stored at high or low temperature. See Applications Information section. U W TYPICAL PERFOR A CE CHARACTERISTICS Characteristic curves are similar for most LT1461s. Curves from the LT1461-2.5 and the LT1461-5 represent the extremes of the voltage options. Characteristic curves for other output voltages fall between these curves and can be estimated based on their output. 2.5V Reference Voltage vs Temperature OUTPUT VOLTAGE CHANGE (ppm) REFERENCE VOLTAGE (V) 1600 TEMPCO –60°C TO 120°C 3 TYPICAL PARTS 2.5010 2.5005 2.5000 2.4995 2.4990 2.4985 2.4980 – 60 – 40 – 20 0 VIN = 7.5V –1 LINE REGULATION (ppm/V) 2.5020 2.5015 2.5V Line Regulation vs Temperature 2.5V Load Regulation 1200 125°C 25°C 800 400 –2 –3 –4 –5 –6 – 55°C –7 0 0.1 0 20 40 60 80 100 120 TEMPERATURE (°C) 1 10 OUTPUT CURRENT (mA) SUPPLY ∆ = 15V 5V – 20V –8 –40 – 20 100 0 20 40 60 80 TEMPERATURE (°C) 100 120 1461 G02 1461 G01 1461 G03 2.5V Ripple Rejection Ratio vs Frequency 2.5V Supply Current vs Input Voltage 2.5V Minimum Input/Output Voltage Differential vs Load Current 10 100 1000 125°C RIPPLE REJECTION RATIO (dB) 1 SUPPLY CURRENT (µA) INPUT/OUTPUT VOLTAGE (V) 90 100 125°C 25°C – 55°C 25°C 0.1 1 10 OUTPUT CURRENT (mA) 100 1461 G04 4 70 60 50 40 30 20 10 – 55°C 0.1 80 10 0 5 10 15 20 INPUT VOLTAGE (V) 25 1461 G05 0 0.01 0.1 1 10 FREQUENCY (kHz) 100 1000 1641 G06 LT1461 U W TYPICAL PERFOR A CE CHARACTERISTICS Characteristic curves are similar for most LT1461s. Curves from the LT1461-2.5 and the LT1461-5 represent the extremes of the voltage options. Characteristic curves for other output voltages fall between these curves and can be estimated based on their output. 2.5V Output Impedance vs Frequency 2.5V Turn-On Time 2.5V Turn-On Time 1000 10 10 10 0 0 2 2 VOUT VOUT 1 1 CIN = 1µF CL = 2µF RL = ∞ 0 1 0.01 0.1 1 FREQUENCY (kHz) VIN 20 VOLTAGE (V) COUT = 1µF 100 VIN 20 VOLTAGE (V) OUTPUT IMPEDANCE (Ω) COUT = 2µF 10 CIN = 1µF CL = 2µF RL = 50Ω 0 TIME (100µs/DIV) TIME (100µs/DIV) 1461 G08 1461 G09 1461 G07 2.5V Transient Response to 10mA Load Step VIN VOUT 50mV/DIV 5V OUTPUT NOISE (10µV/DIV) IOUT 0mA 10mA/DIV 2.5V Output Noise 0.1Hz ≤ f ≤ 10Hz 2.5V Line Transient Response 4V VOUT 50mV/DIV CL = 2µF 1461 G10 CIN = 0.1µF 1461 G11 TIME (2SEC/DIV) 1461 G12 5 LT1461 U W TYPICAL PERFOR A CE CHARACTERISTICS Characteristic curves are similar for most LT1461s. Curves from the LT1461-2.5 and the LT1461-5 represent the extremes of the voltage options. Characteristic curves for other output voltages fall between these curves and can be estimated based on their output. 5V Reference Voltage vs Temperature 2000 5.0040 TEMPCO –60°C TO 120°C 5.0030 3 TYPICAL PARTS 5.0020 VIN = 10V 0 125°C 25°C 5.0010 5.0000 4.9990 4.9980 4.9970 4.9960 4.9950 1600 –1 LINE REGULATION (ppm/V) LOAD REGULATION (ppm) REFERENCE VOLTAGE (V) 5V Line Regulation vs Temperature 5V Load Regulation –55°C 1200 800 25°C 400 125°C –55°C 0 0.1 0 20 40 60 80 100 120 TEMPERATURE (°C) 1 10 OUTPUT CURRENT (mA) –4 –5 –6 SUPPLY ∆ = 14V 6V TO 20V –8 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 100 100 120 1461 G14 1461 G13 5V Minimum Input/Output Voltage Differential vs Load Current 1461 G15 5V Ripple Rejection Ratio vs Frequency 5V Supply Current vs Input Voltage 10000 10 –3 –7 4.9940 4.9930 –60 –40 –20 –2 100 1 25°C 125°C –55°C 0.1 RIPPLE REJECTION RATIO (dB) SUPPLY CURRENT (µA) INPUT/OUTPUT VOLTAGE (V) 90 1000 100 125°C –55°C 25°C 10 80 70 60 50 40 30 20 10 0 0.01 1 0.01 0.1 1 10 OUTPUT CURRENT (mA) 100 0 5 10 15 INPUT VOLTAGE (V) 20 1461 G16 25 0.1 1 10 FREQUENCY (kHz) 100 1461 G17 5V Output Impedance vs Frequency 1000 1461 G18 5V Turn-On Time 5V Turn-On Time 1000 COUT = 2µF COUT = 1µF VIN 4 4 2 2 0 VOUT 4 10 2 1 0.01 0.1 1 FREQUENCY (kHz) 10 0 VOUT 2 CIN = 1µF COUT = 2µF IOUT = 0 CIN = 1µF COUT = 2µF IOUT = 50mA 0 200µs/DIV 200µs/DIV 1461 G20 1461 G19 VIN 4 0 6 6 2V/DIV 100 2V/DIV OUTPUT IMPEDANCE (Ω) 6 1461 G21 LT1461 U W TYPICAL PERFOR A CE CHARACTERISTICS Characteristic curves are similar for most LT1461s. Curves from the LT1461-2.5 and the LT1461-5 represent the extremes of the voltage options. Characteristic curves for other output voltages fall between these curves and can be estimated based on their output. 5V Transient Response to 10mA Load Step 7V VIN 6V OUTPUT NOISE (10µV/DIV) IOUT 5V Output Noise 0.1Hz ≤ f ≤ 10Hz 5V Line Transient Response 0mA 10mA VOUT 50mV/DIV VOUT 50mV/DIV 1461 G22 CL = 2µF 1461 G23 CIN = 0.1µF TIME (2SEC/DIV) 1461 G24 Supply Current vs Temperature SHDN Pin Current vs SHDN Input Voltage Current Limit vs Temperature 200 140 50 180 IS 30 20 SHDN PIN CURRENT (µA) 120 IS(SHDN) CURRENT LIMIT (mA) SUPPLY CURRENT (µA) 40 100 80 125°C 120 25°C – 55°C 100 80 60 40 60 10 160 140 20 0 – 40 –20 0 20 40 60 80 TEMPERATURE (°C) 100 120 1461 G25 40 –50 0 –25 50 25 0 75 TEMPERATURE (°C) 100 125 1461 G26 0 15 10 5 SHDN PIN INPUT VOLTAGE (V) 20 1461 G27 7 LT1461 U W TYPICAL PERFOR A CE CHARACTERISTICS Characteristic curves are similar for most LT1461s. Curves from the LT1461-2.5 and the LT1461-5 represent the extremes of the voltage options. Characteristic curves for other output voltages fall between these curves and can be estimated based on their output. 0°C to 70°C Hysteresis 20 18 WORST-CASE HYSTERESIS ON 35 UNITS NUMBER OF UNITS 16 14 70°C TO 25°C 0°C TO 25°C 12 10 8 6 4 2 0 –100 – 80 – 60 – 40 – 20 0 20 HYSTERESIS (ppm) 40 60 80 100 1461 G29 – 40°C to 85°C Hysteresis 20 18 WORST-CASE HYSTERESIS ON 35 UNITS NUMBER OF UNITS 16 14 85°C TO 25°C 12 – 40°C TO 25°C 10 8 6 4 2 0 –100 – 80 – 60 – 40 – 20 0 20 HYSTERESIS (ppm) 40 60 80 100 1461 G30 – 40°C to 125°C Hysteresis 16 14 NUMBER OF UNITS 12 WORST-CASE HYSTERESIS ON 35 UNITS 125°C TO 25°C – 40°C TO 25°C 10 8 6 4 2 0 –200 –160 –120 –80 –40 0 40 HYSTERESIS (ppm) 80 120 160 200 1461 G31 8 LT1461 U W TYPICAL PERFOR A CE CHARACTERISTICS Characteristic curves are similar for most LT1461s. Curves from the LT1461-2.5 and the LT1461-5 represent the extremes of the voltage options. Characteristic curves for other output voltages fall between these curves and can be estimated based on their output. Long-Term Drift (Number of Data Points Reduced at 650 Hours)* 250 LT1461S8 3 TYPICAL PARTS SOLDERED ONTO PCB TA = 30°C 200 ppm 150 100 50 0 –50 0 200 600 400 800 1000 HOURS 1200 1400 1600 1800 2000 1461 G15 *SEE APPLICATIONS INFORMATION FOR DETAILED EXPLANATION OF LONG-TERM DRIFT U W U U APPLICATIO S I FOR ATIO Examples shown in this Applications section use the LT1461-2.5. The response of other voltage options can be estimated by proper scaling. Bypass and Load Capacitors The LT1461 family requires a capacitor on the input and on the output for stability. The capacitor on the input is a supply bypass capacitor and if the bypass capacitors from other components are close (within 2 inches) they should be sufficient. The output capacitor acts as frequency compensation for the reference and cannot be omitted. For light loads ≤ 1mA, a 1µF nonpolar output capacitor is usually adequate, but for higher loads (up to 75mA), the output capacitor should be 2µF or greater. Figures 1 and 2 show the transient response to a 1mA load step with a 1µF output capacitor and a 50mA load step with a 2µF output capacitor. IOUT 0mA 1mA/DIV 1mA IOUT 50mA/DIV VOUT 20mV/DIV VOUT 200mV/DIV 1461 F01 Figure 1. 1mA Load Step with CL = 1µF 1461 F02 Figure 2. 50mA Load Step with CL = 2µF 9 LT1461 U W U U APPLICATIO S I FOR ATIO Precision Regulator PC Board Layout The LT1461 will deliver 50mA with VIN = VOUT + 2.5V and higher load current with higher VIN. Load regulation is typically 12ppm/mA, which means for a 50mA load step, the output will change by only 1.5mV. Thermal regulation, caused by die temperature gradients and created from load current or input voltage changes, is not measurable. This often overlooked parameter must be added to normal line and load regulation errors. The load regulation photo, on the first page of this data sheet, shows the output response to 200mW of instantaneous power dissipation and the reference shows no sign of thermal errors. The reference has thermal shutdown and will turn off if the junction temperature exceeds 150°C. In 13- to 16-bit systems where initial accuracy and temperature coefficient calibrations have been done, the mechanical and thermal stress on a PC board (in a card cage for instance) can shift the output voltage and mask the true temperature coefficient of a reference. In addition, the mechanical stress of being soldered into a PC board can cause the output voltage to shift from its ideal value. Surface mount voltage references are the most susceptible to PC board stress because of the small amount of plastic used to hold the lead frame. Shutdown The shutdown (Pin 3 low) serves to shut off load current when the LT1461 is used as a regulator. The LT1461 operates normally with Pin 3 open or greater than or equal to 2.4V. In shutdown, the reference draws a maximum supply current of 35µA. Figure 3 shows the transient response of shutdown while the part is delivering 25mA. After shutdown, the reference powers up in about 200µs. 5V A simple way to improve the stress-related shifts is to mount the reference near the short edge of the PC board, or in a corner. The board edge acts as a stress boundary, or a region where the flexure of the board is minimum. The package should always be mounted so that the leads absorb the stress and not the package. The package is generally aligned with the leads parallel to the long side of the PC board as shown in Figure 5a. A qualitative technique to evaluate the effect of stress on voltage references is to solder the part into a PC board and deform the board a fixed amount as shown in Figure 4. The flexure #1 represents no displacement, flexure #2 is concave movement, flexure #3 is relaxation to no displacement and finally, flexure #4 is a convex movement. This motion is repeated for a number of cycles and the PIN 3 1 0V 2 VOUT 3 0V 4 1461 F03 Figure 3. Shutdown While Delivering 25mA, RL = 100Ω 10 1461 F04 Figure 4. Flexure Numbers LT1461 U W U U APPLICATIO S I FOR ATIO relative output deviation is noted. The result shown in Figure 5a is for two LT1461S8-2.5s mounted vertically and Figure 5b is for two LT1461S8-2.5s mounted horizontally. The parts oriented in Figure 5a impart less stress into the package because stress is absorbed in the leads. Figures 5a and 5b show the deviation to be between 125µV and 250µV and implies a 50ppm and 100ppm change respectively. This corresponds to a 13- to 14-bit system and is not a problem for most 10- to 12-bit systems unless the system has a calibration. In this case, as with temperature hysteresis, this low level can be important and even more careful techniques are required. The most effective technique to improve PC board stress is to cut slots in the board around the reference to serve as a strain relief. These slots can be cut on three sides of the reference and the leads can exit on the fourth side. This “tongue” of PC board material can be oriented in the long direction of the board to further reduce stress transferred to the reference. The results of slotting the PC boards of Figures 5a and 5b are shown in Figures 6a and 6b. In this example the slots can improve the output shift from about 100ppm to nearly zero. 2 OUTPUT DEVIATION (mV) OUTPUT DEVIATION (mV) 2 1 LONG DIMENSION 0 0 SLOT –1 –1 0 10 20 30 FLEXURE NUMBER 0 40 10 20 30 FLEXURE NUMBER 1461 F05a Figure 5a. Two Typical LT1461S8-2.5s, Vertical Orientation Without Slots 40 1461 F06a Figure 6a. Same Two LT1461S8-2.5s in Figure 5a, but with Slots 2 2 OUTPUT DEVIATION (mV) OUTPUT DEVIATION (mV) 1 1 LONG DIMENSION 0 –1 0 10 20 30 FLEXURE NUMBER Figure 5b. Two Typical LT1461S8-2.5s, Horizontal Orientation Without Slots 40 1461 F05b 1 0 SLOT –1 0 10 20 FLEXURE NUMBER 30 40 1461 F06b Figure 6b. Same Two LT1461S8-2.5s in Figure 5b, but with Slots 11 LT1461 U W U U APPLICATIO S I FOR ATIO Long-Term Drift Long-term drift cannot be extrapolated from accelerated high temperature testing. This erroneous technique gives drift numbers that are wildly optimistic. The only way long-term drift can be determined is to measure it over the time interval of interest. The erroneous technique uses the Arrhenius Equation to derive an acceleration factor from elevated temperature readings. The equation is: AF EA 1 1 – = e K T 1 T 2 where: EA = Activation Energy (Assume 0.7) K = Boltzmann’s Constant T2 = Test Condition in °Kelvin T1 = Use Condition Temperature in °Kelvin To show how absurd this technique is, compare the LT1461 data. Typical 1000 hour long-term drift at 30°C = 60ppm. The typical 1000 hour long-term drift at 130°C = 120ppm. From the Arrhenius Equation the acceleration factor is: AF 1 0.7 1 – . 0 0000863 303 403 =e = 767 The erroneous projected long-term drift is: 120ppm/767 = 0.156ppm/1000 hr For a 2.5V reference, this corresponds to a 0.39µV shift after 1000 hours. This is pretty hard to determine (read impossible) if the peak-to-peak output noise is larger than this number. As a practical matter, one of the best laboratory references available is the Fluke 732A and its longterm drift is 1.5µV/mo. This performance is only available from the best subsurface zener references utilizing specialized heater techniques. The LT1461 long-term drift data was taken with parts that were soldered onto PC boards similar to a “real world” application. The boards were then placed into a constant temperature oven with TA = 30°C, their outputs were 12 scanned regularly and measured with an 8.5 digit DVM. As an additional accuracy check on the DVM, a Fluke 732A laboratory reference was also scanned. Figure 7 shows the long-term drift measurement system. The data taken is shown at the end of the Typical Performance Characteristics section of this data sheet. The long-term drift is the trend line that asymptotes to a value at 2000 hours. Note the slope in output shift between 0 hours and 1000 hours compared to the slope between 1000 hours and 2000 hours. Long-term drift is affected by differential stresses between the IC and the board material created during board assembly. PCB3 PCB2 PCB1 SCANNER 8.5 DIGIT DVM COMPUTER 1461 F07 FLUKE 732A LABORATORY REFERENCE Figure 7. Long-Term Drift Measurement Setup Hysteresis The hysteresis curves found in the Typical Performance Characteristics represent the worst-case data taken on 35 typical parts after multiple temperature cycles. As expected, the parts that are cycled over the wider – 40°C to 125°C temperature range have more hysteresis than those cycled over lower ranges. Note that the hysteresis coming from 125°C to 25°C has an influence on the – 40°C to 25°C hysteresis. The – 40°C to 25°C hysteresis is different depending on the part’s previous temperature. This is because not all of the high temperature stress is relieved during the 25°C measurement. The typical performance hysteresis curves are for parts mounted in a socket and represent the performance of the LT1461 U W U U APPLICATIO S I FOR ATIO parts alone. What is more interesting are parts IR soldered onto a PC board. If the PC board is then temperature cycled several times from – 40°C to 85°C, the resulting hysteresis curve is shown in Figure 8. This graph shows the influence of the PC board stress on the reference. When the LT1461 is soldered onto a PC board, the output shifts due to thermal hysteresis. Figure 9 shows the effect of soldering 40 pieces onto a PC board using standard IR reflow techniques. The average output voltage shift is –110ppm. Remeasurement of these parts after 12 days shows the outputs typically shift back 45ppm toward their initial value. This second shift is due to the relaxation of stress incurred during soldering. The LT1461 is capable of dissipating high power, i.e., for the LT1461-2.5, 17.5V • 50mA = 875mW. The SO-8 package has a thermal resistance of 190°C/W and this dissipation causes a 166°C internal rise producing a junction temperature of TJ = 25°C + 166°C = 191°C. What will actually occur is the thermal shutdown will limit the junction temperature to around 150°C. This high temperature excursion will cause the output to shift due to thermal hysteresis. Under these conditions, a typical output shift is –135ppm, although this number can be higher. This high dissipation can cause the 25°C output accuracy to exceed its specified limit. For best accuracy and precision, the LT1461 junction temperature should not exceed 125°C. 12 11 WORST-CASE HYSTERESIS ON 35 UNITS 10 85°C TO 25°C NUMBER OF UNITS 9 – 40°C TO 25°C 8 7 6 5 4 3 2 1 0 – 200 –160 –120 – 80 – 40 0 40 HYSTERESIS (ppm) 80 120 160 200 1461 F08 Figure 8. – 40°C to 85°C Hysteresis of 35 Parts Soldered Onto a PC Board 12 NUMBER OF UNITS 10 8 6 4 2 0 –300 200 0 100 –200 –100 OUTPUT VOLTAGE SHIFT (ppm) 300 1461 F09 Figure 9. Typical Distribution of Output Voltage Shift After Soldering Onto PC Board 13 LT1461 W W SI PLIFIED SCHE ATIC 2 VIN 6 VOUT 100k SHDN 3 4 GND 1461 SS 14 LT1461 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.014 – 0.019 (0.355 – 0.483) TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 2 3 4 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC 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. SO8 1298 15 LT1461 U TYPICAL APPLICATIO Low Power 16-Bit A/D VCC 35µA 200µA VCC 1µF VCC FO LTC2400 VREF SCK SD0 CS VIN LT1461-2.5 VOUT 1µF INPUT 0.1µF GND GND SPI INTERFACE 1461 TA03 NOISE PERFORMANCE* VIN = 0V, VNOISE = 1.1ppmRMS = 2.25µVRMS = 16µVP-P VIN = VREF/2, VNOISE = 1.6ppmRMS = 4µVRMS = 24µVP-P VIN = VREF, VNOISE = 2.5ppmRMS = 6.25µVRMS = 36µVP-P *FOR 24-BIT PERFORMANCE USE LT1236 REFERENCE RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1019 Precision Reference Bandgap, 0.05%, 5ppm/°C LT1027 Precision 5V Reference Lowest TC, High Accuracy, Low Noise, Zener Based LT1236 Precision Reference 5V and 10V Zener-Based 5ppm/°C, SO-8 Package LTC 1798 Micropower Low Dropout Reference 0.15% Max, 6.5µA Supply Current LT1460 Micropower Precision Series Reference Bandgap, 130µA Supply Current 10ppm/°C, Available in SOT-23 LT1634 Micropower Precision Shunt Voltage Reference Bandgap 0.05%, 10ppm/°C, 10µA Supply Current LT1790 Precision SOT-23 Series Reference Bandgap 0.05% Max, 10ppm/°C Max ® 16 Linear Technology Corporation 1461f LT/LCG 0800 4K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 1999