PART MAX5544CSA MAX5544ESA REF CS DIN SCLK. Maxim Integrated Products 1

Transcription

1 ; Rev ; 12/99 Low-Cost, +5, Serial-Input, General Description The serial-input, voltage-output, 14-bit monotonic digital-to-analog converter (DAC) operates from a single +5 supply. The DAC output is unbuffered, resulting in low.3ma supply current and low 1 offset error. The DAC output range is to REF. The DAC latch accepts a 16-bit serial word. A power-on reset circuit clears the DAC output to (unipolar mode) when power is initially applied. The 1MHz 3-wire serial interface is SPI /QSPI / MICROWIRE compatible and interfaces directly with optocouplers for applicatio requiring isolation. The is available in an 8-pin SO package. Features Full 14-Bit Performance Without Adjustments +5 Single-Supply Operation Low Power: 1.5mW 1µs Settling Time Unbuffered oltage Output Directly Drives 6kΩ Loads SPI/QSPI/MICROWIRE-Compatible Serial Interface Power-On Reset Circuit Clears DAC Output to (unipolar mode) Schmitt Trigger Inputs for Direct Optocoupler Interface Applicatio High-Resolution Offset and Gain Adjustment Industrial Process Control Automated Test Equipment Data Acquisition Systems PART A ESA Ordering Information TEMP. RANGE PIN-PACKAGE C to +7 C 8 SO -4 C to +85 C 8 SO Pin Configuration Functional Diagram TOP IEW 1 8 REF 14-BIT DAC AGND REF DGND CONTROL LOGIC 16-BIT DATA LATCH SERIAL INPUT REGISTER AGND SO DGND SPI and QSPI are trademarks of Motorola, Inc. MICROWIRE is a trademark of National Semiconductor Corp. Maxim Integrated Products 1 For free samples & the latest literature: or phone For small orders, phone

2 ABSOLUTE MAXIMUM RATINGS to DGND to +6,, to DGND to +6 REF to AGND to ( +.3) AGND to DGND to +.3 to AGND, DGND to Maximum Current into Any Pin...5mA Continuous Power Dissipation (T A = +7 C) 8-Pin SO (derate 5.88mW/ C above +7 C)...471mW Operating Temperature Ranges A... C to +7 C ESA...-4 C to +85 C Junction Temperature C Storage Temperature Range C to +15 C Lead Temperature (soldering, 1s) C 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 conditio beyond those indicated in the operational sectio of the specificatio is not implied. Exposure to absolute maximum rating conditio for extended periods may affect device reliability. ELECTRICAL CHARACTERISTI ( = +5 ±5%, REF = +2.5, AGND = DGND =, T A = T MIN to T MAX, unless otherwise noted. Typical values are at T A = +25 C.) Resolution PARAMETER Gain-Error Tempco DAC Output Resistance Power-Supply Rejection REFERENCE INPUT Reference Input Range Reference Input Resistance (Note 4) N R PSR REF R REF T A = +25 C T A = T MIN to T MAX T A = T MIN to T MAX T A = +25 C T A = T MIN to T MAX (Note 2) (Note 3) CONDITIONS Integral Nonlinearity INL = 5 ±4 ±8 Zero-Code Offset Error Zero-Code Tempco Gain Error (Note 1) SYMBOL STATIC PERFORMANCE ANALOG SECTION (R L = ) Differential Nonlinearity Output Settling Time DNL ZSE ZS TC Guaranteed monotonic DYNAMIC PERFORMANCE ANALOG SECTION (R L = ) oltage-output Slew Rate SR MIN TYP MAX ±.5 ±1. ±.5 ± ±1 ±2 ±5 ±1 ±1. UNITS Bits ppm/ C ppm/ C kω C L = 1pF (Note 5) 25 /µs To ± 1 /2 of FS, C L = 1pF 1 µs kω 2

3 ELECTRICAL CHARACTERISTI (continued) ( = +5 ±5%, REF = +2.5, AGND = DGND =, T A = T MIN to T MAX, unless otherwise noted. Typical values are at T A = +25 C.) PARAMETER DAC Glitch Impulse SYMBOL CONDITIONS Major-carry traition Digital Feedthrough Code = hex, =, = = to levels DYNAMIC PERFORMANCE REFERENCE SECTION Reference -3dB Bandwidth BW Code = FFFC hex Reference Feedthrough Code = hex, REF = 1p-p at 1kHz Signal-to-Noise Ratio SNR Reference Input Capacitance C IN Code = hex Code = FFFC hex STATIC PERFORMANCE DIGITAL INPUTS Input High oltage IH Input Low oltage IL Input Current I IN IN = Input Capacitance C IN (Note 6) Hysteresis oltage H POWER SUPPLY Positive Supply Range Positive Supply Current I DD Power Dissipation PD MIN TYP MAX ± UNITS ns ns MHz mp-p db pf µa pf ma mw TIMING CHARACTERISTI ( = +5 ±5%, REF = +2.5, AGND = DGND =, CMOS inputs, T A = T MIN to T MAX, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Frequency f CLK 1 MHz Pulse Width High t CH Pulse Width Low t CL Low to High Setup t S High to High Setup t S1 High to Low Hold t H (Note 6) 3 High to High Hold t H1 to High Setup t DS 4 to High Hold t DH High to Low (power-up delay) 2 µs Note 1: Gain error tested at REF = +2., +2.5, and +3.. Note 2: R tolerance is typically ±2%. Note 3: Min/max ranges guaranteed by gain-error test. Operation outside min/max limits will result in degraded performance. Note 4: Reference input resistance is code dependent, minimum at 8554 hex. Note 5: Slew-rate value is measured from % to 63%. Note 6: Guaranteed by design. Not production tested. 3

4 ( = +5, REF = +2.5, T A = +25 C, unless otherwise noted.) SUPPLY CURRENT (ma) SUPPLY CURRENT SUPPLY CURRENT (ma) SUPPLY CURRENT vs. REFERENCE OLTAGE REFERENCE OLTAGE () Typical Operating Characteristics -2 ZERO-CODE OFFSET ERROR () ZERO-CODE OFFSET ERROR INL () INTEGRAL NONLINEARITY -INL +INL -4 DNL () DIFFERENTIAL NONLINEARITY +DNL -DNL -5 GAIN ERROR () GAIN ERROR INTEGRAL NONLINEARITY vs. CODE DIFFERENTIAL NONLINEARITY vs. CODE -8 2 REFERENCE CURRENT vs. CODE -9 INL () DNL () REFERENCE CURRENT (µa) k 1k 15k 2k DAC CODE k 1k 15k 2k DAC CODE 4k 8k 12k 16k 2k DAC CODE 4

5 Typical Operating Characteristics (continued) ( = +5, REF = +2.5, T A = +25 C, unless otherwise noted.) FULL-SCALE STEP RESPONSE (f = 1MHz) -1 FULL-SCALE STEP RESPONSE (f = 2MHz) -11 5m/div 5m/div C L = 13pF R L = 1µs/div MAJOR-CARRY PUT GLITCH DIGITAL FEEDTHROUGH C L = 13pF R L = 4/div 5/div 5/div AC-COUPLED 1m/div AC-COUPLED 5m/div 2µs/div CODE = hex 2µs/div Pin Description PIN NAME AGND REF DGND FUNCTION DAC Output oltage Analog Ground oltage Reference Input. Connect to external +2.5 reference. Chip-Select Input Serial-Clock Input. Duty cycle must be between 4% and 6%. Serial-Data Input Digital Ground +5 Supply oltage 5

6 Detailed Description The voltage-output, 14-bit digital-to-analog converter (DAC) offers 14-bit monotonicity with less than 1 differential linearity error. Serial-data trafer minimizes the number of package pi required. The is composed of two matched DAC sectio, with a 12-bit inverted R-2R DAC forming the 12s and the 4MSBs derived from 15 identically matched resistors. This architecture allows the lowest glitch energy to be traferred to the DAC output on major-carry traitio. It also decreases the DAC output impedance by a factor of eight compared to a standard R-2R ladder, allowing unbuffered operation in medium-load applicatio. Figure 1 is the timing diagram. Digital Interface The digital interface is a standard 3-wire connection compatible with SPI/QSPI/MICROWIRE interfaces. The chip-select input () frames the serial data loading at the data input pin (). Immediately following s high-to-low traition, the data is shifted synchronously and latched into the input register on the rising edge of the serial-clock input (). After 16 data bits (14 data bits, plus two sub-bits set to zero) have been loaded into the serial input register, it trafers its contents to the DAC latch on s low-to-high traition (Figure 2). Note that if does not remain low during the entire 16 cycles, data will be corrupted. In this case, reload the DAC latch with a new 16-bit word. External Reference The operates with external voltage references from 2 to 3. The reference voltage determines the DAC s full-scale output voltage. Power-On Reset The has a power-on reset circuit to set the DAC s output to in unipolar mode when is first applied. This eures that unwanted DAC output voltages will not occur immediately following a system power-up, such as after power loss. In bipolar mode, the DAC output is set to - REF. t H1 t HO t SO t CH t CL t S1 t DH t DS D13 D12 S Figure 1. Timing Diagram DAC UPDATED SUB-BITS D13 D12 D11 D1 D9 D8 D7 D6 D5 D4 D3 D2 D1 D S1 S MSB Figure 2. 3-Wire Interface Timing Diagram 6

7 Applicatio Information Reference and Analog Ground Inputs The operates with external voltage references from 2 to 3, and maintai 14-bit performance with proper reference selection and application. Ideally, the reference s temperature coefficient should be less than 1.5ppm/ C to maintain 14-bit accuracy to within 1 over the commercial ( C to +7 C) temperature range. Since this converter is designed as an inverted R-2R voltage-mode DAC, the input resistance seen by the voltage reference is code dependent. The worstcase input-resistance variation is from 11.5kΩ (at code 8555 hex) to 2kΩ (at code hex). The maximum change in load current for a 2.5 reference is 2.5 / 11.5kΩ = 217µA; therefore, the required load regulation is 28ppm/mA for a maximum error of.1. This implies a reference output impedance of <71mΩ. In addition, the impedance of the signal path from the voltage reference to the reference input must be kept low because it contributes directly to the load-regulation error. The requirement for a low-impedance voltage reference is met with capacitor bypassing at the reference inputs and ground. A.1µF ceramic capacitor with short leads between REF and AGND provides high-frequency bypassing. A surface-mount ceramic chip capacitor is preferred because it has the lowest inductance. An additional 1µF between REF and AGND provides lowfrequency bypassing. A low-esr tantalum, film, or organic semiconductor capacitor works well. Leaded capacitors are acceptable because impedance is not as critical at lower frequencies. The circuit can benefit from even larger bypassing capacitors, depending on the stability of the external reference with capacitive loading. If separate force and see lines are not used, connect the appropriate force and see pi together close to the package. AGND must also be low impedance, as load-regulation errors will be introduced by excessive AGND resistance. As in all high-resolution, high-accuracy applicatio, separate analog and digital ground planes yield the best results. Connect DGND to AGND at the AGND pin to form the star ground for the DAC system. For the best possible performance, always refer remote DAC loads to this system ground. Unbuffered Operation Unbuffered operation reduces power coumption as well as offset error contributed by the external output buffer. The R-2R DAC output is available directly at, allowing 14-bit performance from + REF to AGND without degradation at zero-scale. The DAC s output impedance is also low enough to drive medium loads (R L > 6kΩ) without degradation of INL or DNL; only the gain error is increased by externally loading the DAC output. External Output Buffer Amplifier In unipolar mode, the output amplifier is used in a voltage-follower connection. The DAC s output resistance is cotant and is independent of input code; however, the output amplifier s input impedance should still be as high as possible to minimize gain errors. The DAC s output capacitance is also independent of input code, thus simplifying stability requirements on the external amplifier. In single-supply applicatio, precision amplifiers with input common-mode ranges including AGND are available; however, their output swings do not normally include the negative rail (AGND) without significant performance degradation. A single-supply op amp, such as the MAX495, is suitable if the application does not use codes near zero. Since the s for a 14-bit DAC are extremely small (152.6µ for REF = 2.5), pay close attention to the external amplifier s input specification. The input offset voltage can degrade the zero-scale error and might require an output offset trim to maintain full accuracy if the offset voltage is greater than 1/2. Similarly, the input bias current multiplied by the DAC output resistance (typically 6.25kΩ) contributes to the zero-scale error. Temperature effects also must be taken into coideration. Over the commercial temperature range, the offset voltage temperature coefficient (referenced to +25 C) must be less than 1.7µ/ C to add less than 1/2 of zero-scale error. The external amplifier s input resistance forms a resistive divider with the DAC output resistance, which results in a gain error. To contribute less than 1/2 of gain error, the input resistance typically must be greater than: kΩ / 25MΩ = The settling time is affected by the buffer input capacitance, the DAC s output capacitance, and PC board capacitance. The typical DAC output voltage settling time is 1µs for a full-scale step. Settling time can be significantly less for smaller step changes. Assuming a single time-cotant exponential settling respoe, a full-scale step takes 1.4 time cotants to settle to within 1/2 of the final output voltage. The time cotant is equal to the DAC output resistance multiplied by the total output capacitance. The DAC output capacitance is typically 1pF. Any additional output capacitance will increase the settling time. 7

8 The external buffer amplifier s gain-bandwidth product is important because it increases the settling time by adding another time cotant to the output respoe. The effective time cotant of two cascaded systems, each with a single time-cotant respoe, is approximately the root square sum of the two time cotants. The DAC output s time cotant is 1µs / 1.4 = 96, ignoring the effect of additional capacitance. If the time cotant of an external amplifier with 1MHz bandwidth is 1 / 2π (1MHz) = 159, then the effective time cotant of the combined system is: ( ) + ( ) = This suggests that the settling time to within 1/2 of the final output voltage, including the external buffer amplifier, will be approximately = 1.93µs. Digital Inputs and Interface Logic The digital interface for the 14-bit DAC is based on a 3- wire standard that is SPI/QSPI/MICROWIRE compatible. The three digital inputs (,, and ) load the digital input data serially into the DAC. All of the digital inputs include Schmitt-trigger buffers to accept slow-traition interfaces. This mea that optocouplers can interface directly to the without additional external logic. The digital inputs are TTL/ CMOS-logic compatible. Unipolar Configuration Figure 3 shows the configured for unipolar operation with an external op amp. The op amp is set for unity gain, and Table 1 shows the codes for this circuit. Table 1. Unipolar Code Table DAC LATCH CONTENTS MSB () 1 () 1() () REF (16,383 / 16,384) REF (8192 / 16,384) = 1/ 2 REF REF (1 / 16,834) ANALOG PUT, Power-Supply Bypassing and Ground Management For optimum system performance, use PC boards with separate analog and digital ground planes. Wire-wrap boards are not recommended. Connect the two ground planes together at the low-impedance power-supply source. Connect DGND and AGND together at the IC. The best ground connection can be achieved by connecting the DAC s DGND and AGND pi together and connecting that point to the system analog ground plane. If the DAC s DGND is connected to the system digital ground, digital noise may get through to the DAC s analog portion. Bypass with a.1µf ceramic capacitor connected between and AGND. Mount it with short leads close to the device. Ferrite beads can also be used to further isolate the analog and digital power supplies. TRANSISTOR COUNT: 229 SUBSTRATE CONNECTED TO DGND Chip Information µF.1µF.1µF MC68XXXX REF P MOSI MAX495 EXTERNAL OP AMP UNIPOLAR DGND AGND Figure 3. Typical Operating Circuit Maxim cannot assume respoibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licees are implied. Maxim reserves the right to change the circuitry and specificatio without notice at any time. 8 Maxim Integrated Products, 12 San Gabriel Drive, Sunnyvale, CA Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.