LM12458CIV

LM12454/LM12458/LM12H458 12-Bit + Sign Data Acquisition System with Self-Calibration February 2006 LM12454/LM12458/LM12H458 12-Bit + Sign Data Acquisition System with Self-Calibration General Description The LM12458, and LM12H458 are highly integrated Data Acquisition Systems. Operating on just 5V, they combine a fully-differential self-calibrating (correcting linearity and zero errors) 13-bit (12-bit + sign) analog-to-digital converter (ADC) and sample-and-hold (S/H) with extensive analog functions and digital functionality. Up to 32 consecutive conversions, using two’s complement format, can be stored in an internal 32-word (16-bit wide) FIFO data buffer. An internal 8-word RAM can store the conversion sequence for up to eight acquisitions through the LM12(H)458’s eight-input multiplexer. The obsolete LM12454 has a four-channel multiplexer, a differential multiplexer output, and a differential S/H input. The LM12(H)458 can also operate with 8-bit + sign resolution and in a supervisory “watchdog” mode that compares an input signal against two programmable limits. Programmable acquisition times and conversion rates are possible through the use of internal clock-driven timers. The reference voltage input can be externally generated for absolute or ratiometric operation or can be derived using the internal 2.5V bandgap reference. All registers, RAM, and FIFO are directly addressable through the high speed microprocessor interface to either an 8-bit or 16-bit data bus. The LM12(H)458 includes a direct memory access (DMA) interface for high-speed conversion data transfer. Additional applications information can be found in applications notes AN-906, AN-947 and AN-949. Key Specifications (fCLK = 5 MHz; 8 MHz, H) j j j j j j j j j j Resolution 13-bit conversion time 9-bit conversion time 13-bit Through-put rate Comparison time (“watchdog” mode) ILE VIN range Power Consumption Stand-by mode Single supply 12-bit + sign or 8-bit + sign 8.8 µs, 5.5 µs (H) (max) 4.2 µs, 2.6 µs (H) (max) 88k samples/s (min), 140k samples/s (H) (min) 2.2 µs (max), 1.4 µs (H) (max) ± 1 LSB (max) GND to VA+ 30 mW, 34 mW (H) (max) 50 µW (typ) 3V to 5.5V Features n Three operating modes: 12-bit + sign, 8-bit + sign, and “watchdog” n Single-ended or differential inputs n Built-in Sample-and-Hold and 2.5V bandgap reference n Instruction RAM and event sequencer n 8-channel multiplexer n 32-word conversion FIFO n Programmable acquisition times and conversion rates n Self-calibration and diagnostic mode n 8- or 16-bit wide data bus microprocessor or DSP interface Applications n n n n n Data Logging Instrumentation Process Control Energy Management Inertial Guidance TRI-STATE ® is a registered trademark of National Semiconductor Corporation. AT ® is a registered trademark of International Business Machines Corporation. © 2006 National Semiconductor Corporation DS011264 www.national.com LM12454/LM12458/LM12H458 Ordering Information Guaranteed Clock Freq (min) 8 MHz Order Part Number LM12H458CIV LM12H458CIVX LM12H458CIVF LM12454CIV * LM12458CIV LM12458CIVX LM12458CIVF * NS Package V44A (PLCC) V44A (PLCC) (Tape and Reel) VGZ44A (PQFP) V44A (PLCC) V44A (PLCC) V44A (PLCC) (Tape and Reel) VGZ44A (PQFP) 5 MHz * These products are obsolete and shown for reference only. Connection Diagrams 01126434 01126402 Order Number LM12458CIVF or LM12H458CIVF NS Package Number VGZ44A * Pin names in ( ) apply to the obsolete LM12454 and LM12H454. Order Number LM12454CIV, LM12458CIV or LM12H458CIV See NS Package Number V44A www.national.com 2 LM12454/LM12458/LM12H458 Functional Diagrams LM12454 01126401 The LM12(H)454 is obsolete LM12(H)458 01126421 3 www.national.com LM12454/LM12458/LM12H458 Absolute Maximum Ratings (Notes 1, 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (VA+ and VD+) Voltage at Input and Output Pins, except analog inputs Voltage at Analog Inputs |VA+ − VD+| Input Current at Any Pin (Note 3) Package Input Current (Note 3) Power Dissipation, PQFP (Note 4) (TA = 25˚C) Storage Temperature Lead Temperature PQFP, Infrared, 15 sec. PLCC, Solder, 10 sec. ESD Susceptibility (Note 5) +300˚C +250˚C 1.5 kV 6.0V −0.3V to (V+ + 0.3V) − 5V to (V+ + 5V) 300 mV Operating Ratings (Notes 1, 2) Temperature Range (Tmin ≤ TA ≤ Tmax) Supply Voltage VA+, VD+ |VA+ − VD+| VIN+ Input Range VIN− Input Range VREF+ Input Voltage VREF− Input Voltage VREF+ − VREF− VREF Common Mode Range (Note 16) TJ(MAX) −40˚C ≤ TA ≤ 85˚C 3.0V to 5.5V ≤100 mV GND ≤ VIN+ ≤ VA+ GND ≤ VIN− ≤ VA+ 1V ≤ VREF+ ≤ VA+ 0V ≤ VREF− ≤ VREF+ − 1V 1V ≤ VREF ≤ VA+ 0.1 VA+ ≤ VREFCM ≤ 0.6 VA+ 150˚C ± 5 mA ± 20 mA 875 mW −65˚C to +150˚C Reliability Information Transistor Count Device Type P-Chan MOS Transistor N-Chan MOS Transistor Parasitic Vertical Bipolar Junction Transistor Parasitic Lateral Bipolar Junction Transistor TOTAL Transistors Nmber 12,232 15,457 4 2 27,695 See AN-450 “Surface Mounting Methods and Their Effect on Product Reliability” for other methods of soldering surface mount devices. Package Thermal Resistances Package 44-Lead PQFP 44-Lead PLCC θJA 47˚C / W 50˚C / W Converter Characteristics (Notes 6, 7, 8, 9) The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+ = VD+ = 5V, VREF+ = 5V, VREF− = 0V, 12-bit + sign conversion mode, fCLK = 8.0 MHz (LM12H458) or fCLK = 5.0 MHz (LM12454/8), RS = 25Ω, source impedance for VREF+ and VREF− ≤ 25Ω, fully-differential input with fixed 2.5V common-mode voltage, and minimum acquisition time unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C. Symbol ILE TUE Parameter Integral Linearity Error (Notes 12, 17) Total Unadjusted Error(Note 12) Resolution with No Missing Codes (Note 12) DNL Differential Non-Linearity Zero Error (Notes 13, 17) Conditions After Auto-Cal After Auto-Cal After Auto-Cal After Auto-Cal After Auto-Cal LM12H458 Typical (Note 10) Limits (Note 11) Units LSB (max) LSB 13 Bits (max) LSB (max) LSB (max) LSB (max) LSB (max) LSB (max) LSB (max) LSB (max) ± 1/2 ±1 ±1 Positive Full-Scale Error (Notes 12, 17) After Auto-Cal Negative Full-Scale Error (Notes 12, 17) DC Common Mode Error (Note 14) ILE TUE 8-Bit + Sign and “Watchdog” Mode Integral Linearity Error (Note 12) 8-Bit + Sign and “Watchdog” Mode Total Unadjusted Error 8-Bit + Sign and “Watchdog” Mode Resolution with No Missing Codes www.national.com 4 ± 1/2 ± 1/2 ± 1/2 ±2 ± 3⁄4 ±1 ± 1.5 ±2 ±2 ± 3.5 ± 1/2 After Auto-Cal After Auto-Zero ± 1/2 ± 3/4 9 Bits (max) LM12454/LM12458/LM12H458 Converter Characteristics (Notes 6, 7, 8, 9) (Continued) The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+ = VD+ = 5V, VREF+ = 5V, VREF− = 0V, 12-bit + sign conversion mode, fCLK = 8.0 MHz (LM12H458) or fCLK = 5.0 MHz (LM12454/8), RS = 25Ω, source impedance for VREF+ and VREF− ≤ 25Ω, fully-differential input with fixed 2.5V common-mode voltage, and minimum acquisition time unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C. Symbol Parameter 8-Bit + Sign and “Watchdog” Mode Differential Non-Linearity 8-Bit + Sign and “Watchdog” Mode Zero Error 8-Bit + Sign and “Watchdog” Full-Scale Error 8-Bit + Sign and “Watchdog” Mode DC Common Mode Error Multiplexer Channel-to-Channel Matching After Auto-Zero Conditions Typical (Note 10) Limits (Note 11) Units LSB (max) LSB (max) LSB (max) LSB LSB GND VA+ GND VA+ −VA+ VA+ GND VA+ VA+ = VD+ = 5V ± 10% VREF+ = 4.5V, VREF− = GND V (min) V (max) V (min) V (max) V (min) V (max) V (min) V (max) LSB (max) LSB (max) LSB pF pF DNL ± 3/4 ± 1/2 ± 1/2 ± 1/8 ± 0.05 VIN+ VIN− VIN+ − VIN− Non-Inverting Input Range Inverting Input Range Differential Input Voltage Range Common Mode Input Voltage Range Power Supply Sensitivity (Note 15) Zero Error Full-Scale Error Linearity Error PSS CREF CIN ± 0.2 ± 0.4 ± 0.2 85 75 ± 1.75 ±2 VREF+/VREF− Input Capacitance Selected Multiplexer Channel Input Capacitance Converter AC Characteristics (Notes 6, 7, 8, 9) The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+ = VD+ = 5V, VREF+ = 5V, VREF− = 0V, 12-bit + sign conversion mode, fCLK = 8.0 MHz (LM12H458) or fCLK = 5.0 MHz (LM12454/8), RS = 25Ω, source impedance for VREF+ and VREF− ≤ 25Ω, fully-differential input with fixed 2.5V common-mode voltage, and minimum acquisition time unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C. Symbol Parameter Conditions Typical (Note 10) 50 13-Bit Resolution, Sequencer State S5 (Figure 15) 9-Bit Resolution, Sequencer State S5 (Figure 15) Sequencer State S7 (Figure 15) Built-in minimum for 13-Bits Built-in minimum for 9-Bits and “Watchdog” mode Sequencer State S2 (Figure 15) Sequencer State S2 (Figure 15) LM12H458 Limits (Note 11) Units % % (min) % (max) (max) (max) (max) (max) (max) (max) kHz (min) kHz (min) Clock Duty Cycle 40 60 44 (tCLK) + 50 ns 21 (tCLK) + 50 ns 9 (tCLK) + 50 ns 2 (tCLK) + 50 ns 76 (tCLK) + 50 ns 4944 (tCLK) + 50 ns 88 140 44 (tCLK) 21 (tCLK) 9 (tCLK) 2 (tCLK) 76 (tCLK) 4944 (tCLK) 89 142 tC Conversion Time tA Acquisition Time tZ tCAL Auto-Zero Time Full Calibration Time Throughput Rate (Note 18) 5 www.national.com LM12454/LM12458/LM12H458 Converter AC Characteristics (Notes 6, 7, 8, 9) (Continued) The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+ = VD+ = 5V, VREF+ = 5V, VREF− = 0V, 12-bit + sign conversion mode, fCLK = 8.0 MHz (LM12H458) or fCLK = 5.0 MHz (LM12454/8), RS = 25Ω, source impedance for VREF+ and VREF− ≤ 25Ω, fully-differential input with fixed 2.5V common-mode voltage, and minimum acquisition time unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C. Parameter “Watchdog” Mode Comparison Time Differential Signal-to-Noise Ratio Conditions Sequencer States S6, S4, and S5 (Figure 15) VIN = ± 5V fIN = 1 kHz fIN = 20 kHz fIN = 40 kHz VIN = 5 Vp-p Single-Ended Signal-to-Noise Ratio fIN = 1 kHz fIN = 20 kHz fIN = 40 kHz VIN = ± 5V Differential Signal-to-Noise + Distortion Ratio fIN = 1 kHz fIN = 20 kHz fIN = 40 kHz VIN = 5 Vp-p Single-Ended Signal-to-Noise + Distortion Ratio fIN = 1 kHz fIN = 20 kHz fIN = 40 kHz VIN = ± 5V Differential Total Harmonic Distortion fIN = 1 kHz fIN = 20 kHz fIN = 40 kHz VIN = 5 Vp-p Single-Ended Total Harmonic Distortion fIN = 1 kHz fIN = 20 kHz fIN = 40 kHz VIN = ± 5V Differential Effective Number of Bits fIN = 1 kHz fIN = 20 kHz fIN = 40 kHz VIN = 5 Vp-p Single-Ended Effective Number of Bits fIN = 1 kHz fIN = 20 kHz fIN = 40 kHz VIN = ± 5V Differential Spurious Free Dynamic Range fIN = 1 kHz fIN = 20 kHz fIN = 40 kHz Multiplexer Channel-to-Channel Crosstalk VIN = 5 VP-P, fIN = 40 kHz, LM12454 MUXOUT Only VIN = 5 VP-P, fIN = 40 kHz, LM12(H)458 MUX plus Converter Typical (Note 10) 11 (tCLK) Limits (Note 11) 11 (tCLK) + 50 ns Units (max) Symbol tWD DSNR 77.5 75.2 74.7 69.8 69.2 66.6 76.9 73.9 70.7 69.4 68.3 65.7 −85.8 −79.9 −72.9 −80.3 −75.6 −72.8 12.6 12.2 12.1 11.3 11.2 10.8 87.2 78.9 72.8 −76 −78 10 10 dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB Bits Bits Bits Bits Bits Bits dB dB dB dB dB ms ms SESNR DSINAD SESINAD DTHD SETHD DENOB SEENOB DSFDR tPU tWU Power-Up Time Wake-Up Time www.national.com 6 LM12454/LM12458/LM12H458 DC Characteristics (Notes 6, 7, 8) The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+ = VD+ = 5V, VREF+ = 5V, VREF− = 0V, fCLK = 8.0 MHz (LM12H454/8) or fCLK = 5.0 MHz (LM12458), and minimum acquisition time unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C. Symbol Parameter Conditions CS = “1” LM12454/8 LM12H458 CS = “1” LM12454/8 LM12H458 Clock Stopped 8 MHz Clock VA+ = 5.5V ON-Channel = 5.5V, OFF-Channel = 0V ON-Channel = 0V OFF-Channel = 5.5V VA+ = 5.5V ON-Channel = 5.5V OFF-Channel = 0V ON-Channel = 0V OFF-Channel = 5.5V LM12454 RON Multiplexer ON-Resistance VIN = 5V VIN = 2.5V VIN = 0V LM12454 Multiplexer Channel-to-Channel RON matching VIN = 5V VIN = 2.5V VIN = 0V 800 850 760 1500 1500 1500 Ω(max) Ω(max) Ω(max) (max) (max) (max) Typical (Note 10) 0.55 0.55 3.1 3.1 10 40 0.1 0.3 Limits (Note 11) 1.0 1.2 5.0 5.5 Units I D+ VD+ Supply Current mA (max) mA (max) mA (max) mA (max) µA (max) µA (max) µA (max) I A+ VA+ Supply Current Stand-By Supply Current (ID+) + (IA+) [Power-Down Mode Selected] IST Multiplexer ON-Channel Leakage Current 0.1 0.3 µA (max) 0.1 0.3 0.3 µA (max) Multiplexer OFF-Channel Leakage Current 0.1 µA (max) ± 1.0% ± 1.0% ± 1.0% ± 3.0% ± 3.0% ± 3.0% Internal Reference Characteristics (Notes 6, 7) The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+ = VD+ = 5V unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C. Symbol VREFOUT Parameter Internal Reference Output Voltage Sourcing (0 < IL ≤ +4 mA) Sinking (−1 ≤ IIL < 0 mA) 4.5V ≤ VA+ ≤ 5.5V VREFOUT = 0V VA+ = VD+ = 0V → 5V, CL = 100 µF 3 13 200 10 Conditions Typical (Note 10) 2.5 40 0.2 1.2 20 25 Limits (Note 11) 2.5 ± 4% Units V (max) ppm/˚C %/mA (max) %/mA (max) mV (max) mA (max) ppm/kHr ms ∆VREF/∆T Internal Reference Temperature Coefficient ∆REF/∆IL ∆VREF ISC ∆VREF/∆t tSU Internal Reference Load Regulation Line Regulation Internal Reference Short Circuit Current Long Term Stability Internal Reference Start-Up Time 7 www.national.com LM12454/LM12458/LM12H458 Digital Characteristics (Notes 6, 7) The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+ = VD+ = 5V, unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C. Symbol VIN(1) VIN(0) IIN(1) IIN(0) CIN VOUT(1) Parameter Logical “1” Input Voltage Logical “0” Input Voltage Logical “1” Input Current Logical “0” Input Current D0–D15 Input Capacitance VA+ = VD+ = 4.5V Logical “1” Output Voltage IOUT = −360 µA IOUT = −10 µA VOUT(0) IOUT Logical “0” Output Voltage TRI-STATE ® Output Leakage Current VA+ = VD+ = 4.5V IOUT = 1.6 mA VOUT = 0V VOUT = 5V −0.01 0.01 2.4 4.25 0.4 −3.0 3.0 V (min) V (min) V (max) µA (max) µA (max) Conditions VA+ = VD+ = 5.5V VA+ = VD+ = 4.5V VIN = 5V VIN = 0V 0.005 −0.005 6 Typical (Note 10) Limits (Note 11) 2.0 0.8 1.0 −1.0 Units V (min) V (max) µA (max) µA (max) pF Digital Timing Characteristics (Notes 6, 7, 8) The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+ = VD+ = 5V, tr = tf = 3 ns, and CL = 100 pF on data I/O, INT and DMARQ lines unless otherwise specified. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C. Symbol (See Figures 8, 9, 10) 1, 3 2, 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 20 21 19 22 23 Parameter CS or Address Valid to ALE Low Set-Up Time CS or Address Valid to ALE Low Hold Time ALE Pulse Width RD High to Next ALE High ALE Low to RD Low RD Pulse Width RD High to Next RD or WR Low ALE Low to WR Low WR Pulse Width WR High to Next ALE High WR High to Next RD or WR Low Data Valid to WR High Set-Up Time Data Valid to WR High Hold Time RD Low to Data Bus Out of TRI-STATE RD High to TRI-STATE RD Low to Data Valid (Access Time) Address Valid or CS Low to RD Low Address Valid or CS Low to WR Low Address Invalid from RD or WR High INT High from RD Low DMARQ Low from RD Low 30 30 RL = 1 kΩ 40 30 30 Conditions Typical (Note 10) Limits (Note 11) 40 20 45 35 20 100 100 20 60 75 140 40 30 10 70 10 110 10 80 20 20 10 10 60 10 60 Units ns (min) ns (min) ns (min) ns (min) ns (min) ns (min) ns (min) ns (min) ns (min) ns (min) ns (min) ns (min) ns (min) ns (min) ns (max) ns (min) ns (max) ns (min) ns (max) ns (min) ns (min) ns (min) ns (min) ns (max) ns (min) ns (max) www.national.com 8 LM12454/LM12458/LM12H458 Digital Timing Characteristics (Notes 6, 7, 8) (Continued) Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. Note 2: All voltages are measured with respect to GND, unless otherwise specified. Note 3: When the input voltage (VIN) at any pin exceeds the power supply rails (VIN < GND or VIN > (VA+ or VD+)), the current at that pin should be limited to 5 mA. The 20 mA maximum package input current rating allows the voltage at any four pins, with an input current of 5 mA, to simultaneously exceed the power supply voltages. Note 4: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJmax (maximum junction temperature), θJA (package junction to ambient thermal resistance), and TA (ambient temperature). Note 5: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Note 6: Two on-chip diodes are tied to each analog input through a series resistor, as shown below. Input voltage magnitude up to 5V above VA+ or 5V below GND will not damage the LM12454 or the LM12(H)458. However, errors in the A/D conversion can occur if these diodes are forward biased by more than 100 mV. As an example, if VA+ is 4.5 VDC, full-scale input voltage must be ≤4.6 VDC to ensure accurate conversions. 01126403 Note 7: VA+ and VD+ must be connected together to the same power supply voltage and bypassed with separate capacitors at each V+ pin to assure conversion/comparison accuracy. Note 8: Accuracy is guaranteed when operating at fCLK = 5 MHz for the LM12454/8 and fCLK = 8 MHz for the LM12H458. Note 9: With the test condition for VREF (VREF+ − VREF−) given as +5V, the 12-bit LSB is 1.22 mV and the 8-bit/“Watchdog” LSB is 19.53 mV. Note 10: Typical figures are at TA = 25˚C and represent most likely parametric norm. Note 11: Limits are guaranteed to National’s AOQL (Average Output Quality Level). Note 12: Positive integral linearity error is defined as the deviation of the analog value, expressed in LSBs, from the straight line that passes through positive full-scale and zero. For negative integral linearity error the straight line passes through negative full-scale and zero. (See Figure 6 Figure 7). Note 13: Zero error is a measure of the deviation from the mid-scale voltage (a code of zero), expressed in LSB. It is the worst-case value of the code transitions between −1 to 0 and 0 to +1 (see Figure 8). Note 14: The DC common-mode error is measured with both inputs shorted together and driven from 0V to 5V. The measured value is referred to the resulting output value when the inputs are driven with a 2.5V signal. Note 15: Power Supply Sensitivity is measured after Auto-Zero and/or Auto-Calibration cycle has been completed with VA+ and VD+ at the specified extremes. Note 16: VREFCM (Reference Voltage Common Mode Range) is defined as (VREF+ + VREF−)/2. Note 17: The LM12(H)454/8’s self-calibration technique ensures linearity and offset errors as specified, but noise inherent in the self-calibration process will result in a repeatability uncertainty of ± 0.10 LSB. Note 18: The Throughput Rate is for a single instruction repeated continuously. Sequencer states 0 (1 clock cycle), 1 (1 clock cycle), 7 (9 clock cycles) and 5 (44 clock cycles) are used (see Figure 15). One additional clock cycle is used to read the conversion result stored in the FIFO, for a total of 56 clock cycles per conversion. The Throughput Rate is fCLK (MHz)/N, where N is the number of clock cycles/conversion. 9 www.national.com LM12454/LM12458/LM12H458 01126422 VREF = VREF+ − VREF− VIN = VIN+ − VIN− GND ≤ VIN+ ≤VA+ GND ≤ VIN− ≤VA+ FIGURE 1. The General Case of Output Digital Code vs. the Operating Input Voltage Range 01126423 VREF+ − VREF− = 4.096V VIN = VIN+ − VIN− GND ≤ VIN+ ≤VA+ GND ≤ VIN− ≤VA+ FIGURE 2. Specific Case of Output Digital Code vs. the Operating Input Voltage Range for VREF = 4.096V www.national.com 10 LM12454/LM12458/LM12H458 01126424 VREF = VREF+ − VREF− FIGURE 3. The General Case of the VREF Operating Range 01126425 VREF = VREF+ − VREF− VA+ = 5V FIGURE 4. The Specific Case of the VREF Operating Range for VA+ = 5V 11 www.national.com LM12454/LM12458/LM12H458 01126404 FIGURE 5. Transfer Characteristic 01126405 FIGURE 6. Simplified Error Curve vs. Output Code without Auto-Calibration or Auto-Zero Cycles www.national.com 12 LM12454/LM12458/LM12H458 01126406 FIGURE 7. Simplified Error Curve vs. Output Code after Auto-Calibration Cycle 01126407 FIGURE 8. Offset or Zero Error Voltage 13 www.national.com LM12454/LM12458/LM12H458 Typical Performance Characteristics (Note 9) The following curves apply for 12-bit + sign mode after auto-calibration unless otherwise specified. The performance for 8-bit + sign and “watchdog” modes is equal to or better than shown. Linearity Error Change vs. Clock Frequency Linearity Error Change vs. Temperature 01126437 01126438 Linearity Error Change vs. Reference Voltage Linearity Error Change vs. Supply Voltage 01126439 01126440 Full-Scale Error Change vs. Clock Frequency Full-Scale Error Change vs. Temperature 01126441 01126442 www.national.com 14 LM12454/LM12458/LM12H458 Typical Performance Characteristics (Note 9) The following curves apply for 12-bit + sign mode after auto-calibration unless otherwise specified. The performance for 8-bit + sign and “watchdog” modes is equal to or better than shown. (Continued) Full-Scale Error Change vs. Reference Voltage Full-Scale Error vs. Supply Voltage 01126443 01126444 Zero Error Change vs. Clock Frequency Zero Error Change vs. Temperature 01126445 01126446 Zero Error Change vs. Reference Voltage Zero Error Change vs. Supply Voltage 01126447 01126448 15 www.national.com LM12454/LM12458/LM12H458 Typical Performance Characteristics (Note 9) The following curves apply for 12-bit + sign mode after auto-calibration unless otherwise specified. The performance for 8-bit + sign and “watchdog” modes is equal to or better than shown. (Continued) Analog Supply Current vs. Temperature Digital Supply Current vs. Clock Frequency 01126449 01126450 Digital Supply Current vs. Temperature VREFOUT Load Regulation 01126451 01126452 VREFOUT Line Regulation 01126453 www.national.com 16 LM12454/LM12458/LM12H458 Typical Dynamic Performance Characteristics mode after auto-calibration unless otherwise specified. Bipolar Signal-to-Noise Ratio vs. Input Frequency The following curves apply for 12-bit + sign Bipolar Signal-to-Noise + Distortion Ratio vs. Input Frequency 01126454 01126455 Bipolar Signal-to-Noise + Distortion Ratio vs. Input Signal Level Bipolar Spectral Response with 1.028 kHz Sine Wave Input 01126456 01126457 Bipolar Spectral Response with 10 kHz Sine Wave Input Bipolar Spectral Response with 20 kHz Sine Wave Input 01126458 01126459 17 www.national.com LM12454/LM12458/LM12H458 Typical Dynamic Performance Characteristics The following curves apply for 12-bit + sign mode after auto-calibration unless otherwise specified. (Continued) Bipolar Spectral Response with 40 kHz Sine Wave Input Bipolar Spurious Free Dynamic Range 01126460 01126461 Unipolar Signal-to-Noise Ratio vs. Input Frequency Unipolar Signal-to-Noise + Distortion Ratio vs. Input Frequency 01126462 01126463 Unipolar Signal-to-Noise + Distortion Ratio vs. Input Signal Level Unipolar Spectral Response with 1.028 kHz Sine Wave Input 01126464 01126465 www.national.com 18 LM12454/LM12458/LM12H458 Typical Dynamic Performance Characteristics The following curves apply for 12-bit + sign mode after auto-calibration unless otherwise specified. (Continued) Unipolar Spectral Response with 10 kHz Sine Wave Input Unipolar Spectral Response with 20 kHz Sine Wave Input 01126466 01126467 Unipolar Spectral Response with 40 kHz Sine Wave Input 01126468 Test Circuits and Waveforms 01126413 01126412 01126415 01126414 FIGURE 9. TRI-STATE Test Circuits and Waveforms 19 www.national.com LM12454/LM12458/LM12H458 Timing Diagrams VA+ = VD+ = +5V, tR = tF = 3 ns, CL = 100 pF for the INT, DMARQ, D0–D15 outputs. 01126416 FIGURE 10. Multiplexed Data Bus 1, 3: CS or Address valid to ALE low set-up time. 2, 4: CS or Address valid to ALE low hold time. 5: ALE pulse width 6: RD high to next ALE high 7: ALE low to RD low 8: RD pulse width 9: RD high to next RD or WR low 10: ALE low to WR low 11: WR pulse width 12: WR high to next ALE high 13: 14: 15: 16: 17: 18: WR high to next WR or RD low Data valid to WR high set-up time Data valid to WR high hold time RD low to data bus out of TRI-STATE RD high to TRI-STATE RD low to data valid (access time) www.national.com 20 LM12454/LM12458/LM12H458 Timing Diagrams VA+ = VD+ = +5V, tR = tF = 3 ns, CL = 100 pF for the INT, DMARQ, D0–D15 outputs. (Continued) 01126417 FIGURE 11. Non-Multiplexed Data Bus (ALE = 1) 8: RD pulse width 9: RD high to next RD or WR low 11: WR pulse width 13: WR high to next WR or RD low 14: Data valid to WR high set-up time 15: Data valid to WR high hold time 16: RD low to data bus out of TRI-STATE 17: RD high to TRI-STATE 18: RD low to data valid (access time) 19: Address invalid from RD or WR high (hold time) 20: CS low or address valid to RD low 21: CS low or address valid to WR low VA+ = VD+ = +5V, tR = tF = 3 ns, CL = 100 pF for the INT, DMARQ, D0–D15 outputs. 01126418 FIGURE 12. Interrupt and DMARQ 22: INT high from RD low 23: DMARQ low from RD low 21 www.national.com LM12454/LM12458/LM12H458 Pin Descriptions VA+ VD+ Analog and digital supply voltage pins. The LM12(H)454/8’s supply voltage operating range is +3.0V to +5.5V. Accuracy is guaranteed only if VA+ and VD+ are connected to the same power supply. Each pin should have a parallel combination of 10 µF (electrolytic or tantalum) and 0.1 µF (ceramic) bypass capacitors connected between it and ground. D0–D15 The internal data input/output TRI-STATE buffers are connected to these pins. These buffers are designed to drive capacitive loads of 100 pF or less. External buffers are necessary for driving higher load capacitances. These pins allows the user a means of instruction input and data output. With a logic high applied to the BW pin, data lines D8–D15 are placed in a high impedance state and data lines D0–D7 are used for instruction input and data output when the LM12(H)454/8 is connected to an 8-bit wide data bus. A logic low on the BW pin allows the LM12(H)454/8 to exchange information over a 16-bit wide data bus. Input for the active low READ bus control signal. RD The data input/output TRI-STATE buffers, as selected by the logic signal applied to the BW pin, are enabled when RD and CS are both low. This allows the LM12(H)454/8 to transmit information onto the data bus. Input for the active low WRITE bus control signal. WR The data input/output TRI-STATE buffers, as selected by the logic signal applied to the BW pin, are enabled when WR and CS are both low. This allows the LM12(H)454/8 to receive information from the data bus. Input for the active low Chip Select control signal. CS A logic low should be applied to this pin only during a READ or WRITE access to the LM12(H)454/8. The internal clocking is halted and conversion stops while Chip Select is low. Conversion resumes when the Chip Select input signal returns high. ALE Address Latch Enable input. It is used in systems containing a multiplexed data bus. When ALE is asserted high, the LM12(H)454/8 accepts information on the data bus as a valid address. A high-to-low transition will latch the address data on A0–A4 while the CS is low. Any changes on A0–A4 and CS while ALE is low will not affect the LM12(H)454/8. See Figure 10. When a nonmultiplexed bus is used, ALE is continuously asserted high. See Figure 11. CLK External clock input pin. The LM12(H)454/8 operates with an input clock frequency in the range of 0.05 MHz to 10.0 MHz. A0–A4 The LM12(H)454/8’s address lines. They are used to access all internal registers, Conversion FIFO, and Instruction RAM. SYNC Synchronization input/output. When used as an output, it is designed to drive capacitive loads of 100 pF or less. External buffers are necessary for driving higher load capacitances. SYNC is an input if the Configuration register’s “I/O Select” bit is low. A rising edge on this pin causes the internal S/H to hold the input signal. The next rising clock edge either starts a conversion or makes a comwww.national.com 22 parison to a programmable limit depending on which function is requested by a programming instruction. This pin will be an output if “I/O Select” is set high. The SYNC output goes high when a conversion or a comparison is started and low when completed. (See Section 2.2). An internal reset after power is first applied to the LM12(H)454/8 automatically sets this pin as an input. BW Bus Width input pin. This input allows the LM12(H)454/8 to interface directly with either an 8- or 16-bit data bus. A logic high sets the width to 8 bits and places D8–D15 in a high impedance state. A logic low sets the width to 16 bits. Active low interrupt output. This output is designed INT to drive capacitive loads of 100 pF or less. External buffers are necessary for driving higher load capacitances. An interrupt signal is generated any time a non-masked interrupt condition takes place. There are eight different conditions that can cause an interrupt. Any interrupt is reset by reading the Interrupt Status register. (See Section 2.3.) DMARQ Active high Direct Memory Access Request output. This output is designed to drive capacitive loads of 100 pF or less. External buffers are necessary for driving higher load capacitances. It goes high whenever the number of conversion results in the conversion FIFO equals a programmable value stored in the Interrupt Enable register. It returns to a logic low when the FIFO is empty. LM12(H)454/8 ground connection. It should be connected to a low resistance and inductance analog ground return that connects directly to the system power supply ground. IN0–IN7 (IN0–IN3 LM12H454 LM12454) The eight (LM12(H)458) or four (LM12454) analog inputs. A given channel is selected through the instruction RAM. Any of the channels can be configured as an independent single-ended input. Any pair of channels, whether adjacent or non-adjacent, can operate as a fully differential pair. S/H IN+ S/H IN− The LM12454’s non-inverting and inverting inputs to the internal S/H. MUXOUT+ MUXOUT− The LM12454’s non-inverting and inverting outputs from the internal multiplexer. The negative reference input. The VREF− LM12(H)454/8 operate with 0V ≤ VREF− ≤ VREF+. This pin should be bypassed to ground with a parallel combination of 10 µF and 0.1 µF (ceramic) capacitors. The positive reference input. The VREF+ LM12(H)454/8 operate with 0V ≤ VREF+ ≤ VA+. This pin should be bypassed to ground with a parallel combination of 10 µF and 0.1 µF (ceramic) capacitors. The internal 2.5V bandgap’s output pin. This VREFOUT pin should be bypassed to ground with a 100 µF capacitor. GND LM12454/LM12458/LM12H458 1.0 Functional Description The LM12454 and LM12(H)458 are multi-functional Data Acquisition Systems that include a fully differential 12-bitplus-sign self-calibrating analog-to-digital converter (ADC) with a two’s-complement output format, an 8-channel (LM12(H)458) or a 4-channel (LM12454) analog multiplexer, an internal 2.5V reference, a first-in-first-out (FIFO) register that can store 32 conversion results, and an Instruction RAM that can store as many as eight instructions to be sequentially executed. The LM12454 also has a differential multiplexer output and a differential S/H input. All of this circuitry operates on only a single +5V power supply. The LM12(H)454/8 have three modes of operation: 12-bit + sign with correction 8-bit + sign without correction 8-bit + sign comparison mode (“watchdog” mode) The fully differential 12-bit-plus-sign ADC uses a charge redistribution topology that includes calibration capabilities. Charge re-distribution ADCs use a capacitor ladder in place of a resistor ladder to form an internal DAC. The DAC is used by a successive approximation register to generate intermediate voltages between the voltages applied to VREF− and VREF+. These intermediate voltages are compared against the sampled analog input voltage as each bit is generated. The number of intermediate voltages and comparisons equals the ADC’s resolution. The correction of each bit’s accuracy is accomplished by calibrating the capacitor ladder used in the ADC. Two different calibration modes are available; one compensates for offset voltage, or zero error, while the other corrects both offset error and the ADC’s linearity error. When correcting offset only, the offset error is measured once and a correction coefficient is created. During the full calibration, the offset error is measured eight times, averaged, and a correction coefficient is created. After completion of either calibration mode, the offset correction coefficient is stored in an internal offset correction register. The LM12(H)454/8’s overall linearity correction is achieved by correcting the internal DAC’s capacitor mismatch. Each capacitor is compared eight times against all remaining smaller value capacitors and any errors are averaged. A correction coefficient is then created and stored in one of the thirteen internal linearity correction registers. An internal state machine, using patterns stored in an internal 16 x 8-bit ROM, executes each calibration algorithm. Once calibrated, an internal arithmetic logic unit (ALU) uses the offset correction coefficient and the 13 linearity correction coefficients to reduce the conversion’s offset error and linearity error, in the background, during the 12-bit + sign conversion. The 8-bit + sign conversion and comparison modes use only the offset coefficient. The 8-bit + sign mode performs a conversion in less than half the time used by the 12-bit + sign conversion mode. The LM12(H)454/8’s “watchdog” mode is used to monitor a single-ended or differential signal’s amplitude. Each sampled signal has two limits. An interrupt can be generated if the input signal is above or below either of the two limits. This allows interrupts to be generated when analog voltage inputs are “inside the window” or, alternatively, “outside the window”. After a “watchdog” mode interrupt, the processor can then request a conversion on the input signal and read the signal’s magnitude. The analog input multiplexer can be configured for any combination of single-ended or fully differential operation. Each input is referenced to ground when a multiplexer channel operates in the single-ended mode. Fully differential analog input channels are formed by pairing any two channels together. The LM12454’s multiplexer outputs and S/H inputs (MUXOUT+, MUXOUT− and S/H IN+, S/H IN−) provide the option for additional analog signal processing. Fixed-gain amplifiers, programmable-gain amplifiers, filters, and other processing circuits can operate on the signal applied to the selected multiplexer channel(s). If external processing is not used, connect MUXOUT+ to S/H IN+ and MUXOUT− to S/H IN−. The LM12(H)454/8’s internal S/H is designed to operate at its minimum acquisition time (1.13 µs, 12 bits) when the source impedance, RS, is ≤ 60Ω (fCLK ≤ 8 MHz). When 60Ω < RS ≤ 4.17 kΩ, the internal S/H’s acquisition time can be increased to a maximum of 4.88 µs (12 bits, fCLK = 8 MHz). See Section 2.1 (Instruction RAM “00”) Bits 12–15 for more information. An internal 2.5V bandgap reference output is available at pin 44. This voltage can be used as the ADC reference for ratiometric conversion or as a virtual ground for front-end analog conditioning circuits. The VREFOUT pin should be bypassed to ground with a 100 µF capacitor. Microprocessor overhead is reduced through the use of the internal conversion FIFO. Thirty-two consecutive conversions can be completed and stored in the FIFO without any microprocessor intervention. The microprocessor can, at any time, interrogate the FIFO and retrieve its contents. It can also wait for the LM12(H)454/8 to issue an interrupt when the FIFO is full or after any number (≤32) of conversions have been stored. Conversion sequencing, internal timer interval, multiplexer configuration, and many other operations are programmed and set in the Instruction RAM. A diagnostic mode is available that allows verification of the LM12(H)458’s operation. The diagnostic mode is disabled in the LM12454. This mode internally connects the voltages present at the VREFOUT, VREF+, VREF−, and GND pins to the internal VIN+ and VIN− S/H inputs. This mode is activated by setting the Diagnostic bit (Bit 11) in the Configuration register to a “1”. More information concerning this mode of operation can be found in Section 2.2. 23 www.national.com LM12454/LM12458/LM12H458 2.0 Internal User-Programmable Registers 2.1 INSTRUCTION RAM The instruction RAM holds up to eight sequentially executable instructions. Each 48-bit long instruction is divided into three 16-bit sections. READ and WRITE operations can be issued to each 16-bit section using the instruction’s address and the 2-bit “RAM pointer” in the Configuration register. The eight instructions are located at addresses 0000 through 0111 (A4–A1, BW = 0) when using a 16-bit wide data bus or at addresses 00000 through 01111 (A4–A0, BW = 1) when using an 8-bit wide data bus. They can be accessed and programmed in random order. Any Instruction RAM READ or WRITE can affect the sequencer’s operation: The Sequencer should be stopped by setting the RESET bit to a “1” or by resetting the START bit in the Configuration Register and waiting for the current instruction to finish execution before any Instruction RAM READ or WRITE is initiated. Bit 0 of the Configuration Register indicates the Sequencer Status. See paragraph 2.2 for information on the Configuration Register. A soft RESET should be issued by writing a “1” to the Configuration Register’s RESET bit after any READ or WRITE to the Instruction RAM. The three sections in the Instruction RAM are selected by the Configuration Register’s 2-bit “RAM Pointer”, bits D8 and D9. The first 16-bit Instruction RAM section is selected with the RAM Pointer equal to “00”. This section provides multiplexer channel selection, as well as resolution, acquisition time, etc. The second 16-bit section holds “watchdog” limit #1, its sign, and an indicator that shows that an interrupt can be generated if the input signal is greater or less than the programmed limit. The third 16-bit section holds “watchdog” limit #2, its sign, and an indicator that shows that an interrupt can be generated if the input signal is greater or less than the programmed limit. Instruction RAM “00” Bit 0 is the LOOP bit. It indicates the last instruction to be executed in any instruction sequence when it is set to a “1”. The next instruction to be executed will be instruction 0. Bit 1 is the PAUSE bit. This controls the Sequencer’s operation. When the PAUSE bit is set (“1”), the Sequencer will stop after reading the current instruction and before executing it, and the start bit in the Configuration register is automatically reset to a “0”. Setting the PAUSE also causes an interrupt to be issued. The Sequencer is restarted by placing a “1” in the Configuration register’s Bit 0 (Start bit). After the Instruction RAM has been programmed and the RESET bit is set to “1”, the Sequencer retrieves Instruction 000, decodes it, and waits for a “1” to be placed in the Configuration’s START bit. The START bit value of “0” “overrides” the action of Instruction 000’s PAUSE bit when the Sequencer is started. Once started, the Sequencer executes Instruction 000 and retrieves, decodes, and executes each of the remaining instructions. No PAUSE Interrupt (INT 5) is generated the first time the Sequencer executes Instruction 000 having a PAUSE bit set to “1”. When the Sequencer encounters a LOOP bit or completes all eight instructions, Instruction 000 is retrieved and decoded. A set PAUSE bit in Instruction 000 now halts the Sequencer before the instruction is executed. Bits 2–4 select which of the eight input channels (“000” to “111” for IN0–IN7) will be configured as non-inverting inputs to the LM12(H)458’s ADC. (See Table 1.) They select which of the four input channels (“000” to “011” for IN0–IN4) will be configured as non-inverting inputs to the LM12454’s ADC. (See Table 2.) Bits 5–7 select which of the seven input channels (“001” to “111” for IN1 to IN7) will be configured as inverting inputs to the LM12(H)458’s ADC. (See Table 1.) They select which of the three input channels (“001” to “011” for IN1–IN4) will be configured as inverting inputs to the LM12454’s ADC. (See Table 2.) Fully differential operation is created by selecting two multiplexer channels, one operating in the non-inverting mode and the other operating in the inverting mode. A code of “000” selects ground as the inverting input for single ended operation. Bit 8 is the SYNC bit. Setting Bit 8 to “1” causes the Sequencer to suspend operation at the end of the internal S/H’s acquisition cycle and to wait until a rising edge appears at the SYNC pin. When a rising edge appears, the S/H acquires the input signal magnitude and the ADC performs a conversion on the clock’s next rising edge. When the SYNC pin is used as an input, the Configuration register’s “I/O Select” bit (Bit 7) must be set to a “0”. With SYNC configured as an input, it is possible to synchronize the start of a conversion to an external event. This is useful in applications such as digital signal processing (DSP) where the exact timing of conversions is important. When the LM12(H)454/8 are used in the “watchdog” mode with external synchronization, two rising edges on the SYNC input are required to initiate two comparisons. The first rising edge initiates the comparison of the selected analog input signal with Limit #1 (found in Instruction RAM “01”) and the second rising edge initiates the comparison of the same analog input signal with Limit #2 (found in Instruction RAM “10”). Bit 9 is the TIMER bit. When Bit 9 is set to “1”, the Sequencer will halt until the internal 16-bit Timer counts down to zero. During this time interval, no “watchdog” comparisons or analog-to-digital conversions will be performed. Bit 10 selects the ADC conversion resolution. Setting Bit 10 to “1” selects 8-bit + sign and when reset to “0” selects 12-bit + sign. Bit 11 is the “watchdog” comparison mode enable bit. When operating in the “watchdog” comparison mode, the selected analog input signal is compared with the programmable values stored in Limit #1 and Limit #2 (see Instruction RAM “01” and Instruction RAM “10”). Setting Bit 11 to “1” causes two comparisons of the selected analog input signal with the two stored limits. When Bit 11 is reset to “0”, an 8-bit + sign or 12-bit + sign (depending on the state of Bit 10 of Instruction RAM “00”) conversion of the input signal can take place. www.national.com 24 2.0 Internal User-Programmable Registers (Continued) A1 0 Instruction RAM (RAM Pointer = 00) R/W Timer Sync Pause Loop Acquisition Time VIN− (MUXOUT−) (Note 19) VIN+ (MUXOUT+) (Note 19) 1 0 Instruction RAM (RAM Pointer = 01) R/W Sign Limit #1 Don’t Care Watch- 8/12 dog Purpose Type D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 A4 0 to 1 0 to 1 0 to 1 0 0 Configuration Register R/W Don’t Care DIAG * (Note 20) Test =0 RAM Pointer Sequencer Address to Generate INT1 INT7 INT6 INT5 i/O Auto Char StandSel Zeroec Mask by 1 Full CAL Auto- Reset Start Zero Instruction RAM (RAM Pointer = 10) R/W Sign Limit #2 Don’t Care 0 1 A3 A2 0 0 1 0 0 >/< 1 0 0 >/< 1 1 0 1 0 0 1 Interrupt Enable Register R/W Number of Conversions in Conversion FIFO to Generate INT2 Actual Number of Conversion Results in Conversion FIFO Timer Preset High Byte Address or Sign Limit #2: Status Sign Conversion Data: MSBs Address of Sequencer Instruction being Executed INT4 INT3 INT2 INT1 INT0 1 1 0 0 1 Limit Status Register R 0 Conversion FIFO R 1 Timer Register R/W 0 1 0 Interrupt Status Register R INST7 INST6 INST5 INST4 INST3 INST2 INST1 INST0 Timer Preset Low Byte Conversion Data: LSBs Limit #1: Status 1 0 LM12454/LM12458/LM12H458 25 1 1 1 1 Note 19: LM12454 (Refer to Table 2). Note 20: LM12(H)458 only. Must be set to “0” for the LM12454. FIGURE 13. LM12(H)454/8 Memory Map for 16-Bit Wide Data Bus (BW = “0”, Test Bit = “0” and A0 = Don’t Care) www.national.com LM12454/LM12458/LM12H458 2.0 Internal User-Programmable Registers A4 A3 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 1 0 A2 0 to 1 0 to 1 0 to 1 0 to 1 0 to 1 0 to 1 0 1 0 0 Configuration Register R/W I/O Sel Auto Zeroec 1 0 1 1 0 0 Instruction RAM (RAM Pointer = 10) R/W 1 0 1 R/W 1 0 0 Instruction RAM (RAM Pointer = 01) R/W R/W 1 0 1 A1 0 0 Instruction RAM (RAM Pointer = 00) R/W A0 Purpose Type D7 D6 (Continued) D5 D4 D3 D2 D1 Pause D0 Loop VIN− (MUXOUT−) (Note 21) VIN+ (MUXOUT+) (Note 21) Watchdog R/W Acquisition Time 8/12 Timer Sync Comparison Limit #1 Don’t Care Don’t Care >/< >/< Sign Sign Comparison Limit #2 R/W Don’t Care Chan Mask Standby AutoZero Test = 0 INT2 >/< Full Cal DIAG (Note 22) Reset Sign Start 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 1 1 1 1 0 0 0 1 1 1 1 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 1 0 1 0 1 0 1 0 1 0 1 R/W R/W R/W R R R/W R/W R R R R INT7 Don’t Care INT6 INT5 INT4 RAM Pointer INT1 INT0 Interrupt Enable Register Interrupt Status Register Timer Register Conversion FIFO Limit Status Register INT3 Number of Conversions in Conversion FIFO to Generate INT2 INST7 INST6 INST5 INST4 INST3 Sequencer Address to Generate INT1 INST2 INST1 INST0 Address of Sequencer Instruction being Executed Actual Number of Conversions Results in Conversion FIFO Timer Preset: Low Byte Timer Preset: High Byte Conversion Data: LSBs Address or Sign Sign Limit #1 Status Limit #2 Status Conversion Data: MSBs FIGURE 14. LM12(H)454/8 Memory Map for 8-Bit Wide Data Bus (BW = “1” and Test Bit = “0”) Note 21: LM12454 (Refer toTable 2). Note 22: LM12(H)458 only. Must be set to “0” for the LM12454. www.national.com 26 LM12454/LM12458/LM12H458 2.0 Internal User-Programmable Registers (Continued) Bits 12–15 are used to store the user-programmable acquisition time. The Sequencer keeps the internal S/H in the acquisition mode for a fixed number of clock cycles (nine clock cycles, for 12-bit + sign conversions and two clock cycles for 8-bit + sign conversions or “watchdog” comparisons) plus a variable number of clock cycles equal to twice the value stored in Bits 12–15. Thus, the S/H’s acquisition time is (9 + 2D) clock cycles for 12-bit + sign conversions and (2 + 2D) clock cycles for 8-bit + sign conversions or “watchdog” comparisons, where D is the value stored in Bits 12–15. The minimum acquisition time compensates for the typical internal multiplexer series resistance of 2 kΩ, and any additional delay created by Bits 12–15 compensates for source resistances greater than 60Ω (100Ω). (For this acquisition time discussion, numbers in ( ) are shown for the LM12(H)454/8 operating at 5 MHz.) The necessary acquisition time is determined by the source impedance at the multiplexer input. If the source resistance (RS) < 60Ω (100Ω) and the clock frequency is 8 MHz, the value stored in bits 12–15 (D) can be 0000. If RS > 60Ω (100Ω), the following equations determine the value that should be stored in bits 12–15. D = 0.45 x RS x fCLK for 12-bits + sign D = 0.36 x RS x fCLK for 8-bits + sign and “watchdog” RS is in kΩ and fCLK is in MHz. Round the result to the next higher integer value. If D is greater than 15, it is advisable to lower the source impedance by using an analog buffer between the signal source and the LM12(H)458’s multiplexer inputs. The value of D can also be used to compensate for the settling or response time of external processing circuits connected between the LM12454’s MUXOUT and S/H IN pins. Instruction RAM “01” The second Instruction RAM section is selected by placing a “01” in Bits 8 and 9 of the Configuration register. Bits 0–7 hold “watchdog” limit #1. When Bit 11 of Instruction RAM “00” is set to a “1”, the LM12(H)454/8 performs a “watchdog” comparison of the sampled analog input signal with the limit #1 value first, followed by a comparison of the same sampled analog input signal with the value found in limit #2 (Instruction RAM “10”). Bit 8 holds limit #1’s sign. Bit 9’s state determines the limit condition that generates a “watchdog” interrupt. A “1” causes a voltage greater than limit #1 to generate an interrupt, while a “0” causes a voltage less than limit #1 to generate an interrupt. Bits 10–15 are not used. Instruction RAM “10” The third Instruction RAM section is selected by placing a “10” in Bits 8 and 9 of the Configuration register. Bits 0–7 hold “watchdog” limit #2. When Bit 11 of Instruction RAM “00” is set to a “1”, the LM12(H)454/8 performs a “watchdog” comparison of the sampled analog input signal with the limit #1 value first (Instruction RAM “01”), followed by a comparison of the same sampled analog input signal with the value found in limit #2. Bit 8 holds limit #2’s sign. 27 Bit 9 ’s state determines the limit condition that generates a “watchdog” interrupt. A “1” causes a voltage greater than limit #2 to generate an interrupt, while a “0” causes a voltage less than limit #2 to generate an interrupt. Bits 10–15 are not used. 2.2 CONFIGURATION REGISTER The Configuration register, 1000 (A4–A1, BW = 0) or 1000x (A4–A0, BW = 1) is a 16-bit control register with read/write capability. It acts as the LM12454’s and LM12(H)458’s “control panel” holding global information as well as start/stop, reset, self-calibration, and stand-by commands. Bit 0 is the START/STOP bit. Reading Bit 0 returns an indication of the Sequencer’s status. A “0” indicates that the Sequencer is stopped and waiting to execute the next instruction. A “1” shows that the Sequencer is running. Writing a “0” halts the Sequencer when the current instruction has finished execution. The next instruction to be executed is pointed to by the instruction pointer found in the status register. A “1” restarts the Sequencer with the instruction currently pointed to by the instruction pointer. (See Bits 8–10 in the Interrupt Status register.) Bit 1 is the LM12(H)454/8’s system RESET bit. Writing a “1” to Bit 1 stops the Sequencer (resetting the Configuration register’s START/STOP bit), resets the Instruction pointer to “000” (found in the Interrupt Status register), clears the Conversion FIFO, and resets all interrupt flags. The RESET bit will return to “0” after two clock cycles unless it is forced high by writing a “1” into the Configuration register’s Standby bit. A reset signal is internally generated when power is first applied to the part. No operation should be started until the RESET bit is “0”. Writing a “1” to Bit 2 initiates an auto-zero offset voltage calibration. Unlike the eight-sample auto-zero calibration performed during the full calibration procedure, Bit 2 initiates a “short” auto-zero by sampling the offset once and creating a correction coefficient (full calibration averages eight samples of the converter offset voltage when creating a correction coefficient). If the Sequencer is running when Bit 2 is set to “1”, an auto-zero starts immediately after the conclusion of the currently running instruction. Bit 2 is reset automatically to a “0” and an interrupt flag (Bit 3, in the Interrupt Status register) is set at the end of the auto-zero (76 clock cycles). After completion of an auto-zero calibration, the Sequencer fetches the next instruction as pointed to by the Instruction RAM’s pointer and resumes execution. If the Sequencer is stopped, an auto-zero is performed immediately at the time requested. Writing a “1” to Bit 3 initiates a complete calibration process that includes a “long” auto-zero offset voltage correction (this calibration averages eight samples of the comparator offset voltage when creating a correction coefficient) followed by an ADC linearity calibration. This complete calibration is started after the currently running instruction is completed if the Sequencer is running when Bit 3 is set to “1”. Bit 3 is reset automatically to a “0” and an interrupt flag (Bit 4, in the Interrupt Status register) will be generated at the end of the calibration procedure (4944 clock cycles). After completion of a full auto-zero and linearity calibration, the Sequencer fetches the next instruction as pointed to by the Instruction RAM’s pointer and resumes execution. If the Sequencer is stopped, a full calibration is performed immediately at the time requested. Bit 4 is the Standby bit. Writing a “1” to Bit 4 immediately places the LM12(H)454/8 in Standby mode. Normal operation returns when Bit 4 is reset to a “0”. The Standby comwww.national.com LM12454/LM12458/LM12H458 2.0 Internal User-Programmable Registers (Continued) mand (“1”) disconnects the external clock from the internal circuitry, decreases the LM12(H)454/8’s internal analog circuitry power supply current, and preserves all internal RAM contents. After writing a “0” to the Standby bit, the LM12(H)454/8 returns to an operating state identical to that caused by exercising the RESET bit. A Standby completion interrupt is issued after a power-up completion delay that allows the analog circuitry to settle. The Sequencer should be restarted only after the Standby completion is issued. The Instruction RAM can still be accessed through read and write operations while the LM12(H)454/8 are in Standby Mode. Bit 5 is the Channel Address Mask. If Bit 5 is set to a “1”, Bits 13–15 in the conversion FIFO will be equal to the sign bit (Bit 12) of the conversion data. Resetting Bit 5 to a “0” causes conversion data Bits 13 through 15 to hold the instruction pointer value of the instruction to which the conversion data belongs. Bit 6 is used to select a “short” auto-zero correction for every conversion. The Sequencer automatically inserts an autozero before every conversion or “watchdog” comparison if Bit 6 is set to “1”. No automatic correction will be performed if Bit 6 is reset to “0”. The LM12(H)454/8’s offset voltage, after calibration, has a typical drift of 0.1 LSB over a temperature range of −40˚C to +85˚C. This small drift is less than the variability of the change in offset that can occur when using the auto-zero correction with each conversion. This variability is the result of using only one sample of the offset voltage to create a correction value. This variability decreases when using the full calibration mode because eight samples of the offset voltage are taken, averaged, and used to create a correction value. Bit 7 is used to program the SYNC pin (29) to operate as either an input or an output. The SYNC pin becomes an output when Bit 7 is a “1” and an input when Bit 7 is a “0”. With SYNC programmed as an input, the rising edge of any logic signal applied to pin 29 will start a conversion or “watchdog” comparison. Programmed as an output, the logic level at pin 29 will go high at the start of a conversion or “watchdog” comparison and remain high until either have finished. See Instruction RAM “00”, Bit 8. Bits 8 and 9 form the RAM Pointer that is used to select each of a 48-bit instruction’s three 16-bit sections during read or write actions. A “00” selects Instruction RAM section one, “01” selects section two, and “10” selects section three. Bit 10 activates the Test mode that is used only during production testing. Leave this bit reset to “0”. Bit 11 is the Diagnostic bit and is available only in the LM12(H)458. It can be activated by setting it to a “1” (the Test bit must be reset to a “0”). The Diagnostic mode, along with a correctly chosen instruction, allows verification that the LM12(H)458’s ADC is performing correctly. When activated, the inverting and non-inverting inputs are connected as shown in Table 1. As an example, an instruction with “001” for both VIN+ and VIN− while using the Diagnostic mode typically results in a full-scale output. 2.3 INTERRUPTS The LM12454 and LM12(H)458 have eight possible interrupts, all with the same priority. Any of these interrupts will cause a hardware interrupt to appear on the INT pin (31) if they are not masked (by the Interrupt Enable register). The Interrupt Status register is then read to determine which of the eight interrupts has been issued. TABLE 1. LM12(H)458 Input Multiplexer Channel Configuration Showing Normal Mode and Diagnostic Mode Channel Selection Data 000 001 010 011 100 101 110 111 Normal Mode VIN+ IN0 IN1 IN2 IN3 IN4 IN5 IN6 IN7 VIN− GND IN1 IN2 IN3 IN4 IN5 IN6 IN7 Diagnostic Mode VIN+ VREFOUT VREF+ IN2 IN3 IN4 IN5 IN6 IN7 VIN− GND VREF− IN2 IN3 IN4 IN5 IN6 IN7 TABLE 2. LM12454 Input Multiplexer Channel Configuration Channel Selection Data 000 001 010 011 1XX MUX+ IN0 IN1 IN2 IN3 OPEN MUX− GND IN1 IN2 IN3 OPEN NOTE: The LM12(H)454 is no longer available. Information shown for reference only. The Interrupt Status register, 1010 (A4–A1, BW = 0) or 1010x (A4–A0, BW = 1) must be cleared by reading it after writing to the Interrupt Enable register. This removes any spurious interrupts on the INT pin generated during an Interrupt Enable register access. Interrupt 0 is generated whenever the analog input voltage on a selected multiplexer channel crosses a limit while the LM12(H)454/8 are operating in the “watchdog” comparison mode. Two sequential comparisons are made when the LM12(H)454/8 are executing a “watchdog” instruction. Depending on the logic state of Bit 9 in the Instruction RAM’s second and third sections, an interrupt will be generated either when the input signal’s magnitude is greater than or less than the programmable limits. (See the Instruction RAM, Bit 9 description.) The Limit Status register will indicate which preprogrammed limit, #1 or #2 and which instruction was executing when the limit was crossed. Interrupt 1 is generated when the Sequencer reaches the instruction counter value specified in the Interrupt Enable register’s bits 8–10. This flag appears before the instruction’s execution. Interrupt 2 is activated when the Conversion FIFO holds a number of conversions equal to the programmable value stored in the Interrupt Enable register’s Bits 11–15. This value ranges from 0001 to 1111, representing 1 to 31 conversions stored in the FIFO. A user-programmed value of 0000 has no meaning. See Section 3.0 for more FIFO information. www.national.com 28 LM12454/LM12458/LM12H458 2.0 Internal User-Programmable Registers (Continued) The completion of the short, single-sample auto-zero calibration generates Interrupt 3. The completion of a full auto-zero and linearity selfcalibration generates Interrupt 4. Interrupt 5 is generated when the Sequencer encounters an instruction that has its Pause bit (Bit 1 in Instruction RAM “00”) set to “1”. The LM12(H)454/8 issues Interrupt 6 whenever it senses that its power supply voltage is dropping below 4V (typ). This interrupt indicates the potential corruption of data returned by the LM12(H)454/8. Interrupt 7 is issued after a short delay (10 ms typ) while the LM12(H)454/8 returns from Standby mode to active operation using the Configuration register’s Bit 4. This short delay allows the internal analog circuitry to settle sufficiently, ensuring accurate conversion results. 2.4 INTERRUPT ENABLE REGISTER The Interrupt Enable register at address location 1001 (A4–A1, BW = 0) or 1001x (A4–A0, BW = 1) has READ/ WRITE capability. An individual interrupt’s ability to produce an external interrupt at pin 31 (INT) is accomplished by placing a “1” in the appropriate bit location. Any of the internal interrupt-producing operations will set their corresponding bits to “1” in the Interrupt Status register regardless of the state of the associated bit in the Interrupt Enable register. See Section 2.3 for more information about each of the eight internal interrupts. Bit 0 enables an external interrupt when an internal “watchdog” comparison limit interrupt has taken place. Bit 1 enables an external interrupt when the Sequencer has reached the address stored in Bits 8–10 of the Interrupt Enable register. Bit 2 enables an external interrupt when the Conversion FIFO’s limit, stored in Bits 11–15 of the Interrupt Enable register, has been reached. Bit 3 enables an external interrupt when the single-sample auto-zero calibration has been completed. Bit 4 enables an external interrupt when a full auto-zero and linearity self-calibration has been completed. Bit 5 enables an external interrupt when an internal Pause interrupt has been generated. Bit 6 enables an external interrupt when a low power supply condition (VA+ < 4V) has generated an internal interrupt. Bit 7 enables an external interrupt when the LM12(H)454/8 return from power-down to active mode. Bits 8 – 10 form the storage location of the userprogrammable value against which the Sequencer’s address is compared. When the Sequencer reaches an address that is equal to the value stored in Bits 8–10, an internal interrupt is generated and appears in Bit 1 of the Interrupt Status register. If Bit 1 of the Interrupt Enable register is set to “1”, an external interrupt will appear at pin 31 (INT). The value stored in bits 8–10 ranges from 000 to 111, representing 0 to 7 instructions stored in the Instruction RAM. After the Instruction RAM has been programmed and the RESET bit is set to “1”, the Sequencer is started by placing a “1” in the Configuration register’s START bit. Setting the INT 1 trigger value to 000 does not generate an INT 1 the first time the Sequencer retrieves and decodes 29 Instruction 000. The Sequencer generates INT 1 (by placing a “1” in the Interrupt Status register’s Bit 1) the second time and after the Sequencer encounters Instruction 000. It is important to remember that the Sequencer continues to operate even if an Instruction interrupt (INT 1) is internally or externally generated. The only mechanisms that stop the Sequencer are an instruction with the PAUSE bit set to “1” (halts before instruction execution), placing a “0” in the Configuration register’s START bit, or placing a “1” in the Configuration register’s RESET bit. Bits 11–15 hold the number of conversions that must be stored in the Conversion FIFO in order to generate an internal interrupt. This internal interrupt appears in Bit 2 of the Interrupt Status register. If Bit 2 of the Interrupt Enable register is set to “1”, an external interrupt will appear at pin 31 (INT). 3.0 Other Registers and Functions 3.1 INTERRUPT STATUS REGISTER This read-only register is located at address 1010 (A4–A1, BW = 0) or 1010x (A4–A0, BW = 1). The corresponding flag in the Interrupt Status register goes high (“1”) any time that an interrupt condition takes place, whether an interrupt is enabled or disabled in the Interrupt Enable register. Any of the active (“1”) Interrupt Status register flags are reset to “0” whenever this register is read or a device reset is issued (see Bit 1 in the Configuration Register). Bit 0 is set to “1” when a “watchdog” comparison limit interrupt has taken place. Bit 1 is set to “1” when the Sequencer has reached the address stored in Bits 8–10 of the Interrupt Enable register. Bit 2 is set to “1” when the Conversion FIFO’s limit, stored in Bits 11–15 of the Interrupt Enable register, has been reached. Bit 3 is set to “1” when the single-sample auto-zero has been completed. Bit 4 is set to “1” when an auto-zero and full linearity selfcalibration has been completed. Bit 5 is set to “1” when a Pause interrupt has been generated. Bit 6 is set to “1” when a low-supply voltage condition (VA+ < 4V) has taken place. Bit 7 is set to “1” when the LM12(H)454/8 return from power-down to active mode. Bits 8–10 hold the Sequencer’s actual instruction address while it is running. Bits 11–15 hold the actual number of conversions stored in the Conversion FIFO while the Sequencer is running. 3.2 LIMIT STATUS REGISTER The read-only register is located at address 1101 (A4–A1, BW = 0) or 1101x (A4–A0, BW = 1). This register is used in tandem with the Limit #1 and Limit #2 registers in the Instruction RAM. Whenever a given instruction’s input voltage exceeds the limit set in its corresponding Limit register (#1 or #2), a bit, corresponding to the instruction number, is set in the Limit Status register. Any of the active (“1”) Limit Status flags are reset to “0” whenever this register is read or a device reset is issued (see Bit 1 in the Configuration register). This register holds the status of limits #1 and #2 for each of the eight instructions. Bits 0–7 show the Limit #1 status. Each bit will be set high (“1”) when the corresponding instruction’s input voltage exwww.national.com LM12454/LM12458/LM12H458 3.0 Other Registers and Functions (Continued) ceeds the threshold stored in the instruction’s Limit #1 register. When, for example, instruction 3 is a “watchdog” operation (Bit 11 is set high) and the input for instruction 3 meets the magnitude and/or polarity data stored in instruction 3’s Limit #1 register, Bit 3 in the Limit Status register will be set to a “1”. Bits 8–15 show the Limit #2 status. Each bit will be set high (“1”) when the corresponding instruction’s input voltage exceeds the threshold stored in the instruction’s Limit #2 register. When, for example, the input to instruction 6 meets the value stored in instruction 6’s Limit #2 register, Bit 14 in the Limit Status register will be set to a “1”. 3.3 TIMER The LM12(H)454/8 have an on-board 16-bit timer that includes a 5-bit pre-scaler. It uses the clock signal applied to pin 23 as its input. It can generate time intervals of 0 through 221 clock cycles in steps of 25. This time interval can be used to delay the execution of instructions. It can also be used to slow the conversion rate when converting slowly changing signals. This can reduce the amount of redundant data stored in the FIFO and retrieved by the controller. The user-defined timing value used by the Timer is stored in the 16-bit READ/WRITE Timer register at location 1011 (A4–A1, BW = 0) or 1011x (A4–A0, BW = 1) and is preloaded automatically. Bits 0–7 hold the preset value’s low byte and Bits 8–15 hold the high byte. The Timer is activated by the Sequencer only if the current instruction’s Bit 9 is set (“1”). If the equivalent decimal value “N” (0 ≤ N ≤ 216 − 1) is written inside the 16-bit Timer register and the Timer is enabled by setting an instruction’s bit 9 to a “1”, the Sequencer will delay the same instruction’s execution by halting at state 3 (S3), as shown in Figure 15, for 32 x N + 2 clock cycles. 3.4 DMA The DMA works in tandem with Interrupt 2. An active DMA Request on pin 32 (DMARQ) requires that the FIFO interrupt be enabled. The voltage on the DMARQ pin goes high when the number of conversions in the FIFO equals the 5-bit value stored in the Interrupt Enable register (bits 11–15). The voltage on the INT pin goes low at the same time as the voltage on the DMARQ pin goes high. The voltage on the DMARQ pin goes low when the FIFO is emptied. The Interrupt Status register must be read to clear the FIFO interrupt flag in order to enable the next DMA request. DMA operation is optimized through the use of the 16-bit data bus connection (a logic “0” applied to the BW pin). Using this bus width allows DMA controllers that have single address Read/Write capability to easily unload the FIFO. Using DMA on an 8-bit data bus is more difficult. Two read operations (low byte, high byte) are needed to retrieve each conversion result from the FIFO. Therefore, the DMA controller must be able to repeatedly access two constant addresses when transferring data from the LM12(H)454/8 to the host system. Bits 0–3 hold the four LSB’s in the 12 bits + sign mode or “1110” in the 8 bits + sign mode. Bits 4–11 hold the eight MSB’s and Bit 12 holds the sign bit. Bits 13–15 can hold either the sign bit, extending the register’s two’s complement data format to a full sixteen bits or the instruction address that generated the conversion and the resulting data. These modes are selected according to the logic state of the Configuration register’s Bit 5. The FIFO status should be read in the Interrupt Status register (Bits 11–15) to determine the number of conversion results that are held in the FIFO before retrieving them. This will help prevent conversion data corruption that may take place if the number of reads are greater than the number of conversion results contained in the FIFO. Trying to read the FIFO when it is empty may corrupt new data being written into the FIFO. Writing more than 32 conversion data into the FIFO by the ADC results in loss of the first conversion data. Therefore, to prevent data loss, it is recommended that the LM12(H)454/8’s interrupt capability be used to inform the system controller that the FIFO is full. The lower portion (A0 = 0) of the data word (Bits 0–7) should be read first followed by a read of the upper portion (A0 = 1) when using the 8-bit bus width (BW = 1). Reading the upper portion first causes the data to shift down, which results in loss of the lower byte. Bits 0–12 hold 12-bit + sign conversion data. Bits 0–3 will be 1110 (LSB) when using 8-bit plus sign resolution. Bits 13–15 hold either the instruction responsible for the associated conversion data or the sign bit. Either mode is selected with Bit 5 in the Configuration register. Using the FIFO’s full depth is achieved as follows. Set the value of the Interrupt Enable register’s Bits 11–15 to 11111 and the Interrupt Enable register’s Bit 2 to a “1”. This generates an external interrupt when the 31st conversion is stored in the FIFO. This gives the host processor a chance to send a “0” to the LM12(H)454/8’s Start bit (Configuration register) and halt the ADC before it completes the 32nd conversion. The Sequencer halts after the current (32) conversion is completed. The conversion data is then transferred to the FIFO and occupies the 32nd location. FIFO overflow is avoided if the Sequencer is halted before the start of the 32nd conversion by placing a “0” in the Start bit (Configuration register). It is important to remember that the Sequencer continues to operate even if a FIFO interrupt (INT 2) is internally or externally generated. The only mechanisms that stop the Sequencer are an instruction with the PAUSE bit set to “1” (halts before instruction execution), placing a “0” in the Configuration register’s START bit, or placing a “1” in the Configuration register’s RESET bit. 5.0 Sequencer The Sequencer uses a 3-bit counter (Instruction Pointer, or IP, in Figure 9) to retrieve the programmable conversion instructions stored in the Instruction RAM. The 3-bit counter is reset to 000 during chip reset or if the current executed instruction has its Loop bit (Bit 1 in any Instruction RAM “00”) set high (“1”). It increments at the end of the currently executed instruction and points to the next instruction. It will continue to increment up to 111 unless an instruction’s Loop bit is set. If this bit is set, the counter resets to “000” and execution begins again with the first instruction. If all instructions have their Loop bit reset to “0”, the Sequencer will execute all eight instructions continuously. Therefore, it is important to realize that if less than eight instructions are programmed, the Loop bit on the last instruction must be set. 4.0 FIFO The result of each conversion stored in an internal read-only FIFO (First-In, First-Out) register. It is located at 1100 (A4–A1, BW = 0) or 1100x (A4–A0, BW = 1). This register has 32 16-bit wide locations. Each location holds 13-bit data. www.national.com 30 LM12454/LM12458/LM12H458 5.0 Sequencer (Continued) 16 32T + 2 where 0 ≤ T ≤ 2 −1. State 7: Run the acquisition delay and read Limit #1’s value if needed. The number of clock cycles for 12-bit + sign mode varies according to 9 + 2D where D is the user-programmable 4-bit value stored in bits 12–15 of Instruction RAM “00” and is limited to 0 ≤ D ≤ 15. The number of clock cycles for 8-bit + sign or “watchdog” mode varies according to 2 + 2D where D is the user-programmable 4-bit value stored in bits 12–15 of Instruction RAM “00” and is limited to 0 ≤ D ≤ 15. State 6: Perform first comparison. This state is 5 clock cycles long. State 4: Read Limit #2. This state is 1 clock cycle long. State 5: Perform a conversion or second comparison. This state takes 44 clock cycles when using the 12-bit + sign mode or 21 clock cycles when using the 8-bit + sign mode. The “watchdog” mode takes 5 clock cycles. Leaving this bit reset to “0” allows the Sequencer to execute “unprogrammed” instructions, the results of which may be unpredictable. The Sequencer’s Instruction Pointer value is readable at any time and is found in the Status register at Bits 8–10. The Sequencer can go through eight states during instruction execution: State 0: The current instruction’s first 16 bits are read from the Instruction RAM “00”. This state is one clock cycle long. State 1: Checks the state of the Calibration and Start bits. This is the “rest” state whenever the Sequencer is stopped using the reset, a Pause command, or the Start bit is reset low (“0”). When the Start bit is set to a “1”, this state is one clock cycle long. State 2: Perform calibration. If bit 2 or bit 6 of the Configuration register is set to a “1”, state 2 is 76 clock cycles long. If the Configuration register’s bit 3 is set to a “1”, state 2 is 4944 clock cycles long. State 3: Run the internal 16-bit Timer. The number of clock cycles for this state varies according to the value stored in the Timer register. The number of clock cycles is found by using the expression below 31 www.national.com LM12454/LM12458/LM12H458 5.0 Sequencer (Continued) 01126419 FIGURE 15. Sequencer Logic Flow Chart (IP = Instruction Pointer) www.national.com 32 LM12454/LM12458/LM12H458 6.0 Design Considerations 6.1 REFERENCE VOLTAGE The difference in the voltages applied to the VREF+ and VREF− defines the analog input voltage span (the difference between the voltages applied between two multiplexer inputs or the voltage applied to one of the multiplexer inputs and analog ground), over which 4095 positive and 4096 negative codes exist. The voltage sources driving VREF+ or VREF− must have very low output impedance and noise. The ADC can be used in either ratiometric or absolute reference applications. In ratiometric systems, the analog input voltage is proportional to the voltage used for the ADC’s reference voltage. When this voltage is the system power supply, the VREF+ pin is connected to VA+ and VREF− is connected to GND. This technique relaxes the system reference stability requirements because the analog input voltage and the ADC reference voltage move together. This maintains the same output code for given input conditions. For absolute accuracy, where the analog input voltage varies between very specific voltage limits, a time and temperature stable voltage source can be connected to the reference inputs. Typically, the reference voltage’s magnitude will require an initial adjustment to null reference voltage induced full-scale errors. When using the LM12(H)454/8’s internal 2.5V bandgap reference, a parallel combination of a 100 µF capacitor and a 0.1 µF capacitor connected to the VREFOUT pin is recommended for low noise operation. When left unconnected, the reference remains stable without a bypass capacitor. However, ensure that stray capacitance at the VREFOUT pin remains below 50 pF. 6.2 INPUT RANGE The LM12(H)454/8’s fully differential ADC and reference voltage inputs generate a two’s-complement output that is found by using the equation below. 6.4 INPUT SOURCE RESISTANCE For low impedance voltage sources ( < 100Ω for 5 MHz operation and < 60Ω for 8 MHz operation), the input charging current will decay, before the end of the S/H’s acquisition time, to a value that will not introduce any conversion errors. For higher source impedances, the S/H’s acquisition time can be increased. As an example, operating with a 5 MHz clock frequency and maximum acquisition time, the LM12(H)454/8’s analog inputs can handle source impedance as high as 6.67 kΩ. When operating at 8 MHz and maximum acquisition time, the LM12H454/8’s analog inputs can handle source impedance as high as 4.17 kΩ. Refer to Section 2.1, Instruction RAM “00”, Bits 12–15 for further information. 6.5 INPUT BYPASS CAPACITANCE External capacitors (0.01 µF to 0.1 µF) can be connected between the analog input pins, IN0–IN7, and analog ground to filter any noise caused by inductive pickup associated with long input leads. It will not degrade the conversion accuracy. 6.6 NOISE The leads to each of the analog multiplexer input pins should be kept as short as possible. This will minimize input noise and clock frequency coupling that can cause conversion errors. Input filtering can be used to reduce the effects of the noise sources. 6.7 POWER SUPPLIES Noise spikes on the VA+ and VD+ supply lines can cause conversion errors; the comparator will respond to the noise. The ADC is especially sensitive to any power supply spikes that occur during the auto-zero or linearity correction. Low inductance tantalum capacitors of 10 µF or greater paralleled with 0.1 µF monolithic ceramic capacitors are recommended for supply bypassing. Separate bypass capacitors should be used for the VA+ and VD+ supplies and placed as close as possible to these pins. 6.8 GROUNDING The LM12(H)454/8’s nominal performance can be maximized through proper grounding techniques. These include the use of a single ground plane and meticulously separating analog and digital areas of the board. The use of separate analog and digital digital planes within the same board area generally provides best performance. All components that handle digital signals should be placed within the digital area of the board, as defined by the digital power plane, while all analog components should be placed in the analog area of the board. Such placement and the routing of analog and digital signal lines within their own respective board areas greatly reduces the occurrence of ground loops and noise. This will also minimize EMI/RFI radiation and susceptibility. It is recommended that stray capacitance between the analog inputs or outputs, including the reference pins, be kept to a minimum by increasing the clearance (+1/16th inch) between the analog signal and reference pins and the ground plane. 6.9 CLOCK SIGNAL CONSIDERATIONS The LM12(H)458’s performance is optimized by routing the analog input/output and reference signal conductors (pins 34–44) as far as possible from the conductor that carries the clock signal to pin 23. Avoid overshoot and undershoot on the clock line by treating this line as a transmission line (use proper termination tech33 www.national.com Round up to the next integer value between −4096 to 4095 for 12-bit resolution and between −256 to 255 for 8-bit resolution if the result of the above equation is not a whole number. As an example, VREF+ = 2.5V, VREF− = 1V, VIN+ = 1.5V and VIN− = GND. The 12-bit + sign output code is positive full-scale, or 0,1111,1111,1111. If VREF+ = 5V, VREF− = 1V, VIN+ = 3V, and VIN− = GND, the 12-bit + sign output code is 0,1100,0000,0000. 6.3 INPUT CURRENT A charging current flows into or out of (depending on the input voltage polarity) the analog input pins, IN0–IN7 at the start of the analog input acquisition time (tACQ). This current’s peak value will depend on the actual input voltage applied. This charging current causes voltage spikes at the inputs. This voltage spikes will not corrupt the conversion results. LM12454/LM12458/LM12H458 6.0 Design Considerations (Continued) niques). Failure to do so can result in erratic operation. Generally, a series 30Ω to 50Ω resistor in the clock line, located as close to the clock source as possible, will prevent most problems. The clock source should drive ONLY the LM12(H)458 clock pin. 7.0 Common Application Problems Driving the analog inputs with op-amp(s) powered from supplies other than the supply used for the LM12(H)458. This practice allows for the possibility of the amplifier output (LM12(H)458 input) to reach potentials outside of the 0V to VA+ range. This could happen in normal operation if the amplifier use supply voltages outside of the range of the LM12(H)458 supply rails. This could also happen upon power up if the amplifier supply or supplies ramp up faster than the supply of the LM12(H)458. If any pin experiences a potential more than 100 mV below ground or above the supply voltage, even on a fast transient basis, the result could be erratic operation, missing codes, one channel interacting with one or more of the others, skipping channels or a complete malfunction, depending upon how far the input is driven beyond the supply rails. Not performing a full calibration at power up. This can result in missing codes. The device needs to have a full calibration run and completed after power up and BEFORE attempting to perform even a single conversion or watchdog operation. The only way to recover if this is violated is to interrupt the power to the device. Not waiting for the calibration process to complete before trying to write to the device. Once a calibration is requested, the ONLY read of the LM12(H)458 should be if the Interrupt Status Register to check for a completed calibration. Attempting a write or any other read during calibration would cause a corruption of the calibration process, resulting in missing codes. The only way to recover would be to interrupt the power. Improper termination of digital lines. Improper termination can result in energy reflections that build up to cause overshoot that goes above the supply potential and undershoot that goes below ground. It is never good to drive a device beyond the supply rails, unless the device is specifically designed to handle this situation, but the LM12(H)458 is more sensitive to this condition that most devices. Again, if any pin experiences a potential more than 100 mV below ground or above the supply voltage, even on a fast transient basis, the result could be erratic operation, missing codes, or a complete malfunction, depending upon how far the input is driven beyond the supply rails. The clock input is the most sensitive digital one. Generally, a 50Ω series resistor, located very close to the signal source, will keep digital lines "clean". Excessive output capacitance on the digital lines. The current required to charge the capacitance on the digital outputs can cause noise on the supply bus within the LM12(H)458, causing internal supply "bounce" even when the external supply pin is pretty stable. The current required to discharge the output capacitance can cause die ground "bounce". Either of these can cause noise to be induced at the analog inputs, resulting in conversion errors. Output capacitance should be limited as much as possible. A series 100Ω resistor in each digital output line, located very close to the output pin, will limit the charge and discharge current, minimizing the extent of the conversion errors. Improper CS decoding. If address decoder is used, care must be exercised to ensure that no "runt" (very narrow) pulse is produced on theCS line when trying to address another device or memory. Even sub-nanosecond spikes on the CS line can cause the chip to be reprogrammed in accordance with what happens to be on the data lines at the time. The result is unexpected operation. The worst case result is that the device is put into the "Test" mode and the on-board EEPROM that corrects linearity is corrupted. If this happens, the only recourse is to replace the device. www.national.com 34 LM12454/LM12458/LM12H458 Physical Dimensions inches (millimeters) unless otherwise noted Order Number LM12454CIV, LM12458CIV or LM12H458CIV NS Package Number V44A Order Number LM12H458CIVF or LM12458CIVF NS Package Number VGZ44A 35 www.national.com LM12454/LM12458/LM12H458 12-Bit + Sign Data Acquisition System with Self-Calibration Notes National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. 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