IXYS MX868 12 Bit Digital Output Magnetic Flux Sensor Features: General Description * Single 5 Volt Power Supply * Externally Configurable 50A Bi-Direction Current Sense per Turn * 12-Bit Serial Digital Output * Full Scale Magnetic Flux Intensity of 500 Gauss * 2K Conversions/Second * Microcontroller Compatible * Standard 3 Wire Serial Interface plus Chip Select * In System Calibration: OTP Full Scale Trim via the Serial I/O Port * Programmable Digital Filter Time Constant * 4mm x 4mm 8 Lead DFN package RoHS Compliant The MX868 is a 12 Bit Digital Output Magnetic Flux Sensor. The device is a complete sampled data subsystem that converts a magnetic flux intensity of 500 Gauss full scale into a 12-bit digital output word. The sensor operates as a slave on the serial interface with TTL-level compatible inputs SDI (serial data input), SCK (serial clock), and CS* (chip select, active low). Terminal SDO is the tri-state serial data output. An adjustable exponentially weighted moving average digital filter is included that is capable of improving the signal to noise ratio while reducing the signal bandwidth. The full scale trim and/or the digital filter time constant are controllable through the serial I/O interface and are one-time programmable through the serial interface (once programmed, the values are loaded at every poweron). Applications: * Load Detection and Management * Motor Control * Power Supplies The MX868 can be mounted onto a PCB or incorporated into a magnetic assembly and then calibrated in-system through the serial interface. The operating voltage range is 4.5V to 5.5V. Ordering Information Part No. MX868R MX868RTR Description DFN-8 Tube DFN-8 Tape & Reel Qty 91 2500 Functional Block Diagram Typical Application Circuit Power SDI PWR 1 PWR SCK Hall Plate I/O Reg SDO Microcontroller CS* A/D MISO 2 Select 8 MOSI 5 SCK 4 SDO CS* MX868 SDI SCK GND GND 7 Ground MX868 Drawing No. 086809 1 03/03/08 www.claremicronix.com IXYS MX868 Absolute Maximum Ratings TA = +25C unless otherwise noted Parameter Voltage (Any Pin to GND) JA, DFN-8 Package Operating Temperature Range Storage Temperature Range Min -40 -65 Max +7 30 +85 150 Unit V C/W C C ESD Warning ESD (electrostatic discharge) sensitive device. Although the MX868 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. Electrical Characteristics PWR= 5V, T = +25C Parameter Operating Voltage Range (PWR) Supply Current (IPWR) Average A/D Reading Average A/D Reading Output Noise SCK pulse period SCK pulse width CS* pulse period CS* falling to first SCK rising Last SCK falling to CS* rising SCK falling to SDO valid Digital output high Digital output low Digital input low Digital input high Digital input current MX868 Drawing No. 086809 Condition Min 4.5 Zero Magnetic Flux 100 Gauss, North Pole 2040 Digital Filter Off high or low Typ 3 2048 2458 Max 5.5 2056 1.5 5 200 500 100 50 60 PWR-0.5 GND 2 2 0.5 0.8 PWR 1 Unit V mA LSB LSB RMS LSB S nS S nS nS nS V V A 03/03/08 www.claremicronix.com IXYS MX868 Pin Description Pin No. 1 2 3 4 5 6 7 Name PWR SDO NC SCK SDI NC GND 8 CS* Description Input Voltage Supply Serial Data Output No Connect Serial Clock Input Serial Data Input No Connect Connect to Ground Active low chip select for the serial interface. When a logic "high" is on this pin, the MX868 is tracking the hall input signal. Detailed Circuit Description The hall plate senses the magnetic field that is applied normal (perpendicular) to the package surface. The signal from the hall plate is offset-corrected by detecting the difference between a pair of analog samples during the acquisition time. During idle time (CS* high) the MX868 tracks the first analog sample. Immediately (~10 nS) after the falling edge of CS* the first sample is held. The track mode for the second sample starts nominally 32 S after the falling edge of CS*. Typically 96 S after the falling edge of CS* the second sample is held and the resulting analog value is then converted by the A/D. The result of the A/D conversion is loaded into the I/O register at the next falling edge of CS*, in preparation for output on SDO. The internal acquisition and A/D timing is asynchronous to the SCK serial interface clock. The magnetic field sampling period is controlled externally by the time between consecutive CS* falling edges. For zero magnetic field input the nominal A/D output is 2048 decimal. North pole towards the top surface of the MX868 increases the A/D output count. Applications that require non-continuous one measurement at a time operation should pulse CS* low twice, reading the data when CS* is low for the second time. Acquisition (n+1) Acquisition (n) A/D Convert (n) A/D Convert (n+1) Serial Output (n) CS* SCK SDO 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 externally controlled sampling period MX868 Drawing No. 086809 3 03/03/08 www.claremicronix.com IXYS MX868 POWER-ON RESET The MX868 contains a power-on reset circuit that resets all the internal flip-flops and initializes the internal registers to zero. The MX868 will reset if the voltage at terminal PWR drops below 3.2 V to 3.8 V. SYNCHRONOUS SERIAL I/O The MX868 (slave) can communicate with a microcomputer (master) via a three wire plus chip select serial interface. Chip select CS*, serial clock SCK, and serial data input SDI are output from the master controller to the MX868. Serial data output SDO is driven by the MX868 when selected by CS* = 0. SDO is high impedance when CS* = 1. SCK and SDI are don't care when CS* = 1. SDI is captured by the rising edge of SCK. SDO changes in response to the falling edge of SCK. Read 12-bit data D[11:0] when SDI = logic 0 200 nS min CS* SCK SDI D11 D10 D9 SDO D8 D7 D6 D5 D4 D3 D2 D1 D0 60 nS max Write command timing: (Bit Field A[2:0] , B[5:0], OTP Bit Zp) 20 nS min CS* SCK SDI 1 0 A2 A1 A0 B5 B4 B3 B2 B1 B0 Zp The write command SDI input bit pattern is internally latched at the rising edge of CS* and takes effect at the end of the next A/D conversion following CS* rising. The exponentially weighted moving average digital filter has a transfer function equivalent to a first order low pass filter. The I/O timing remains exactly the same when the filter is used. No decimation is performed. Let T = Sample interval (the time from CS* falling edge to CS* falling edge). Then bandwidth = 1/(2*pi*T). Also if W = Sample weighting, then the digital output = W*(current sample) + (1-W)*(previous value). At power-on the previous value is initialized to zero. A programmed change in A[2:0] does not reset the previous value. Therefore when using the filter, multiple samples must be taken at power-on or after changing A[2:0] before the filtered output will be correct. MX868 Drawing No. 086809 4 03/03/08 www.claremicronix.com IXYS MX868 Bit field A[2:0] controls the digital filter operation: A[2:0] 000 001 010 011 100 101 110 111 Time Constant No Filter T 3T 7T 15T 31T 63T 127T Sample Weighting 1 1/2 1/4 1/8 1/16 1/32 1/64 1/128 Bit field B[5:0] is the full scale adjust. Characteristics are 0.8% step size, 25% total range. B[5:0] = 000000 is the lowest sensitivity (highest full scale) B[5:0] = 111111 is the highest sensitivity One-Time Programming: Bit Zp, when logic 1 along with A[2:0] and B[5:0] values, programs those values into the internal nonvolatile memory. Programming a bit to logic 1 is permanent. A bit programmed to logic 1 cannot be made to go back to logic 0. Always send a write command with Zp = 0 and SDI = 0 immediately after the programming command. The actual programming pulse occurs internally at the falling edge of CS* in the command following the command in which Zp = logic 1. The write command can be used to preview the trim bits as long as Zp is logic 0. Examples: The bit field B[5:0] can be programmed while the A[2:0] bit field is "000", or vice versa. For example the total SDI bit pattern could be 10 000 001100 0000 1. This would permanently set the B[5:0] bit field to 001100 but the filter setting could still be subsequently changed by a different write command, either in preview or programming. The SDI bit pattern 10 010 010000 0000 0 would set the filter time constant to 3T and the full scale field to 010000 as a preview, without making it permanent (because bit Zp = 0). If the sample interval T = 1 mS and A[2:0] = 001 then the effective bandwidth would be 1/(2*3.14*1e-3) = 159 Hz. For this condition, if the steady state output was 2000 counts and a step input was applied that would drive the output to 3000 counts then the digital output response would be 2000, 2500, 2750, 2875, 2937, 2968, 2984, 2992, 2996, 2998, 2999, 2999, 3000. MX868 Drawing No. 086809 5 03/03/08 www.claremicronix.com IXYS MX868 Cascade Configurations Sensor Location MX868 Drawing No. 086809 6 03/03/08 www.claremicronix.com IXYS MX868 Application Example This application example illustrates one method of incorporating the MX868 into a power circuit board design. The double-sided 8oz copper traces carry 50A (25 A on the top trace and 25A on the bottom trace) around the center section of the planar E-core. The MX868 is mounted on a small single layer flex circuit that effectively adds a third layer. The flex also fans out the fine pitch DFN package to a pitch compatible with the power board. The magnetic circuit consists of two ferrite E14 planar cores. The center post of one of the cores is gapped to accommodate the MX868 package thickness plus the flex circuit thickness. For the 50A full scale application a gap of 47 to 52 mils is appropriate (1.2 to 1.32 mm). The gain trim range of the MX868 can accommodate even larger gaps if required. Flex circuit MX868 (2) E14 planar cores Cross Section (drawing not to scale) PCB top layer: (scale 1X) PCB bottom layer: (top view, 1X) Flex circuit: (component side, 1X) This following example illustrates the MX868 mounted directly on a 1oz PCB with a copper strap positioned around the Hall element to carry the current being measured. MX868 Copper stamping, thickness as required Design alternatives: The use of an E-I core pair results in a lower profile than E-E however a thinner board must be used. A thinner sensor can be obtained by FCOF (flip chip on flex) packaging of the MX868 bumped die. The maximum mounting height of the DFN package is 1.1 mm whereas the chip height is about 0.4 mm. MX868 Drawing No. 086809 7 03/03/08 www.claremicronix.com IXYS MX868 8 Lead DFN IXYS Corporation makes no representations or warranties with respect to the accuracy or completeness of the contents of this publication and reserves the right to make changes to specifications and product descriptions at any time without notice. Neither circuit patent licenses nor indemnity are expressed or implied. Except as set forth in IXYS' Standard Terms and Conditions of Sale, IXYS Corporation assumes no liability whatsoever, and disclaims any expressed or implied warranty, relating to its products including, but not limited to, the implied warranty of merchantability, fitness for a particular purpose, or infringement of any intellectual property right. MX868 Drawing No. 086809 8 03/03/08 www.claremicronix.com IXYS World Wide Sales Offices United Kingdom IXYS Semiconductor Limited Langley Park Way Langley Park Chippenham Wiltshire SN 15 1GE - England Tel: 44-1249-444524 Fax: 44-1249-659448 sales@ixys.co.uk IXYS Corporation 3540 Bassett Street Santa Clara, CA 925054 Tel: 1-408-982-0700 Fax: 1-408-496-0670 e-mail:sales@ixys.net Micronix 145 Columbia Aliso Viejo, CA 92656-1490 Tel: 1-949-831-4622 Fax: 1-949-831-4628 Sales Offices ASIA / PACIFIC Asian Headquarters IXYS Room 1016, Chia-Hsin, Bldg II, 10F, No. 96, Sec. 2 Chung Shan North Road Taipei, Taiwan R.O.C. Tel: 886-2-2523-6368 Fax: 886-2-2523-6368 bradley.green@ixys.co.uk Jhong@clare.com SALES OFFICES AMERICAS Eastern Region [Eastern North America, Mexico, South America] IXYS Corporation Beverly, MA Tel: 508-528-6883 Fax: 508-528-4562 wgh@ixys.net Central Region [Central North America] Check the IXYS Website for the local sales office nearest you. (www.ixys.com) IXYS Corporation Greensburg, PA Tel: 724-836-8530 Fax: 724-836-8540 neil.lejeune@westcode.com Western Region [Western North America] IXYS Coporation Solana Beach, CA Tel: 858-792-1101 slodor@ix.netcom.com SALES OFFICES EUROPE http://www.claremicronix.com European Headquarters IXYS Semiconductor GMBH Edisonstrasse 15 D- 68623 Lampertheim Germany Tel : 49-6206-503203 Fax: 49-6206-503286 marcom@ixys.de IXYS cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in this IXYS product. No circuit patent licenses nor indemnity are expressed or implied. IXYS reserves the right to change the specification and circuitry, without notice at any time. The products described in this document are not intended for use in medical implantation or other direct life support applications where malfunction may result in direct physical harm, injury or death to a person. Specification: MX868 (c)Copyright 2007, IXYS Corporation All rights reserved. Printed in USA. MX868 Drawing No. 086809 9 03/03/08 www.claremicronix.com