MAX6682 19-2219 Rev 0 2/02 Thermistor-to-Digital Converter General Description Features The MAX6682 converts an external thermistors temper- Converts Thermistor Temperature to Digital Data ature-dependent resistance directly into digital form. Low Average Thermistor Current Minimizes Self- The thermistor and an external fixed resistor form a volt- Heating Errors age-divider that is driven by the MAX6682s internal voltage reference. The MAX6682 measures the voltage Low Supply Current, 21A (typ) Including 10k across the external resistor and produces a 10-bit + Thermistor Current sign output code dependent on that voltage. Internal Voltage Reference Isolates Thermistor The MAX6682 does not linearize the highly nonlinear from Power-Supply Noise transfer function of a typical negative temperature coef- ficient (NTC) thermistor, but it does provide linear out- 10-Bit Resolution put data over limited temperature ranges when used Accommodates Any Thermistor Temperature with an external resistor of the correct value. Over the Range 0 to +50C temperature range, the MAX6682 produces output data that is scaled to 8LSBs/C (for 0.125C res- Output Data Scaled for Direct Temperature olution), provided that the correct thermistor and exter- Readings from 0C to +50C nal resistor values are used. Other temperature ranges Simple SPI-Compatible Interface can be easily accommodated, but do not necessarily yield data scaled to an even number of LSBs per Small, 8-Pin MAX Package degree. The 3-wire SPI-compatible interface can be readily connected to a variety of microcontrollers. The MAX6682 is a read-only device, simplifying use in systems where only temperature data is required. Ordering Information Power-management circuitry reduces the average ther- PART TEMP RANGE PIN-PACKAGE mistor current, minimizing self-heating. Between con- MAX6682MUA -55C to +125C 8 MAX versions, supply current is reduced to 21A (typ). The internal voltage reference is shut down between mea- surements. The MAX6682 is available in a small, 8-pin MAX pack- age and is specified over the -55C to +125C temper- ature range. Typical Operating Circuit Applications 3.3V HVAC 0.1 F Medical Devices Battery Packs/Chargers V CC Home Appliances R+ R EXT MAX6682 R- Pin Configuration appears at end of data sheet. MC68HCXX CS I/O THERMISTOR SCLK SCLK SPI is a trademark of Motorola, Inc. GND SO MISO Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct at 1-888-629-4642, or visit Maxims website at www.maxim-ic.com.Thermistor-to-Digital Converter ABSOLUTE MAXIMUM RATINGS Supply Voltage (V to GND) .................................-0.3V to +6V Continuous Power Dissipation (T = +70C) CC A SO, SCK, CS, R-, R+ to GND ....................-0.3V to (V + 0.3V) 8-Pin MAX (derate 4.1mW/C above +70C) ............ 328mW CC R+ Current........................................................................20mA Operating Temperature Range R- Current ...........................................................................1mA (T to T ) ...............................................-55C to +125C MIN MAX SCK, CS, SO Current .........................................-1mA to +50mA Storage Temperature Range .............................-65C to +150C ESD Protection (Human Body Model) .............................2000V Junction Temperature .....................................................+150C 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 = 3V to 5.5V, T = -55C to +125C, unless otherwise noted. Typical values are specified at V = 3.3V and T = +25C.) (Note 1) CC A CC A PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Supply Voltage V 3.0 5.5 V CC DOUT = 768.935 x (V /V ) - 134.0923 REXT R+ ADC Total Unadjusted Error TUE -3 +3 LSB V > 0.1V IN REF ADC Conversion Time t 64 80 ms CONV R- Input Impedance Z 1M IN R- Leakage Current 150 nA Conversion Rate 0.5 Hz Reference Voltage Output V I = 1mA 1.10 1.22 1.40 V REF LOAD Reference Load Regulation 0 < I < 2mA 0 0.1 %/mA LOAD Reference Supply Regulation 0.7 mV/V Conversion Supply Current I During conversion, no load 220 300 A C Average Supply Current I 0.5 conversions/s, no load 17 29 A A Standby Current I CS low, SCK inactive 3 7 A S Idle Current I CS high, analog circuits off 10 17 A ID SERIAL INTERFACE 0.2 x Input Low Voltage V V IL V CC 0.8 x Input High Voltage V V IH V CC Input Leakage Current I V = GND or V 1A LEAK IN CC V - CC Output High Voltage V I = 1.6mA V OH SOURCE 0.4 Output Low Voltage V I = 1.6mA 0.4 V OL SINK 2 MAX6682