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19-1726; Rev 0; 5/00
12-Bit Serial-Output Temperature Sensors with 5-Channel ADC
General Description
The MAX1298/MAX1299 implement local and remote temperature sensing with 12-bit resolution, using +5V and +3V supply voltages, respectively. Accuracy is 1C from 0 to +70C, with no calibration needed. The devices feature an algorithmic switched-capacitor analog-to-digital converter (ADC), an on-chip clock, and a 3-wire serial interface compatible with SPITM, QSPITM, and MICROWIRETM. The MAX1298/MAX1299 also perform fully differential voltage measurements with 12-bit resolution and separate track-and-hold (T/H) for positive and negative inputs. Both devices accept versatile input modes consisting of two 3-channel signal pairs, five 1-channel signals relative to a floating common, or VDD/4 relative to ground. An external reference may be used for more accurate voltage measurements. Typical power consumption is only 1.3mW (MAX1299). A shutdown mode and two standby modes provide multiple strategies for prolonging battery life in portable applications that require limited sampling throughput. The MAX1298/MAX1299 are available in 16-pin SSOP packages.
Features
o Local and Remote Temperature Sensing o 12-Bit Resolution for Temperature and Voltage Inputs o 1C Accuracy from -40C to +85C o Fully Differential Inputs o Single-Supply Operation +4.75V to +5.25V (MAX1298) +2.7V to +3.6V (MAX1299) o 3-Wire SPI/QSPI/MICROWIRE-Compatible Interface o Internal Precision Voltage Reference 2.50V (MAX1298) 1.20V (MAX1299) o Space-Saving 16-Pin SSOP Package
MAX1298/MAX1299
Ordering Information
PART TEMP. RANGE TEMP. SENSE PINACCURACY PACKAGE (C) 16 SSOP 16 SSOP 16 SSOP 16 SSOP 16 SSOP 0.75 1.0 4.0 0.75 1.0 4.0
________________________Applications
Temperature/Voltage Supervision of Workstations and Communications Equipment Hand-Held Instruments Medical Equipment Industrial Process Control
MAX1298AEAE -40C to +85C MAX1298BEAE* -40C to +85C MAX1298CEAE -40C to +85C MAX1299AEAE -40C to +85C MAX1299BEAE* -40C to +85C
MAX1299CEAE -40C to +85C 16 SSOP *Future product--contact factory for availability.
Pin Configuration
TOP VIEW
AIN1 1 SHO 2 AIN2 3 AIN3 4 AIN4 5 GND 6 SSTRB 7 16 AIN0 15 AIN5 14 REF
MAX1298 MAX1299
13 GND 12 VDD 11 SCLK 10 DIN 9 DOUT
Typical Operating Circuit appears at end of data sheet. SPI and QSPI are trademarks of Motorola, Inc. MICROWIRE is a trademark of National Semiconductor Corp.
CS 8
SSOP
________________________________________________________________ Maxim Integrated Products
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
ABSOLUTE MAXIMUM RATINGS
VDD to GND....................................................-0.3V to +6V SHO to GND ...............................................-0.3V to (VDD + 0.3V) Analog Inputs to GND (AIN0, AIN1, AIN2, AIN3, AIN4, AIN5, REF).............................................-0.3V to (VDD + 0.3V) Digital Inputs to GND (DIN, SCLK, CS)......-0.3V to (VDD + 0.3V) Digital Outputs to GND (DOUT, SSTRB) ....-0.3V to (VDD + 0.3V) Digital Output Sink Current .........................................25mA Maximum Current into Any Pin.....................................50mA Continuous Power Dissipation (TA = +70C) 16-Pin SSOP (derate 8.00mW/C above +70C) ........667mW Operating Temperature Range MAX129_ _EAE ...............................................-40C to +85C Junction Temperature..............................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) ............................+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
(VDD = 4.75V to 5.25V (MAX1298), VDD = +2.7V to 3.6V (MAX1299), external reference, VREF = +2.5V (MAX1298), VREF = +1.2V (MAX1299), fSCLK = 2.5MHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER DC ACCURACY (Note 1) Resolution Relative Accuracy (Note 2) Differential Nonlinearity Offset Error Offset Temperature Coefficient Gain Error VDD /4 Absolute Error Gain Temperature Coefficient Channel-to-Channel Offset Matching CONVERSION RATE Conversion Time (Note 3) Track/Hold Acquisition Time Aperture Delay Internal Clock Frequency ANALOG INPUTS (AIN0-AIN5) Input Voltage Range (Note 4) Common-Mode Range Input Current (Note 5) Input Capacitance Measurement with respect to IN-, Figure 1 -2V REF 0 0.1 16 +2V REF VDD 5 V V A pF tCONV tACQ tAPR fCLK 57.6 Voltage measurement Temperature measurement 16 30 62.3 65.5 1.1 2.2 ms s ns kHz 2 0.5 Inputs AIN0-AIN5, offset nulled RES INL DNL Inputs AIN0-AIN5 10 4 2 12 1 1 2 Bits LSB LSB LSB V/C LSB LSB ppm/ C LSB SYMBOL CONDITIONS MIN TYP MAX UNITS
2
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC
ELECTRICAL CHARACTERISTICS (continued)
(VDD = 4.75V to 5.25V (MAX1298), VDD = +2.7V to 3.6V (MAX1299), external reference, VREF = +2.5V (MAX1298), VREF = +1.2V (MAX1299), fSCLK = 2.5MHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER DIGITAL INPUTS Input Voltage Low Input Voltage High Input Hysteresis Input Leakage Current Input Capacitance DIGITAL OUTPUTS Output Low Voltage Output High Voltage Three-State Output Leakage Current Three-State Output Capacitance POWER REQUIREMENTS Positive Supply Voltage VDD MAX1298 MAX1299 Full-on, voltage measurements, internal reference Full-on, voltage measurements, external reference Positive Supply Current (Note 6) IDD Full-on, temperature measurements, internal reference Full-on, temperature measurements, external reference Standby, SCLK = GND Standby-plus, SCLK = GND Shutdown, SCLK = GND Power-Supply Rejection Ratio PSRR (Note 7) MAX1298 MAX1299 50 2.494 1.197 INTERNAL VOLTAGE REFERENCE CHARACTERISTICS VDD = 5V Reference Voltage VREF VDD = 3V Reference Tempco Output Short-Circuit Current Capacitive Bypass at REF REF Output Noise REF Line Regulation REF Load Regulation 0 to 100A output current (Note 8) fN = 10Hz to 10kHz MAX1298 MAX1299 MAX1298 MAX1299 MAX1298 MAX1299 0.1 130 65 +3.0 +0.2 4 2 10 10 TC VREF MAX1298 MAX1299 MAX1298 MAX1299 MAX1298 MAX1299 MAX1298 MAX1299 4.75 2.7 390 350 310 280 440 400 360 330 120 190 2 65 2.50 1.20 20 1.25 2.506 1.203 500 500 A 5.25 3.6 V VOL VOH IOUT 15 ISINK = 5mA ISOURCE = 0.5mA 0.6 VDD - 0.6 10 VIL VIH VHYST IIN 16 VDD - 0.8 0.2 1 0.8 V V V A pF V V V A pF SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX1298/MAX1299
10 dB
V ppm/C mA F VRMS mV/V V/A
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
ELECTRICAL CHARACTERISTICS (continued)
(VDD = 4.75V to 5.25V (MAX1298), VDD = +2.7V to 3.6V (MAX1299), external reference, VREF = +2.5V (MAX1298), VREF = +1.2V (MAX1299), fSCLK = 2.5MHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER SYMBOL EXTERNAL VOLTAGE REFERENCE CHARACTERISTICS MAX1298 Reference Voltage Range VREF MAX1299 REF Input Resistance REF Input Capacitance INTERNAL TEMPERATURE MEASUREMENT CHARACTERISTICS Resolution MAX129_A TA = +85C, P D = 1mW MAX129_B MAX129_C MAX129_A Output Error (Notes 1, 9) TA = 0C to +70C MAX129_B MAX129_C MAX129_A TA = -40C to 0C, TA = +70C to +85C Power-Supply Rejection Ratio Noise EXTERNAL TEMPERATURE MEASUREMENT CHARACTERISTICS Output Error Remote Diode Excitation (1X) Remote Diode Excitation (10X) 2N3904 (Note 10) 2 10 100 4 C A A PSRR (Note 7) MAX129_B MAX129_C 0.2 0.18 0.13 0.75 1 1 0.75 1 2 0.75 1 4 C/V CRMS C C Converting Shutdown CONDITIONS MIN 0.8 0.8 10 25 24 TYP MAX 2.5 1.2 UNITS
V M pF
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC
TIMING CHARACTERISTICS
(VDD = +4.75V to 5.25V (MAX1298), VDD = +2.7V to +3.6V (MAX1299), external reference, VREF = +2.5V (MAX1298), VREF = +1.2V (MAX1299), fSCLK = 2.5MHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Figures 4, 6)
PARAMETER SCLK Frequency SCLK Pulse Width Low SCLK Pulse Width High CS Low to SCLK High SCLK High to CS Setup CS Pulse Width SCLK High to CS Low Setup SCLK High to CS High Setup DIN Setup to SCLK High Time DIN Hold Time SCLK Fall to Output Data Valid CS Fall to Output Enable CS Rise to Output Disable SSTRB Rise to SCLK Rise SCLK Fall to SSTRB Fall SYMBOL fSCLK tCL tCH tCSS tCSH tCS tCS0 tCS1 tDS tDH tDO tDV tTR tSCLK tSSTRB RL = 100k, CL = 50pF RL = 100k, CL = 50pF RL = 100k, CL = 50pF 0 200 CONDITIONS MIN 200 200 100 100 100 50 100 100 0 150 150 50 TYP MAX 2.5 UNITS MHz ns ns ns ns ns ns ns ns ns ns ns ns ns ns
MAX1298/MAX1299
Note 1: Tested at VDD = +5.0V (MAX1298) and VDD = +3.0V (MAX1299). Note 2: Relative accuracy is the deviation of the analog value at any code from its theoretical value after the full-scale range has been calibrated. Note 3: Conversion time is defined as the number of clock cycles (64 for voltage measurements, 125 for temperature measurements) multiplied by the internal clock period. Note 4: Individual analog input voltages cannot extend beyond the power-supply rails. Note 5: Input resistance is typically 250M; 5A limit reflects limitations in production testing. Note 6: Specifications for full-on status assume continuous conversions. Power modes are software selected (Table 4). Note 7: Measured at VFS(+4.75V) - VFS(+5.25V) for the MAX1298 and at VFS(+2.7V) - VFS(+3.6V) for the MAX1299. Note 8: External load should not change during conversions for specified accuracy. Note 9: Excludes noise and self-heating effects. Output error for MAX129_C guaranteed by design. Note 10: External temperature sensing over -40C to +85C range, device at +25C. Guaranteed by design.
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
MAX1298 INTEGRAL NONLINEARITY vs. OUTPUT CODE
MAX1298/9-01
MAX1299 INTEGRAL NONLINEARITY vs. OUTPUT CODE
MAX1298/9-02
MAX1298 DIFFERENTIAL NONLINEARITY vs. OUTPUT CODE
0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8
MAX1298/9-03
1.0 0.8 INTEGRAL NONLINEARITY (LSB) 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -2500 -1250 0 OUTPUT CODE 1250
1.0 0.8 INTEGRAL NONLINEARITY (LSB) 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8
1.0 DIFFERENTIAL NONLINEARITY (LSB)
2500
-1.0 -2500
-1250
0 OUTPUT CODE
1250
2500
-1.0 -2500
-1250
0 OUTPUT CODE
1250
2500
MAX1299 DIFFERENTIAL NONLINEARITY vs. OUTPUT CODE
MAX1298/9-04
MAX1298 SUPPLY CURRENT vs. SUPPLY VOLTAGE (VOLTAGE MEASUREMENT MODE)
MAX1298/9-05
MAX1299 SUPPLY CURRENT vs. SUPPLY VOLTAGE (VOLTAGE MEASUREMENT MODE)
450 400 SUPPLY CURRENT (A) 350 300 250 200 150 100 50 0 INTERNAL REFERENCE EXTERNAL REFERENCE
MAX1298/9-06
1.0 DIFFERENTIAL NONLINEARITY (LSB) 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -2500 -1250 0 OUTPUT CODE 1250
500 450 400 SUPPLY CURRENT (A) 350 300 250 200 150 100 50 0 INTERNAL REFERENCE EXTERNAL REFERENCE
500
2500
4.7
4.8
4.9
5.0
5.1
5.2
2.7
2.9
3.1
3.3
3.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
MAX1298 SUPPLY CURRENT vs. SUPPLY VOLTAGE (TEMPERATURE MEASUREMENT MODE)
MAX1298/9-07
MAX1299 SUPPLY CURRENT vs. SUPPLY VOLTAGE (TEMPERATURE MEASUREMENT MODE)
450 400 SUPPLY CURRENT (A) 350 300 250 200 150 100 50 0 EXTERNAL REFERENCE
MAX1298/9-08
MAX1298 SUPPLY CURRENT vs. TEMPERATURE (VOLTAGE MEASUREMENT MODE)
450 400 SUPPLY CURRENT (A) 350 300 250 200 150 100 50 0 INTERNAL REFERENCE EXTERNAL REFERENCE
MAX1298/9-09
500 450 400 SUPPLY CURRENT (A) 350 300 250 200 150 100 50 0 4.7 4.8 4.9 5.0 5.1 5.2 SUPPLY VOLTAGE (V) INTERNAL REFERENCE EXTERNAL REFERENCE
500 INTERNAL REFERENCE
500
2.7
2.9
3.1
3.3
3.5
-40
-20
0
20
40
60
80
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
MAX1299 SUPPLY CURRENT vs. TEMPERATURE (VOLTAGE MEASUREMENT MODE)
MAX1298/9-10
MAX1298 SUPPLY CURRENT vs. TEMPERATURE (TEMPERATURE MEASUREMENT MODE)
MAX1298/9-11
MAX1299 SUPPLY CURRENT vs. TEMPERATURE (TEMPERATURE MEASUREMENT MODE)
450 400 SUPPLY CURRENT (A) 350 300 250 200 150 100 50 0 EXTERNAL REFERENCE INTERNAL REFERENCE
MAX1298/9-12
500 450 400 SUPPLY CURRENT (A) 350 300 250 200 150 100 50 0 -40 -20 0 20 40 60 80 TEMPERATURE (C) EXTERNAL REFERENCE INTERNAL REFERENCE
500 450 400 SUPPLY CURRENT (A) 350 300 250 200 150 100 50 0 -40 -20 0 20 40 60 80 TEMPERATURE (C) INTERNAL REFERENCE EXTERNAL REFERENCE
500
-40
-20
0
20
40
60
80
TEMPERATURE (C)
MAX1298 POWER-DOWN SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX1298/9-13
MAX1299 POWER-DOWN SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX1298/9-14
MAX1298 POWER-DOWN SUPPLY CURRENT vs. TEMPERATURE
450 400 SUPPLY CURRENT (A) 350 300 250 200 150 100 50 0 STANDBY+ STANDBY
MAX1298/9-15
500 450 400 SUPPLY CURRENT (A) 350 300 250 200 150 100 50 0 4.7 4.8 4.9 5.0 5.1 5.2 SUPPLY VOLTAGE (V) STANDBY STANDBY+
500 450 400 SUPPLY CURRENT (A) 350 300 250 200 150 100 50 0 2.7 2.9 3.1 3.3 3.5 SUPPLY VOLTAGE (V) STANDBY+ STANDBY
500
-40
-20
0
20
40
60
80
TEMPERATURE (C)
MAX1299 POWER-DOWN SUPPLY CURRENT vs. TEMPERATURE
MAX1298/9-16
MAX1298 INTERNAL REFERENCE VOLTAGE vs. SUPPLY VOLTAGE
MAX1298/9-17
MAX1299 INTERNAL REFERENCE VOLTAGE vs. SUPPLY VOLTAGE
MAX1298/9-18
500 450 400 SUPPLY CURRENT (A) 350 300 250 200 150 100 50 0 -40 -20 0 20 40 60 80 TEMPERATURE (C) STANDBY+ STANDBY
2.52
1.22
REFERENCE VOLTAGE (V)
2.51
REFERENCE VOLTAGE (V) 4.7 4.8 4.9 5.0 5.1 5.2
1.21
2.50
1.20
2.49
1.19
2.48 SUPPLY VOLTAGE (V)
1.18 2.7 2.9 3.1 3.3 3.5 SUPPLY VOLTAGE (V)
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.) MAX1298 INTERNAL REFERENCE VOLTAGE vs. TEMPERATURE
MAX1298/9-19
MAX1299 INTERNAL REFERENCE VOLTAGE vs. TEMPERATURE
MAX1298/9-20
2.52
1.22
REFERENCE VOLTAGE (V)
2.50
REFERENCE VOLTAGE (V) -40 -20 0 20 40 60 80
2.51
1.21
1.20
2.49
1.19
2.48 TEMPERATURE (C)
1.18 -40 -20 0 20 40 60 80 TEMPERATURE (C)
MAX1298 OFFSET vs. SUPPLY VOLTAGE
MAX1298/9-21
MAX1299 OFFSET vs. SUPPLY VOLTAGE
MAX1298/9-22
1.0
1.0
0.5 OFFSET (LSB) OFFSET (LSB)
0.5
0
0
-0.5
-0.5
-1.0 4.7 4.8 4.9 5.0 5.1 5.2 SUPPLY VOLTAGE (V)
-1.0 2.7 2.9 3.1 3.3 3.5 SUPPLY VOLTAGE (V)
MAX1298 OFFSET vs. TEMPERATURE
MAX1298/9-23
MAX1299 OFFSET vs. TEMPERATURE
MAX1298/9-24
1.0
1.0
0.5 OFFSET (LSB) OFFSET (LSB) -40 -20 0 20 40 60 80
0.5
0
0
-0.5
-0.5
-1.0 TEMPERATURE (C)
-1.0 -40 -20 0 20 40 60 80 TEMPERATURE (C)
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
MAX1298 GAIN ERROR vs. TEMPERATURE
MAX1298/9-27
MAX1299 GAIN ERROR vs. TEMPERATURE
MAX1298/9-28
1.0
1.0
0.5 GAIN ERROR (LSB) GAIN ERROR (LSB) -40 -20 0 20 40 60 80
0.5
0
0
-0.5
-0.5
-1.0 TEMPERATURE (C)
-1.0 -40 -20 0 20 40 60 80 TEMPERATURE (C)
MAX1298 TEMPERATURE ERROR vs. INTERNAL DIODE TEMPERATURE
MAX1298/9-29
MAX1299 TEMPERATURE ERROR vs. INTERNAL DIODE TEMPERATURE
MAX1298/9-30
1.0
1.0
TEMPERATURE ERROR (C)
0.5
TEMPERATURE ERROR (C) -60 -40 -20 0 20 40 60 80 100
0.5
0
0
-0.5
-0.5
-1.0 TEMPERATURE (C)
-1.0 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
MAX1298 TEMPERATURE ERROR vs. REMOTE DIODE TEMPERATURE
MAX1298/9-31
MAX1299 TEMPERATURE ERROR vs. REMOTE DIODE TEMPERATURE
1.5 TEMPERATURE ERROR (C) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -60 -40 -20 0 20 40 60 80 100
MAX1298/9-32
2.0 1.5 TEMPERATURE ERROR (C) 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -60 -40 -20 0 20 40 60 80
2.0
100
TEMPERATURE (C)
TEMPERATURE (C)
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
Pin Description
PIN 1 NAME AIN1 FUNCTION Analog Input 1. Negative differential input relative to AIN0 or positive differential input relative to AIN5 (Table 5). Connect to the cathode of external diode 1 for remote temperature sensing. Shield Output. Used to suppress leakage currents at the anodes of remote temperature sensors (see Remote Diode Shielding). May also be connected to the shield of twisted-pair input cables used for remote temperature measurements. Leave unconnected for other applications. Analog Input 2. Positive differential input relative to AIN3 or positive differential input relative to AIN5 (Table 5). Connect to the anode of external diode 2 for remote temperature sensing. Analog Input 3. Negative differential input relative to AIN2 or positive differential input relative to AIN5 (Table 5). Connect to the cathode of external diode 2 for remote temperature sensing. Analog input 4. Positive differential input relative to AIN5 (Table 5). Ground. Connect to pin 13. Serial Strobe Output. SSTRB goes low at the beginning of an A/D conversion, and it goes high when the conversion is finished. Active-Low Chip Select. Data will not be clocked into DIN unless CS is low. When CS is high, DOUT is at high impedance. Serial Data Output. DOUT transitions on the falling edge of SCLK. Serial Data Input. DIN latches data on the rising edge of SCLK. Serial Clock Input. Clocks data in and out of the serial interface. Positive Supply Voltage. Bypass with a 0.1F capacitor to GND (pin 13). Ground (star ground) Reference-Buffer Output/ADC Reference Input. Reference voltage for A/D conversion. Bypass to GND (pin 13) with a 0.1F capacitor. Select reference mode by writing to configuration byte (Table 2). Analog Input 5. Negative differential input relative to AIN0-AIN4 (Table 5). Analog Input 0. Positive differential input relative to AIN1 or positive differential input relative to AIN5 (Table 5). Connect to the anode of external diode 1 for remote temperature sensing.
2
SHO
3 4 5 6 7 8 9 10 11 12 13 14 15 16
AIN2 AIN3 AIN4 GND SSTRB CS DOUT DIN SCLK VDD GND REF AIN5 AIN0
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
CS
SCLK INPUT REGISTER OUTPUT REGISTER DOUT
DIN
MAX1298 MAX1299
DIODE BIAS CONTROL
CONTROL LOGIC
CLOCK AIN0 AIN1 AIN2 AIN3 AIN4 AIN5 T/H ININPUT MUX T/H IN+
12-BIT ADC VDD
GND
VDD/4
SHIELD OUTPUT
REF
SHO
REF
Figure 1. Functional Diagram
Detailed Description
The MAX1298/MAX1299 are low-power, serial-output, multichannel ADCs with temperature-sensing capability for thermostatic, process-control, and monitoring applications. An algorithmic switched-capacitor converter with T/H circuitry for both positive and negative inputs supports fully differential 12-bit conversions from an internal temperature sensor, two external temperature sensors, or voltage sources in a variety of channel con-
figurations. Microprocessor (P) control is made easy through a flexible 3-wire serial interface. Figure 1 shows a simplified functional diagram of the internal architecture for the MAX1298/MAX1299. In temperature-sensing mode, the multiplexer (mux) steers bias currents through internal or external diodes while the ADC computes their temperature in relation to changes in forward voltage. Channels not used for temperature measurement can be configured to measure other system voltages.
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
TIMING/CONTROL LOGIC
RIN 40k IN+ T/H CHOLDP 4pF FULLY DIFFERENTIAL A/D RIN 40k INT/H CHOLDN 4pF OUTPUT
TRACK AND HOLD
RR 30k REF CREF 4pF
GAIN OF 2
Figure 2. Converter Input Structure
Converter Operation
Figure 2 shows a simplified model of the converter input structure. Once initiated, a voltage conversion requires 64 fCLK periods, where fCLK is the internal master clock. Each conversion is preceded by 13 fCLK periods of warm-up time, performed in twelve 4 fCLK period cycles, and followed by 3 fCLK periods to load the output register. SSTRB falls at the beginning of a conversion and rises at the end of a conversion. Inputs IN+ and IN- charge capacitors CHOLDP and CHOLDN, respectively, during the acquisition interval that occurs during the first fCLK period of the first conversion cycle. In the second f CLK period, the T/H switches open so that charge is retained on CHOLDP and CHOLDN as a sample of the differential voltage between IN+ and IN-. This charge is transferred to the ADC during the third and fourth fCLK periods. The reference sampling process begins in the second conversion cycle and continues until the conversion is complete. Sampling occurs during the second and fourth fCLK periods to yield an effective doubling of the reference voltage. The reference sampling requirement
is signal dependent and may or may not occur in every subsequent conversion cycle. Temperature conversion is essentially nothing more than subtracting the results of two sequential voltage conversions. The only difference is that output registers are not loaded at the end of the first conversion. Thus, temperature conversions require 2 x 64 - 3 = 125 fCLK periods. Figures 3a and 3b show timing diagrams for voltage and temperature conversions, respectively.
Track/Hold
The T/H stage for the MAX1298/MAX1299 is a simple switched-capacitor sampling operation. The time required for the T/H stage to acquire an input signal is a function of how fast its input capacitance is charged. If the signal source impedance is high, the acquisition time lengthens and more time must be allowed between conversions. The acquisition time (tACQ) is the maximum time the device takes to acquire the signal. Calculate this with the following equation: tACQ = 7 (Rs + RIN) CIN where Rs is the source impedance of the input signal, RIN is the T/H input impedance (40k), and CIN is the
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
SSTRB
FCLK
13 fCLKs WARMUP INPUT ACQUISITION fCLKs CONVERSION CYCLE 1
REF ACQUISITION 1
REF ACQUISITION 2 44 fCLKs
3 fCLKs WRITE TO OUTPUT REGISTER
CONVERSION CYCLES 2-12 REFERENCE SAMPLING
Figure 3a. Voltage Conversion Timing Diagram
SSTRB
FCLK
13 fCLKs WARMUP INPUT ACQUISITION 4 fCLKs CONVERSION CYCLE 1
44 fCLKs CONVERTION CYCLES 2-12 REFERENCE SAMPLING
13 fCLKs WARMUP INPUT ACQUISITION 48 fCLKs CONVERTION CYCLES 1-12 SECOND CONVERSION
3 fCLKs SUBTRACTION AND WRITE TO OUTPUT REGISTER
FIRST CONVERSION
Figure 3b. Temperature Conversion Timing Diagram
input sampling capacitance of the ADC (4pF). Source impedances below 100k have no significant effect on MAX1298/MAX1299 AC performance.
Serial Digital Interface
The MAX1298/MAX1299 feature a serial interface that is fully compatible with SPI, QSPI, and MICROWIRE devices. For SPI/QSPI, ensure that the CPU serial interface runs in master mode so it generates the serial clock signal. Select a 2.5MHz clock frequency or less, and set zero values for clock polarity (CPOL) and phase (CPHA) in the P control registers. Figure 4 shows detailed serial interface timing information. See Tables 2-5 for programming information.
Analog Input Protection
Internal protection diodes clamp the analog inputs to VDD and GND, so channels can swing within GND 0.3V and VDD + 0.3V without damage. However, for accurate conversions, the inputs should not extend beyond the supply rails. If an off-channel analog input extends beyond the supply rails, limit the input current to 2mA.
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
CS t CS t CSO SCLK t DH t DS DIN X VALID t DV DOUT X VALID VALID X t CL t CSS t CH t CSH t CS1
t DO
t TR
Figure 4. Detailed Serial Interface Timing
OUTPUT CODE 011111111111 011111111110 000000000010 000000000001 000000000000 111111111111 111111111110 111111111101 100000000010 100000000001 - FS + 1LSB 0 IN+ - IN - (LSB) + FS - 1LSB +FS = + 2VREF -FS = - 2VREF 1LSB = 2VREF 2048
Output Data Format Output data from the MAX1298/MAX1299 are clocked onto DOUT on the falling edge of SCLK in the form of two 8-bit words, MSB first (Table 1). For temperature conversions, the output is 12-bit binary (D10-S0) padded with 2 leading extraneous bits and two trailing zeros. For voltage conversions, the output is 12-bit two's-complement binary (D11-D0) with 1 sub-bit and two trailing zeros. Figure 5 shows the bipolar transfer function.
Performing a Conversion
On power-up, the MAX1298/MAX1299 defaults to shutdown mode. Start a conversion by transferring a configuration byte and a conversion byte into DIN with the control formats shown in Tables 2 and 3, respectively. (See Power Modes for related discussion.) SSTRB goes low on the falling edge of the last bit of the conversion byte, and it returns high when the conversion is complete. For best noise performance, SCLK should remain low while SSTRB is low. Typical conversion times are 2.2ms for temperature measurements and 1.1ms for voltage measurements. The MSB of the 2 output bytes is present at DOUT starting at the rising edge of SSTRB. Successive SCLK falling edges shift the two 8-bit data bytes out from an internal register. Additional (>16) SCLK edges will result in zeros on DOUT. SSTRB does not go into a high-impedance state when CS goes high. Pulling CS high prevents data from being clocked in or out, but it does not adversely affect a conversion in progress. Figure 6 shows SSTRB timing details. Subsequent conversions with the same reference mode do not require a configuration byte.
Figure 5. Bipolar Transfer Function
Input Data Format Input data (configuration and conversion bytes) are clocked into the MAX1298/MAX1299 at DIN on the rising edge of SCLK when CS is low. The start bit (MSB) of an input data byte is the first logic 1 bit that arrives: After CS falls, OR after receipt of a complete configuration byte with no conversion in progress, OR after 16 bits have been clocked onto DOUT following a conversion.
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
Table 1. Output Data Format
D11 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 S0 0 0
Table 2. Configuration-Byte Format
BIT 7 (MSB) Start BIT 7 (MSB) 6, 5, 4, 3 2, 1 0 PM1, PM0 REF BIT 6 0 NAME Start BIT 5 0 BIT 4 0 BIT 3 0 BIT 2 PM1 DESCRIPTION First logic 1 after CS goes low. (See Input Data Format.) Must be 0000 to load a configuration byte. These 2 bits select the desired power mode (Table 4). A logic high enables the internal reference. A logic low disables the internal reference and selects the external reference mode. BIT 1 PM0 BIT 0 (LSB) REF
Table 3. Conversion-Byte Format
BIT 7 (MSB) Start BIT 7 (MSB) 6, 5, 4 3, 2, 1, 0 SEL3, SEL2, SEL1, SEL0 BIT 6 0 NAME Start Must be 010 to load a conversion byte. These 4 bits select the input configuration (Table 5). BIT 5 1 BIT 4 0 BIT 3 SEL3 BIT 2 SEL2 BIT 1 SEL1 BIT 0 (LSB) SEL0
DESCRIPTION First logic 1 after CS goes low. (See Input Data Format.)
CSB t CSH SSTRB t CONV t SSTRB SCLK PDO CLOCKED IN DOUT SSTRB TIMING t SCK
t CSS
t DO
Internal Reference The MAX1298 has a 2.50V internal reference, while the MAX1299 has a 1.20V internal reference. Both are factory trimmed for accuracy. When internal reference is selected, REF can be used to drive an external load with 100A capability. Bypass REF to GND with a 0.1F (min) capacitance. Wake-up time is C x 2.5 x 104s for the MAX1298 and C x 1.2 x 104s for the MAX1299. External Reference The MAX1298 can directly accept reference voltages at REF from 0.8V to 2.5V, while the MAX1299 can directly accept reference voltages from 0.8V to 1.2V. Bypass REF to GND with a 0.1F capacitor. Temperature measurements always use internal reference.
Figure 6. Detailed SSTRB Timing
Reference Selection
Select between internal and external voltage modes through bit REF of the configuration byte. Set REF = 1 for internal reference mode and REF = 0 for external reference mode.
Power Modes
The MAX1298 (MAX1299) typically requires supply currents of 380A (350A) or 310A (280A) when performing voltage conversions at 100% duty cycle with internal or external references, respectively. The differ-
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
ence reflects the power requirement of an internal reference buffer amplifier that can accommodate external loads. Temperature conversions at 100% duty cycle increase supply currents to 440A (400A) through additional amplification, buffer, and bias circuitry that is otherwise inactive. Place the MAX1298/MAX1299 in a low-current powerdown state between conversions to conserve power. Select standby, standby-plus, or shutdown through bits PM1 and PM0 of the initialization byte (Table 4). The MAX1298/MAX1299 assume the shutdown power mode when VDD is first applied. Standby Mode Standby mode turns off the MAX1298/MAX1299 ADC, internal clock, and reference buffer amplifier. Special circuitry for temperature conversions is also deactivated. Wake-up time is limited by the reference buffer amplifier and the associated bypass capacitor (see Internal Reference). When an external reference is used, wake-up time is 0.1ms. Standby-Plus Mode Standby-plus mode is similar to the standby mode, but the internal reference output buffer remains active to shorten the wake-up time to 0.1ms for internal reference mode. When using an external reference, standby-plus mode is equivalent to standby mode. Shutdown Mode Shutdown mode turns off all functions other than startup circuitry, thereby reducing typical supply current to 2A. Data registers are cleared. Use this power mode when interconversion times are no less than 5ms.
Table 4. Power-Mode Selection
PM1 0 0 1 1 PM0 0 1 0 1 MODE Shutdown Standby-plus Standby Normal operation
achieve a digital output that is proportional to absolute temperature in degrees Kelvin. The reference voltage used in conjunction with temperature measurements is derived from the internal reference source to ensure that 1LSB corresponds to 1/8 of a degree. To convert to degrees Celsius, subtract 273.15 from the temperature inferred from the ADC output. Temperature measurements require a conversion time of 2.2ms.
Shield Output Buffer
The MAX1298/MAX1299 provide a shield output buffer voltage at SHO that is approximately 0.6V (one diode drop) above V DD /2. When performing temperature measurements with an external diode, use this voltage to suppress error-producing leakage currents (see Remote Diode Shielding). Figure 7 shows the SHO output circuit.
5A SHO
Monitoring VDD
This mode of operation samples and converts the supply voltage, VDD/4, which is internally generated. The reference voltage must be larger than VDD/8 for the operation to work properly. From the result of a conversion (CODE), CODE = 256 VDD / VREF.
VDD 2
Figure 7. SHO Output Circuit
Temperature Measurements
The MAX1298/MAX1299 perform temperature measurements with internal or external diode-connected transistors through a three-step process. First, the diode bias current changes from 31.6A to 10A to produce a temperature-dependent bias voltage difference, which is amplified by a factor of 20 and converted to digital format. Second, the bias current changes from 31.6A to 100A, and the bias voltage difference is similarly amplified by a factor of 20 and converted to digital format. Third, the intermediate results are subtracted to
Applications Information
Remote Diode Selection
Temperature accuracy depends on having a goodquality, diode-connected small-signal transistor. Accuracy has been experimentally verified for 2N3904 devices. CPUs and other ICs having on-board temperature-sensing diodes can also be monitored if the diode connections are floating.
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
Table 5. Input Selection
SEL3 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 SEL2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 SEL1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 SEL0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 POSITIVE INPUT (IN+) AIN0 AIN1 AIN2 AIN3 AIN4 -- AIN5 Internal diode anode* AIN0 AIN2 -- VDD/4 External diode 1 anode* (AIN0) External diode 2 anode* (AIN2) -- -- NEGATIVE INPUT (IN-) AIN5 AIN5 AIN5 AIN5 AIN5 -- AIN5 Internal diode cathode AIN1 AIN3 -- GND External diode 1 cathode (AIN1) External diode 2 cathode (AIN3) -- --
*Temperature-measurement mode
Table 6. Remote-Sensor Transistor Manufacturer
MANUFACTURER Central Semiconductor (USA) Fairchild Semiconductor (USA) Motorola (USA) Rohm Semiconductor (Japan) Siemens (Germany) Zetex (England) MODEL NUMBER CMPT3904 MMBT3904 MMBT3904 SST3904 SMB3904 FMMT3904CT-ND
device consists of a diode-connected transistor, an aluminum plate with screw hole, and twisted-pair cable (Fenwal Inc., Milford MA, 508-478-6000).
Twisted-Pair and Shielded Cables
For remote-sensor distances greater than 8 inches, or in particularly noisy environments, use a twisted pair. A practical length is 6 to 12 feet. For longer distances, the best solution is a shielded twisted pair such as that used for audio microphones. For example, the Belden 8451 works well for distances up to 100 feet in a noisy environment. Connect the shield to SHO. Cable resistances affect remote-sensor accuracy; 1 series resistance introduces +0.004C error.
Remote Diode Shielding
Temperature measurements will reflect significant error if a portion of the bias current supplied to the diode anode is allowed to flow through parallel paths to ground. If the diode-connected transistor is mounted on a PC board, suppress error-producing "leakage" current by surrounding the collector/base leads with a metal trace that is connected to the SHO shield output (Figure 8).
The transistor must be a small-signal type with a base resistance less than 100. Tight specifications for forward current gain (+50 to +150, for example) indicate that the manufacturer has good process controls and that the devices have consistent Vbe characteristics. (See Table 6 for recommended devices.) For heatsink mounting, the 500-32BT02-000 thermal sensor from Fenwal Electronics is a good choice. This
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
SHIELD ANODE
between the endpoints of the transfer function, once offset and gain errors have been nullified. The static linearity parameters for the MAX1298/MAX1299 are measured using the best-straight-line-fit method.
Differential Nonlinearity (DNL)
Differential nonlinearity is the difference between an actual step width and the ideal value of 1LSB. A DNL error specification of less than 1LSB guarantees no missing codes and a monotonic transfer function.
Offset Error
The offset error is the difference between the ideal and the actual offset points. For an ADC, the offset point is the midstep value when the digital output is zero.
CATHODE
Gain Error
The gain or full-scale error is the difference between the ideal and actual gain points on the transfer function, after the offset error has been canceled out. For an ADC, the gain point is the midstep value when the digital output is full scale.
Figure 8. Remote Diode Shielding for PC Boards
Layout, Grounding, and Bypassing
For best performance, use PC boards. Do not use wirewrap boards. Board layout should ensure that digital and analog signal lines are separated from each other. Do not run analog and digital (especially clock) signals parallel to one another or run digital lines underneath the ADC package. High-frequency noise in the VDD power supply may affect ADC performance. Bypass the supply with a 0.1F capacitor close to pin VDD. Minimize capacitor lead lengths for best supply-noise rejection. If the power supply is very noisy, connect a 10 resistor in series with the supply to provide lowpass filtering.
Aperture Delay
Aperture delay (tAD) is the time defined between the rising edge of the sampling clock and the instant when an actual sample is taken.
Chip Information
TRANSISTOR COUNT: 13,669 PROCESS: BiCMOS
Definitions
Relative Accuracy
Relative accuracy is the deviation of the values on an actual transfer function from a straight line. This straight line can be either a best-straight-line fit or a line drawn
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC
Typical Operating Circuit
+5V
MAX1298/MAX1299
0.1F
VDD AIN0
2N3904
AIN1
CS
MAX1298
AIN2 SCLK
2N3904
(SHIELD)
AIN3
DIN
SHO
DOUT
AIN4
SSTRB
AIN5 GND GND
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12-Bit Serial-Output Temperature Sensors with 5-Channel ADC MAX1298/MAX1299
Package Information
SSOP.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.
20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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