PRELIMINARY TECHNICAL DATA a Nonvolatile Memory, Dual 1024 Position Digital Potentiometers AD5235 FEATURES Dual, 1024 Position Resolution 25K, 250K Ohm Terminal Resistance with 50ppm/°C Tempco Nonvolatile Memory Preset SPI Compatible Serial Data Input with Readback Function Increment/Decrement Commands, Push Button Command +3 to +5V Single Supply Operation ±2.5V Dual Supply Operation 30 bytes of general purpose nonvolatile memory FUNCTIONAL BLOCK DIAGRAMS RDAC1 CS ADDRESS DECODE A1 RDAC1 REGISTER W1 CLK SDI B1 SER IAL IN P U T R E G IS T E R EEMEM1 SDO RDAC2 APPLICATIONS Mechanical Potentiometer Replacement Instrumentation: Gain, Offset Adjustment Programmable Voltage to Current Conversion Programmable Filters, Delays, Time Constants Line Impedance Matching Power Supply Adjustment DIP Switch Setting PR RDAC2 REGISTER PWR ON PRESET A2 W2 B2 WP RDY EEMEM CONTROL V SS EEMEM2 G ND G ND SPARE EEMEM GENERAL DESCRIPTION The AD5235 provides a dual channel, digitally controlled variable resistor (VR) with resolutions of 1024 positions. These devices perform the same electronic adjustment function as a potentiometer or variable resistor. The AD5235’s versatile programming via a Micro Controller allows multiple modes of operation and adjustment. In the direct program mode a predetermined setting of the RDAC register can be loaded directly from the micro controller. Another key mode of operation allows the RDAC register to be refreshed with the setting previously stored in the EEMEM register. When changes are made to the RDAC register to establish a new wiper position, the value of the setting can be saved into the EEMEM by executing an EEMEM save operation. Once the settings are saved in the EEMEM register, these values will be transferred automatically to the RDAC register to set the wiper position at system power ON. Such operation is enabled by the internal preset strobe and the preset can also be accessed externally. An internal scratch pad RDAC register can be programmed by the micro controller to set the resistance between terminals W-and-B. Once the target value is achieved, the RDAC content register can be placed in the non-volatile memory for automatic recall during Power Up. The AD5235 is available in the thin TSSOP-16 package. All parts are guaranteed to operate over the extended industrial temperature range of -40°C to +85°C. REV PrD 6 Nov 2000 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. V DD One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106 U.S.A. Tel: 781/329-4700 Fax:781/326-8703 PRELIMINARY TECHNICAL DATA AD5235 Nonvolatile Memory Digital Potentiometers ELECTRICAL CHARACTERISTICS 25K, 250K OHM VERSIONS (VDD = +3V±10% or +5V±10% and VSS=0V, VA = +VDD, VB = 0V, -40°C < TA < +85°C unless otherwise noted.) Parameter Symbol Conditions Min Typ 1 Max Units DC CHARACTERISTICS RHEOSTAT MODE Specifications apply to all VRs Resistor Differential NL2 R-DNL RWB, VA=NC -1 ±1/4 +1 LSB Resistor Nonlinearity2 R-INL RWB, VA=NC -2 ±1/2 +2 LSB Nominal resistor tolerance Resistance Temperature Coefficent Wiper Resistance Wiper Resistance ∆R RAB/∆T RW RW TA = 25°C, VAB = VDD,Wiper (VW) = No connect VAB = VDD, Wiper (VW) = No Connect IW = 1 V/R, VDD = +5V IW = 1 V/R, VDD = +3V -30 30 % ppm/°C Ω Ω 50 50 200 100 DC CHARACTERISTICS POTENTIOMETER DIVIDER MODE Specifications apply to all VRs Resolution Integral Nonlinearity3 Differential Nonlinearity3 Voltage Divider Temperature Coefficent Full-Scale Error Zero-Scale Error N INL DNL ∆VW/∆T VWFSE VWZSE 10 –2 –1 Code = Half-scale Code = Full-scale Code = Zero-scale –3 0 ±1/2 ±1/4 15 -1 +1 +2 +1 +0 +3 Bits LSB LSB ppm/°C LSB LSB RESISTOR TERMINALS Voltage Range4 VA,B,W Capacitance5 Ax, Bx CA,B f = 1 MHz, measured to GND, Code = Half-scale Capacitance5 Wx CW f = 1 MHz, measured to GND, Code = Half-scale Common-mode Leakage Current7 ICM VA = VB = VDD/2 Input Logic High Input Logic Low Output Logic High Output Logic High Output Logic Low Input Current VIH VIL VOH VOH VOL IIL with respect to GND with respect to GND RPULL-UP = 2.2KΩ to +5V IOH = 40µA, VLOGIC = +5V IOL = 1.6mA, VLOGIC = +5V VIN = 0V or VDD Input Capacitance5 CIL VSS VDD 45 60 0.01 V pF pF 1 µA 0.3•VDD V V V V V µA DIGITAL INPUTS & OUTPUTS 0.7•VDD 4.9 4 0.4 ±1 5 pF POWER SUPPLIES Single-Supply Power Range VDD VSS = 0V 2.7 5.5 V Dual-Supply Power Range Positive Supply Current Programming Mode Current Read Mode Current Negative Supply Current VDD/VSS IDD IDD(PG) IDD(READ) ISS VSS = 0V VIH = VDD or VIL = GND VIH = VDD or VIL = GND VIH = VDD or VIL = GND VIH = VDD or VIL = GND, VDD = 2.5V, VSS = -2.5V ±2.2 ±2.7 20 10 V µA mA µA µA Power Dissipation6 Power Supply Sensitivity PDISS PSS VIH = VDD or VIL = GND ∆VDD = +5V ±10% 0.05 0.01 mW %/% Bandwidth –3dB Total Harmonic Distortion VW Settling Time BW_25K THDW tS R = 12KΩ VA =1Vrms, VB = 0V, f=1KHz VA= VDD, VB=0V, 50% of final value 400 0.003 KHz % Resistor Noise Voltage eN_WB 25K/250K RWB = 10KΩ, f = 1KHz 0.6/3/6 9 µs nV√Hz Crosstalk CT 2 15 650 0.002 DYNAMIC CHARACTERISTICS5, 7 VA = VDD, VB = 0V, Measue VW with adjacent VR making full scale change -65 dB REV PrD 6 NOV, 2000 2 Information contained in this Product Concept data sheet describes a product in the early definition stage. There is no guarantee that the information contained here will become a final product in its present form. For latest information contact Walt Heinzer/Analog Devices, Santa Clara, CA. TEL(408)562-7254; FAX (408)727-1550; [email protected] PRELIMINARY TECHNICAL DATA AD5235 Nonvolatile Memory Digital Potentiometers ELECTRICAL CHARACTERISTICS 25K, 250K OHM VERSIONS (VDD = +3V±10% to +5V±10% and VSS=0V, VA = +VDD, VB = 0V, -40°C < TA < +85°C unless otherwise noted.) Parameter Symbol Conditions Min Typ 1 Max Units INTERFACE TIMING CHARACTERISTICS applies to all parts(Notes 5, 8) Clock Cycle Time Input Clock Pulse Width CS Setup Time Data Setup Time Data Hold Time CLK Shutdown Time CS Rise to Clock Rise Setup CS High Pulse Width CLK to SDO Propagation Delay9 Store to Nonvolatile EEMEM Save Time10 CS to SDO - SPI line acquire CS to SDO - SPI line release RDY Rise to CLK Rise Startup Time CLK Setup Time Preset Pulse Width t1 t 2, t 3 t4 t5 t6 t7 t8 t9 t 10 t 11 t 12 t 13 t 14 t 15 t 16 tPR 20 10 10 5 5 0 10 10 1 Clock level high or low From Positive CLK transition From Positive CLK transition RL = 1KΩ, CL < 20pF Applies to Command 2H, 3H 25 25 For 1 CLK period (t4 - t3 = 1 CLK period) 50 ns ns ns ns ns ns ns ns ns ms ns ns ns ms ns ns NOTES: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Typicals represent average readings at +25°C and VDD = +5V. Resistor position nonlinearity error R-INL is the deviation from an ideal value measured between the maximum resistance and the minimum resistance wiper positions. R-DNL measures the relative step change from ideal between successive tap positions. Parts are guaranteed monotonic. See figure 20 test circuit. IW = VDD/R for both VDD=+3V or VDD=+5V. INL and DNL are measured at VW with the RDAC configured as a potentiometer divider similar to a voltage output D/A converter. VA = VDD and VB = 0V. DNL specification limits of ±1LSB maximum are Guaranteed Monotonic operating conditions. See Figure 19 test circuit. Resistor terminals A,B,W have no limitations on polarity with respect to each other. Guaranteed by design and not subject to production test. PDISS is calculated from (IDD x VDD=+5V). All dynamic characteristics use VDD = +5V. See timing diagram for location of measured values. All input control voltages are specified with tR=tF=2.5ns(10% to 90% of 3V) and timed from a voltage level of 1.5V. Switching characteristics are measured using both VDD = +3V or +5V. Propagation delay depends on value of VDD, RPULL_UP, and CL see applications text. Low only for commands 8, 9,10, 2, 3: CMD_8 ~ 1ms; CMD_9,10 ~0.1ms; CMD_2,3 ~20ms. Timing Diagram CLK t 16 t1 t3 t8 t2 t7 t4 CS t9 t5 SDI t6 SDO LSB MSB t 12 t 10 1 t 13 LSB MSB S D O2 LSB MSB t 14 t 15 RDY SDO 1 CLK IDLES LOW t 11 SDO 2 CLK IDLES HIGH Figure 1. Timing Diagram REV PrD 6 NOV, 2000 3 Information contained in this Product Concept data sheet describes a product in the early definition stage. There is no guarantee that the information contained here will become a final product in its present form. For latest information contact Walt Heinzer/Analog Devices, Santa Clara, CA. TEL(408)562-7254; FAX (408)727-1550; [email protected] PRELIMINARY TECHNICAL DATA AD5235 Nonvolatile Memory Digital Potentiometers AD5235 PIN CONFIGURATION Absolute Maximum Rating (TA = +25°C, unless otherwise noted) VDD to GND..............................................................-0.3, +7V VSS to GND ................................................................. 0V, -7V VDD to VSS ......................................................................... +7V VA, VB, VW to GND ................................................. VSS, VDD AX – BX, AX – WX, BX – WX ...................................... ±20mA Ox to GND...................................................................0V, VDD Digital Inputs & Output Voltage to GND .................. 0V, +7V Operating Temperature Range......................... -40°C to +85°C Maximum Junction Temperature (TJ MAX)...................+150°C Storage Temperature ..................................... -65°C to +150°C Lead Temperature (Soldering, 10 sec)..........................+300°C Thermal Resistance θJA, TSSOP-16...................................................... 180°C/W Model #CHs/ k Ohm AD5235BRU25 X2/25 AD5235BRU250 X2/250 Temp Range Package Package Description Option -40/+85°C TSSOP-16 -40/+85°C TSSOP-16 The AD5235 contains 16,000 transistors. Die size: 100 x 105 mil = 10,500 sq. mil RU-16 RU-16 1 16 RDY SDI 2 15 CS SDO 3 14 PR GND 4 13 WP VSS 5 12 VDD A1 6 11 A2 W1 7 10 W2 B1 8 9 B2 AD5235 PIN FUNCTION DESCRIPTION # Name Description 1 CLK Serial Input Register clock pin. Shifts in one bit at a time on positive clock edges. 2 SDI Serial Data Input Pin. Shifts in one bit at a time on positive clock CLK edges. 3 SDO Serial Data Output Pin. Open Drain Output requires external pull-up resistor. Commands 9 and 10 activate the SDO output. See Instruction operation Truth Table. Table 2. 4 GND Ground pin, logic ground reference 5 VSS Negative Supply. Connect to zero volts for single supply applications. Package Power Dissipation = (TJMAX - TA) / θJA Ordering Guide CLK 6 A1 A terminal of RDAC1. 7 W1 Wiper terminal of RDAC1, ADDR(RDAC1) = 0H. 8 B1 B terminal of RDAC1. 9 B2 B terminal of RDAC2. 10 W2 Wiper terminal of RDAC2, ADDR(RDAC3) = 1H. 11 A2 A terminal of RDAC2. 12 VDD Positive Power Supply Pin. Should be ≥ the input-logic HIGH voltage. 13 WP Write Protect Pin. Prevents any changes to the present EEMEM contents when active low. 14 PR Hardware over ride preset pin. Refreshes the scratch pad register with current contents of the EEMEM register. Factory default loads midscale 51210. 15 CS Serial Register chip select active low. Serial register operation takes place when CS returns to logic high. 16 RDY Ready. Active-high open drain output. Identifies completion of commands 2, 3, 8, 9, 10. REV PrD 6 NOV, 2000 4 Information contained in this Product Concept data sheet describes a product in the early definition stage. There is no guarantee that the information contained here will become a final product in its present form. For latest information contact Walt Heinzer/Analog Devices, Santa Clara, CA. TEL(408)562-7254; FAX (408)727-1550; [email protected] PRELIMINARY TECHNICAL DATA AD5235 Nonvolatile Memory Digital Potentiometers OPERATIONAL OVERVIEW • The AD5235 digital potentiometer is designed to operate as a true variable resistor replacement device for analog signals that remain within the terminal voltage range of VSS<VTERM<VDD. The basic voltage range is limited to a VDD - VSS<5.5V. Control of the digital potentiometer allows both scratch pad register (RDAC register) changes to be made, as well as 100,000 times of nonvolatile electrically erasable memory (EEMEM) register operations. The EEMEM update process takes approximately 20.2ms, during this time the shift register is locked preventing any changes from taking place. The RDY pin flags the completion of this EEMEM save. The EEMEM retention is designed to last 10 years without refresh. The scratch pad register can be changed incrementally by using the software controlled Increment/Decrement instruction or the Shift Left/Right instruction command. Once an Increment, Decrement or Shift command has been loaded into the shift register, subsequent CS strobes will repeat this command. This is useful for push button control applications. Alternately the scratch pad register can be programmed with any position value using the standard SPI serial interface mode by loading the representative data word. The scratch pad register can be loaded with the current contents of the nonvolatile EEMEM register under the program control. At system power ON, the default value of the scratch pad memory is the value previously saved in the EEMEM register. The factory EEMEM preset value is midscale 51210. • A serial data output pin is available for daisy chaining and for readout of the internal register contents. The serial input data register uses a 24-bit instruction/address/data WORD. The writeprotect (WP) pin provides a hardware EEMEM protection feature disabling any changes of the present EEMEM contents. SERIAL DATA INTERFACE The AD5235 contains a four-wire SPI compatible digital interface (SDI, SDO, CS, and CLK). Key features of this interface include: • • Permanent storage of the present scratch pad RDAC register values into the corresponding EEMEM register 30 bytes of user addressable electrical-erasable memory The serial interface of AD5235 digital potentiometer uses a 24-bit serial word loaded with MSB first. The format of the SPI compatible word is shown in Table 1. The Command Bits (Cx) control the operation of the digital potentiometer according to the command instruction shown in Table 2. The Address Bits (Ax) determine which register is activated. The Data Bits (Dx) are the values that are loaded into the decoded register. The last instruction executed prior to a period of no programming activity should be the NOP instruction. This will place the internal logic circuitry in a minimum power dissipation state. PR V A L ID CO MMAND CO UNTER C LK CO MMAND PROCESSOR & ADDRESS DECODE +5V R P U L LU P S E R IA L R E G IS T E R SDO CS GND SDI Figure 2. Equivalent Digital Input-Output Logic The equivalent serial data input and output logic is shown in figure 2. The open drain output SDO is disabled whenever chip select CS is logic high. The SPI interface can be used in two slave modes CPHA=1, CPOL=1 and CPHA=0, CPOL=0. CPHA and CPOL refer to the control bits, which dictate SPI timing in the following microprocessors/MicroConverters: ADuC812/824, M68HC11, and MC68HC16R1/916R1. Independently Programmable Read & Write to all registers Direct parallel refresh of all RDAC wiper registers from corresponding EEMEM registers Table 1. AD5235 24-bit Serial Data Word M S B AD5235 C3 C2 C1 C0 A3 A2 A1 A0 X X X X X X D9 D8 D7 D6 D5 D4 Command bits are identified as Cx, address bits are Ax, and data bits are Dx. Command instruction codes are defined in table 2. D3 D2 D1 L S B D0 REV PrD 6 NOV, 2000 5 Information contained in this Product Concept data sheet describes a product in the early definition stage. There is no guarantee that the information contained here will become a final product in its present form. For latest information contact Walt Heinzer/Analog Devices, Santa Clara, CA. TEL(408)562-7254; FAX (408)727-1550; [email protected] PRELIMINARY TECHNICAL DATA AD5235 Nonvolatile Memory Digital Potentiometers Table 2. AD5235 Instruction/Operation Truth Table Inst No. Data Byte 1 B15 •••• B8 X ••• D9 D8 X ••• X X Data Byte 0 B7 ••• B0 D7 ••• D0 X ••• X Operation 0 Instruction Byte 1 B15 •••••••••••••••• B8 C3 C2 C1 C0 A3 A2 A1 A0 0 0 0 0 X X X X 1 0 0 0 1 << ADDR >> X ••• X X X ••• X Write contents of EEMEM(ADDR) to RDAC(ADDR) Register 2 0 0 1 0 << ADDR >> X ••• X X X ••• X SAVE WIPER SETTING: Write contents of RDAC(ADDR) to EEMEM(ADDR) 3 0 0 1 1 << ADDR >> X ••• D9 D8 D7 ••• D0 Write contents of Serial Register Data Byte 0 & 1 to EEMEM(ADDR) 4 0 1 0 0 << ADDR >> X ••• X X X ••• X DEC 6dB: Right Shift contents of RDAC(ADDR) , LSB rolls over to MSB position 5 0 1 0 1 X X X ••• X X X ••• X DEC All 6dB: Right Shift contents of all RDAC Registers, LSB rolls over to MSB position 6 0 1 1 0 << ADDR >> X ••• X X X ••• X Decrement contents of RDAC(ADDR) by One, does not rollover at zero-scale 7 0 1 1 1 X X X X X ••• X X X ••• X Decrement contents of all RDAC Registers by One, does not rollover at zero-scale 8 1 0 0 0 0 0 0 0 X ••• X X X ••• X RESET: Load all RDACs with their corresponding EEMEM previously-saved values 9 1 0 0 1 << ADDR >> X ••• X X X ••• X Write contents of EEMEM(ADDR) to Serial Register Data Byte 0 & 1 10 1 0 1 0 << ADDR >> X ••• X X X ••• X Write contents of RDAC(ADDR) to Serial Register Data Byte 0 & 1 11 1 0 1 1 << ADDR >> X ••• D9 D8 D7 ••• D0 Write contents of Serial Register Data Byte 0 &1 to RDAC(ADDR) 12 1 1 0 0 << ADDR >> X ••• X X X ••• X INC 6dB: Left Shift contents of RDAC(ADDR), stops at all 'Ones'. 13 1 1 0 1 X X X ••• X X X ••• X INC All 6dB: Right Shift contents of all RDAC Registers, stops at all 'Ones'. 14 1 1 1 0 << ADDR >> X ••• X X X ••• X Increment contents of RDAC(ADDR) by One, does not rollover at full-scale stops at all 'Ones'. 15 1 1 1 1 X X ••• X X X ••• X Increment contents of all RDAC Registers by One, does not rollover at full-scale stops at all 'Ones'. X X X X X X X NOP: Do nothing NOTES: 1. The SDO output shifts-out the last 24-bits of data clocked into the serial register for daisy chain operation. Exception, following Instruction #9 or #10 the selected internal register data will be present in data byte 0 & 1. Instructions following #9 & #10 must be a full 24-bit data word to completely clock out the contents of the serial register. 2. The RDAC register is a volatile scratch pad register that is refreshed at power ON from the corresponding non-volatile EEMEM register. 3. The increment, decrement and shift commands ignore the contents of the shift register Data Byte 0. 4. Execution of the Operation column noted in the table takes place when the CS strobe returns to logic high. . REV PrD 6 NOV, 2000 6 Information contained in this Product Concept data sheet describes a product in the early definition stage. There is no guarantee that the information contained here will become a final product in its present form. For latest information contact Walt Heinzer/Analog Devices, Santa Clara, CA. TEL(408)562-7254; FAX (408)727-1550; [email protected] PRELIMINARY TECHNICAL DATA AD5235 Nonvolatile Memory Digital Potentiometers Detail Potentiometer Operation The actual structure of the RDAC is designed to emulate the performance of a mechanical potentiometer. The RDAC contains a string of connected resistor segments, with an array of analog switches that act as the wiper connection to several points along the resistor array. The number of points is the resolution of the device. The AD5235 has 1024 connection points allowing it to provide better than 0.5% set-ability resolution. Figure 3 provides an equivalent diagram of the connections between the three terminals that make up one channel of the RDAC. The SWA and SWB will always be ON while one of the switches SW(0) to SW(2N-1) will be ON one at a time depends upon the resistance step decoded from the Data Bits. Note that there are two 50Ω wiper resistances, RW. The resistance contributed by RW must be accounted for when calculating the output resistance. RW is the sum of the resistances of SWA + SWX and SWB + SWX for A-to-Wiper and B-to-Wiper respectively. SW A AX ladder until the last tap point is reached at RWB=25025Ω. See figure 3 for a simplified diagram of the equivalent RDAC circuit. The general equation, which determines the digitally programmed output resistance between Wx and Bx, is: RWB(Dx) = (Dx/2N) * RAB + RW eqn. 1 Where N is the resolution of the VR, Dx is the data contained in the RDACx latch, and RAB is the nominal end-to-end resistance. Since N=10 and RW=50Ω for AD5235, eqn. 1 becomes: RWB(Dx) = (Dx/1024) * RAB + 50Ω eqn. 2 For example, when VB = 0V and A–terminal is open circuit the following output resistance values will be set for the following RDAC latch codes (applies to RAB=25KΩ potentiometers): Dx (DEC) RWB (Ω) Output State 1023 512 1 0 25025Ω 12500Ω 74Ω 50Ω Full-Scale Mid-Scale 1 LSB Zero-Scale (Wiper contact resistance) SW(2 N -1) RDAC WX RS WIPER SW(2 N -2) REGISTER & DECODER Note that in the zero-scale condition a finite wiper resistance of 50Ω is present. Care should be taken to limit the current flow between W and B in this state to no more than 20mA to avoid degradation or possible destruction of the internal switch contact. RS SW(1 ) RS SW(0 ) N RS = R AB /2 DIGITAL CIRCUITRY OMITTED FOR CLARITY SW B BX Figure 3. Equivalent RDAC structure PROGRAMMING THE VARIABLE RESISTOR Rheostat Operation The nominal resistance of the RDAC between terminals A and B are available with values of 25KΩ, and 250KΩ. The final digits of the part number determine the nominal resistance value, e.g., 25KΩ = 25; 250KΩ = 250. The nominal resistance (RAB) of the AD5235 VR has 1024 contact points accessed by the wiper terminal, plus the B terminal contact. The 10-bit data word in the RDAC latch is decoded to select one of the 1024 possible settings. The wiper's first connection starts at the B terminal for data 00H. This B– terminal connection has a wiper contact resistance, RW of 50Ω, regardless of what the nominal resistance RAB is. The second connection (25KΩ part) is the first tap point where RWB =74Ω [RWB =RAB/1024 + RW = 24Ω+50Ω)] for data 01H. The third connection is the next tap point representing RWB =49+50=99Ω for data 02H. Each LSB data value increase moves the wiper up the resistor Figure 4. Symmetrical RDAC Operation Like the mechanical potentiometer the RDAC replaces, the AD5235 part is totally symmetrical. The resistance between the wiper W and terminal A also produces a digitally controlled resistance RWA. Figure 4 shows the symmetrical programmability of the various terminal connections. When these terminals are used, the B–terminal should be tied to the wiper. Setting the resistance value for RWA starts at a maximum value of resistance and decreases as the data loaded in the latch is increased in value. The general equation for this operation is: REV PrD 6 NOV, 2000 7 Information contained in this Product Concept data sheet describes a product in the early definition stage. There is no guarantee that the information contained here will become a final product in its present form. For latest information contact Walt Heinzer/Analog Devices, Santa Clara, CA. TEL(408)562-7254; FAX (408)727-1550; [email protected] PRELIMINARY TECHNICAL DATA AD5235 Nonvolatile Memory Digital Potentiometers RWA(Dx) = [ (2N-Dx)/2N ] * RAB + RW eqn. 3 ESD PROTECTION CIRCUITS VDD Similarly, eqn. 3 becomes: RWA(Dx) = [ (1024-Dx)/1024 ] * RAB + 50Ω For example, when VA = 0V and B–terminal is tied to the wiper W the following output resistance values will be set for the following RDAC latch codes (applies to RAB=10KΩ potentiometers): Dx (DEC) RWA (Ω) IN P U T S eqn. 4 L O G IC P IN S Output State GND Figure 5A. Equivalent Digital Input ESD Protection 1023 512 1 0 74 12500 25000 25050 Full-Scale Mid-Scale 1 LSB Zero-Scale V DD O UTPU TS O1 & O2 P IN S A ±1% typical distribution of RAB from channel-to-channel occurs within the same package. On the other hand, device to device matching is process lot dependent such that a maximum of ±30% variation is possible. The change in RAB with temperature has a 50 ppm/°C temperature coefficient. PROGRAMMING THE POTENTIOMETER DIVIDER Voltage Output Operation The digital potentiometer easily generates an output voltage proportional to the input voltage applied to a given terminal. For example connecting A–terminal to +5V and B–terminal to ground produces an output voltage at the wiper which can be any value starting at zero volts and up to 1 LSB less than +5V. Each LSB of voltage is equal to the voltage applied across terminal AB divided by the 2N resolution of the potentiometer divider. The general equation defining the output voltage with respect to ground for any given input voltage applied to terminals AB is: GND Figure 5B. Equivalent Digital Output ESD Protection VDD O U TPUTS SDO P IN VW(Dx) = Dx/2N * VAB + VB eqn. 5 GND Since N=10, VW(Dx) = (Dx/1024) * VAB + VB Figure 5C. Equivalent SDO Output ESD Protection Circuit eqn. 6 Operation of the digital potentiometer in the divider mode results in more accurate operation over temperature. Here the output voltage is dependent on the ratio of the internal resistors and not the absolute value. Therefore, the drift reduces to 15ppm/°C. Figure 5 shows the equivalent ESD protection circuit for digital pins. Figure 6 shows the equivalent analog-terminal protection circuit for the variable resistors. P O T E N T IO M E T E R T E R M IN A L S A, B, W P IN S V SS Figure 6. Equivalent VR-Terminal ESD Protection REV PrD 6 NOV, 2000 8 Information contained in this Product Concept data sheet describes a product in the early definition stage. There is no guarantee that the information contained here will become a final product in its present form. For latest information contact Walt Heinzer/Analog Devices, Santa Clara, CA. TEL(408)562-7254; FAX (408)727-1550; [email protected] PRELIMINARY TECHNICAL DATA AD5235 Nonvolatile Memory Digital Potentiometers TEST CIRCUITS Figures 7 to 15 define the test conditions used in the product specification's table. Figure 12. Non-Inverting Gain test circuit Figure 7. Potentiometer Divider Nonlinearity error test circuit (INL, DNL) Figure 13. Gain Vs Frequency test circuit Figure 8. Resistor Position Nonlinearity Error (Rheostat Operation; R-INL, R-DNL) Figure 14. Incremental ON Resistance Test Circuit Figure 9. Wiper Resistance test Circuit Figure 15. Common Mode Leakage current test circuit Figure 10. Power supply sensitivity test circuit (PSS, PSSR) TYPICAL PERFORMANCE GRAPHS TBD Figure 11. Inverting Gain test Circuit REV PrD 6 NOV, 2000 9 Information contained in this Product Concept data sheet describes a product in the early definition stage. There is no guarantee that the information contained here will become a final product in its present form. For latest information contact Walt Heinzer/Analog Devices, Santa Clara, CA. TEL(408)562-7254; FAX (408)727-1550; [email protected] PRELIMINARY TECHNICAL DATA Nonvolatile Memory Digital Potentiometers AD5235 OUTLINE DIMENSIONS Dimensions shown in inches and (mm) REV PrD 6 NOV, 2000 10 Information contained in this Product Concept data sheet describes a product in the early definition stage. There is no guarantee that the information contained here will become a final product in its present form. For latest information contact Walt Heinzer/Analog Devices, Santa Clara, CA. TEL(408)562-7254; FAX (408)727-1550; [email protected]