MAX159BEPA

19-1388; Rev 0; 11/98 +2.7V, Low-Power, 2-Channel, 108ksps, Serial 10-Bit ADCs in 8-Pin µMAX General Description The MAX157/MAX159 low-power, 10-bit analog-to-digital converters (ADCs) are available in 8-pin µMAX and DIP packages. Both devices operate with a single +2.7V to +5.25V supply and feature a 7.4µs successive-approximation ADC, automatic power-down, fast wake-up (2.5µs), an on-chip clock, and a high-speed, 3-wire serial interface. Power consumption is only 3.2mW (VDD = +3.6V) at the maximum sampling rate of 108ksps. At slower throughput rates, the 0.2µA automatic shutdown further reduces power consumption. The MAX157 provides 2-channel, single-ended operation and accepts input signals from 0 to VREF. The MAX159 accepts pseudo-differential inputs ranging from 0 to V REF . An external clock accesses data through the 3-wire serial interface, which is SPI™, QSPI™, and MICROWIRE™ compatible. Excellent dynamic performance and low power, combined with ease of use and a small package size, make these converters ideal for battery-powered and data acquisition applications, or for other circuits with demanding power-consumption and space requirements. For pin-compatible 12-bit upgrades, see the MAX144/MAX145 data sheet. Features o Single-Supply Operation (+2.7V to +5.25V) o Two Single-Ended Channels (MAX157) Single Pseudo-Differential Channel (MAX159) o Low Power 0.9mA (at 108ksps, +3V) 100µA (at 10ksps, +3V) 10µA (at 1ksps, +3V) 3.6V Input Low Voltage Input Hysteresis Input Leakage Current Input Capacitance Output Low Voltage Output High Voltage Three-State Output Leakage Current Three-State Output Capacitance COUT VIL VHYS IIN CIN VOL VOH VIN = 0 or VDD (Note 8) ISINK = 5mA ISINK = 16mA ISOURCE = 0.5mA CS/SHDN = VDD CS/SHDN = VDD (Note 8) VDD - 0.5 ±10 15 0.5 0.2 ±1 15 0.4 2.0 3.0 0.8 VREF VREF = 2.5V 18 0 VDD + 50mV 100 25 0.01 10 140 V µA kΩ µA CIN VIN On/off-leakage current, VIN = 0 to VDD 0 ±0.01 16 VREF ±1 V µA µA fSCLK External clock mode Internal clock mode, for data transfer only 0.1 0 tCONV tACQ 25 2.17MHz) In internal clock mode, the MAX157/MAX159 run from an internal, laser-trimmed oscillator to within 20% of the 2MHz specified clock rate. This releases the system microprocessor from running the SAR conversion clock and allows the conversion results to be read back at the processor’s convenience, at any clock rate from 0 to 5MHz. Operating the MAX157/MAX159 in internal clock mode is necessary for serial interfaces operating with clock frequencies lower than 100kHz or greater than 2.17MHz. Select internal clock mode (Figure 5) by hold- External Clock (fSCLK = 100kHz to 2.17MHz) External clock mode (Figure 6) is selected by transitioning CS/SHDN from high to low while SCLK is low. The external clock signal not only shifts data out, but also drives the analog-to-digital conversion. The input is sampled and conversion begins on the falling edge of the second clock pulse. Conversion must be completed within 140µs to prevent degradation in the conversion results caused by droop on the T/H capacitors. External clock mode provides the best throughput for clock frequencies between 100kHz and 2.17MHz. VDD 4 VDD SHDN 7 470Ω 0.1µF 2 CH0 1 VDD REF 5 EXTERNAL REFERENCE 2 fCORNER = 15kHz IN MAX7410 MAX7414 OUT 5 8 CLK MAX157 3 0.01µF 8 6 CH1 DOUT 7 COM 1 0.01µF OS 6 GND 3 1.5MHz CLOCK SCLK GND 4 CS/SHDN µP/µC Figure 4. Analog Input with Anti-Aliasing Filter Structure ACTIVE POWER DOWN tCS ACTIVE tWAKE (tACQ) tCONV CS/SHDN SCLK 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 HIGH-Z DOUT HIGH-Z SAMPLING INSTANT EOC 1 1 CHID MSB D8 D7 D6 D5 D4 D3 D2 D1 D0 S1 S0 Figure 5. Internal Clock Mode Timing _______________________________________________________________________________________ 9 +2.7V, Low-Power, 2-Channel, 108ksps, Serial 10-Bit ADCs in 8-Pin µMAX MAX157/MAX159 Output Data Format Table 1 illustrates the 16-bit, serial data-stream output format for both the MAX157 and MAX159. The first three bits are always logic high (including the EOC bit for internal clock mode), followed by the channel identification (CHID = 0 for CH0, CHID = 1 for CH1, CHID = 1 for MAX159), the 10 bits of data in MSB first format, and two sub-LSB bits (S1 and S0). After the last bit has been read out, additional SCLK pulses will clock out trailing zeros. DOUT transitions on the falling edge of SCLK. The output remains high impedance when CS/SHDN is high. Automatic Power-Down Mode Whenever the MAX157/MAX159 are not selected (CS/SHDN = VDD), the parts enter their shutdown mode. In shutdown all internal circuitry is turned off, which reduces the supply current to typically less than 0.2µA. With an external reference stable to within 1LSB, the wake-up time is 2.5µs. If the external reference is not stable within 1LSB, the wake-up time must be increased to allow the reference to stabilize. Applications Information Signal-to-Noise Ratio (SNR) For a waveform perfectly reconstructed from digital samples, SNR is the ratio of full-scale analog input (RMS value) to the RMS quantization error (residual error). The ideal, theoretical minimum analog-to-digital noise is caused by quantization error only and results directly from the ADC’s resolution (N bits): SNR(MAX) = (6.02 · N + 1.76)dB In reality, there are other noise sources besides quantization noise: thermal noise, reference noise, clock jitter, External Reference An external reference is required for both the MAX157 and MAX159. At REF, the DC input resistance is a minimum of 18kΩ. During a conversion, a reference must be able to deliver 250µA of DC load current and have an output impedance of 10 Ω or less. Use a 0.1µF bypass capacitor for best performance. The reference input structure allows a voltage range of 0 to (VDD + 50mV) although noise levels will decrease effective resolution at lower reference voltages. ACTIVE POWER DOWN tCS ACTIVE SAMPLING INSTANT tWAKE (tACQ) CS/SHDN SCLK HIGH-Z DOUT 1 2 3 4 5 6 7 D7 8 D6 9 D5 10 D4 11 D3 12 D2 13 D1 14 D0 15 S1 16 S0 HIGH-Z CHID MSB D8 Figure 6. External Clock Mode Timing CS/SHDN ••• tSCLKS tCL tCH tCS SCLK ••• tDV DOUT HIGH-Z ••• tDO tTR HIGH-Z Figure 7. Detailed Serial-Interface Timing Sequence 10 ______________________________________________________________________________________ +2.7V, Low-Power, 2-Channel, 108ksps, Serial 10-Bit ADCs in 8-Pin µMAX Table 1. Serial Output Data Stream for Internal and External Clock Mode SCLK CYCLE DOUT (Internal Clock) DOUT (External Clock) 1 EOC 1 2 1 1 3 1 1 4 5 6 D8 D8 7 D7 D7 8 D6 D6 9 D5 D5 10 D4 D4 11 D3 D3 12 D2 D2 13 D1 D1 14 D0 D0 15 S1 S1 16 S0 S0 CHID D9 CHID D9 MAX157/MAX159 etc. Therefore, SNR is computed by taking the ratio of the RMS signal to the RMS noise (which includes all spectral components minus the fundamental), the first five harmonics, and the DC offset. serial clock for the MAX157/MAX159. Select a clock frequency from 100kHz to 2.17MHz (external clock mode). 1) Use a general-purpose I/O line on the CPU to pull CS/SHDN low while SCLK is low. 2) Wait for the minimum wake-up time (tWAKE) specified before activating SCLK. 3) Activate SCLK for a minimum of 16 clock cycles. The first falling clock edge will generate a serial datastream of three leading ones, followed by the channel identification, the MSB of the digitized input signal, and two sub-bits. DOUT transitions on SCLK’s falling edge and is available in MSB-first format. Observe the SCLK to DOUT valid timing characteristic. Data should be clocked into the µP on SCLK’s rising edge. 4) Pull CS/SHDN high at or after the 16th falling clock edge. If CS/SHDN remains low, trailing zeros will be clocked out after the sub-bits. 5) With CS/SHDN high, wait at least 60ns (tCS), before starting a new conversion by pulling CS/SHDN low. A conversion can be aborted by pulling CS/SHDN high before the conversion ends; wait at least 60ns before starting a new conversion. Data can be output either in two 8-bit sequences or continuously. The bytes will contain the result of the conversion padded with three leading ones, the channel identification before the MSB, and two trailing subbits. If the serial clock hasn’t been idled after the last sub-bit (S0) and CS/SHDN is kept low, DOUT sends trailing zeros. Signal-to-Noise Plus Distortion (SINAD) Signal-to-noise plus distortion is the ratio of the fundamental input frequency’s RMS amplitude to RMS equivalent of all other ADC output signals: SINAD(dB) = 20 ⋅ log  (Noise SignalRMS  + Distortion)  RMS    Effective Number of Bits (ENOB) ENOB indicates the global accuracy of an ADC at a specific input frequency and sampling rate. An ideal ADC’s error consists of quantization noise only. With an input range equal to the full-scale range of the ADC, calculate the effective number of bits as follows: ENOB = (SINAD - 1.76) / 6.02 Total Harmonic Distortion (THD) THD is the ratio of the RMS sum of the first five harmonics of the input signal to the fundamental itself. This is expressed as: THD = 20 ⋅   log    (V 22 + V32 + V4 2 + V52  V12 )    where V1 is the fundamental amplitude and V2 through V5 are the amplitudes of the 2nd through 5th-order harmonics. SPI and MICROWIRE Interface When using SPI (Figure 8a) or MICROWIRE (Figure 8b) interfaces, set CPOL = 0 and CPHA = 0. Conversion begins with a falling edge on CS/SHDN (Figure 8c). Two consecutive 8-bit readings are necessary to obtain the entire 10-bit result from the ADC. DOUT data transitions on the serial clock’s falling edge and is clocked into the µP on SCLK’s rising edge. The first 8-bit data stream contains three leading ones, followed by channel identification and the first four data bits starting with the MSB. The second 8-bit data stream contains the remaining bits, D5 through D0, and the sub-bits S1 and S0. Spurious-Free Dynamic Range (SFDR) SFDR is the ratio of RMS amplitude of the fundamental (maximum signal component) to the RMS value of the next largest spurious component, excluding DC offset. Connection to Standard Interfaces The MAX157/MAX159 interface is fully compatible with SPI/QSPI and MICROWIRE standard serial interfaces. If a serial interface is available, establish the CPU’s serial interface as master so that the CPU generates the ______________________________________________________________________________________ 11 +2.7V, Low-Power, 2-Channel, 108ksps, Serial 10-Bit ADCs in 8-Pin µMAX MAX157/MAX159 I/O SCK MISO CS/SHDN SCLK DOUT VDD I/O SK SI CS/SHDN SCLK DOUT SPI MICROWIRE MAX157 MAX159 SS MAX157 MAX159 Figure 8a. SPI Connections Figure 8b. MICROWIRE Connections 1ST BYTE READ SCLK CS/SHDN DOUT* SAMPLING INSTANT *WHEN CS/SHDN IS HIGH, DOUT = HIGH -Z 1 2 3 4 5 6 7 8 9 10 11 2ND BYTE READ 12 13 14 15 16 CHID D9 MSB D8 D7 D6 D5 D4 D3 D2 D1 D0 LSB S1 S0 HIGH-Z Figure 8c. SPI/MICROWIRE Interface Timing Sequence (CPOL = CPHA = 0) QSPI Interface Using the high-speed QSPI interface with CPOL = 0 and CPHA = 0, the MAX157/MAX159 supports a maximum fSCLK of 2.17MHz. The QSPI circuit in Figure 9a can be programmed to perform a conversion on each of the two channels for the MAX157. Figure 9b shows the QSPI interface timing. CS SCK MISO CS/SHDN SCLK DOUT VDD QSPI PIC16 with SSP Module and PIC17 Interface The MAX157/MAX159 are compatible with a PIC16/ PIC17 microcontroller (µC), using the synchronous serial port (SSP) module. To establish SPI communication, connect the controller as shown in Figure 10a and configure the PIC16/PIC17 as system master by initializing its synchronous serial port control register (SSPCON) and synchronous serial port status register (SSPSTAT) to the bit patterns shown in Tables 2 and 3. In SPI mode, the PIC16/PIC17 µCs allow eight bits of data to be synchronously transmitted and received simultaneously. Two consecutive 8-bit readings (Figure 10b) are necessary to obtain the entire 10-bit result from the ADC. DOUT data transitions on the serial clock’s falling edge and is clocked into the µC on SCLK’s rising edge. The first 8-bit data stream contains 12 SS MAX157 MAX159 Figure 9a. QSPI Connections three leading ones, the channel identification, and the first four data bits starting with the MSB. The second 8bit data stream contains the remaining bits, D5 through D0, and the two sub-bits S1 and S0. Layout, Grounding, and Bypassing For best performance use printed circuit boards (PCBs), wire-wrap configurations are not recommended, since the layout should ensure proper separation of analog and digital traces. Run analog and digital lines anti-parallel to each other, and don’t layout digital signal paths underneath the ADC package. Use separate analog and digital PCB ground sections with only one ______________________________________________________________________________________ +2.7V, Low-Power, 2-Channel, 108ksps, Serial 10-Bit ADCs in 8-Pin µMAX MAX157/MAX159 SCLK CS/SHDN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 HIGH-Z DOUT CHID D9 MSB D8 D7 D6 D5 D4 D3 D2 D1 D0 LSB S1 S0 SAMPLING INSTANT *WHEN CS/SHDN IS HIGH, DOUT = HIGH - Z Figure 9b. QSPI Interface Timing Sequence (CPOL = CPHA = 0) VDD VDD SCLK DOUT CS/SHDN SCK SDI I/O MAX157 MAX159 GND PIC16/PIC17 GND Figure 10a. SPI Interface Connection for a PIC16/PIC17 Controller star-point (Figure 11) connecting the two ground systems (analog and digital). For lowest-noise operation, ensure the ground return to the star ground’s power supply is low impedance and as short as possible. Route digital signals far away from sensitive analog and reference inputs. High-frequency noise in the power supply (VDD) could influence the proper operation of the ADC’s fast comparator. Bypass VDD to the star ground with a network of two parallel capacitors, 0.1µF and 1µF, located as close as possible to the power supply pin of the MAX157/MAX159. Minimize capacitor lead length for best supply-noise rejection and add an attenuation resistor (10Ω) if the power supply is extremely noisy. 1ST BYTE READ SCLK CS/SHDN 1 2 3 4 5 6 7 8 9 10 11 2ND BYTE READ 12 13 14 15 16 HIGH-Z DOUT* CHID D9 MSB D8 D7 D6 D5 D4 D3 D2 D1 D0 LSB S1 S0 SAMPLING INSTANT *WHEN CS/SHDN IS HIGH, DOUT = HIGH - Z Figure 10b. SPI Interface Timing Sequence with PIC16/17 in Master Mode (CKE = 1, CKP = 0, SMP = 0, SSPM3–SSPM0 = 0001) POWER SUPPLIES +3V R* = 10Ω 1µF +3V GND 0.1µF VDD GND +3V DGND MAX157 MAX159 * OPTIONAL FILTER RESISTOR DIGITAL CIRCUITRY Figure 11. Power-Supply Bypassing and Grounding ______________________________________________________________________________________ 13 +2.7V, Low-Power, 2-Channel, 108ksps, Serial 10-Bit ADCs in 8-Pin µMAX MAX157/MAX159 Table 2. Detailed SSPCON Register Content CONTROL BIT WCOL SSPOV SSPEN CKP SSPM3 SSPM2 SSPM1 SSPM0 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 MAX157/MAX159 SETTINGS X X 1 0 0 0 0 1 Synchronous Serial Port Mode Select Bit. Sets SPI master mode and selects fCLK = fOSC / 16. SYNCHRONOUS SERIAL PORT CONTROL REGISTER (SSPCON) Write Collision Detection Bit Receive Overflow Detect Bit Synchronous Serial Port Enable Bit 0: Disables serial port and configures these pins as I/O port pins. 1: Enables serial port and configures SCK, SDO and SCI pins as serial port pins. Clock Polarity Select Bit. CKP = 0 for SPI master mode selection. X = Don’t care Table 3. Detailed SSPSTAT Register Content CONTROL BIT SMP CKE D/A P S R/W UA BF Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 MAX157/MAX159 SETTINGS 0 1 X X X X X X SYNCHRONOUS SERIAL STATUS REGISTER (SSPSTAT) SPI Data Input Sample Phase. Input data is sampled at the middle of the data output time. SPI Clock Edge Select Bit. Data will be transmitted on the rising edge of the serial clock. Data Address Bit Stop Bit Start Bit Read/Write Bit Information Update Address Buffer Full Status Bit X = Don’t care 14 ______________________________________________________________________________________ +2.7V, Low-Power, 2-Channel, 108ksps, Serial 10-Bit ADCs in 8-Pin µMAX Chip Information TRANSISTOR COUNT: 2,058 SUBSTRATE CONNECTED TO GND MAX157/MAX159 Package Information 8LUMAXD.EPS ______________________________________________________________________________________ 15 +2.7V, Low-Power, 2-Channel, 108ksps, Serial 10-Bit ADCs in 8-Pin µMAX MAX157/MAX159 Package Information (continued) PDIPN.EPS 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 © 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.