19-1319; Rev 1; 1/98 KIT ATION EVALU E L B AVAILA 2x4-Channel, Simultaneous-Sampling 14-Bit DAS ____________________________Features The MAX125/MAX126 are high-speed, multichannel, 14-bit data-acquisition systems (DAS) with simultaneous track/holds (T/Hs). These devices contain a 14-bit, 3s, successive-approximation analog-to-digital converter (ADC), a +2.5V reference, a buffered reference input, and a bank of four simultaneous-sampling T/H amplifiers that preserve the relative phase information of the sampled inputs. The MAX125/MAX126 have two multiplexed inputs for each T/H, allowing a total of eight inputs. In addition, the converter is overvoltage tolerant to 17V; a fault condition on any channel will not harm the IC. Available input ranges are 5V (MAX125) and 2.5V (MAX126). An on-board sequencer converts one to four channels per CONVST pulse. In the default mode, one T/H output (CH1A) is converted. An interrupt signal (INT) is provided after the last conversion is complete. Convert two, three, or four channels by reprogramming the MAX125/MAX126 through the bidirectional parallel interface. Once programmed, the MAX125/MAX126 continue to convert the specified number of channels per CONVST pulse until they are reprogrammed. The channels are converted sequentially, beginning with CH1. The INT signal always follows the end of the last conversion in a conversion sequence. The ADC converts each assigned channel in 3s and stores the result in an internal 14x4 RAM. Upon completion of the conversions, data can be accessed by applying successive pulses to the RD pin. Four successive reads access four data words sequentially. The parallel interface's data-access and bus-release timing specifications are compatible with most popular digital signal processors and 16-bit/32-bit microprocessors, so the MAX125/MAX126 conversion results can be accessed without resorting to wait states. Four Simultaneous-Sampling T/H Amplifiers with Two Multiplexed Inputs (eight single-ended inputs total) ________________________Applications Multiphase Motor Control Power-Grid Synchronization Power-Factor Monitoring 3s Conversion Time per Channel Throughput: 250ksps (1 channel) 142ksps (2 channels) 100ksps (3 channels) 76ksps (4 channels) Input Range: 5V (MAX125) 2.5V (MAX126) Fault-Protected Input Multiplexer (17V) 5V Supplies Internal +2.5V or External Reference Operation Programmable On-Board Sequencer High-Speed Parallel DSP Interface ______________Ordering Information INL (LSB) PART TEMP. RANGE MAX125ACAX 0C to +70C 36 SSOP* 2 MAX125BCAX 0C to +70C 36 SSOP* 4 MAX125CCAX MAX125AEAX MAX125BEAX MAX125CEAX MAX126ACAX 0C to +70C -40C to +85C -40C to +85C -40C to +85C 0C to +70C 36 SSOP 36 SSOP* 36 SSOP* 36 SSOP 36 SSOP* 4 2 4 4 2 MAX126BCAX 0C to +70C 36 SSOP* 4 MAX126CCAX MAX126AEAX MAX126BEAX MAX126CEAX 0C to +70C -40C to +85C -40C to +85C -40C to +85C 36 SSOP 36 SSOP* 36 SSOP* 36 SSOP 4 2 4 4 PIN-PACKAGE *Contact factory for availability. Digital Signal Processing Vibration and Waveform Analysis Typical Operating Circuit appears at end of data sheet. Pin Configuration appears at end of data sheet. ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 408-737-7600 ext. 3468. MAX125/MAX126 ________________General Description MAX125/MAX126 2x4-Channel, Simultaneous-Sampling 14-Bit DAS ABSOLUTE MAXIMUM RATINGS AVDD to AGND ...........................................................-0.3V to 6V AVSS to AGND ............................................................0.3V to -6V DVDD to DGND ...........................................................-0.3V to 6V AGND to DGND .......................................................-0.3V to 0.3V CH_ _ to AGND....................................................................17V REFIN, REFOUT to AGND ..........................................-0.3V to 6V Digital Inputs/Outputs to DGND ..............-0.3V to (DVDD + 0.3V) Continuous Power Dissipation (TA = +70C) SSOP (derate 11.8mW/C above +70C) .....................941mW Operating Temperature Ranges MAX125_CAX/MAX126_CAX ...............................0C to +70C MAX125_EAX/MAX126_EAX ............................-40C to +85C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10sec)................................300C Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (AVDD = +5V 5%, AVSS = -5V 5%, DVDD = +5V 5%, VREFIN = 2.5V, AGND = DGND = 0V, 4.7F capacitor from REFOUT to AGND, 0.1F capacitor from REFIN to AGND, fCLK = 16MHz, external clock, 50% duty cycle, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DC ACCURACY (Note 1) Resolution N Integral Nonlinearity (Note 2) INL Differential Nonlinearity DNL All channels 14 2 MAX12_B/C 2 1 MAX125C/MAX126C, guaranteed monotonic to 13 bits 2 5 TA = TMIN to TMAX Bipolar Zero-Error Match 4 MAX12_A/B, guaranteed monotonic to 14 bits TA = +25C Bipolar Zero Error Bits MAX125A/MAX126A 15 25 Between all channels 1.2 Zero-Code Tempco 5 5 TA = +25C Gain Error 5 TA = TMIN to TMAX Gain Error Match 1.2 Gain Error Tempco LSB mV mV ppm/C 10 15 Between all channels LSB 5 5 mV mV ppm/C DYNAMIC PERFORMANCE (fCLK = 16MHz, fIN = 10.06kHz) (Notes 1, 3) Signal-to-Noise Plus Distortion (Note 4) SINAD Single-channel mode, channel 1A, 250ksps MAX125 MAX125 72 75 MAX126 70 72 Total Harmonic Distortion (Notes 4, 5) THD Single-channel mode, channel 1A, 250ksps Spurious-Free Dynamic Range (Note 4) SFDR Single-channel mode, channel 1A, 250ksps Channel-to-Channel Isolation (Note 6) 2 Single-channel mode, channel 1A, 250ksps -89 80 dB -80 dB 90 dB 80 dB _______________________________________________________________________________________ 2x4-Channel, Simultaneous-Sampling 14-Bit DAS (AVDD = +5V 5%, AVSS = -5V 5%, DVDD = +5V 5%, VREFIN = 2.5V, AGND = DGND = 0V, 4.7F capacitor from REFOUT to AGND, 0.1F capacitor from REFIN to AGND, fCLK = 16MHz, external clock, 50% duty cycle, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS ANALOG INPUT Input Voltage Range VIN Input Current IIN Input Capacitance CIN MAX125 5 MAX126 2.5 MAX125, VIN = 5V MAX126, VIN = 2.5V (Note 7) V 667 A A 16 pF TRACK/HOLD Acquisition Time tACQ 1 Small-Signal Bandwidth s 8 Full-Power Bandwidth Droop Rate MHz 0.5 MHz 2 mV/ms Aperture Delay 5 ns Aperture Jitter 30 psRMS Aperture-Delay Matching 500 ps REFERENCE OUTPUT (Note 8) Output Voltage VREFOUT TA = +25C 2.475 2.500 2.525 V External Load Regulation 0mA < ILOAD < 1mA 1 % REFOUT Tempco (Note 9) 30 ppm/C External Capacitive Bypass at REFIN 0.1 External Capacitive Bypass at REFOUT 4.7 F 22 F REFERENCE INPUT Input Voltage Range 2.50 10% Input Current REFIN = 2.5V Input Resistance (Note 10) Input Capacitance (Note 7) V 10 10 A k 10 pF 16 MHz EXTERNAL CLOCK External Clock Frequency 0.1 DIGITAL INPUTS (CONVST, RD, WR, CS, CLK, A0-A3) (Note 1) Input High Voltage VIH Input Low Voltage VIL Input Current IIN Input Capacitance CIN 2.4 V 0.8 CONVST, RD, WR, CS, CLK 1 A0-A3 10 (Note 7) 15 V A pF _______________________________________________________________________________________ 3 MAX125/MAX126 ELECTRICAL CHARACTERISTICS (continued) MAX125/MAX126 2x4-Channel, Simultaneous-Sampling 14-Bit DAS ELECTRICAL CHARACTERISTICS (continued) (AVDD = +5V 5%, AVSS = -5V 5%, DVDD = +5V 5%, VREFIN = 2.5V, AGND = DGND = 0V, 4.7F capacitor from REFOUT to AGND, 0.1F capacitor from REFIN to AGND, fCLK = 16MHz, external clock, 50% duty cycle, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DIGITAL OUTPUTS (D0-D13, INT) (Note 1) Output High Voltage VOH IOUT = 1mA Output Low Voltage VOL IOUT = -1.6mA 4 0.4 V V Three-State Leakage Current D0-D13 10 A Three-State Output Capacitance (Note 7) 10 pF POWER REQUIREMENTS Positive Supply Voltage AVDD 4.75 5 5.25 V Negative Supply Voltage AVSS -5.25 -5 -4.75 V Digital Supply Voltage DVDD 4.75 5 5.25 V Positive Supply Current I(AVDD) 17 25 mA Negative Supply Current I(AVSS) Digital Supply Current I(DVDD) -17 -13 3 Shutdown Positive Current Shutdown Negative Current Positive Supply Rejection PSRR+ (Note 11) Negative Supply Rejection PSRR- (Note 11) 4 5 mA 3 mA -1 mA Shutdown Digital Current Power Dissipation mA (Note 12) 1 165 _______________________________________________________________________________________ 3 mA 2 LSB 2 LSB 250 mW 2x4-Channel, Simultaneous-Sampling 14-Bit DAS (AVDD = +5V, AVSS = -5V, DVDD = +5V, AGND = DGND = 0V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER CONVST Pulse Width SYMBOL CONDITIONS MIN TYP MAX UNITS tCW 30 ns CS to WR Setup Time tCWS 0 ns CS to WR Hold Time tCWH 0 ns WR Low Pulse Width tWR 30 ns CS to CONVST Delay tCSD 125 ns Address Setup Time tAS 30 ns Address Hold Time tAH 0 ns RD to INT Delay tID Delay Time Between Reads tRD 40 ns CS to RD Setup Time tCRS 0 ns CS to RD Hold Time tCRH 0 ns RD Low Pulse Width tRD 30 Data-Access Time tDA 25pF load (Note 13) Bus-Relinquish Time tDH 25pF load (Note 14) Conversion Time tCONV Conversion Rate/Channel 25pF load 30 ns 5 30 ns 45 ns Mode 1, 1 channel 3 Mode 2, 2 channel 6 Mode 3, 3 channel 9 Mode 4, 4 channel 12 Mode 1, 1 channel 250 Mode 2, 2 channel 142 Mode 3, 3 channel 100 Mode 4, 4 channel Start-Up Time Exiting shutdown ns s ksps 76 5 s Note 1: AVDD = +5V, AVSS = -5V, DVDD = +5V, VREFIN = 2.500V (external), VIN = 5V (MAX125) or 2.5V (MAX126). Note 2: Relative accuracy is the analog value's deviation at any code from its theoretical value after the full-scale range has been calibrated. Note 3: CLK synchronized with CONVST. Note 4: fIN = 10.06kHz, VIN = 5V (MAX125) or 2.5V (MAX126). Note 5: First five harmonics. Note 6: All inputs except CH1A driven with 5V (MAX125) or 2.5V (MAX126) 10kHz signal; CH1A connected to AGND and digitized. Note 7: Guaranteed by design. Not production tested. Note 8: AVDD = +5V, AVSS = -5V, DVDD = +5V, VIN = 0V (all channels). Note 9: Temperature drift is defined as the change in output voltage from +25C to TMIN or TMAX. It is calculated as TC = [REFOUT/REFOUT] / T. Note 10: See Figure 2. Note 11: Defined as the change in positive full scale caused by a 5% variation in the nominal supply voltage. Tested with one input at full scale and all others at AGND. VREFIN = 2.5V (internal). Note 12: Tested with VIN = AGND on all channels, VREFIN = 2.5V (internal). Note 13: The data-access time is defined as the time required for an output to cross 0.8V or 2.0V. It is measured using the circuit of Figure 1. The measured number is then extrapolated back to determine the value with a 25pF load. Note 14: The bus-relinquish time is derived from the measured time taken for the data outputs to change 0.5V when loaded with the circuit of Figure 1. The measured number is then extrapolated back to remove the effects of charging/discharging the 120pF capacitor. Thus, the time given is the part's true bus-relinquish time, independent of the external bus loading capacitance. _______________________________________________________________________________________ 5 MAX125/MAX126 TIMING CHARACTERISTICS (Figure 4) MAX125/MAX126 2x4-Channel, Simultaneous-Sampling 14-Bit DAS ______________________________________________________________Pin Description PIN NAME FUNCTION 1, 2 CH2B, CH2A Channel 2 Multiplexed Inputs, single-ended 3, 4 CH1B, CH1A Channel 1 Multiplexed Inputs, single-ended 5 AVDD +5V 5% Analog Supply Voltage 6 REFIN External Reference Input/Internal Reference Output. Bypass with a 0.1F capacitor to AGND. 7 REFOUT 8, 36 AGND 9-16 D13-D6 17 DVDD +5V 5% Digital Supply Voltage 18 DGND Digital Ground 19, 20 D5, D4 Data Bits 21-24 D3/A3-D0/A0 25 CLK 26 CS Chip-Select Input (active-low) 27 WR Write Input (active-low) 28 RD Read Input (active-low) 29 CONVST 30 INT 31 AVSS 32, 33 CH4A, CH4B Channel 4 Multiplexed Inputs, single-ended 34, 35 CH3A, CH3B Channel 3 Multiplexed Inputs, single-ended Reference-Buffer Output. Bypass with a 4.7F capacitor to AGND. Analog Ground. Both pins must be tied to ground. Data Bits. D13 = MSB. Bidirectional Data Bits/Address Bits. D0/A0 = LSB. Clock Input (duty cycle must be 30% to 70%). Conversion-Start Input. Rising edge initiates sampling and conversion sequence. Interrupt Output. Falling edge indicates the end of a conversion sequence. -5V 5% Analog Supply Voltage _______________Detailed Description The MAX125/MAX126 use a successive-approximation conversion technique and four simultaneous-sampling track/hold (T/H) amplifiers to convert analog signals into 14-bit digital outputs. Each T/H has two multiplexed inputs, allowing a total of eight inputs. Each T/H output is converted and stored in memory to be accessed sequentially by the parallel interface with successive read cycles. The MAX125/MAX126 internal microsequencer can be programmed to digitize one, two, three, or four inputs sampled simultaneously from either of the two banks of four inputs (see Figure 2). The conversion timing and control sequences are derived from a 16MHz external clock, the CONVST 6 1.6mA TO OUTPUT PIN 1.6V 120pF 1.0mA Figure 1. Load Circuit for Access Time and Bus Relinquish Time _______________________________________________________________________________________ 2x4-Channel, Simultaneous-Sampling 14-Bit DAS AGND MAX125/MAX126 REFIN REFOUT BANDGAP REFERENCE 10k CH1A A CH1B CH2A B A B MUX T/H 2.50V MUX T/H VREF CH2B MUX COMP CH3A A B MUX T/H CH3B 14-BIT DAC CH4A A CH4B B MUX SAR T/H VREF 14x4 RAM D0/A0 (LSB) AVDD D1/A1 AGND THREE-STATE OUTPUT DRIVERS AVSS D3/A3 D13 (MSB) CONTROL LOGIC MAX125 MAX126 D2/A2 BUS INTERFACE CLK CONVST INT CS RD WR DVDD DGND Figure 2. Functional Diagram _______________________________________________________________________________________ 7 MAX125/MAX126 2x4-Channel, Simultaneous-Sampling 14-Bit DAS HOLD BUFFER C HOLD 7pF HOLD 5k CH_A S1A C IN S2A FROM MICROSEQUENCER TRACK TRACK 5k S3A MUX S1B 5k CH_B C IN S2B 5k S3B REFOUT DAC MAX125 MAX126 SAR Figure 3. Equivalent Input Circuit signal, and the programmed mode. The T/H amplifiers hold the input voltages at the CONVST rising edge. Additional CONVST pulses are ignored until the last conversion for the sample is complete. The ADC converts each assigned channel in 3s and stores the result in an internal 4x14-bit memory. At the end of the last conversion, INT goes low and the T/H amplifiers begin to track the inputs again. The data can be accessed by applying successive pulses to the RD pin. Successive reads access data words sequentially. The memory is not random-access; data from CH1 is always read first. After accessing all programmed channels, the address pointer selects CH1 again. Additional read pulses cycle through the data words. CS can be held low during successive reads. Input Bandwidth The T/H's input tracking circuitry has an 8MHz smallsignal bandwidth, so it is possible to digitize highspeed transient events and measure periodic signals with bandwidths exceeding the ADC's sampling rate by using undersampling techniques. To avoid highfrequency signals being aliased into the frequency band of interest, anti-alias filtering is recommended. 8 Analog Input Range and Input Protection The MAX125's input range is 5V, and the MAX126's input range is 2.5V. The input resistance for both parts is 10k. An input protection structure allows input voltages to 17V without harming the IC. This protection is also active in shutdown mode. Track/Holds The MAX125/MAX126 feature four simultaneous T/Hs. Each T/H has two multiplexed inputs. A T-switch input configuration provides excellent hold-mode isolation. Allow 1s acquisition time for 14-bit accuracy. The T/H aperture delay is typically 10ns. The 500ps aperture-delay mismatch between the T/Hs allows the relative phase information of up to four different inputs to be preserved. Figure 3 shows the equivalent input circuit, illustrating the ADC's sampling architecture. Only one of four T/H stages with its two multiplexed inputs (CH_A and CH_B) is shown. All switches are in track configuration for channel A. An internal buffer charges the hold capacitor to minimize the required acquisition time between conversions. The analog input appears as a 10k resistor in parallel with a 16pF capacitor. _______________________________________________________________________________________ 2x4-Channel, Simultaneous-Sampling 14-Bit DAS MAX125/MAX126 tCW CONVST tCONV INT tACQ tID tCWH tCSD tCWS CS tCRS tCRH RD tRD t WR t RD WR tDA tDH DATA CH1 DATA IN CH2 CH3 CH4 tAS tAH Figure 4. Timing Diagram RD inputs and forces the interface into a high-Z state. Figure 4 details the interface timing. CS Programming Modes WR A0 (LSB) A1 A2 A3 Figure 5. Programming a Four-Channel Conversion, Input Mux A Between conversions, the buffer input is connected to channel 1 of the selected track/hold bank. When a channel is not selected, switches S1, S2, and S3 are placed in hold mode to improve channel-to-channel isolation. Digital Interface Input data (A0-A3) and output data (D0-D13) are multiplexed on a three-state bidirectional interface. This parallel I/O can easily be interfaced with a microprocessor (P) or DSP. CS, WR, and RD control the write and read operations. CS is the standard chip-select signal, which enables the controller to address the MAX125/MAX126 as an I/O port. When CS is high, it disables the WR and The MAX125/MAX126 have eight conversion modes plus power-down, which are programmed through a bidirectional parallel interface. At power-up, the devices default to the mode Input Mux A/Single-Channel Conversion. The user can select between two banks (mux inputs A or mux inputs B) of four simultaneoussampled input channels, as illustrated in Figure 2. An internal microsequencer can be programmed to convert one, two, three, or four channels of the selected bank per sample. For a single-channel conversion, CH1 is digitized, and then INT goes low to indicate completion of the conversion. For multichannel conversions, INT goes low after the last channel has been digitized. To input data into the MAX125/MAX126, pull CS low, program the bidirectional pins A0-A3 (Table 1), and pulse WR low. Data is latched into the devices on the WR or CS rising edge. The ADC is now ready to convert. Once programmed, the ADCs continue operating in the same mode until they are reprogrammed or until power is removed. Figure 5 shows an example of programming a four-channel conversion using Input Mux A. Starting a Conversion After programming the MAX125/MAX126 as outlined in the Programming Modes section, pulse CONVST low to initiate a conversion sequence. The analog inputs are sampled at the CONVST rising edge. Do not start a new conversion while the conversion is in progress. Monitor the INT output. A falling edge indicates the end of a conversion sequence. _______________________________________________________________________________________ 9 MAX125/MAX126 2x4-Channel, Simultaneous-Sampling 14-Bit DAS Table 1. Modes of Operation A3 A2 A1 A0 CONVERSION TIME (s) 0 0 0 0 3 Input Mux A/Single-Channel Conversion (default at power-up) 0 0 0 1 6 Input Mux A/Two-Channel Conversion 0 0 1 0 9 Input Mux A/Three-Channel Conversion 0 0 1 1 12 Input Mux A/Four-Channel Conversion 0 1 0 0 3 Input Mux B/Single-Channel Conversion 0 1 0 1 6 Input Mux B/Two-Channel Conversion 0 1 1 0 9 Input Mux B/Three-Channel Conversion 0 1 1 1 12 Input Mux B/Four-Channel Conversion 1 X X X -- Power-Down MODE X = Don't care REFOUT TO DAC 7 (2.5V) 4.7F AV = 1 address pointer is reset to CH_1. For multichannel conversions, up to four RD falling edges sequentially access the data for channels 1 through 4. For n channels converted (1 < n 4), the address pointer is reset to CH_1 after n RD pulses. Do not perform a read operation during conversion, as it will corrupt the conversion's accuracy. __________Applications Information REFIN MAX125 MAX126 6 (2.5V) External Clock 0.1F 10k The MAX125/MAX126 require a TTL-compatible clock up to 16MHz for proper operation. The clock duty cycle's range is between 30% and 70%. Internal and External Reference 2.5V Figure 6. Internal Reference Reading a Conversion Digitized data from up to four channels are stored in memory to be read out through the parallel interface. After receiving an INT signal, the user can access up to four conversion results by performing up to four read operations. With CS low, the conversion result from CH_1 is accessed, and INT is reset high on the first RD falling edge. On the RD rising edge, the internal address pointer is advanced. If a single conversion is programmed, only one RD pulse is required, and the 10 The MAX125/MAX126 can be used with an internal or external reference voltage. An external reference can be connected directly at REFIN. An internal buffer with a gain of +1 provides 2.5V at REFOUT. Internal Reference The full-scale range with the internal reference is 5V for the MAX125 and 2.5V for the MAX126. Bypass REFIN with a 0.1F capacitor to AGND and bypass the REFOUT pin with a 4.7F (min) capacitor to AGND (Figure 6). The maximum value to compensate the reference buffer is 22F. Larger values are acceptable if low-ESR capacitors are used. External Reference For operation over a wide temperature range, an external 2.5V reference with tighter specifications improves accuracy. The MAX6325 is an excellent choice to match the MAX125/MAX126 accuracy over the commercial and extended temperature ranges with a ______________________________________________________________________________________ 2x4-Channel, Simultaneous-Sampling 14-Bit DAS MAX125/MAX126 OUTPUT CODE REFOUT TO DAC 7 (2.5V) 011 . . . 111 011 . . . 110 4.7F 000 . . . 010 AV = 1 000 . . . 001 REFIN MAX125 MAX126 6 1LSB = 000 . . . 000 (2.5V) OUT 4VREFOUT 16384 111 . . . 111 111 . . . 110 MAX6325 111 . . . 101 10k 100 . . . 001 100 . . . 000 2.5V - FS ZERO +FS - 1LSB INPUT VOLTAGE (LSB) FS = 2 x VREFOUT (MAX125) FS = VREFOUT (MAX126) Figure 7. External Reference Figure 8. Bipolar Transfer Function 1ppm/C (max) temperature drift. Connect an external reference at REFIN as shown in Figure 7. The minimum impedance is 7k for DC currents in both normal operation and shutdown. Bypass REFOUT with a 4.7F lowESR capacitor. buffer's settling time and the bypass capacitor's value dominate the power-up delay. With the recommended 4.7F at REFOUT, the power-up delay is typically 5s. Power-On Reset When power is first applied, the internal power-on-reset circuitry activates the MAX125/MAX126 with INT = high, ready to convert. The default conversion mode is Input Mux A/Single-Channel Conversion. See the Programming Modes section if other configurations are desired. After the power supplies have been stabilized, the reset time is 5s; no conversions should be performed during this phase. At power-up, data in memory is undefined. Software Power-Down Software power-down is activated by setting bit A3 of the control word high (Table 1). It is asserted after the WR or CS rising edge, at which point the ADC immediately powers down to a low quiescent-current state. AVDD drops to less than 1.5mA, and AVSS is reduced to less than 1mA. The ADC blocks and reference buffer are turned off, but the digital interface and the reference remain active for fast power-up recovery. Wake up the MAX125/MAX126 by writing a control word (A0-A3, Table 1). The bidirectional interface interprets a logic zero at A3 as the start signal and powers up in the mode selected by A0, A1, and A2. The reference Transfer Function The MAX125/MAX126 have bipolar input ranges. Figure 8 shows the bipolar/output transfer function. Code transitions occur at successive-integer least significant bit (LSB) values. Output coding is twos-complement binary with 1LSB = 610V for the MAX125 and 1LSB = 305V for the MAX126. Output Demultiplexer An output demultiplexer circuit is useful for isolating data from one channel in a four-channel conversion sequence. Figure 9's circuit uses the external 16MHz clock and the INT signal to generate four RD pulses and a latch clock to save data from the desired channel. CS must be low during the four RD pulses. The channel is selected with the binary coding of two switches. A 16-bit 16373 latch simplifies layout. Motor-Control Applications Vector motor control requires monitoring of the individual phase currents. In their most basic application, the MAX125/MAX126 simultaneously sample two currents (CH1A and CH2A, Figure 10) and preserve the necessary relative phase information. Only two of the three phase currents have to be digitized, because the third component can be mathematically derived with a coordinate transformation. ______________________________________________________________________________________ 11 MAX125/MAX126 2x4-Channel, Simultaneous-Sampling 14-Bit DAS VCC VCC HC161 1/2 HC74 PRE D CLR ENP ENT Q Q RD LOAD HC688 CLR VCC INT A B (LSB) 0 P0 1 C 2 D 3 RCO P1 P2 P3 P4 P5 P6 P7 EXTERNAL CLOCK VCC P=Q Q0 Q1 LATCH CLOCK (TO 16373 LATCH) Q2 Q3 10k Q4 Q5 Q6 Q7 G CH1 0 0 CH2 1 0 CH3 0 1 CH4 1 1 EXTERNAL CLOCK Figure 9. Output Demultiplexer Circuit The circuit of Figure 10 shows a typical vector motorcontrol application using all available inputs of the MAX125/MAX126. CH1A and CH2A are connected to two isolated Hall-effect current sensors and are a part of the current (torque) feedback loop. The MAX125/MAX126 digitize the currents and deliver raw data to the following DSP and controller stages, where the vector processing takes place. Sensorless vector control uses a computer model for the motor and an algorithm to split each output current into its magnetizing (stator current) and torque-producing (rotor current) components. 12 If a 2- to 3-phase conversion is not practical, three currents can be sampled simultaneously with the addition of a third sensor (not shown). Optional voltage (position) feedback can be derived by measuring two phase voltages (CH3A, CH4A). Typically, an isolated differential amplifier is used between the motor and the MAX125/MAX126. Again, the third phase voltage can be derived from the magnitude (phase voltage) and its relative phase. For optimum speed control and good load regulation close to zero speed, additional velocity and position feedback are derived from an encoder or resolver and ______________________________________________________________________________________ 2x4-Channel, Simultaneous-Sampling 14-Bit DAS MAX125/MAX126 MAIN DC RESOLVER/ ENCODER AC AC MOTOR MOTOR 14 CH1 MAX125 MAX126 14 BIT ADC + MICROSEQUENCER B AUX A SIMULTANEOUS T/H DSP BUFFER A CH2 B MAIN DC R/E VOLTAGE/POSITION FEEDBACK POWER STAGE CONTROLLER CURRENT/TORQUE FEEDBACK EXTERNAL SETPOINTS A CH3 B A CH4 B TEMP VELOCITY FEEDBACK C Figure 10. Vector Motor Control brought to the MAX125/MAX126 at CH4B. The additional channels can be used to evaluate slower analog inputs, such as the main DC bus voltage (CH2B), temperature sensors (CH3B), or other analog inputs (AUX, CH1B). Power-Supply Bypassing and Ground Management For optimum system performance, use printed circuit boards with separate analog and digital ground planes. Wire-wrapped boards are not recommended. Connect the two ground planes together at the lowimpedance power-supply source. Connect DGND and AGND together at the IC. For the best ground connection, connect the DGND and AGND pins together and connect that point to the system analog ground plane to avoid interference from other digital noise sources. If DGND is connected to the system digital ground, digital noise may get through to the ADC's analog portion. The AGND pins must be connected directly to a lowimpedance ground plane. Extra impedance between the pins and the ground plane increases crosstalk and degrades INL. Bypass AVDD and AVSS with 0.1F ceramic capacitors to AGND. Mount them with short leads close to the device. Ferrite beads may also be used to further isolate the analog and digital power supplies. Bypass DVDD with a 0.1F ceramic capacitor to DGND. ______________________________________________________________________________________ 13 MAX125/MAX126 2x4-Channel, Simultaneous-Sampling 14-Bit DAS __________________Pin Configuration __________Typical Operating Circuit TOP VIEW CH2B 1 36 AGND CH2A 2 35 CH3B CH1B 3 34 CH3A CH1A 4 33 CH4B AVDD 32 CH4A 5 REFIN 6 MAX125 MAX126 REFOUT 7 AVSS D0/A0 D1/A1 D2/A2 D3/A3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 REFIN DVDD 31 AVSS 30 INT AGND 8 CH1A CH1B CH2A CH2B CH3A CH3B CH4A CH4B +5V 28 RD D12 10 27 WR D11 11 26 CS D10 12 25 CLK D9 13 24 D0/A0 (LSB) D8 14 23 D1/A1 D7 15 22 D2/A2 D6 16 21 D3/A3 DVDD 17 20 D4 DGND 18 19 D5 SSOP AVDD 0.1F 29 CONVST D13 (MSB) 9 MAX125 MAX126 AGND 0.1F -5V 0.1F REFOUT DGND 4.7F CLK CONVST INT CS RD 16MHz CONTROL INTERFACE ___________________Chip Information TRANSISTOR COUNT: 4219 SUBSTRATE CONNECTED TO AVSS 14 +5V 0.1F ______________________________________________________________________________________ WR 2x4-Channel, Simultaneous-Sampling 14-Bit DAS SSOP2.EPS ______________________________________________________________________________________ 15 MAX125/MAX126 ________________________________________________________Package Information MAX125/MAX126 2x4-Channel, Simultaneous-Sampling 14-Bit DAS NOTES Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.