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| Final Electrical Specifications LTC6910-1 Digitally Controlled Programmable Gain Amplifier in SOT-23 August 2002 FEATURES s s s s s s s s s s DESCRIPTIO 3-Bit Digital Gain Control (0, 1, 2, 5, 10, 20, 50 and 100V/V) 8-Pin TSOT-23 Package Rail-to-Rail Input Range Rail-to-Rail Output Swing Single or Dual Supply: 2.7V to 10V Total 10MHz Gain Bandwidth Product 9nV/Hz Input Noise at Gain of 100 119dB Total System Dynamic Range Input Offset Voltage: 3mV (Gain-of-1) Input Offset Voltage: 2mV (Gain-of-10) The LTC(R)6910-1 is a low noise digitally programmable gain amplifier (PGA) that is easy to use and occupies very little PC board space. The gain is adjustable using a 3-bit digital input to select gains of 0, 1, 2, 5, 10, 20, 50 and 100V/V. The LTC6910-1 is an inverting amplifier with a rail-to-rail output. When operated with unity gain, the LTC6910-1 will also process rail-to-rail input signals. A half-supply reference generated internally at the AGND pin supports single power supply applications. Operating from single or split supplies from 2.7V to 10.5V, the LTC6910-1 is offered in an 8-lead TSOT-23 package. APPLICATIO S s s s s Data Acquisition Systems Dynamic Gain Changing Automatic Ranging Circuits Automatic Gain Control , LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATIO Single Supply Programmable Amplifier V+ 2.7V TO 10V 0.1F GAIN G2 G1 G0 000 0 001 -1 010 -2 011 -5 -10 1 0 0 -20 1 0 1 -50 1 1 0 -100 1 1 1 50 Frequency Response 111 (GAIN OF 100) 40 110 (GAIN OF 50) 8 GAIN (dB) 4 VIN 3 LTC6910-1 5 7 6 1 2 AGND 1F OR LARGER 6910 TA01 30 101 (GAIN OF 20) 100 (GAIN OF 10) VOUT = GAIN * VIN 20 011 (GAIN OF 5) 10 010 (GAIN OF 2) G2 G1 G0 PIN 2 (AGND) PROVIDES BUILT-IN HALF-SUPPLY REFERENCE WITH INTERNAL RESISTANCE OF 5k. AGND CAN ALSO BE DRIVEN BY A SYSTEM ANALOG GROUND REFERENCE NEAR HALF SUPPLY 001 (GAIN OF 1) 0 100 1k 10k 100k FREQUENCY (Hz) 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. U 1M 6010 TA02 U U 69101i 1 LTC6910-1 ABSOLUTE (Note 1) AXI U RATI GS PACKAGE/ORDER I FOR ATIO TOP VIEW OUT 1 AGND 2 IN 3 V- 4 8 V+ 7 G2 6 G1 5 G0 Total Supply Voltage (V+ to V-) ............................. 11V Operating Temperature Range (Note 2) LTC6910-1C ....................................... - 40C to 85C LTC6910-1I ........................................ - 40C to 85C Specified Temperature Range (Note 3) LTC6910-1C ....................................... - 40C to 85C LTC6910-1I ........................................ - 40C to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C ORDER PART NUMBER LTC6910-1CTS8 LTC6910-1ITS8 TS8 PART MARKING* LTB5 TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 TJMAX = 150C, JA = 230C/W *The temperature grades are identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges or other gain ranges. GAI SETTI GS A D PROPERTIES Table 1 NOMINAL VOLTAGE GAIN G2 0 0 0 0 1 1 1 1 G1 0 0 1 1 0 0 1 1 G0 0 1 0 1 0 1 0 1 Volts/Volt 0 -1 -2 -5 -10 -20 -50 -100 (dB) -120 0 6 14 20 26 34 40 MAXIMUM INPUT SIGNAL (FOR UNCLIPPED OUTPUT SIGNAL) (VP-P) Dual 5V Supply 10 10 5 2 1 0.5 0.2 0.1 Single 5V Supply 5 5 2.5 1 0.5 0.25 0.1 0.05 Single 3V Supply 3 3 1.5 0.6 0.3 0.15 0.06 0.03 NOMINAL INPUT IMPEDANCE (k) (Open) 10 5 2 1 1 1 1 ELECTRICAL CHARACTERISTICS PARAMETER Voltage Gain (Note 4) The q denotes the specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25C. VS = 2.5V, AGND to 0V, Gain = 1 (Digital Inputs 001), RL = 10k, unless otherwise noted. CONDITIONS VS = 1.35V, Gain = 1, RL = 10k VS = 1.35V, Gain = 1, RL = 500 VS = 1.35V, Gain = 2, RL = 10k VS = 1.35V, Gain = 5, RL = 10k VS = 1.35V, Gain = 10, RL = 10k VS = 1.35V, Gain = 10, RL = 500 VS = 1.35V, Gain = 20, RL = 10k VS = 1.35V, Gain = 50, RL = 10k VS = 1.35V, Gain = 100, RL = 10k VS = 1.35V, Gain = 100, RL = 500 q q q q q q q q q q MIN - 0.05 - 0.1 5.96 13.85 19.7 19.6 25.7 33.5 39 37.4 TYP 0 - 0.02 6.02 13.95 19.9 19.85 25.9 33.8 39.6 39 MAX 0.07 0.06 6.08 14.05 20.1 20.1 26.1 34.1 40.2 40.1 UNITS dB dB dB dB dB dB dB dB dB dB 69101i 2 U W U U WW U W U U LTC6910-1 ELECTRICAL CHARACTERISTICS PARAMETER Voltage Gain (Note 4) The q denotes the specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25C. VS = 2.5V, AGND to 0V, Gain = 1 (Digital Inputs 001), RL = 10k, unless otherwise noted. CONDITIONS VS = 2.5V, Gain = 1, RL = 10k VS = 2.5V, Gain = 1, RL = 500 VS = 2.5V, Gain = 2, RL = 10k VS = 2.5V, Gain = 5, RL = 10k VS = 2.5V, Gain = 10, RL = 10k VS = 2.5V, Gain = 10, RL = 500 VS = 2.5V, Gain = 20, RL = 10k VS = 2.5V, Gain = 50, RL = 10k VS = 2.5V, Gain = 100, RL = 10k VS = 2.5V, Gain = 100, RL = 500 VS = 5V, Gain = 1, RL = 10k VS = 5V, Gain = 1, RL = 500 VS = 5V, Gain = 2, RL = 10k VS = 5V, Gain = 5, RL = 10k VS = 5V, Gain = 10, RL = 10k VS = 5V, Gain = 10, RL = 500 VS = 5V, Gain = 20, RL = 10k VS = 5V, Gain = 50, RL = 10k VS = 5V, Gain = 100, RL = 10k VS = 5V, Gain = 100, RL = 500 q q q q q q q q q q q q q q q q q q q q q q MIN - 0.05 - 0.1 5.96 13.8 19.8 19.6 25.8 33.5 39.3 38 - 0.05 - 0.1 5.96 13.80 19.8 19.7 25.8 33.7 39.4 38.8 2.7 TYP 0 - 0.01 6.02 13.95 19.9 19.85 25.9 33.8 39.7 39.2 0 - 0.01 6.02 13.95 19.9 19.9 25.95 33.85 39.8 39.6 - 122 MAX 0.07 0.08 6.08 14.1 20.1 20.1 26.1 34.1 40.1 40.1 0.07 0.08 6.08 14.1 20.1 20.1 26.1 34 40.2 40.1 10.5 UNITS dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB V mA mA mA mA mV mV mV mV mV mV mV mV mV mV mV mV mA mA Signal Attenuation at Gain = 0 Setting Total Supply Voltage Supply Current Gain = 0 (Digital Inputs 000), f = 20kHz VS = 1.35V, VIN = 0V VS = 2.5V, VIN = 0V VS = 5V, VIN = 0V, Pins 5, 6, 7 = - 5V or 5V VS = 5V, VIN = 0V, Pins 5, 6, 7 = 0V VS = 1.35V, RL = 10k to 0V VS = 1.35V, RL = 500 to 0V VS = 2.5V, RL = 10k to 0V VS = 2.5V, RL = 500 to 0V VS = 5V, RL = 10k to 0V VS = 5V, RL = 500 to 0V q q q q q q q q q q q q q q q q 2 2.4 3 3.5 12 50 20 90 30 80 10 50 15 80 20 180 27 35 3 3.5 4.5 4.9 30 100 40 160 50 250 20 80 30 150 40 250 Output Voltage Swing LOW (Note 5) Output Voltage Swing HIGH (Note 5) VS = 1.35V, RL = 10k to 0V VS = 1.35V, RL = 500 to 0V VS = 2.5V, RL = 10k to 0V VS = 2.5V, RL = 500 to 0V VS = 5V, RL = 10k to 0V VS = 5V, RL = 500 to 0V Output Short-Circuit Current (Note 6) AGND Open-Circuit Voltage AGND (Common Mode) Input Voltage Range VS = 1.35V VS = 5V VS = Single 5V Supply VS = Single 2.7V VS = Single 5V VS = Single 5V q q q q 2.45 0.55 0.7 - 4.3 2.5 2.55 1.6 3.65 3.5 V V V V 69101i 3 LTC6910-1 ELECTRICAL CHARACTERISTICS PARAMETER AGND Rejection (i.e., Common Mode Rejection or CMRR) Power Supply Rejection Ratio (PSRR) Offset Voltage Magnitude (Referred to Input) DC Input Resistance (Note 7) The q denotes the specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25C. VS = 2.5V, AGND to 0V, Gain = 1 (Digital Inputs 001), RL = 10k, unless otherwise noted. CONDITIONS VS = 1.35V, VAGND = - 0.25 to 0.25 VS = 5V, VAGND = - 2.5 to 2.5 VS = 1.35V to 5V Gain = 1 Gain = 10 DC VIN = 0V Gain = 0 Gain = 1 Gain = 2 Gain = 5 Gain = 10, 20, 50, 100 Gain = 0 Gain = 1 Gain = 2 Gain = 5 Gain = 10 Gain = 20 Gain = 50 Gain = 100 Gain = 100, fIN = 200kHz q q q q q q MIN 55 55 60 TYP 80 75 80 3 2 >100 10 5 2 1 0.4 0.7 1 1.9 3.4 6.4 15 30 MAX UNITS dB dB dB 15 10 mV mV M k k k k q q q q DC Small-Signal Output Resistance Gain-Bandwidth Product Slew Rate Wideband Noise (Referred to Input) 8 6 11 11 12 16 5.8 11 7.6 5.3 4.5 4.2 4 3.9 25 17 12 10 9.4 8.9 8.7 -90 0.003 -77 0.014 14 16 MHz MHz V/s V/s VRMS VRMS VRMS VRMS VRMS VRMS VRMS VRMS nV/Hz nV/Hz nV/Hz nV/Hz nV/Hz nV/Hz nV/Hz dB % dB % VS = 2.5V, VOUT = 1.4V VS = 5V, VOUT = 1.4V f = 1kHz to 200kHz Gain = 0 Output Noise Gain = 1 Gain = 2 Gain = 5 Gain = 10 Gain = 20 Gain = 50 Gain = 100 f = 50kHz Gain = 1 Gain = 2 Gain = 5 Gain = 10 Gain = 20 Gain = 50 Gain = 100 Gain = 10, fIN = 10kHz, VOUT = 1VRMS Gain = 10, fIN = 100kHz, VOUT = 1VRMS Voltage Noise Density (Referred to Input) Total Harmonic Distortion 69101i 4 LTC6910-1 ELECTRICAL CHARACTERISTICS PARAMETER Digital Input "High" Voltage The q denotes the specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25C. VS = 2.5V, AGND to 0V, Gain = 1 (Digital Inputs 001), RL = 10k, unless otherwise noted. CONDITIONS VS = Single 2.7V VS = Single 5V VS = Single 5V VS = Single 2.7V VS = Single 5V VS = Single 5V MIN 2.43 4.5 4.5 0.27 0.5 0.5 Note 4: Gain is measured with a DC large-signal test using an output excursion between approximately - 40% and 40% of supply voltage. Note 5: Output voltage swings are measured as differences between the output and the respective supply rail. Note 6: Extended operation with output shorted may cause junction temperature to exceed the 150C limit and is not recommended. Note 7: Input resistance can vary by approximately 30%. TYP MAX UNITS V V V V V V Digital Input "Low" Voltage Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: The LTC6910-1C and LTC6910-1I are guaranteed functional over the operating temperature range of - 40C to 85C. Note 3: The LTC6910-1C is guaranteed to meet specified performance from 0C to 70C. The LTC6910-1C is designed, characterized and expected to meet specified performance from - 40C to 85C but is not tested or QA sampled at these temperatures. LTC6910-1I is guaranteed to meet specified performance from - 40C to 85C. PI FU CTIO S OUT (Pin 1): Analog Output. This is the output of an internal operational amplifier and swings within 30mV of the power supply rails (V+ and V-). The internal op amp remains active at all times, including the zero gain setting (digital input 000). As with other amplifier circuits, loading the output as lightly as possible will minimize signal distortion and gain error. The Electrical Characteristics table shows performance at output currents up to 10mA. Currents above 10mA are possible but current-limiting circuitry will begin to affect amplifier performance at approximately 20mA. Long-term operation above 20mA output is not recommended. Do not exceed maximum junction temperature of 150C. The output will drive capacitive loads up to 50pF. Capacitances higher than 50pF should be isolated by a series resistor to preserve AC stability. AGND (Pin 2): Analog Ground. The AGND pin is at the midpoint of an internal resistive voltage divider, developing a potential halfway between the V+ and V- pins, with an equivalent series resistance to the pin of nominally 5k (Figure 3). AGND is also the noninverting input of the internal op amp, which makes it the ground reference voltage for the IN and OUT pins. Because of this, very "clean" grounding is important, including an analog ground plane surrounding the package. For dual supply operation, this ground plane should be at zero volts and the AGND pin should connect directly to the ground plane (Figure 1). For single supply operation, in contrast, the V- pin typically connects to system signal ground. The ground plane should then tie to V- and the AGND pin should be ACbypassed to the ground plane (Figure 2) by at least a 1F high quality capacitor. In noise-sensitive single-supply applications, it is important to AC-bypass the AGND pin. Otherwise wideband noise will enter the signal path from the internal voltagedivider resistors that set the DC voltage on AGND in singlesupply applications. This noise can reduce SNR by 3dB at high gain settings. The resistors present a Thevenin equivalent of approximately 5k to the AGND pin. An external capacitor from AGND to the ground plane, whose impedance is well below 5k at frequencies of interest, will suppress this noise. A 1F high quality capacitor is effective for frequencies down to 1kHz. Larger capacitors extend this suppression to proportionately lower frequencies. This issue does not arise in dual supply applications because AGND goes directly to ground. 69101i U U U 5 LTC6910-1 PI FU CTIO S V+ 0.1F V+ 0.1F ANALOG GROUND PLANE SINGLE-POINT SYSTEM GROUND Figure 1. Dual Supply Ground Plane Connection MOS-INPUT OP AMP V+ 8 V+ 10k 2 AGND Figure 3. Block Diagram 69101i 6 + - IN (Pin 3): Analog Input. The input signal to the amplifier in the LTC6910-1 is the voltage difference between the IN and AGND pins. The IN pin connects internally to a digitally controlled resistance whose other end is a current summing point at the same potential as the AGND pin (Figure 3). At unity gain (digital input 001), the value of this input resistance is approximately 10k and the IN voltage range is rail-to-rail (V+ to V-). At gain settings above unity (digital input 010 or higher), the input resistance falls, to nominally 1k at gain settings of 10V/V or greater (digital input 100 or greater). Also, the linear input range falls in inverse proportion to gain. (The higher gains are designed to boost lower level signals with good noise performance.) In the "zero" gain state (digital input 000), analog switches disconnect the IN pin internally and this pin presents a very high input resistance. The input may vary from rail to rail in the "zero" gain setting but the output is insensitive to it and remains at the AGND potential. Table 1 summarizes the LTC6910's behavior for all gain codes. Circuitry driving the IN pin must consider the LTC6910-1's input resistance and the variation of this resistance when used at multiple gain settings. Signal sources with significant output resistance may introduce a gain error as the source's output resistance and the LTC6910-1's input resistance form a voltage divider. This is especially true at the higher gain settings where the input resistance is lowest. U U U 8 7 6 5 8 7 6 5 LTC6910-1 LTC6910-1 1 2 3 4 0.1F ANALOG GROUND PLANE V- SINGLE-POINT SYSTEM GROUND 1 2 3 4 V+ REFERENCE 2 1F DIGITAL GROUND PLANE (IF ANY) 6910 F01 DIGITAL GROUND PLANE (IF ANY) 6910 F02 Figure 2. Single Supply Ground Plane Connection In single supply voltage applications at elevated gain settings (digital input 010 or higher), it is important to remember that the LTC6910-1's DC ground reference for both input and output is AGND, not V-. With increasing gains, the LTC6910-1's input voltage range for unclipped output is no longer rail-to-rail but shrinks toward AGND. G2 7 G1 6 G0 5 CMOS LOGIC IN 3 INPUT R ARRAY FEEDBACK R ARRAY 1 OUT 10k V- 4 V- 6910 F03 LTC6910-1 PI FU CTIO S The OUT pin also swings positive or negative with respect to AGND. At unity gain (digital input 001), both IN and OUT voltages can swing from rail to rail (Table 1). V-, V+ (Pins 4, 8): Power Supply Pins. The V+ and V- pins should be bypassed with 0.1F capacitors to an adequate analog ground plane using the shortest possible wiring. Electrically clean supplies and a low impedance ground are important for the high dynamic range available from the LTC6910-1 (see further details under AGND). Low noise linear power supplies are recommended. Switching power supplies require special care to prevent switching noise coupling into the signal path, reducing dynamic range. G0, G1, G2 (Pins 5, 6, 7): CMOS-Level Digital GainControl Inputs. G2 is the most significant bit (MSB). These pins control the voltage gain from IN to OUT pins. In the LTC6910-1, the voltage gain range is 0 to 100V/V in eight discrete values 0, 1, 2, 5, 10, 20, 50, 100, set respectively by digital inputs 000 through 111 (or in decimal form, 0 through 7). Digital input code 000 causes a "zero" gain with very low output noise. In this "zero" gain state the IN pin is disconnected internally, but the OUT pin remains active and forced by the internal op amp to the voltage present on the AGND pin. Note that the voltage gain is inverting: OUT and IN pins always swing on opposite sides of the AGND potential. The G pins are high impedance CMOS logic inputs and must be connected (they will float to unpredictable voltages if open circuited). Table 1 summarizes the effects of the G-pin code. APPLICATIO S I FOR ATIO Functional Description The LTC6910-1 is a small outline, wideband inverting DC amplifier whose voltage gain is digitally programmable. It delivers a choice of eight voltage gains, controlled by the 3-bit digital inputs to the G pins, which accept CMOS logic levels. The gain code is always monotonic; an increase in the 3-bit binary number (G2 G1 G0) causes an increase in the gain. LTC6910-1's nominal gain magnitudes are 0, 1, 2, 5, 10, 20, 50, and 100Volts/Volt (like a gain knob on an instrument). At nonzero gains, the signal bandwidth varies roughly inversely with gain, so that the product of gain and bandwidth (to -3dB rolloff) is typically 10MHz. Gain control within the amplifier occurs by switching resistors from a matched array in or out of a closed-loop op amp circuit using MOS analog switches (Figure 3). Digital Control Logic levels for the LTC6910-1 digital gain control inputs (Pins 5, 6, 7) are nominally rail-to-rail CMOS. Logic 1 is V+, logic 0 is V - or alternatively 0V when using 5V supplies. The part is tested with the values listed in the Electrical Characteristics table (Digital Input "High" and "Low" Voltages), which are 10% and 90% of full excursion on the U W UU U U U inputs. That is, the tested logic levels are 1.08V with 1.35V supplies, 2V with 2.5V supplies (equivalently, 0.5V and 4.5V levels with 0V and 5V supply rails), and 0.5V and 4.5V logic levels at 5V supplies. Construction and Instrumentation Cautions Electrically clean construction is important in applications seeking the full dynamic range of the LTC6910-1 amplifier. Short, direct wiring will minimize parasitic capacitance and inductance. High quality supply bypass capacitors of 0.1F near the chip provide good decoupling from a clean, low inductance power source. But several cm of wire (i.e., a few microhenrys of inductance) from the power supplies, unless decoupled by substantial capacitance (10F) near the chip, can cause a high-Q LC resonance in the hundreds of kHz in the chip's supplies or ground reference. This may impair circuit performance at those frequencies. A compact, carefully laid out printed circuit board with a good ground plane makes a significant difference in distortion minimizing. Finally, equipment to measure amplifier performance can itself introduce distortion or noise floors. Checking for these limits with a wire replacing the chip is a prudent routine procedure. 69101i 7 LTC6910-1 TYPICAL APPLICATIO U Expanding an ADC's Dynamic Range 5V 0.1F LTC1864 4 VIN 3 LTC6910-1 6 2 AGND 1F ADC GAIN CONTROL CONTROL LTC6910-1 (IN TSOT-23 PACKAGE) COMPACTLY ADDS 40dB OF INPUT GAIN RANGE 1610 TA03 TO THE LTC1864 (IN MSOP 8-PIN PACKAGE). SINGLE 5V SUPPLY 7 1 499 5 270pF VREF IN+ IN- VCC SCK SDO 1F 5V 8 GND CONV 0.30 - 0.50 REF 0.09 - 0.20 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193 PACKAGE DESCRIPTIO 0.52 MAX 3.85 MAX 2.62 REF RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.20 BSC 1.00 MAX DATUM `A' RELATED PARTS PART NUMBER LT(R)1228 LT1251/LT1256 LTC1564 DESCRIPTION 100MHz Gain Controlled Transconductance Amplifier 40MHz Video Fader and Gain Controlled Amplifier 10kHz to 150kHz Digitally Controlled Filter and PGA COMMENTS Differential Input, Continuous Analog Gain Control Two Input, One Output, Continuous Analog Gain Control Continuous Time, Low Noise 8th Order Filter and 4-Bit PGA 69101i LT/TP 0802 1.5K * PRINTED IN USA 8 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 q FAX: (408) 434-0507 q U 0.65 REF TS8 Package 8-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1637) 2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 2.80 BSC 1.50 - 1.75 (NOTE 4) PIN ONE ID 0.65 BSC 0.22 - 0.36 8 PLCS (NOTE 3) 0.80 - 0.90 0.01 - 0.10 1.95 BSC TS8 TSOT-23 0302 www.linear.com (c) LINEAR TECHNOLOGY CORPORATION 2002 |
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