Document
19-2304; Rev 0; 1/02
Four-Channel Thermistor Temperature-to-PulseWidth Converter
General Description
The MAX6691 four-channel thermistor temperature-topulse-width converter measures the temperatures of up to four thermistors and converts them to a series of output pulses whose widths are related to the thermistors’ temperatures. Each of the four thermistors and an external fixed resistor (REXT) form a voltage-divider that is driven by the MAX6691’s internal voltage reference (VREF). VREF and the voltage across REXT are measured and converted to a pulse. The MAX6691 has a single open-drain I/O pin that can be readily connected to a variety of microcontrollers. The microcontroller initiates a conversion by pulling the I/O pin low and releasing it. When conversion is done, the MAX6691 signals the end of conversion by pulling the I/O pin low once again. The pulse corresponding to the first thermistor is sent immediately after the release of the I/O pin. The on-chip power-management circuitry reduces the average thermistor current to minimize errors due to thermistor self-heating. Between conversions, the MAX6691 falls into a 10µA (max) sleep mode, where the voltage reference is disabled and the supply current is at its minimum. The MAX6691 is available in a 10-pin µMAX package and is specified from -55°C to +125°C temperature range. o Simple Single-Wire Interface o Measures Up to Four Thermistor Temperatures o Low-Average Thermistor Current Minimizes SelfHeating Errors o Internal Voltage Reference Isolates Thermistor from Power-Supply Noise o Accommodates Any Thermistor Temperature Range
Features
MAX6691
Ordering Information
PART MAX6691MUB TEMP RANGE -55°C to +125°C PIN-PACKAGE 10 µMAX
Applications
HVAC Home Appliances Medical Devices
Typical Application Circuit
VCC
Pin Configuration
TOP VIEW
TOP VIEW
T1 T2 T1 T2 T3 T4 T3 T4 R1 2 3 4 5 REXT 10 9 VCC I/O N.C. GND R+ 10kΩ
T1 1
MICROCONTROLLER
10 VCC 9 I/O N.C. GND R+
T2 T3 T4 R-
2 3 4 5
MAX6691
8 7 6
MAX6691
8 7 6
µMAX
________________________________________________________________ Maxim Integrated Products
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For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Four-Channel Thermistor Temperature-to-PulseWidth Converter MAX6691
ABSOLUTE MAXIMUM RATINGS
VCC to GND ...........................................................-0.3V to +6.0V All Other Pins to GND.................................-0.3V to (VCC + 0.3V) I/O, R+, R-, T1–T4 Current................................................±20mA ESD Protection (Human Body Model) .............................±2000V Continuous Power Dissipation (TA = +70°C) 10-Pin µMAX (derate 5.6mW/°C above +70°C) ........444.4mW Operating Temperature Range .........................-55°C to +125°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other 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
(VCC = 3.0V to 5.5V, TA = -55°C to +125°C, unless otherwise noted. Typical values are specified at VCC = 3.3V and TA = +25°C.) (Note1)
PARAMETER THIGH/TLOW Accuracy Supply Voltage Range Supply Current Sleep-Mode Supply Current Input Leakage Current Reference Voltage Output Reference Load Regulation Reference Supply Rejection Logic Input Low Voltage Logic Input High Voltage VIL VIH 0.7 ✕ VCC SYMBOL VREXT VCC ICC ISTANDBY ILEAKAGE VREF IREF = 1mA, TA = +25°C 0 < IREF < 2mA 1.19 1.24 0.1 0.2 0.3 VCC
✕
CONDITIONS TA = +25°C, VCC = 3.3V TA = TMIN to TMAX
MIN
TYP
MAX 0.5 1.0
UNITS % FS V µA µA µA V % % V V
3.0 During conversion, no load 300 3.5
5.5 600 10 1.0 1.32 0.2
TIMING CHARACTERISTICS
(VCC = 3.0V to 5.5V, TA = -55°C to +125°C, unless otherwise noted. Typical values are specified at VCC = 3.3V and TA = +25°C.) (Figure 1) (Note1)
PARAMETER Glitch Immunity on I/O Input Conversion Time Nominal Pulse Width Start Pulse Width Data Ready Pulse Width Error Pulse Width Rise Time Fall Time tCONV tLOW tSTART tREADY tERROR tRISE tFALL CL = 15pF, RL = 10kΩ CL = 15pF, RL = 10kΩ 86 4.0 5 103 103 122 122 600 600 188 188 SYMBOL CONDITIONS MIN TYP 500 102 4.9 156 7.5 MAX UNITS ns ms ms µs µs µs ns ns
Note 1: Specification limits over temperature are guaranteed by design, not production tested.
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Four-Channel Thermistor Temperature-to-PulseWidth Converter MAX6691
__________________________________________Typic.