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19-0876; Rev 1; 5/96
CMOS, P-Compatible, 5s/10s, 8-Bit ADCs
_______________General Description
Maxim's MX7575/MX7576 are high-speed (5s/10s), microprocessor (P) compatible, 8-bit analog-to-digital converters (ADCs). The MX7575 provides an on-chip track/hold function that allows full-scale signals up to 50kHz (386mV/s slew rate) to be acquired and digitized accurately. Both ADCs use a successive-approximation technique to achieve their fast conversions and low power dissipation. The MX7575/MX7576 operate with a +5V supply and a 1.23V external reference. They accept input voltages ranging from 0V to 2VREF. The MX7575/MX7576 are easily interfaced to all popular 8-bit Ps through standard CS and RD control signals. These signals control conversion start and data access. A BUSY signal indicates the beginning and end of a conversion. Since all the data outputs are latched and three-state buffered, the MX7575/MX7576 can be directly tied to a P data bus or system l/O port. Maxim also makes the MAX165, a plug-in replacement for the MX7575 with an internal 1.23V reference. For applications that require a differential analog input and an internal reference, the MAX166 is recommended.
____________________________Features
o Fast Conversion Time: 5s (MX7575) 10s (MX7576)
MX7575/MX7576
o Built-In Track/Hold Function (MX7575) o Low Total Unadjusted Error (1LSB max) o 50kHz Full-Power Signal Bandwidth (MX7575) o Single +5V Supply Operation o 8-Bit P Interface o 100ns Data-Access Time o Low Power: 15mW o Small-Footprint Packages
______________Ordering Information
PART MX7575JN TEMP. RANGE 0C to +70C PIN-PACKAGE 18 Plastic DIP INL (LSB) 1 1/2 1 1/2 1 1/2 1 1 1/2
________________________Applications
Digital Signal Processing High-Speed Data Acquisition Telecommunications Audio Systems High-Speed Servo Loops Low-Power Data Loggers
MX7575KN 0C to +70C 18 Plastic DIP MX7575JCWN 0C to +70C 18 Wide SO MX7575KCWN 0C to +70C 18 Wide SO MX7575JP 0C to +70C 20 PLCC MX7575KP 0C to +70C 20 PLCC MX7575J/D 0C to +70C Dice* MX7575AQ -25C to +85C 18 CERDIP** MX7575BQ -25C to +85C 18 CERDIP** Ordering Information continued at end of data sheet. * Contact factory for dice specifications. ** Contact factory for availability.
_________________Pin Configurations
TOP VIEW
CS 1 RD 2 TP (MODE) 3 BUSY 4 CLK 5 D7 (MSB) 6 D6 7 D5 8 18 VDD 17 REF
_______________Functional Diagrams
VDD 18 16
MX7575
AIN
MX7575 MX7576
TRACK/ HOLD
COMP
16 AIN 15 AGND 14 D0 (LSB) 13 D1 12 D2 11 D3 10 D4
AGND 15 REF 17 CLK 5 CLOCK OSCILLATOR DAC
SAR 6 LATCH AND THREE-STATE OUTPUT DRIVERS 14 9 DGND D7 D0
DGND 9
CS RD TP
1 2 3
CONTROL LOGIC
. .
( ) ARE FOR MX7576 ONLY.
DIP/SO
Pin Configurations continued at end of data sheet.
4 BUSY Functional Diagrams continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products
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CMOS, P-Compatible, 5s/10s, 8-Bit ADCs MX7575/MX7576
ABSOLUTE MAXIMUM RATINGS
VDD to AGND...............................................................-0.3V, +7V VDD to DGND ..............................................................-0.3V, +7V AGND to DGND ...............................................-0.3V, VDD + 0.3V Digital Input Voltage to DGND (CS, RD, TP, MODE) ......................................-0.3V, VDD + 0.3V Digital Output Voltage to DGND (BUSY, D0-D7) ..............................................-0.3V, VDD + 0.3V CLK Input Voltage to DGND ............................-0.3V, VDD + 0.3V REF to AGND ...................................................-0.3V, VDD + 0.3V AIN to AGND....................................................-0.3V, VDD + 0.3V Continuous Power Dissipation (TA = +70C) Plastic DIP (derate 11.11mW/C above +70C) ...............889mW Wide SO (derate 9.52mW/C above +70C)..................762mW CERDIP (derate 10.53mW/C above +70C) .................842mW PLCC (derate 10.00mW/C above +70C) ....................800mW Operating Temperature Ranges MX757_J/K ............................................................0C to +70C MX757_A/B ........................................................-25C to +85C MX757_JE/KE ....................................................-40C to +85C MX757_S/T.......................................................-55C to +125C Storage Temperature Range .............................-65C to +160C 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
(V DD = +5V; V REF = 1.23V; AGND = DGND = 0V; f CLK = 4MHz external for MX7575; f CLK = 2MHz external for MX7576; TA = TMIN to TMAX, unless otherwise noted.) PARAMETER ACCURACY Resolution Total Unadjusted Error Relative Accuracy No-Missing-Codes Resolution Full-Scale Error Full-Scale Tempco Offset Error (Note 1) Offset Tempco ANALOG INPUT Voltage Range DC Input Impedance Slew Rate, Tracking Signal-to-Noise Ratio (Note 2) REFERENCE INPUT Reference Voltage Reference Current LOGIC INPUTS CS, RD, MODE Input Low Voltage Input High Voltage Input Current Input Capacitance (Note 2) VREF IREF VINL VINH IIN CIN VIN = 0V or VDD TA = +25C TA = TMIN to TMAX 2.4 1 10 10 5% variation for specified performance 1.23 500 0.8 V A V V A pF SNR MX7575 MX7575, VIN = 2.46Vp-p at 10kHz, Figure 13 45 1LSB = 2VREF/256 0 10 0.386 2VREF V M V/s dB 5 5 1/2 TUE INL MX757_K/B/T MX757_J/A/S MX757_K/B/T MX757_J/A/S 8 1 8 1 2 1/2 1 Bits LSB LSB Bits LSB ppm/C LSB ppm/C SYMBOL CONDITIONS MIN TYP MAX UNITS
2
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CMOS, P-Compatible, 5s/10s, 8-Bit ADCs
ELECTRICAL CHARACTERISTICS (continued)
(V DD = +5V; V REF = 1.23V; AGND = DGND = 0V; f CLK = 4MHz external for MX7575; f CLK = 2MHz external for MX7576; TA = TMIN to TMAX, unless otherwise noted.) PARAMETER CLOCK Input Low Voltage Input High Voltage Input Low Current Input High Current LOGIC OUTPUTS (D0-D7, BUSY) Output Low Voltage Output High Voltage Floating State Leakage Current Floating State Output Capacitance (Note 2) CONVERSION TIME (Note 3) Conversion Time with External Clock Conversion Time with Internal Clock POWER REQUIREMENTS (Note 4) Supply Voltage VDD Supply Current Power Dissipation Power-Supply Rejection Note 1: Note 2: Note 3: Note 4: IDD MX7575: fCLK = 4MHz MX7576: fCLK = 2MHz Using recommended clock components: RCLK = 100k, CCLK = 100pF; TA = +25C MX7575 MX7576 5 10 5 10 15 s 30 s VOL VOH ISINK = 1.6mA ISOURCE = 40A VOUT = 0V to VDD, D0-D7 D0-D7 TA = +25C TA = TMIN to TMAX 4.0 1 10 10 0.4 V V A pF VINL VINH IINL IINH VIN = 0V VIN = VDD MX757_J/A/K/B MX757_S/T MX757_J/A/K/B MX757_S/T 2.4 700 800 700 800 0.8 V V A A SYMBOL CONDITIONS MIN TYP MAX UNITS
MX7575/MX7576
5% for specified performance MX757_J/A/K/B MX757_S/T 4.75V < VDD < 5.25V
5 3 15
V 6 7 1/4 mA mW LSB
Offset Error is measured with respect to an ideal first-code transition that occurs at 1/2LSB. Sample tested at +25C to ensure compliance. Accuracy may degrade at conversion times other than those specified. Power-supply current is measured when MX7575/MX7576 are inactive, i.e.: For MX7575 CS = RD = BUSY = high; For MX7576 CS = RD = BUSY = MODE = high.
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CMOS, P-Compatible, 5s/10s, 8-Bit ADCs MX7575/MX7576
TIMING CHARACTERISTICS (Note 5)
(VDD = +5V, VREF = 1.23V, AGND = DGND = 0V.) TA = +25C PARAMETER CS to RD Setup Time RD to BUSY Propagation Time Data-Access Time after RD RD Pulse Width CS to RD Hold Time Data-Access Time after BUSY Data-Hold Time BUSY to CS Delay SYMBOL t1 t2 t3 t4 t5 t6 t7 t8 (Note 6) (Note 7) 10 0 (Note 6) 100 0 80 80 10 0 CONDITIONS MIN 0 100 100 100 0 80 80 10 0 ALL MAX 0 100 100 120 0 100 100 MIN TA = TMIN to TMAX J/K/A/B MAX MIN 0 120 120 S/T MAX ns ns ns ns ns ns ns ns UNITS
Note 5: Timing specifications are sample tested at +25C to ensure compliance. All input control signals are specified with tr = tf = 20ns (10% to 90% of +5V) and timed from a voltage level of 1.6V. Note 6: t3 and t6 are measured with the load circuits of Figure 1 and defined as the time required for an output to cross 0.8V or 2.4V. Note 7: t7 is defined as the time required for the data lines to change 0.5V when loaded with the circuits of Figure 2.
______________________________________________________________Pin Description
PIN DIP/SO 1 2 PLCC 2 3 NAME CS RD FUNCTION Chip Select Input. CS must be low for the device to be selected or to recognize the RD input. Read Input. RD must be low to access data. RD is also used to start conversions. See the Microprocessor Interface section.
3
4
TP Test Point. Connect to VDD. (MX7575) MODE Mode Input. MODE = low puts the ADC into its asynchronous conversion mode. MODE has to be (MX7576) tied high for the synchronous conversion mode and the ROM interface mode. BUSY CLK D7 D6, D5 DGND D4-D1 D0 AGND AIN REF VDD N.C. BUSY Output. BUSY going low indicates the start of a conversion. BUSY going high indicates the end of a conversion. External Clock Input/Internal Oscillator Pin for frequency setting RC components. Three-State Data Output, bit 7 (MSB) Three-State Data Outputs, bits 6 and 5 Digital Ground Three-State Data Outputs, bits 4-1 Three-State Data Output, bit 0 (LSB) Analog Ground Analog Input. 0V to 2VREF input range. Reference Input. +1.23V nominal. Power-Supply Voltage. +5V nominal. No Connect
4 5 6 7, 8 9 10-13 14 15 16 17 18 --
5 6 7 8, 9 10 12-15 16 17 18 19 20 1, 11
4
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CMOS, P-Compatible, 5s/10s, 8-Bit ADCs MX7575/MX7576
+5V 3k D_ 3k DGND a) HIGH-Z TO VOH NOTE: D_ REPRESENTS ANY OF THE DATA OUTPUTS 100pF DGND b) HIGH-Z TO VOL D_ 100pF D_ 3k DGND a) VOH TO HIGH-Z NOTE: D_ REPRESENTS ANY OF THE DATA OUTPUTS 10pF DGND b) VOL TO HIGH-Z D_ 10pF +5V 3k
Figure 1. Load Circuits for Data-Access Time Test
Figure 2. Load Circuits for Data-Hold Time Test
_______________Detailed Description
Converter Operation
The MX7575 and MX7576 use the successive-approximation technique to convert an unknown analog input voltage to an 8-bit digital output code (see Functional Diagrams). The MX7575 samples the input voltage on an internal capacitor once (at the beginning of the conversion), while the MX7576 samples the input signal eight times during the conversion (see MX7575 Track/Hold and MX7576 Analog Input sections). The internal DAC is initially set to half scale, and the comparator determines whether the input signal is larger than or smaller than half scale. If it is larger than half scale, the DAC MSB is kept. But if it is smaller, the MSB is dropped. At the end of each comparison phase, the SAR (successive-approximation register) stores the results of the previous decision and determines the next trial bit. This information is then loaded into the DAC after each decision. As the conversion proceeds, the analog input is approximated more closely by comparing it to the combination of the previous DAC bits and a new DAC trial bit. After eight comparison cycles, the eight bits stored in the SAR are latched into the output latches. At the end of the conversion, the BUSY signal goes high, and the data in the output latches is ready for microprocessor (P) access. Furthermore, the DAC is reset to half scale in preparation for the next conversion.
are performed. In the slow-memory interface mode, CS and RD are taken low to start a conversion and they remain low until the conversion ends, at which time the conversion result is latched. This mode is designed for Ps that can be forced into a wait state. In the ROM interface mode, however, the P is not forced into a wait state. A conversion is started by taking CS and RD low, and data from the previous conversion is read. At the end of the most recent conversion, the P executes a read instruction and starts another conversion. For the MX7575, TP should be hard-wired to V DD to ensure proper operation of the device. Spurious signals may occur on TP, or excessive currents may be drawn from VDD if TP is left open or tied to a voltage other than VDD.
Microprocessor Interface
The CS and RD logic inputs are used to initiate conversions and to access data from the devices. The MX7575 and MX7576 have two common interface modes: slowmemory interface mode and ROM interface mode. In addition, the MX7576 has an asynchronous conversion mode (MODE pin = low) where continuous conversions
Slow-Memory Mode Figure 3 shows the timing diagram for slow-memory interface mode. This is used with Ps that have a waitstate capability of at least 10s (such as the 8085A), where a read instruction is extended to accommodate slow-memory devices. A conversion is started by executing a memory read to the device (taking CS and RD low). The BUSY signal (which is connected to the P READY input) then goes low and forces the P into a wait state. The MX7575 track/hold, which had been tracking the analog input signal, holds the signal on the third falling clock edge after RD goes low (Figure 12). The MX7576, however, samples the analog input eight times during a conversion (once before each comparator decision). At the end of the conversion, BUSY returns high, the output latches and buffers are updated with the new conversion result, and the P completes the memory read by acquiring this new data. The fast conversion time of the MX7575/MX7576 ensures that the P is not forced into a wait state for an excessive amount of time. Faster versions of many Ps,
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CMOS, P-Compatible, 5s/10s, 8-Bit ADCs MX7575/MX7576
CS RD BUSY t3 DATA HIGHIMPEDANCE BUS OLD DATA t1 t2 tCONV t5
CS t1 RD t2 BUSY
t6 NEW DATA t7 HIGHIMPEDANCE BUS
t5 t4 t8
t3 HIGHDATA IMPEDANCE BUS
t7 OLD DATA
t3 NEW DATA
t7 HIGHIMPEDANCE BUS
HIGH-IMPEDANCE BUS
Figure 3. Slow-Memory Interface Timing Diagram
Figure 5. ROM Interface Timing Diagram
A8-A15
ADDRESS BUS +5V TP/MODE ADDRESS DECODE
A0-A15
ADDRESS BUS +5V TP/MODE ADDRESS EN DECODE CS RD D0-D7
8085A-2
S0 ALE AD0-AD7 READY ADDRESS LATCH
6502-6809
R/W 2 OR E
MX7575* RD MX7576
BUSY D0-D7
CS
MX7575* MX7576
DATA BUS
D0-D7
DATA BUS
* SOME CIRCUITRY OMITTED FOR CLARITY S0 IS LOW FOR READ CYCLES
* SOME CIRCUITRY OMITTED FOR CLARITY
Figure 4. MX7575/MX7576 to 8085A-2 Slow-Memory Interface
Figure 6. MX7575/MX7576 to 6502/6809 ROM Interface
including the 8085A-2, test the status of the READY input immediately after the start of an instruction cycle. Therefore, if the MX7575/MX7576 are to be effective in placing the P in a wait state, their BUSY output should go low very early in the cycle. When using the 8085A-2, the earliest possible indication of an upcoming read operation is provided by the S0 status signal. Thus, S0, which is low for a read cycle, should be connected to the RD input of the MX7575/MX7576. Figure 4 shows the connection diagram for the 8085A-2 to the MX7575/MX7576 in slow-memory interface mode.
ROM Interface Mode Figure 5 shows the timing diagram for ROM interface mode. In this mode, the P does not need to be placed in a wait state. A conversion is started with a read instruction (RD and CS go low), and old data is accessed. The BUSY signal then goes low to indicate the start of a conversion. As before, the MX7575 track/hold acquires the signal on the third falling clock edge after RD goes low, while the MX7576 samples it eight times during a conversion. At the end of a conversion (BUSY going high), another read instruction always accesses the new data and normally starts a second conversion. However, if RD and CS go low within one
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external clock period of BUSY going high, then the second conversion is not started. Furthermore, for correct operation in this mode, RD and CS should not go low before BUSY returns high. Figures 6 and 7 show the connection diagrams for interfacing the MX7575/MX7576 in the ROM interface mode. Figure 6 shows the connection diagram for the 6502/6809 Ps, and Figure 7 shows the connections for the Z-80. Due to their fast interface timing, the MX7575/MX7576 will interface to the TMS32010 running at up to 18MHz. Figure 8 shows the connection diagram for the TMS32010. In this example, the MX7575/MX7576 are mapped as a port address. A conversion is initiated by using an IN A and a PA instruction, and the conversion result is placed in the TMS32010 accumulator.
Asynchronous Conversion Mode (MX7576) Tying the MODE pin low places the MX7576 into a continuous conversion mode. The RD and CS inputs are only used for reading data from the converter. Figure 9 shows the timing diagram for this mode of operation, and Figure 10 shows the connection diagram for the 8085A. In this mode, the MX7576 looks like a ROM to
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CMOS, P-Compatible, 5s/10s, 8-Bit ADCs MX7575/MX7576
Z-80
MREQ RD ADDRESS BUS +5V TP/MODE ADDRESS EN DECODE CS CS RD D7 D0 DB7 DB0 DATA BUS UPDATE LATCH DEFER UPDATING
MX7575* MX7576
RD BUSY
t1 t4
t5
t3 HIGHDATA IMPEDANCE BUS
t7 VALID DATA HIGH-IMPEDANCE BUS VALID DATA HIGHIMPEDANCE BUS
* SOME CIRCUITRY OMITTED FOR CLARITY
Figure 7. MX7575/MX7576 to Z-80 ROM Interface
Figure 9. MX7576 Asynchronous Conversion Mode Timing Diagram
A0-A15 ADDRESS BUS MODE ADDRESS ENCODE RD ALE AD0-AD7 ADDRESS LATCH DATA BUS CS RD D0-D7
PA2 PA0
ADDRESS BUS +5V TP/MODE ADDRESS EN DECODE CS RD D7 D0
TMS32010
MEN DEN
8085A
MX7575* MX7576
MX7576*
DB7 DB0
DATA BUS
* SOME CIRCUITRY OMITTED FOR CLARITY
* SOME CIRCUITRY OMITTED FOR CLARITY
Figure 8. MX7575/MX7576 to TMS32010 ROM Interface
Figure 10. MX7576 to 8085A Asynchronous Conversion Mode Interface
the P, in that data can be accessed independently of the clock. The output latches are normally updated on the rising edge of BUSY. But if CS and RD are low when BUSY goes high, the data latches are not updated until one of these inputs returns high. Additionally, the MX7576 stops converting and BUSY stays high until RD or CS goes high. This mode of operation allows a simple interface to the P.
Processor Interface for Signal Acquisition (MX7575) In many applications, it is necessary to sample the input signal at exactly equal intervals to minimize errors due to sampling uncertainty or jitter. In order to achieve this objective with the previously discussed interfaces, the user must match software delays or count the number of elapsed clock cycles. This becomes difficult in interrupt-driven systems where the uncertainty in interrupt servicing delays is another complicating factor. The solution is to use a real-time clock to control the start of a conversion. This should be synchronous with
the CLK input to the ADC (both should be derived from the same source), because the sampling instants occur three clock cycles after CS and RD go low. Therefore, the sampling instants occur at exactly equal intervals if the conversions are started at equal intervals. In this scheme, the output data is fed into a FIFO latch, which allows the P to access data at its own rate. This guarantees that data is not read from the ADC in the middle of a conversion. If data is read from the ADC during a conversion, the conversion in progress may be disturbed, but the accessed data that belonged to the previous conversion will be correct. The track/hold starts holding the input on the third falling edge of the clock after CS and RD go low. If CS and RD go low within 20ns of a falling clock edge, the ADC may or may not consider this falling edge as the first of the three edges that determine the sampling instant. Therefore, the CS and RD should not be allowed to go low within this period when sampling accuracy is required.
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CMOS, P-Compatible, 5s/10s, 8-Bit ADCs MX7575/MX7576
MX7575 Track/Hold
The track/hold consists of a sampling capacitor and a switch to capture the input signal. The simplified diagram of this block is shown in Figure 11. At the beginning of the conversion, switch S1 is closed, and the input signal is tracked. The input signal is held (switch S1 opens) on the third falling edge of clock after CS and RD go low (Figure 12). This allows a minimum of two clock cycles for the input capacitor to be charged to the input voltage through the switch resistance. The time required for the hold capacitor to settle to 1/4LSB is typically 7ns. Therefore, the input signal is allowed ample time to settle before it is acquired by the track/hold. When a conversion ends, switch S1 closes, and the input signal is tracked. The track/hold is capable of acquiring signals with slew rates of up to 386mV/s (or equivalently a 50kHz sine wave with 2.46Vp-p amplitude). Figure 13 shows the signal-to-noise ratio (SNR) versus input frequency for the ADC. The SNR plot is generated at a sampling rate of 200kHz using sinusoidal inputs with a peak-to-peak amplitude of 2.46V. The reconstructed sine wave is passed through a 50kHz 8th-order Chebychev filter. The improvement in SNR at high frequencies is due to the filter cutoff. The switching nature of the analog input results in transient currents that charge the input capacitance of the track/hold. Keep the driving source impedance low (below 2k), so that the settling characteristics of the track/hold are not degraded. A low driving impedance also minimizes undesirable noise pickup and reduces DC errors caused by transient currents at the analog input. As with any ADC, it is important to keep external sources of noise to a minimum during a conversion. Therefore, keep the data bus as quiet as possible during a conversion, especially when the track/hold is making the transition to the hold mode. For conversion times that are significantly longer than 5s, the device's accuracy may degrade slightly, as shown in Figure 14. This degradation is due to the charge that is lost from the hold capacitor in the presence of small on-chip leakage currents.
MX7576 Analog Input
The MX7576 analog input can also be modeled with the switch and capacitor as shown in Figure 11. However, unlike the MX7575, the MX7576 samples the input voltage eight times during a conversion (once before each comparator decision). Therefore, the precautions that apply to the MX7575 also apply to the MX7576. These include minimizing the analog source impedance and reducing noise coupling from the digital circuitry during a conversion, especially near a sampling instant.
Reference Input
The high speed of this ADC can be partially attributed to the "inverted voltage output" topology of the DAC that it uses. This topology provides low offset and gain errors and fast settling times. The input current to the DAC, however, is not constant. During a conversion, as different DAC codes are tried, the DC impedance of the DAC can vary between 6k and 18k. Furthermore, when the DAC codes change, small amounts of transient current are drawn from the reference input. These characteristics require a low DC and AC driving impedance for the reference circuitry to minimize conversion errors. Figure 15 shows the reference circuitry recommended to drive the reference input of the MX7575/MX7576.
CS
RD
BUSY
EXTERNAL CLOCK
a) WITH EXTERNAL CLOCK
CS RD BUSY
INPUT SIGNAL HELD HERE
RON 500 VIN CS 0.5pF
S1 CH 2pF INTERNAL CLOCK INPUT SIGNAL HELD HERE
b) WITH INTERNAL CLOCK
Figure 11. Equivalent Input Circuit
Figure 12. MX7575 Track/Hold (Slow-Memory Interface) Timing Diagrams
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CMOS, P-Compatible, 5s/10s, 8-Bit ADCs
TA = +25C
MX7575/6 FIG13
40 42 44 SNR (dB) 46 48 50 52 54
The decoupling capacitors are necessary to provide a low AC source impedance.
MX7575/MX7576
Internal/External Clock
The MX7575/MX7576 can be run with either an externally applied clock or their internal clock. In either case, the signal appearing at the clock pin is internally divided by two to provide an internal clock signal that is relatively insensitive to the input clock duty cycle. Therefore, a single conversion takes 20 input clock cycles, which corresponds to 10 internal clock cycles.
100
1k
10k
100k
INPUT FREQUENCY (Hz)
Figure 13. MX7575 SNR vs. Input Frequency
RELATIVE ACCURACY (LSB)
2.0
A: TA = +125C B: TA = +85C C: TA = +25C
1.5
1.0 A 0.5 B C
0 10 100 1000 10000 CONVERSION TIME (s)
Figure 14. MX7575 Accuracy vs. Conversion Time
MX7575/6 FIG14
2.5
Internal Clock The internal oscillator frequency is set by an external capacitor, CCLK, and an external resistor, RCLK, which are connected as shown in Figure 16a. During a conversion, a sawtooth waveform is generated on the CLK pin by charging CCLK through RCLK and discharging it through an internal switch. At the end of a conversion, the internal oscillator is shut down by clamping the CLK pin to VDD through an internal switch. The circuit for the internal oscillator can easily be overdriven with an external clock source. The internal oscillator provides a convenient clock source for the MX7575. Figure 17 shows typical conversion times versus temperature for the recommended RCLK and CCLK combination. Due to process variations, the oscillation frequency for this RCLK/CCLK combination may vary by as much as 50% from the nominal value shown in Figure 17. Therefore, an external clock should be used in the following situations: 1) Applications that require the conversion time to be within 50% of the minimum conversion time for the specified accuracy (5s MX7575/10s MX7576). 2) Applications in which time-related software constraints cannot accommodate conversion-time differences that may occur from unit to unit or over temperature for a given device. External Clock The CLK input of the MX7575/MX7576 may be driven directly by a 74HC or 4000B series buffer (e g., 4049), or by an LS TTL output with a 5.6k pull-up resistor. At the end of a conversion, the device ignores the clock input and disables its internal clock signal. Therefore, the external clock may continue to run between conversions without being disabled. The duty cycle of the external clock may vary from 30% to 70%. As discussed previously, in order to maintain accuracy, clock rates significantly lower than the data sheet limits (4MHz for MX7575 and 2MHz for MX7576) should not be used.
+5V 3.3k 1.23V REF + + 47F 0.1F
ICL8069
_
Figure 15. External Reference Circuit
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CMOS, P-Compatible, 5s/10s, 8-Bit ADCs MX7575/MX7576
+5V 47F 0.1F +5V 18 VDD AIN REF AGND CLK BUSY 17 15 CS RCLK 100k, 2% 5 4 1 CCLK 100pF, 1% CONTROL INPUTS D7-D0 DATA OUT 0000 0011 0000 0010 0000 0001 0000 0000 0 OUTPUT CODE 1111 1111 1111 1110 1111 1101 FULL-SCALE TRANSITION (FS - 3/2LSB)
+5V 3.3k + 2.46V(max) +1.23V 47F 0.1F 16
2 RD TP/ 3 MODE
FS = 2VREF 2FS 1LSB = --- 256
MX7575 MX7576
9
FS - 1LSB 1LSB 3LSBs 2LSBs AIN, INPUT VOLTAGE (IN TERMS OF LSBs)
Figure 16a. Unipolar Configuration
Figure 16b. Nominal Transfer Characteristic for Unipolar Operation
______________ Typical Applications
Unipolar Operation
Figure 16a shows the analog circuit connections for unipolar operation, and Figure 16b shows the nominal transfer characteristic for unipolar operation. Since the offset and full-scale errors of the MX7575/MX7576 are very small, it is not necessary to null these errors in most cases. If calibration is required, follow the steps in the sections below.
accurate enough that calibration will not be necessary. If calibration is not needed, resistors R1-R7 should have a 0.1% tolerance, with R4 and R5 replaced by one 10k resistor, and R2 and R3 with one 1k resistor. If calibration is required, follow the steps in the sections below.
Offset Adjust Adjust the offset error by applying an analog input voltage of 2.43V (+FS - 3/2LSB). Then adjust resistor R5 until the output code flickers between 1111 1110 and 1111 1111. Full-Scale Adjust Null the full-scale error by applying an analog input voltage of -2.45V (-FS + 1/2LSB). Then adjust resistor R3 until the output code flickers between 0000 0000 and 0000 0001.
14 13 CONVERSION TIME (s) 12 11 10 9 8 7 -55 -25 0 25 50 RCLK = 100k CCLK = 100pF 75 100 125 AMBIENT TEMPERATURE (C) MX7576 MX7575
Offset Adjust The offset error can be adjusted by using the offset trim capability of an op amp (when it is used as a voltage follower) to drive the analog input, AIN. The op amp should have a common-mode input range that includes 0V. Set its initial input to 4.8mV (1/2LSB), while varying its offset until the ADC output code flickers between 0000 0000 and 0000 0001. Full-Scale Adjustment Make the full-scale adjustment by forcing the analog input, AIN, to 2.445V (FS - 3/2LSB). Then vary the reference input voltage until the ADC output code flickers between 1111 1110 and 1111 1111.
Bipolar Operation
Figure 18a shows an example of the circuit connection for bipolar operation, and Figure 18b shows the nominal transfer characteristic for bipolar operation. The output code provided by the MX7575 is offset binary. The analog input range for this circuit is 2.46V (1LSB = 19.22mV), even though the voltage appearing at AIN is in the 0V to 2.46V range. In most cases, the MX7575 is
10
Figure 17. Typical Conversion Times vs. Temperature Using Internal Clock
______________________________________________________________________________________
CMOS, P-Compatible, 5s/10s, 8-Bit ADCs MX7575/MX7576
+5V 47F +5V R6 3.3k 0.1F 18 VDD 5 17 CLK REF +5V TLC271
ICL8069 1.2V REFERENCE
+5V RCLK CL 100pF 2% OUTPUT CODE 111...111 111...110 100...010 100...001 R5 5k R4 8.2k R1 1k 16 100...000 011...111 011...110 000...001 FS = 2VREF 1LSB = 2FS 256 -FS 2 -1/2LSB 1/2LSB FS -1LSB 2 AIN
0.1F 47F
+
MX7575
AIN D7-D0 AGND DGND DATA OUT R2 9 15 820 R3 500 INPUT VOLTAGE
R7 10k
000...000
Figure 18a. MX7575 Bipolar Configuration
Figure 18b. Nominal Transfer Characteristic for Bipolar Operation
__________Applications Information
Noise
To minimize noise coupling, keep both the input signal lead to AIN and the signal return lead from AGND as short as possible. If this is not possible, a shielded cable or a twisted-pair transmission line is recommended. Additionally, potential differences between the ADC ground and the signal-source ground should be minimized, since these voltage differences appear as errors superimposed on the input signal. To minimize system noise pickup, keep the driving source resistance below 2k.
__Functional Diagrams (continued)
VDD 18 AIN AGND 16 15
MX7576
DAC CLOCK OSCILLATOR
COMP
REF 17 CLK 5
SAR 6 LATCH AND THREE-STATE OUTPUT DRIVERS 14 9 DGND D7 D0
Proper Layout
For PC board layouts, take care to keep digital lines well separated from any analog lines. Establish a single-point, analog ground (separate from the digital system ground) near the MX7575/MX7576. This analog ground point should be connected to the digital system ground through a single-track connection only. Any supply or reference bypass capacitors, analog input filter capacitors, or input signal shielding should be returned to the analog ground point.
CS RD MODE
1 2 3
CONTROL LOGIC
. .
4 BUSY
______________________________________________________________________________________
11
CMOS, P-Compatible, 5s/10s, 8-Bit ADCs MX7575/MX7576
____Pin Configurations (continued)
TOP VIEW
N.C. VDD REF RD CS 3 2 1 20 19
_Ordering Information (continued)
PART TEMP. RANGE PIN-PACKAGE INL (LSB) 1 1/2 1 1/2 1 1/2 1 1/2 1 1/2 1 1/2 1 1 1/2 1 1/2 1 1/2 1 1/2
TP (MODE) BUSY CLK D7 (MSB) D6
4 5 6 7 8
18 17
AIN AGND D0 (LSB)
MX7575 MX7576
16
15 D1 14 D2
9 D5
10 DGND
11 N.C.
12 D4
13 D3
PLCC
( ) ARE FOR MX7576 ONLY.
MX7575JEWN -40C to +85C 18 Wide SO MX7575KEWN -40C to +85C 18 Wide SO MX7575JEQP -40C to +85C 20 PLCC MX7575KEQP -40C to +85C 20 PLCC MX7575SQ -55C to +125C 18 CERDIP** MX7575TQ -55C to +125C 18 CERDIP** MX7576JN 0C to +70C 18 Plastic DIP MX7576KN 0C to +70C 18 Plastic DIP MX7576JCWN 0C to +70C 18 Wide SO MX7576KCWN 0C to +70C 18 Wide SO MX7576JP 0C to +70C 20 PLCC MX7576KP 0C to +70C 20 PLCC MX7576J/D 0C to +70C Dice* MX7576AQ -25C to +85C 18 CERDIP** MX7576BQ -25C to +85C 18 CERDIP** MX7576JEWN -40C to +85C 18 Wide SO MX7576KEWN -40C to +85C 18 Wide SO MX7576JEQP -40C to +85C 20 PLCC MX7576KEQP -40C to +85C 20 PLCC MX7576SQ -55C to +125C 18 CERDIP** MX7576TQ -55C to +125C 18 CERDIP** * Contact factory for dice specifications. ** Contact factory for availability.
__________________________________________________________Chip Topographies
MX7575
D6 D7 CLK BUSY N.C. D6
MX7576
D7 (MSB) CLK MODE BUSY
D5 DGND D4 0.081" (2.057mm) D3 TP RD CS V DD REF 0.081" (2.057mm)
D5 DGND D4 N.C. RD CS V DD REF D3
D2
D1
D0
AGND*
AIN AGND*
D2
D1
D0 (LSB)
AGND*
AIN AGND*
0.130" (3.302mm)
0.130" (3.302mm)
*The two AGND pads must both be used (bonded together). TRANSISTOR COUNT: 768 SUBSTRATE CONNECTED TO VDD
*The two AGND pads must both be used (bonded together). TRANSISTOR COUNT: 768 SUBSTRATE CONNECTED TO VDD
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.
12 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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