LOG114AIRGVT

LOG114 SBOS301A − MAY 2004 − REVISED MARCH 2007 Single-Supply, High-Speed, Precision LOGARITHMIC AMPLIFIER FEATURES D ADVANTAGES: − Tiny for High Density Systems − Precision on One Supply − Fast Over Eight Decades − Fully-Tested Function TWO SCALING AMPLIFIERS WIDE INPUT DYNAMIC RANGE: Eight Decades, 100pA to 10mA 2.5V REFERENCE STABLE OVER TEMPERATURE LOW QUIESCENT CURRENT: 10mA DUAL OR SINGLE SUPPLY: +5V, +5V PACKAGE: Small QFN-16 (4mm x 4mm) SPECIFIED TEMPERATURE RANGE: −5°C to +75°C DESCRIPTION The LOG114 is specifically designed for measuring low-level and wide dynamic range currents in communications, lasers, medical, and industrial systems. The device computes the logarithm or log-ratio of an input current or voltage relative to a reference current or voltage (logarithmic transimpedance amplifier). High precision is ensured over a wide dynamic range of input signals on either bipolar (±5V) or single (+5V) supply. Special temperature drift compensation circuitry is included on-chip. In log-ratio applications, the signal current may be from a high impedance source such as a photodiode or resistor in series with a low impedance voltage source. The reference current is provided by a resistor in series with a precision internal voltage reference, photo diode, or active current source. The output signal at VLOGOUT has a scale factor of 0.375V out per decade of input current, which limits the output so that it fits within a 5V or 10V range. The output can be scaled and offset with one of the available additional amplifiers, so it matches a wide variety of ADC input ranges. Stable dc performance allows accurate measurement of low-level signals over a wide temperature range. The LOG114 is specified over a −5°C to +75°C temperature range and can operate from −40°C to +85°C. R5 R6 D D D D D D D D APPLICATIONS D ONET ERBIUM-DOPED FIBER OPTIC D D D LOG, LOG-RATIO FUNCTION D ANALOG SIGNAL COMPRESSION IN FRONT D OF ANALOG-TO-DIGITAL (ADC) CONVERTER ABSORBANCE MEASUREMENT AMPLIFIER (EDFA) LASER OPTICAL DENSITY MEASUREMENT PHOTODIODE SIGNAL COMPRESSION AMP V LOGOUT 9 (2) Q1 I1 4 V CM IN 5 I1 and I 2 are current inputs from a photodiode or other current source Q2 I2 3 R REF 16 VREF 2.5V 1 V REF GND 8 V+ 6 V− 7 REF A2 200Ω R (1) 3 10 +IN 4 11 − IN 4 LOG114 200Ω R (1) 1 1250Ω R2 A4 A 3(4) 13 1250Ω R4 +IN 5 VO4(3) A1 12 A5 15 VO5 IREF Com 14 − IN 5 NOTES: (1) Thermally dependent R 1 and R 3 provide temperature compensation. (2) V LOGOUT = 0.375 × log(I1/I2). (3) V O4 = 0.375 × K × log(I1/I2) K = 1 + R 6/R 5. (4) Differential Amplifier (A3 ) Gain = 6.25 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright  2004−2007, Texas Instruments Incorporated www.ti.com LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 ABSOLUTE MAXIMUM RATINGS(1) Supply Voltage, V+ to V− . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12V Signal Input Terminals, Voltage(2) . . . . . (V−) −0.5V to (V+) + 0.5V Current(2) . . . . . . . . . . . . . . . . . . . . ±10mA Output Short-Circuit(3) . . . . . . . . . . . . . . . . . . . . . . . . . . Continuous Operating Temperature . . . . . . . . . . . . . . . . . . . . . . −40°C to +85°C Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . −55°C to +125°C Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +150°C ESD Rating (Human Body Model) . . . . . . . . . . . . . . . . . . . . 2000V (1) Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those specified is not implied. (2) Input terminals are diode-clamped to the power-supply rails. Input signals that can swing more than 0.5V beyond the supply rails should be current-limited to 10mA or less. (3) Short-circuit to ground. This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. PRECISION CURRENT MEASUREMENT PRODUCTS FEATURES Logarithmic Transimpedance Amplifier, 5V, Eight Decades Logarithmic Transimpedance, 36V, 7.5 Decades Resistor-Feedback Transimpedance, 5V, 5.5 Decades Switched Integrator Transimpedance, Six Decades Direct Digital Converter, Six Decades PRODUCT LOG114 LOG112 OPA380, OPA381 IVC102 DDC112 ORDERING INFORMATION(1) PRODUCT LOG114 PACKAGE-LEAD QFN-16 PACKAGE DESIGNATOR RGV PACKAGE MARKING LOG114 (1) For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI web site at www.ti.com. PIN CONFIGURATION Top View VREF − IN5 +IN5 VO5 QFN-16 16 VREF GND NC I2 I1 1 2 3 4 15 14 13 12 VO4 Exposed thermal die pad on underside (Must be connected to V− ) 11 − IN4 10 +IN4 9 VLOGOUT 5 VCM IN 6 V− 7 Com 8 V+ QFN−16 (4mm x 4mm) NC = No Connection 2 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 ELECTRICAL CHARACTERISTICS: VS = +5V Boldface limits apply over the specified temperature range, TA = −5°C to +75°C. All specifications at TA = +25°C, RVLOGOUT = 10kΩ, VCM = GND, unless otherwise noted. LOG114 PARAMETER CORE LOG FUNCTION LOG CONFORMITY ERROR(1) Initial 1nA to 100µA (5 decades) 100pA to 3.5mA (7.5 decades) 1mA to 10mA Over Temperature 1nA to 100µA (5 decades) 100pA to 3.5mA (7.5 decades) 1mA to 10mA TRANSFER FUNCTION (GAIN)(2) Initial Scaling Factor Scaling Factor Error Over Temperature 100pA to 10mA 1nA to 100µA TMIN to TMAX +15°C to +50°C INPUT, A1 and A2 Offset Voltage vs Temperature vs Power Supply Input Bias Current vs Temperature Input Common-Mode Voltage Range Voltage Noise Current Noise OUTPUT, A3 (VLOGOUT) Output Offset, VOSO, Initial Over Temperature Full-Scale Output (FSO)(3) Gain Bandwidth Product Short-Circuit Current Capacitive Load OP AMP, A4 and A5 Input Offset Voltage vs Temperature vs Supply vs Common-Mode Voltage Input Bias Current Input Offset Current Input Voltage Range Input Noise f = 0.1Hz to 10Hz f = 1kHz Current Noise Open-Loop Voltage Gain Gain Bandwidth Product Slew Rate Settling Time 0.01% Rated Output Short-Circuit Current ISC in AOL GBW SR tS G = −1, 3V Step, CL = 100pF (V−) + 0.5 +4/−10 VOS dV/dT PSRR CMRR IB IOS (V−) 2 13 2 100 15 5 1.5 (V+) − 0.5 TMIN to TMAX VS = ±4.5V to ±5.5V ±250 ±2 30 74 −1 ±0.05 (V+) − 2 250 ±1000 µV µV/°C µV/V dB µA µA V µVPP nV/√Hz pA/√Hz dB MHz V/µs µs V mA GBW ISC IIN = 1µA VOSO TMIN to TMAX (V−) + 0.6 50 ±18 100 ±11 ±15 ±50 ±65 (V+) − 0.6 mV mV V MHz mA pF VCM en in f = 0.1Hz to 10kHz f = 1kHz f = 1kHz VOS dV/dT PSRR IB TMIN to TMAX TMIN to TMAX VS = ±2.25V to ±5.5V ±1 +15 75 ±5 Doubles every 10°C (V−)+1.5 to (V+)−1.5 3 30 4 V µVrms nV/√Hz fA/√Hz 400 ±4 mV µV/°C µV/V pA 0.375 0.4 0.035 1.5 0.7 ±2.5 0.21 ±3.5 ±3 V/decade % dB % % 0.1 0.009 0.9 0.08 See Typical Characteristics 0.1 0.5 See Typical Characteristics 0.4 % % % 0.2 0.017 % dB % dB CONDITIONS IIN/VOUT Equation MIN TYP VO = (0.375V) Log (I1/I2) MAX UNITS V 3 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 ELECTRICAL CHARACTERISTICS: VS = +5V (continued) All specifications at TA = +25°C, RVLOGOUT = 10kΩ, VCM = GND, unless otherwise noted. Boldface limits apply over the specified temperature range, TA = −5°C to +75°C. LOG114 PARAMETER TOTAL ERROR(4, 5) FREQUENCY RESPONSE, Core Log(6) BW, 3dB I1 or I2 = 1nA 10nA 100nA 1µA 10µA to 1mA (ratio 1:100) 1mA to 3.5mA (ratio 1:3.5) 3.5mA to 10mA (ratio 1:2.9) Step Response Increasing (I1 or I2) 8nA to 240nA (ratio 1:30) 10nA to 100nA (ratio 1:10) 10nA to 1µA (ratio 1:100) 10nA to 10µA (ratio 1:1k) 10nA to 1mA (ratio 1:100k) 1mA to 10mA (ratio 1:10) Decreasing (I1 or I2) 8nA to 240nA (ratio 1:30) 10nA to 100nA (ratio 1:10) 10nA to 1µA (ratio 1:100) 10nA to 10µA (ratio 1:1k) 10nA to 1mA (ratio 1:100k) 1mA to 10mA (ratio 1:10) VOLTAGE REFERENCE Bandgap Voltage Error, Initial vs Temperature vs Supply vs Load Short-Circuit Current POWER SUPPLY Dual Supply Operating Range Quiescent Current TEMPERATURE RANGE Specification, TMIN to TMAX Operating Storage Thermal Resistance, qJA −5 −40 −55 62 +75 +85 +125 °C °C °C °C/W VS IQ IO = 0 ±2.4 ±10 ±5.5 ±15 V mA VS = ±4.5V to ±5.5V IO = ±2mA 2.5 ±0.15 ±25 ±30 ±200 ±10 ±1 V % ppm/°C ppm/V ppm/mA mA IREF = 1µA 1 2 0.25 0.05 0.03 1 µs µs µs µs µs µs 0.7 1.5 0.15 0.07 0.06 1 µs µs µs µs µs µs IREF = 1µA IAC = 10% of IDC value, IREF = 1µA 5 12 120 2.3 >5 >5 >5 kHz kHz kHz MHz MHz MHz MHz CONDITIONS MIN TYP See Typical Characteristics MAX UNITS (1) Log conformity error is peak deviation from the best-fit straight line of VO vs Log (I1/I2) curve expressed as a percent of peak-to-peak full-scale output. Scale factor, K, equals 0.375V output per decade of input current. (2) Scale factor of core log function is trimmed to 0.375V output per decade change of input current. (3) Specified by design. (4) Worst-case total error for any ratio of I1/I2, as the largest of the two errors, when I, and I2 are considered separately. (5) Total error includes offset voltage, bias current, gain, and log conformity. (6) Small signal bandwidth (3dB) and transient response are a function of the level of input current. Smaller input current amplitude results in lower bandwidth. 4 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 ELECTRICAL CHARACTERISTICS: VS = +5V Boldface limits apply over the specified temperature range, TA = −5°C to +75°C. All specifications at TA = +25°C, RVLOGOUT = 10kΩ, VCM = +2.5V, unless otherwise noted. LOG114 PARAMETER CORE LOG FUNCTION LOG CONFORMITY ERROR(1) Initial 1nA to 100µA (5 decades) 100pA to 3.5mA (7.5 decades) 1mA to 10mA Over Temperature 1nA to 100µA (5 decades) 100pA to 3.5mA (7.5 decades) 1mA to 10mA TRANSFER FUNCTION (GAIN)(2) Initial Scaling Factor Scaling Factor Error Over Temperature 10nA to 100µA 1nA to 100µA TMIN to TMAX +15°C to +50°C INPUT, A1 and A2 Offset Voltage vs Temperature vs Power Supply Input Bias Current vs Temperature Input Common-Mode Voltage Range Voltage Noise Current Noise OUTPUT, A3 (VLOGOUT) Output Offset, VOSO, Initial Over Temperature Full Scale Output (FSO)(3) Gain Bandwidth Product Short-Circuit Current Capacitive Load OP AMP, A4 and A5 Input Offset Voltage vs Temperature vs Supply vs Common-Mode Voltage Input Bias Current Input Offset Current Input Voltage Range Input Noise f = 0.1Hz to 10Hz f = 1kHz Current Noise Open-Loop Voltage Gain Gain Bandwidth Product Slew Rate Settling Time 0.01% Rated Output Short-Circuit Current ISC in AOL GBW SR tS G = −1, 3V Step, CL = 100pF (V−) + 0.5 +4/−10 VOS dV/dT PSRR CMRR IB IOS (V−) 1 28 2 100 15 5 1.5 (V+) − 0.5 TMIN to TMAX VS = +4.8V to +5.5V ±250 ±2 30 70 −1 ±0.05 (V+) − 1.5 ±4000 µV µV/°C µV/V dB µA µA V µVPP nV/√Hz pA/√Hz dB MHz V/µs µs V mA GBW ISC VOSO TMIN to TMAX VS = +5V IIN = 1µA (V−) + 0.6 50 ±18 100 ±14 ±18 ±65 ±80 (V+) − 0.6 mV mV V MHz mA pF VCM en in f = 0.1Hz to 10kHz f = 1kHz f = 1kHz VOS dV/dT PSRR IB TMIN to TMAX TMIN to TMAX VS = +4.5V to +5.5V ±1 +30 300 ±5 Doubles every 10°C (V−)+1.5 to (V+)−1.5 3 30 4 V µVrms nV/√Hz fA/√Hz ±7 mV µV/°C µV/V pA 0.375 0.4 0.0.35 0.035 0.7 ±2.5 0.21 ±3.5 ±3 V/decade % dB % % 0.1 0.009 0.9 0.08 See Typical Characteristics 0.1 0.5 See Typical Characteristics 0.4 % % 0.25 0.022 % dB % dB CONDITIONS IIN/VOUT Equation MIN TYP MAX UNITS V VO = (0.375V) Log (I1/I2) + VCM 5 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 ELECTRICAL CHARACTERISTICS: VS = +5V (continued) All specifications at TA = +25°C, RVLOGOUT = 10kΩ, VCM = +2.5V, unless otherwise noted. Boldface limits apply over the specified temperature range, TA = −5°C to +75°C. LOG114 PARAMETER TOTAL ERROR(4, 5) FREQUENCY RESPONSE, Core Log(6) BW, 3dB I1 or I2 = 1nA 10nA 100nA 1µA 10µA to 1mA (ratio 1:100) 1mA to 3.5mA (ratio 1:3.5) 3.5mA to 10mA (ratio 1:2.9) Step Response Increasing (I1 or I2) 8nA to 240nA (ratio 1:30) 10nA to 100nA (ratio 1:10) 10nA to 1µA (ratio 1:100) 10nA to 10µA (ratio 1:1k) 10nA to 1mA (ratio 1:100k) 1mA to 10mA (ratio 1:10) Decreasing (I1 or I2) 8nA to 240nA (ratio 1:30) 10nA to 100nA (ratio 1:10) 10nA to 1µA (ratio 1:100) 10nA to 10µA (ratio 1:1k) 10nA to 1mA (ratio 1:100k) 1mA to 10mA (ratio 1:10) VOLTAGE REFERENCE Bandgap Voltage Error, Initial vs Temperature vs Supply vs Load Short-Circuit Current POWER SUPPLY Single Supply Operating Range Quiescent Current TEMPERATURE RANGE Specification, TMIN to TMAX Operating Storage Thermal Resistance, qJA −5 −40 −55 62 +75 +85 +125 °C °C °C °C/W VS IQ IO = 0 4.8 ±10 11 ±15 V mA VS = +4.8V to +11V IO = ±2mA 2.5 ±0.15 ±25 ±30 ±200 ±10 ±1 V % ppm/°C ppm/V ppm/mA mA IREF = 1µA 1 2 0.25 0.05 0.03 1 µs µs µs µs µs µs 0.7 1.5 0.15 0.07 0.06 1 µs µs µs µs µs µs IREF = 1µA IAC = 10% of IDC value, IREF = 1µA 5 12 120 2.3 >5 >5 >5 kHz kHz kHz MHz MHz MHz MHz CONDITIONS MIN TYP See Typical Characteristics MAX UNITS (1) Log conformity error is peak deviation from the best-fit straight line of VO vs Log (I1/I2) curve expressed as a percent of peak-to-peak full-scale output. Scale factor, K, equals 0.375V output per decade of input current. (2) Scale factor of core log function is trimmed to 0.375V output per decade change of input current. (3) Specified by design. (4) Worst-case total error for any ratio of I1/I2, as the largest of the two errors, when I, and I2 are considered separately. (5) Total error includes offset voltage, bias current, gain, and log conformity. (6) Small signal bandwidth (3dB) and transient response are a function of the level of input current. Smaller input current amplitude results in lower bandwidth. 6 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 TYPICAL CHARACTERISTICS: VS = +5V All specifications at TA = +25°C, RVLOGOUT = 10kΩ, VCM = GND, unless otherwise noted. NORMALIZED TRANSFER FUNCTION 2.0 Normalized Output Voltage (V) Normalized Output Voltage (V) 1.5 1.0 0.5 0 − 0.5 − 1.0 − 1.5 − 2.0 10− 4 10−3 10−2 10−1 1 101 102 103 104 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0 1 ONE CYCLE OF NORMALIZED TRANSFER FUNCTION 10 Current Ratio (I 1/ I2) Current Ratio (I1/I2) 40 30 Gain Error (%) 20 SCALING FACTOR ERROR (I2 = reference 100pA to 10mA) 2.5 2.0 1.5 1.0 VLOGOUT (V) VLOGOUT vs I 1 INPUT (I2 = 1µA) 10 0 − 10 − 20 +70_ C 0_ C +25_ C 0.5 0 − 0.5 − 1.0 − 1.5 − 2.0 − 2.5 − 10_ C +80_ C +90_ C 10nA 100nA 1µA 10µA 100µA 1mA 10mA 100pA 1nA 100pA 1nA 10nA 100nA 1µ A 10µA 100µ A 1mA 10mA Input Current (I1) Input Current (I1) 2.0 1.5 1.0 VLOGOUT (V) VLOGOUT vs I2 INPUT (I1 = 1µA) 4 3 2 1µ A VLOGOUT (V) 1 0 −1 −2 −3 VLOGOUT vs I REF 100pA 1nA 10nA 100nA 0.5 0 − 0.5 − 1.0 − 1.5 − 2.0 − 2.5 100pA 1nA 10nA 100nA 1µA 10µA 100µA 1mA 10mA 10µ A 1mA 100µA 10mA 10nA 100nA 1µ A IREF (I2) 10µA 100µ A 1mA 10mA −4 100pA 1nA Input Current (I1) 7 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 TYPICAL CHARACTERISTICS: VS = +5V (continued) All specifications at TA = +25°C, RVLOGOUT = 10kΩ, VCM = GND, unless otherwise noted. 100 80 60 Total Error (mV) 40 20 0 − 20 − 40 − 60 − 80 − 100 AVERAGE TOTAL ERROR AT +80_ C 100 80 I1 = 1mA Total Error (mV) 60 40 20 0 − 20 − 40 − 60 I1 = 10nA I1 = 1nA 200µA I 1 = 100nA 400µA I2 I1 = 1µ A 600µA 800µA 1mA − 80 − 100 100µ A AVERAGE TOTAL ERROR AT +25_ C I1 = 1mA I1 = 100µA I1 = 10µ A I = 100µ A 1 I 1 = 10µA I 1 = 1µ A I1 = 1nA, 10nA, 100nA 800µA 1mA 100µ A 200µA 400µA I2 600µA 100 80 60 Total Error (mV) 40 20 0 − 20 − 40 − 60 − 80 − 100 100µ A AVERAGE TOTAL ERROR AT − 10_ C 1.4 LOG CONFORMITY vs TEMPERATURE 7.5 Decade 1.2 I1 = 1mA Linearity (%) I1 = 1nA 1.0 0.8 7 Decade 0.6 6 Decade 0.4 5 Decade 4 Decade I1 = 10nA I1 = 100µ A I1 = 10µ A I = 100nA 1 I1 = 1µ A 0.2 0 200µA 400µA I2 600µA 800µA 1mA − 10 0 10 20 30 40 50 60 70 80 90 Temperature (_ C) 0.09 4 DECADE LOG CONFORMITY vs IREF 0.40 0.35 5 DECADE LOG CONFORMITY vs I REF 0.08 Linearity (%) +90_ C Linearity (%) +90_ C 0.30 0.25 0.20 0.15 0.10 +25_ C +70_ C 0.05 − 10_ C, 0_ C, +25_ C 0 100pA 1nA 10nA 100nA 1µ A I REF (I1) 10µA 100µ A 1mA +70_ C +80_ C 0_ C 0.07 +80_ C − 10_ C 0.06 0.05 0.04 100pA 1nA 10nA 100nA 1µ A IREF (I1) 10µ A 100µ A 1mA 10mA 10mA 8 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 TYPICAL CHARACTERISTICS: VS = +5V (continued) All specifications at TA = +25°C, RVLOGOUT = 10kΩ, VCM = GND, unless otherwise noted. For ac measurements, small signal means up to approximately 10% of dc level. 0.45 6 DECADE LOG CONFORMITY vs IREF 1.6 1.5 8 DECADE LOG CONFORMITY (100pA to 3.5mA) 0.40 +90_ C Linearity (%) 0.35 +80_ C +70_ C Linearity (%) 1.4 1.3 1.2 1.1 0.25 − 10_ C, 0_ C, +25_ C 0.20 100pA 1nA 10nA 100nA 1µ A IREF (I1) 10µA 100µ A 1mA 10mA 1.0 0.9 100pA 1nA +90_ C 0.30 +80_ C 0_ C +70_ C − 10_ C +25_ C 10nA 100nA 1µA 10µ A 100µA 1mA 10mA Input Current (I1 or I 2) 20 10 Normalized VLOGOUT (%) 0 − 10 − 20 SMALL−SIGNAL VLOGOUT 10mA Normalized LOG Output (dB) 1µA 1mA 100nA 10nA 100µA SMALL−SIGNAL AC RESPONSE I1 (10% sine modulation) 0 −5 − 10 − 15 − 20 − 25 − 30 − 35 − 40 − 45 − 50 100 1k 10k 100k 1M 10M 100M 10nA 1nA 1 µA 1mA 10µ A 100µA 100nA − 30 − 40 10 100 1k 10k 100k 1M 10M 10µA 100M Frequency (Hz) Frequency (Hz) SMALL−SIGNAL AC RESPONSE I2 (10% sine modulation) 0 −5 Normalized LOG Output (dB) − 10 − 15 − 20 − 25 − 30 − 35 − 40 − 45 − 50 100 1k 10k 100k 1M 10M 100M Frequency (Hz) 1nA 10nA 100nA 1µ A 1mA 10µ A 100µA Gain (dB) 160 140 120 100 A3 GAIN AND PHASE vs FREQUENCY 225 180 60 40 20 0 − 20 − 40 100 Gain Phase 90 45 1k 10k 100k 1M 10M 0 40M Frequency (Hz) Phase (_ ) 80 135 9 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 TYPICAL CHARACTERISTICS: VS = +5V (continued) All specifications at TA = +25°C, RVLOGOUT = 10kΩ, VCM = GND, unless otherwise noted. A4 and A5 GAIN AND PHASE vs FREQUENCY 140 120 100 Gain (dB) 80 60 40 20 0 − 20 1 10 100 1k 10k 100k 1M 10M Frequency (Hz) 0 18M 45 Gain Phase 90 135 Phase (_ ) Normalized Output (dB) 180 3 0 −3 A4 and A5 NONINVERTING CLOSED−LOOP RESPONSE G=1 G = 10 −6 −9 −12 −15 1k 10k 100k 1M 10M 100M Frequency (Hz) 30 20 10 0 Gain (dB) − 10 − 20 − 30 − 40 − 50 − 60 − 70 − 80 1k A4 and A5 INVERTING CLOSED−LOOP RESPONSE 10 0 − 10 Gain (dB) A4 and A5 CAPACITIVE LOAD RESPONSE G = +1 G = − 10 G = −1 C = 100pF − 20 − 30 − 40 − 50 C < 10pF 10k 100k 1M 10M 60M 1k 10k 100k 1M 10M 50M Frequency (Hz) Frequency (Hz) 10 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 APPLICATIONS INFORMATION OVERVIEW The LOG114 is a precision logarithmic amplifier that is capable of measuring currents over a dynamic range of eight decades. It computes the logarithm, or log ratio, of an input current relative to a reference current according to equation (1). V LOGOUT + 0.375 log 10 I1 I2 Either I1 or I2 can be held constant to serve as the reference current, with the other input being used for the input signal. The value of the reference current is selected such that the output at VLOGOUT (pin 9) is zero when the reference current and input current are equal. An onchip 2.5V reference is provided for use in generating the reference current. Two additional amplifiers, A4 and A5, are included in the LOG114 for use in scaling, offsetting, filtering, threshold detection, or other functions. (1) The output at VLOGOUT can be digitized directly, or scaled for an ADC input using an uncommitted or external op amp. An offsetting voltage (VCom) can be connected to the Com pin to raise the voltage at VLOGOUT. When an offsetting voltage is used, the transfer function becomes: V LOGOUT + 0.375 log 10 I1 ) VCom I2 BASIC CONNECTIONS Figure 1 and Figure 2 show the LOG114 in typical dual and single-supply configurations, respectively. To reduce the influence of lead inductance of power-supply lines, it is recommended that each supply be bypassed with a 10µF tantalum capacitor in parallel with a 1000pF ceramic capacitor as shown in Figure 1 and Figure 2. Connecting these capacitors as close to the LOG114 V+ supply pin to ground as possible improves supply− related noise rejection. (2) R7 100kΩ R8 56.2kΩ R5 100kΩ 9 IREF 1µF 4 I1 5 VCM IN A1 Q1 VLOGOUT(1) 10 11 R6 66.5kΩ +IN4 −IN4 LOG114 R1 R2 A4 VO4(2) 12 Input Signal RREF 100pA to 10mA 2.5MΩ Q2 3 I2 A2 A3 R3 R4 +IN5 13 A5 VO5 15 16 VREF 2.5VREF VREF GND 1 V+ 8 1000pF 10µF + +5V −5V V− 6 1000pF 10µF + Com 7 −IN5 14 NOTE: (1) VLOGOUT = 0.375 × log(I1/I2) (2) VO4 = −0.249 × log(I1/I2) + 1.5V Figure 1. Dual Supply Configuration Example for Best Accuracy Over Eight Decades. 11 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 R5 100kΩ R7 100kΩ R6 66.5kΩ R8 316kΩ 9 VLOGOUT(2) 10 +IN4 11 − IN4 LOG114 REF3040 or REF3240 4.096V Reference I1 IµA 4 RREF 1.62MΩ 5 I1 VCM IN(1) A1 Q1 R1 R2 A4 VO4(3) 12 Input current from photodiode or current source Photodiode(4) Q2 I2 3 I2 A2 A3 +IN5 13 R3 R4 A5 VO5 15 +2.5V 16 VREF 2.5VREF VREF GND 1 V 8 1000pF +5V + V− Com 6 10µ F VCom = +2.5V 7 − IN5 1 NOTE: (1) (2) (3) (4) In single−supply configuration, VCM IN must be connected to ≥ 1V. VLOGOUT = 0.375 × log(I1/I2) + 2.5V. VO4 = − 0.249 × log(I 1/I2) + 1.5V. The cathode of the photodiode is returned to VREF resulting in zero bias across it. The cathode could be returned to a voltage more positive than VCM IN to create a reverse bias for reducing photodiode capacitance, which increases speed. Figure 2. Single-Supply Configuration Example for Measurement Over Eight Decades. 12 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 DESIGN EXAMPLE FOR DUAL-SUPPLY CONFIGURATION Given these conditions: 4. The A4 amplifier scales and offsets the VLOGOUT signal for use by the ADC using the equation: V O4 + *SFACTOR VLOGOUT ) VOFFSET (5) D V+ = 5V and V− = −5V D 100pA ≤ Input signal D The stage following the LOG114 is an analog-todigital converter (ADC) with +5V supply and +2.5V reference voltage, so VO4 swings from +0.5V to +2.5V. 1. Due to LOG114 symmetry, you can choose either I1 or I2 as the signal input pin. Choosing I1 as the reference makes the resistor network around A4 simpler. (Note: Current must flow into pins 3 (I1) and pin 4 (I2).) 2. Select the magnitude of the reference current. Since the signal (I2) spans eight decades, set I1 to 1µA − four decades above the minimum I2 value. (Note that it does not have to be placed in the middle. If I2 spanned seven decades, I1 could be set three decades above the minimum and four decades below the maximum I2 value.) This configuration results in more swing amplitude in the negative direction, which provides more sensitivity (∆VO4 per ∆I2) when the current signal decreases. The A4 amplifier is specified with a rated output swing capability from (V−) +0.5V to (V+) − 0.5V. Therefore, choose the final A4 output: 0V ≤ VO4 ≤ +2.5V This output results in a 2.5V range for the 3V VLOGOUT range, or 2.5V/3V scaling factor. 5. When I2 = 10mA, VLOGOUT = −1.5V. Using the equation in step 5: V O4 + *SFACTOR Therefore, VOFFSET = 0V The A4 amplifier configuration for VO4 = −2.5/3(VLOGOUT) + 0V is seen in Figure 3. The overall transer function is: V O4 + *0.249 log I1 ) 1.5V I2 VLOGOUT ) VOFFSET (6) 0V + *2.5V 3V(*1.5V) ) VOFFSET (7) 3. Using Equation (1) calculate the expected range of log outputs at VLOGOUT: For I2 + 10mA : VLOGOUT + 0.375 + 0.375 log log I1 I2 VLOGOUT R5 100kΩ Internal A4 Output Amplifier R6 82.5kΩ +5V VO4 = − 2/3 (VLOGOUT) A4 I2 100pA 10mA 1mA + * 1.5V 10mA I1 I2 + ) 1.5V For I2 + 100pA : VLOGOUT + 0.375 + 0.375 log log VREF +2.5V − 5V R7 100kΩ R8 37.4kΩ (3) Therefore, the expected voltage range at the output of amplifier A3 is: * 1.5V v V LOGOUT v ) 1.5V (4) 1mA 100pA VO4 0V +2.5V A4 amplifier used to scale and offset VLOGOUT for 0V to 2.5V output. Figure 3. Operational Amplifier Configuration for Scaling the Output Going to ADC Stage. 13 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 DESIGN EXAMPLE FOR SINGLE-SUPPLY CONFIGURATION Given these conditions: D D D D V+ = 5V V− = GND 100pA ≤ Input signal ≤ 10mA The stage following the LOG114 is an analog to digital converter (ADC) with +5V supply and +2.5V reference voltage This result would be fine in a dual−supply system (V+ = +5V, V− = −5V) where the output can swing below ground, but does not work in a single supply +5V system. Therefore, an offset voltage must be added to the system. 4. Select an offset voltage, VCom to use for centering the output between (V−) + 0.6V and (V+) − 0.6V, which is the full-scale output capability of the A3 amplifier. Choosing VCom = 2.5V, and recalculating the expected voltage output range for VLOGOUT using Equation (2), results in: ) 1V v V LOGOUT v ) 4V (10) 1. Choose either I1 or I2 as the signal input pin. For this example, I2 is used. Choosing I1 as the reference current makes the resistor network around A4 simpler. (Note: Current only flows into the I1 and I2 pins.) 2. Select the magnitude of the reference current. Since the signal (I2) spans eight decades, set I1 to 1µA − four decades above the minimum I2 value, and four decades below the maximum I2 value. (Note that it does not have to be placed in the middle. If I2 spanned seven decades, I1 could be set three decades above the minimum and four decades below the maximum I2 value.) This configuration results in more swing amplitude in the negative direction, which provides more sensitivity (∆VO4 per ∆I2) when the current signal decreases. 5. The A4 amplifier scales and offsets the VLOGOUT signal for use by the ADC using the equation: V O4 + *SFACTOR VLOGOUT ) VOFFSET (11) The A4 amplifier is specified with a rated output swing capability from (V−) +0.5V to (V+) − 0.5V. Therefore, choose the final A4 output: +0.5V ≤ VO4 ≤ +2.5V This output results in a 2V range for the 3V VLOGOUT range, or 2V/3V scaling factor. 6. When I2 = 10mA, VLOGOUT = +1V, and VO4 = 2.5V. Using the equation in step 5: V O4 + *SFACTOR Therefore, VOFFSET = 3.16V VLOGOUT ) VOFFSET (12) 2.5V + *2V 3V(1V) ) VOFFSET 3. Using Equation (1) calculate the expected range of log outputs at VLOGOUT: For I2 + 10mA : VLOGOUT + 0.375 + 0.375 log log I1 I2 The A4 amplifier configuration for VO4 = −2/3(VLOGOUT) + 3.16 is seen in Figure 4a. The overall transer function is: V O4 + *0.249 log I1 ) 1.5V I2 1mA + * 1.5V 10mA I1 log I2 + ) 1.5V For I2 + 100pA : VLOGOUT + 0.375 + 0.375 log (8) Therefore, the expected voltage range at the output of amplifier A3 is: * 1.5V v V LOGOUT v ) 1.5V (9) 1mA 100pA (13) A similar process can be used for configuring an external rail-to-rail output op amp, such as the OPA335. Because the OPA335 op amp can swing down to 0V using a pulldown resistor, RP, connected to −5V (for details, refer to the OPA335 data sheet, available for download at www.ti.com), the scaling factor is 2.5V/3V and the corresponding VOFFSET is 3.3V. This circuit configuration is shown in Figure 4b. 14 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 Internal A4 Output Amplifier R5 100kΩ VLOGOUT R6 66.5kΩ VLOGOUT R5 100kΩ External Output Amplifier R6 82.5kΩ +5V A4 VO4 = −2/3 (VLOGOUT) + 3.16 I2 10mA 100pA VREF +2.5V 2.5V 0.5V OPA335 VOUT = −2.5/3 (VLOGOUT) + 3.3 RP(1) −5V I2 100pA 10mA VREF +2.5V R7 100kΩ R8 316kΩ VO4 R7 100kΩ R8 267kΩ VOUT 0.5V 2.5V a) A4 amplifier used to scale and offset VLOGOUT for 0.5V to 2.5V output. b) OPA335 amplifier used to scale and offset VLOGOUT for 0V to 2.5V output. NOTE: (1) See OPA335 data sheet for use of RP connected to −5V to achieve 0V output. Figure 4. Operational Amplifier Configuration for Scaling and Offsetting the Output Going to ADC Stage. ADVANTAGES OF DUAL−SUPPLY OPERATION The LOG114 performs very well on a single +5V supply by level-shifting pin 7 (Com) to half-supply and raising the common-mode voltage (pin 5, VCM IN) of the input amplifiers. This level−shift places the input amplifiers in the linear operating range. However, there are also some advantages to operating the LOG114 on dual ±5V supplies. These advantages include: 1) eliminating the need for the +4.096V precision reference; 2) eliminating a small additional source of error arising from the noise and temperature drift of the level−shifting voltage; and 3) allowing increased magnitude of a reverse bias voltage on the photodiode. COM (PIN 7) VOLTAGE RANGE The voltage on the Com pin is used to bias the differential amplifier, A3, within its linear range. This voltage can provide an asymmetrical offset of the VLOGOUT voltage. VCM IN (Pin 5) The VCM IN pin is used to bias the A1 and A2 amplifier into its common-mode input voltage range, (V−) + 1.5V to (V+) − 1.5V. INPUT CURRENT RANGE To maintain specified accuracy, the input current range of the LOG114 should be limited from 100pA to 3.5mA. Input currents outside of this range may compromise the LOG114 performance. Input currents larger than 3.5mA result in increased nonlinearity. An absolute maximum input current rating of 10mA is included to prevent excessive power dissipation that may damage the input transistor. 15 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 SETTING THE REFERENCE CURRENT When the LOG114 is used to compute logarithms, either I1 or I2 can be held constant to become the reference current to which the other is compared. If IREF is set to the lowest current in the span of the signal current (as shown in the front page figure), VLOGOUT will range from: V LOGOUT + 0.375 log 10 I 1 min ^ 0V I 1 max signal ply system, and a maximum value of 7mV in a +5V supply system. Resistor temperature stability and noise contributions should also be considered. VREF = 100mV R1 R3 1 R2 R3 >> R2 IREF (14) +5V VOS − + A1 to some maximum value: V LOGOUT + 0.375 log 10 I 1 min I 1 max signal (15) While convenient, this approach does not usually result in best performance, because I1 min accuracy is difficult to achieve, particularly if it is < 20nA. A better way to achieve higher accuracy is to choose IREF to be in the center of the full signal range. For example, for a signal range of 1nA to 1mA, it is better to use this approach: I REF + I SIGNAL min 1mA 1nA + 1mA dc (16) Figure 5. T-Network for Reference Current. VREF may be an external precision voltage reference, or the on-chip 2.5V voltage reference of the LOG114. IREF can be derived from an external current source, such as that shown in Figure 6. than it is to set IREF = 1nA. It is much easier and more precise (that is, dc accuracy, temperature stability, and lower noise) to establish a 1mA dc current level than a 1nA level for the reference current. 2N2905 IREF The reference current may be derived from a voltage source with one or more resistors. When a single resistor is used, the value may be large depending on IREF. If IREF is 10nA and +2.5V is used: RREF = 2.5V/10nA = 250MΩ A voltage divider may be used to reduce the value of the resistor, as shown in Figure 5. When using this method, one must consider the possible errors caused by the amplifier input offset voltage. The input offset voltage of amplifier A1 has a maximum value of 4mV in a ±5V sup- RREF +15V 6V IN834 2N2905 3.6kΩ − 15V 6V RREF IREF = Figure 6. Temperature-Compensated Current Source. 16 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 NEGATIVE INPUT CURRENTS The LOG114 functions only with positive input currents (conventional current flows into input current pins). In QA situations where negative input currents are needed, the example circuits in Figure 7, Figure 8, and Figure 9 may be used. I IN QB National LM394 D1 D2 OPA703 IOUT Figure 7. Current Inverter/Current Source. +5V +3.3V 1/2 OPA2335 1.5kΩ 1kΩ +5V 10nA to 1mA (+3.3V Back Bias) 1/2 OPA2335 BSH203 10nA to 1mA Pin 3 or Pin 4 Photodiode LOG114 Figure 8. Precision Current Inverter/Current Source. 1kΩ 100kΩ +5V 10nA to 1mA +3.3V Back Bias 100kΩ 1/2 OPA2335 +5V 1.5kΩ +3.3V Photodiode 1/2 OPA2335 1.5kΩ 100kΩ 100kΩ 10nA to 1mA Pin 3 or Pin 4 LOG114 Figure 9. Precision Current Inverter/Current Source. 17 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 VOLTAGE INPUTS The LOG114 provides the best performance with current inputs. Voltage inputs may be handled directly by using a low-impedance voltage source with series resistors, but the dynamic input range is limited to approximately three decades of input voltage. This limitation exists because of the magnitude of the required input voltage and size of the corresponding series resistor. For 10nA of input current, a 10V voltage source and a 1GΩ resistor would be required. Voltage and current noise from these sources must be considered and can limit the usefulness of this technique. APPLICATION CIRCUITS LOG RATIO One of the more common uses of log ratio amplifiers is to measure absorbance. See Figure 10 for a typical application. Absorbance of the sample is A = log λ1′/λ1. If D1 and D2 are matched, A ∝ (0.375V) log(I1/I2). R5 R6 9 Q1 I1 V CM IN A1 V LOGOUT(1) 10 +IN 4 10 − IN 4 LO G114 4 R1 R2 A4 V O4(2) 12 I1 5 Sample λ1 λ1 λ 1′ D1 Q2 I2 R3 A3 +IN 5 13 I2 Light Source D2 3 R4 A2 A5 V O5 15 16 V REF 2.5V REF V REF GND 1 V+ 8 +5V NO TES: (1) V LOGOUT = 0.375 × log(I1/I 2). (2) V O4 = 0.375 × K × log(I1/I 2) K = 1 + R 6/R 5. V− 6 Com 7 − IN 5 14 Figure 10. Using the LOG114 to Measure Absorbance. 18 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 DATA COMPRESSION In many applications, the compressive effects of the logarithmic transfer function are useful. For example, a LOG114 preceding a 12-bit ADC can produce the dynamic range equivalent to a 20-bit converter. (Suggested products: ADS7818, ADS7834). +3.3V OPERATION For systems with only a +3.3V power supply, the TPS60241 zero-ripple switched cap buck-boost 2.7V to 5.5V input to 5V output converter may be used to generate a +5V supply for the LOG114, as shown in Figure 11. Likewise, the TPS6040 negative charge pump may be connected to the +5V output of the TPS60241 to generate a −5V supply to create a ±5V supply for the LOG114, as Figure 12 illustrates. Figure 11. Creating a +5V Supply from a +3.3V Supply. +3.3V C1 1µF I1 VLOGOUT LOG114 I2 V+ V− TPS60241 VIN C1+ C1− GND VOUT C2+ C2− EN +5V C1 1µ F C2 1µF C0 1µ F I1 VLOGOUT LOG114 I2 V+ +5V V− − 5V CFLY 1µF TPS60241 +3.3V C1 1µ F C1 1µ F +5V VIN C1+ C1− GND VOUT C2+ C2− EN C2 1µ F CO 1µ F CI 1 µF IN TPS60400 GND OUT CFLY− CFLY+ − 5V CO 1µ F Figure 12. Creating a ±5V Supply from a +3.3V Supply. 19 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 ERBIUM-DOPED FIBER OPTIC AMPLIFIER (EDFA) The LOG114 was designed for optical networking systems. Figure 13 shows a block diagram of the LOG114 in a typical EDFA application. This application uses two log amps to measure the optical input and output power of the amplifier. A difference amplifier subtracts the log output signals of both log amps and applies an error voltage to the proportional-integral-derivative (PID) controller. The controller output adjusts a voltage-controlled current source (VCCS), which then drives the power op amp and pump laser. The desired optical gain is achieved when the error voltage at the PID is zero. The log ratio function is the optical power gain of the EDFA. This circuitry forms an automatic power level control loop. An alternate design of the system shown in Figure 13 is possible because the LOG114 inherently takes the log ratio. Therefore, one log amp can be eliminated by connecting one of the photodiodes to the LOG114 I1 input, and the other to the I2 input. The differential amplifier would then be eliminated. The LOG114 is uniquely suited for most EDFA applications because of its fast rise and fall times (typically less than 1µs for a 100:1 current input step). It also measures a very wide dynamic range of up to eight decades. Tap 1% Fiber Tap 1% Pump Laser OPA569 Power Op Amp IL VCCS PID VERROR I1 LOG114 Diff VOUT1 VOUT2 LOG114 I2 IREF1 DAC RREF1 REF IREF2 RREF2 Figure 13. Erbium-Doped Fiber Optic Amplifier (EDFA) block diagram. 20 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 INSIDE THE LOG114 The LOG114 uses two matched logarithmic amplifiers (A1 and A2 with logging diodes in the feedback loops) to generate the outputs log (I1) and log (I2), respectively. The gain of 6.25 differential amplifier (A3) subtracts the output of A2 from the output of A1, resulting in [log (I1) − log (I2)], or log (I1/I2). The symmetrical design of the A1 and A2 logarithmic amps allows I1 and I2 to be used interchangeably, and provides good bandwidth and phase characteristics with frequency. DEFINITION OF TERMS Transfer Function The ideal transfer function of the LOG114 is: V LOGOUT + 0.375 I log 1 12 Log Conformity For the LOG114, log conformity is calculated in the same way as linearity and is plotted as I1/I2 on a semilog scale. In many applications, log conformity is the most important specification. This condition is true because bias current errors are negligible (5pA for the LOG114), and the scale factor and offset errors may be trimmed to zero or removed by system calibration. These factors leave log conformity as the major source of error. Log conformity is defined as the peak deviation from the best fit straight line of the VLOGOUT versus log (I1/I2) curve. Log conformity is then expressed as a percent of ideal full−scale output. Thus, the nonlinearity error expressed in volts over m decades is: VLOGOUT (NONLIN) = 0.375V/decade • 2Nm where N is the log conformity error, in percent. INDIVIDUAL ERROR COMPONENTS The ideal transfer function with current input is: V LOGOUT IDEAL (17) This transfer function can be seen graphically in the typical characteristic curve, VLOGOUT vs IREF. When a pedestal, or offset, voltage (VCom) is connected to the Com pin, an additional offset term is introduced into the equation: V LOGOUT + 0.375 log I1 ) V Com 12 + 0.375 log (18) (19) The actual transfer function with the major components of error is: 0.375(1 " DK) where: ∆K = gain error (0.4%, typ, as specified in the Electrical Characteristics table) IB1 = bias current of A1 (5pA, typ) IB2 = bias current of A2 (5pA, typ) m = number of decades over which the log conformity error is specified N = log conformity error (0.1%, typ for m = 5 decades; 0.9% typ for m = 7.5 decades) VOSO = output offset voltage (11mV, typ for ±5V supplies; 14mV, typ for +5V supplies) To determine the typical error resulting from these error components, first compute the ideal output. Then calculate the output again, this time including the individual error components. Then determine the error in percent using Equation (21): %error + V LOGOUT IDEAL*V LOGOUT V LOGOUTIDEAL TYP I1 12 Accuracy Accuracy considerations for a log ratio amplifier are somewhat more complicated than for other amplifiers. This complexity exists because the transfer function is nonlinear and has two inputs, each of which can vary over a wide dynamic range. The accuracy for any combination of inputs is determined from the total error specification. Total Error The total error is the deviation of the actual output from the ideal output. Thus, VLOGOUT(ACTUAL) = VLOGOUT(IDEAL) ± Total Error It represents the sum of all the individual components of error normally associated with the log amp when operating in the current input mode. The worst-case error for any given ratio of I1/I2 is the largest of the two errors when I1 and I2 are considered separately. Temperature can also affect total error. Errors RTO and RTI As with any transfer function, errors generated by the function may be Referred-to-Output (RTO) or Referredto-Input (RTI). In this respect, log amps have a unique property: given some error voltage at the log amp output, that error corresponds to a constant percent of the input, regardless of the actual input level. log I1 " 2Nm " V OSO I2 (20) 100% (21) 21 LOG114 www.ti.com SBOS301A − MAY 2004 − REVISED MARCH 2007 For example, in a system configured for measurement of five decades, with I1 = 1mA, and I2 = 10µA: V LOGOUT VLOGOUT IDEAL + 0.375 *3 log 10*5 + 0.75V 10 (22) TYP + 0.375(1 " 0.004) log 10−3*5 10−5*5 10−12 10−12 The QFN package can be easily mounted using standard printed circuit board (PCB) assembly techniques. See Application Note QFN/SON PCB Attachment (SLUA271) and Application Report Quad Flatpack No− Lead Logic Packages (SCBA017), both available for download at www.ti.com. The exposed leadframe die pad on the bottom of the package should be connected to V−. QFN LAYOUT GUIDELINES The exposed leadframe die pad on the QFN package should be soldered to a thermal pad on the PCB. A mechanical drawing showing an example layout is attached at the end of this data sheet. Refinements to this layout may be necessary based on assembly process requirements. Mechanical drawings located at the end of this data sheet list the physical dimensions for the package and pad. The five holes in the landing pattern are optional, and are intended for use with thermal vias that connect the leadframe die pad to the heatsink area on the PCB. Soldering the exposed pad significantly improves board-level reliability during temperature cycling, key push, package shear, and similar board-level tests. Even with applications that have low-power dissipation, the exposed pad must be soldered to the PCB to provide structural integrity and long-term reliability. (23) Using the positive error components (+∆K, +2Nm, and +VOSO) to calculate the maximum typical output: V LOGOUT TYP " 2(0.001)(5) " 0.011 + 0.774V (24) Therefore, the error in percent is: %error + |0.75*0.774| 0.75 100% + 3.2% (25) QFN PACKAGE The LOG114 comes in a QFN-16 package. This leadless package has lead contacts on all four sides of the bottom of the package, thereby maximizing board space. An exposed leadframe die pad on the bottom of the package enhances thermal and electrical characteristics. QFN packages are physically small, have a smaller routing area, improved thermal performance, and improved electrical parasitics. Additionally, the absence of external leads eliminates bent-lead issues. 22 PACKAGE OPTION ADDENDUM www.ti.com 7-May-2007 PACKAGING INFORMATION Orderable Device LOG114AIRGVR LOG114AIRGVRG4 LOG114AIRGVT LOG114AIRGVTG4 (1) Status (1) ACTIVE ACTIVE ACTIVE ACTIVE Package Type QFN QFN QFN QFN Package Drawing RGV RGV RGV RGV Pins Package Eco Plan (2) Qty 16 16 16 16 2500 Green (RoHS & no Sb/Br) 2500 Green (RoHS & no Sb/Br) 250 250 Green (RoHS & no Sb/Br) Green (RoHS & no Sb/Br) Lead/Ball Finish CU NIPDAU CU NIPDAU CU NIPDAU CU NIPDAU MSL Peak Temp (3) Level-2-260C-1 YEAR Level-2-260C-1 YEAR Level-2-260C-1 YEAR Level-2-260C-1 YEAR The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis. Addendum-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 17-May-2007 TAPE AND REEL INFORMATION Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 17-May-2007 Device Package Pins Site Reel Diameter (mm) 330 Reel Width (mm) 12 A0 (mm) B0 (mm) K0 (mm) P1 (mm) 12 W Pin1 (mm) Quadrant 12 PKGORN T2TR-MS P PKGORN T2TR-MS P LOG114AIRGVR RGV 16 MLA 4.3 4.3 1.5 LOG114AIRGVT RGV 16 MLA 180 12 4.3 4.3 1.5 12 12 TAPE AND REEL BOX INFORMATION Device LOG114AIRGVR LOG114AIRGVT Package RGV RGV Pins 16 16 Site MLA MLA Length (mm) 346.0 190.0 Width (mm) 346.0 212.7 Height (mm) 29.0 31.75 Pack Materials-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 17-May-2007 Pack Materials-Page 3 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. 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